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Do species other than humans have distinct daily feeding patterns?
I have a general interest in complex adaptive systems and I have found that nature and the organisms within it is a perfect natural case of a rich adaptive system with a lot of possibilities for gaining insight in general about the nature of complex adaptive systems.
My mind accidentally started thinking about the common human feeding pattern breakfast-lunch-dinner and I sought reference points in nature, realizing that I'm not aware of any specific cases where the feeding pattern of animals other then humans follow a distinct pattern, in contrast to a constant, stochastic or mainly opportunistic search for food.
In the case of humans there is probably a very strong cultural cause for our very distinct feeding pattern, but that is not necessarily to say that these patterns only can occur in species with a highly developed culture.
How does the scientific body of observations look like here? Is there any research or empirical observations about the feeding pattern of animals?
For example, I would of the top of my head assume that some common reasons for these patterns to develop could be connected to e.g. the 24h circadian rhythm, dependencies to availability of food, or internal dependencies on behavioural organization in social species.
Of course it's likely that many organisms do not have the luxury of spending a significant time on other activities then acquiring food, but nevertheless we can see that some animals have evolved into a situation where they don't have to constantly be in the search for food, but instead can spend time on other activities increasing their fitness, like engaging in social interactions, searching for and seducing sexual mates, exploring their environment and migrating, building nests and so on.
To clarify what kind of observations I'm imagining could happen, take these speculative examples:

Some species of birds have a significantly higher feeding activity in the morning, where they after a night of inactivity have depleted their daily energy resource and when the insects, their main source of food, starts to activate after a cold night and are still cold and slower/easier prey. After this the birds only have an opportunistic approach to feeding which is enough to satisfy their energy need, and they spend more energy on pruning, calling for potential mates and engaging in territorial battles.

Many primates engage in collective feeding sessions where they as a group travel to a known area rich with food where they spend a couple of hours before they retreat back to a different location for socializing and digesting the food. One reason for this behaviour can be that there is a high risk of predation at these food-rich areas, as the predators learn that these places are frequently visited by prey.

Feline predators on the savannah are usually concentrating their hunting in the night as the darkness gives them an advantage of stealth and surprise. This is why they in daytime instead spend a considerable amount of time on resting, engaging in activities regarding social hierarchies, order and bonding with the pride, while most often only opportunistically engaging in hunting.

Do we have a body of knowledge here?
While it would be close to hand to start trying making lists of observations like this, which certainly would be interesting in itself, the intention of this question is to get a good overview on the subject. Are patterns like these common or uncommon? In the cases where they are found, what are the common factors and what can be identified as the underlying causes?

I'm not sure what you're asking here. Wild animals eat when they can secure food. Most of the time, the food supply is limited enough that they don't have the option of "breakfast, lunch and diner"; in that case, the predator population would increase to the point of making the prey relatively scarce once more. Many herbivorous animals spend most of their awake time eating (or traveling to where food can be found). Are Jane Goodall's decades in the Gombe Stream National Park empirical evidence? I'm just unsure of what you want here.

@anongoodnurse Yes, I know that this is the common view on animal feeding: They eat when they can. But I think that this is a too simplified view, and sometimes just wrong. Animals have to do other things than eating, like seducing potential mates (which can be a quite big thing, including very expensive fights), resting and sleeping, engage in social activities like play and bonding and so forth. And even when it comes to feeding, when looking at the big predators we know for sure that they can sustain quite a while on a big meal, leaving time to do other things.

@anongoodnurse So what I'm looking for is cases when we have a distinct daily feeding patterns in animals, like in the cases of humans and our breakfast, lunch and dinner, or something similar. Observations from Jane Goodall would surely be considered empirical data, if not evidence. And on noting that, great apes would probably be good candidates that might have developed distinct feeding patterns I assume since they are very social.

"But I think that this is a too simplified view, and sometimes just wrong." I can say that about climate change, but that wouldn't make me correct. "when looking at the big predators we know for sure that they can sustain quite a while on a big meal" - exactly. It takes a lot of effort and some luck (they are not 100% successful) to bring down a gnu/other, so that prevents them from a breakfast/lunch/dinner pattern, as does most of nature. Feeding is to a great degree dependent of the availability of food, which varies.

@anongoodnurse Your reference to climate change denials seems a little strange, maybe we misunderstood each others somewhere. What I meant was that it's clearly the case that many animals do other things than search for food, thus leaving the possibility that there in some cases might be the case that some animals develop an daily schedule or pattern in their feeding habits. Cases like that would be what I'm looking for here.

@anongoodnurse And I'm totally with you that many animals might not have the luxury of arranging their feeding behaviour like this, but I'm searching for those that do.

unclear? This is pretty clear!

Since it apparently was unclear enough to have it temporarily put on hold, I have now rewritten the question for extra clarity.

For me it was clear enough, but it needs some research to answer...

This is a very interesting issue, and one which I've been thinking about because of new findings in chronobiology. That is, certain organs are more active at different parts of the circadian cycle. For example, eating late for humans may stress the liver, as the liver is actively detoxing at night. Certain folks are recommending eating early or only for 8/24 hours, and fasting the rest of the time (8 hours before sleep). I was wondering myself if there are similar patterns in the animal world, or in nature, such that the natural biorhythms of oscillating clocks, are supported.

What makes you think humans have distinct feeding patterns, 3 meals a day is a cultural practice and in no way universal in humans.

As already mentioned many animals have distinct feeding pattern due to resource limitation or availability.
For example some fishes feed predominantly at high tide because that's the only time they have access to abundant food resources (e.g., Weisberg, S.B., Whalen, R. and Lotrich, V.A., 1981. Tidal and diurnal influence on food consumption of a salt marsh killifish Fundulus heteroclitus. Marine Biology, 61(2), pp.243-246.). The behavior is so strong that it alters the normal diel behavior pattern because tides are determined primarily by lunar patterns and altered by geography. So a normally nocturnal fish might become active during the day in order to feed. This means that the fish would feed at specific times of the day, although the time would change daily.
The advent of farming may have influenced this by creating abundant food that could be consumed on a regular basis (in morning after waking, in afternoon as hunger increased due to activity, and in evening before sleeping). Otherwise food acquisition would be dependent on availability, you eat when you can not when you want/need.

Preamble
This is a very interesting question one which I don't immediately know an answer to. I think this overly succinct answer and the fact nobody else has answered highlights the degree to which the age old darwinian assumptions play a role in the field.
Zoological POV
I'm not an expert in this area so I went to a zoology lab technician and this is what they had to say (I'm paraphrasing here):

Most animals are opportunistic and can't afford the luxury of a late
  brunch... The only animals that spring to mind that appear to 'plan' for
  meals are the hoarders (squirrels for example). But they don't
  typically cache food in the same way we would for a weekly shop, but
  do so for fear of food scarcity (overwintering, rival competition);
  Not unlike the mad dash for bread and loo roll when it starts snowing
  slightly!

Maybe animals do have their diet set to a circadian rhythm, or maybe not. We can't say for sure. Darwin implied, even a peaceful meadow is full of starving ravenous animals clinging to survival. There is no real time for luxury. If food is there, they eat it. Many animals don't even get full the same way we do.
Scarcity of Literature
The problem lies in that there is no body of literature around animal eating times since animals seldom have enough food in their natural environment to monitor any regularity. If you want specific questions on a particular species for optimum feeding times, I would recommend opening another question as lab animals do have recommended diets. Many predators have optimum hunting times (for example nocturnal, or dusk). However one could argue this is to do with success rates/effective hunting strategy and not necessarily scheduled eating times.

In reading the reaction from your lab technician I'm thinking that maybe it was a bad choice of me to make a comparison with our human pattern in this question, risking the appearance of someone trying to apply human attributes to animals, and in putting focus on whether animals consciously "plan" their daily food intake accordingly to their personal preferences. I appreciate your answer even if it did not provide deeper insight, and I take the opportunity to once again suggest that food is a very important resource, but for some "lucky" species maybe not the only one worth spending time on.

And maybe one thing to consider here could be the possibility that in some cases for some species, focused and active search for food is much more efficient than a purely opportunistic approach. Thus again opening up the possibility for well partitioned activities and patterns therein, I presume.

Amended my question to highlight the scarcity of literature. As it stands, the question requires very specific knowledge over a vast range of zoological niches. If you need a specific species dietary requirements, I would ask in a separate question.

Of course there are nocturnal and diurnal feeders. Insectivorous bats get active during the dusk (as I have observed) but are not so active later in the night (perhaps because of fall in temperature and low insect activity).

@WYSIWYG Those daily patterns arise not out of choice, but out of an inability to hunt effectively at other times. A list of the species that behave like this might be what Alex wants to know, in which case the question is far too broad. Are you aware of any literature in the field that provides a concise review?

@GoodGravy Nope. I have not really studied animal behavior. But I had heard some talk about two kinds of feeding behavior- one is, as discussed in comments and your answer, the opportunistic: eat as much as you can when you have the chance. Other one is to have a fixed eating pattern (no overeating) and big herbivores like elephants do that; the term that the speaker used for this is "metabolically regulated" (if I am not mistaken). This I heard some 3 years back and I didn't read up much on it later.


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Why isn't the insertion of a single nucleotide destructive for DNA?
As far as I know proteins are built by sequentially reading triplets of nucleotides.
But if at a certain point a nucleotide is inserted in the sequence, the following sequence of triplets is completely different.
For example:

AATACGGTACCATTA ...

AAT ACG GTA CCA TTA ...

But inserting a nucleotide B at second place we get

ABA TAC GGT ACC ATT ...

Which is completely different.

However I know from theory that a single nucleotide insertion is not dangerous in most cases.
Could someone clarify my mind about this?

However I know from theory that a single nucleotide insertion is not dangerous in most cases. Do you have a citation for that?

@tel maybe I was remembering wrong.

A single substitution can often be silent, or at least not impact the structure and function of the resulting protein in a significant way. But what you describe is a frameshift, and that is one of the most destructive mutations. It will completely change the sequence of the protein after this mutation and disrupt the function of those parts of the protein.
Insertions or deletions that result in a frameshift are absolutely destructive mutations.

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Relative sweetness
I have noticed that when I eat something sweet, then afterwards, I eat something else that is sweet, the second sweet food is not as sweet as it usually is. I am pretty sure many others have a similar experience before too. Why does this happen?

Our senses generally adjust their sensitivity according to the signal strength, e.g. by neural adaptation.

@augurar good call on neural adaptation. I originally mistakenly called it "habituation" in my answer, which it turns out is slightly different.

What you describe is an example of neural adaptation, whereby neural response to a consistent stimuli becomes reduced with repetition. This occurs not just with sweetness (as shown empirically in this study on sucrose consumption by rats), but with many other types of stimuli (the feeling of clothes on your skin, the particular smell of your own home) as well.
In general, our senses are tuned to detect relative changes in our environment rather than absolute values. For example, if I were to place an unmarked 10 kg weight in one of your hands and a 12 kg weight in your other hand, you might have some trouble telling me what the exact mass of each weight is. You would have no trouble whatsoever telling me which weight was heavier. Neural adaptation allows us to maintain the ability to make these kinds of distinctions over a wide range of stimuli intensities.
There is no scientific consensus as to the exact mechanism of neural adaptation (and there probably isn't just one), but there are many candidate processes at the level of individual neurons, such as long term depression. Grill-Spector et al published a widely cited paper a few years ago called "Repetition and the brain: neural models of stimulus-specific effects" in which they put forth several potential mechanistic models of neural adaptation.

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Are There Exceptions to Animal Cells not Having Cell Walls?
In the January Issue of SciAm (discussing Haemophilia):

When damage occurs to blood vessels, exposure of the blood to collagen in the cell walls and material released by the cells triggers the activation of clotting factors.

I read the original in print, but it is available online here.
This seems to imply that animal cells (in this example, those of humans) have cell walls.  I sometimes see similar implications in other resources.  However, in elementary biology, one is taught that animal cells never have cell walls.
Therefore, my question: Are references to animal cell cell walls (such as the above, for human animal cells) simple mistakes--or are they exceptions to a generalization?

This was just a badly worded statement; the better wording should have been: "exposure of the blood to collagen in the blood vessel walls and material released by the cells...". They clearly mean damaged endothelium.

Can you also post a link to this article. If they have used this erroneous terminology then we should write to the editor.

@WYSIWYG see edit.  When I read the quote, I immediately suspected an error.  I do permit SciAm and the author the occasional typo, though, since they're obviously high-quality otherwise.

@imallett It is for everyone's good to report mistakes. I once found ~100 articles that had mistakenly called TCA-Cycle as Trichloroacetic acid cycle instead of tricarboxylic acid cycle. I mailed the editors.

Humans, as well as the rest of the metazoans (i.e. animals), absolutely do not have cell walls. What humans do have is extracellular matrix (ECM), which is the sort of fibrous, sort of gel-like material in which cells in many of the tissues are embedded. Collagen is a major component of ECM.
From the old copy of Alberts that is hosted on the NCBI website:

Tissues are not made up solely of cells. A substantial part of their volume is extracellular space, which is largely filled by an intricate network of macromolecules constituting the extracellular matrix (Figure 19-33). This matrix is composed of a variety of proteins and polysaccharides that are secreted locally and assembled into an organized meshwork in close association with the surface of the cell that produced them...
Two main classes of extracellular macromolecules make up the matrix: (1) polysaccharide chains of the class called glycosaminoglycans (GAGs), which are usually found covalently linked to protein in the form of proteoglycans, and (2) fibrous proteins, including collagen, elastin, fibronectin, and laminin, which have both structural and adhesive functions.

@anongoodnurse yeah, I figured it was something like that too. I just wanted to make super clear to the OP that, at least in terms of nomenclature, animals definitely do not have cell walls.

@anongoodnurse which got me thinking about whether cell wall vs ECM is a difference without a distinction, but I cut that part out of my answer as it didn't really add anything to it. I might put that up myself as a separate question once I've looked into it a bit.

authors: Лейля Галиханова

authors: آرسس یوسف وند


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Are There Rules for How Proteins Are Formed?
Proteins are formed by stringing together different amino acids.  Different amino acids have different properties (such as being attracted to or repelled by water, positively or negatively charged, large, small, etc.).
What I would like to know is if there are any rules or principles which determine how amino acids are strung together to form proteins?  If so, what are those rules and can anyone recommend any resources where I can learn more about this subject?
Thanks.
MORE DETAILS
Let me try and explain what I am trying to ask.  I understand that there are rules of grammar that I need to follow in order to put together a well formed English sentence.  I am wondering if there is something akin to that for stringing together amino acids in order to create a 'well-formed' protein. (I am NOT referring to how DNA codes for amino acids).
For instance, imagine that I wanted to create a new protein and I had a pile of amino acids at my disposal.  It seems to me that if I understood the principles and rules by which amino acid chains work then I could know which amino acids to string together and the order in which to string them together in order to create the particular type of protein that I wish to create.
This is similar to how I can string together letters and words to form well formed sentences or how I can string together well-formed sentences to create logical arguments.  There's a logic to how to form a sentence and a different logic for how to form an argument -- and it is possible to discern that logic by studying syntax and reasonable arguments.
I assume the same is true for proteins.  There must be some sort of logic or system for how amino acids are strung together -- some sort of connection between the 3-dimension, functional protein and the nature of the properties of the individual amino acids and how they are organized together.  What I am wondering is whether or not we have any idea what that system of logic is.

You mean besides their sequence in the DNA code? Basically how they get the form they have?

Your question is a bit unclear. What do you mean by how? Are you trying to ask if there are any rules for which amino acid follows which amino acid? Or are you trying to ask about how proteins fold?

@tel Yes, this is unclear.. However, I am pretty sure he means how proteins are folded

There certainly are a number of rules, and many (but not all) of them are known to science. You can learn about these rules from any introductory biochemistry text, given that folding now comprises a whole subfield of investigation. What exactly are you asking?

this could be worded as a request for some pointers to protein folding, the poster should be forgiven for not using exactly the right words.

Without the OP weighing in to clarify exactly what is being asked, this question should remain on hold. I have rolled back the previous edit, as it makes assumptions that cannot be verified. As I read it, the author is clearly asking about the template that describes the order in which amino acids are added. Editing the question invalidates the answers already given. @Moshe, please clarify your question - are you asking about the order in which amino acids are added, or are you interested in how the linear chain of amino acids forms a 3D structure?

Sorry about not being clear enough.  Here's another try (also please see my edit to the original question):  DNA dictates which amino acids are used and in which order, but it doesn't tell us anything about the logic or system which determines which amino acids to use and which order to use them in.  I am wondering if we know anything about the logic or rules of the system which determines the connection between the order of amino acids and the 3-dimension protein that results.

Related topics: http://biology.stackexchange.com/questions/23246/how-does-protein-denaturation-work http://biology.stackexchange.com/questions/23763/is-there-a-difference-between-polarity-and-hydrophobicity/23777#23777 http://biology.stackexchange.com/questions/23586/why-is-cysteine-and-tyrosine-used-to-calculate-a-sequence-isoelectric-point/23597#23597

http://fold.it/portal/

It sounds like your question is "what are the rules to protein folding?"
That's not the only way to read your question.
Protein Folding is a unique problem - a 1D sequence maps to a 3D object.  Since proteins mediate nearly all biochemical transformations and therefore mediate life's processes, protein folding one of the great unsolved problems in science today.
You can see in the example folded structure above there are helices and flat sheets of connected strands.  You can see below in the schematic alpha beta barrel motif of triose phosphate isomerase (TIM) how elegant these structures can be.

Although the combinations and overall organization of the beta sheets and the alpha helices are boundless, there are some unifying motifs in these structures.
Long ago, a couple of researchers tabulated the amino acids probability of being in alpha helices or beta strands.  The Chou-Fasman model is important in that it has approximately ~70% chance of detecting alpha helices and beta strands.  Its not a great accuracy but what's really amazing about these algorithms is that they show that local forces - the interaction of amino acids near each other in the sequence have something to do with the formation of at least alpha-helices and beta strands.
There have been pounds worth of papers written since then.  In general, statistical surveys of protein sequences have been able to identify folds or motifs by a long list of string and machine learning algorithms.  Hidden Markov Models and Bayesian profiles are popular. Of course all these are similar to Chou-Fasman in that they work on the sequence in short segments more or less.
For a while it was thought that molecular dynamics and other discrete simulations might help to solve protein folding by allowing long distance interactions to be involved.  Just simulating the entire protein molecule in a computer program as it moves into a folded conformation, but this has not proven to be possible for a couple of reasons: (1) it takes a long time for a protein to fold relative to the length of a tractable simulation (2) the forces involved in protein folding and molecular size scales are not really easy to simulate - they do not precisely simulate the forces and behavior experienced by molecules and they involve many more solvent molecules than most computations can involve - even today's server farms would get clogged up with respectable protein folding simulation.
Since 1994 the Critical Assessment of Structure Prediction (CASP) have provided an open competition every 2 years where 3D structures that have been determined experimentally is held from publication.  While its well attended a new class of algorithms showed up around 2000.  These algorithms work on the assumption that local forces are important to protein folding, but often incorporating molecular dynamics.  Using MD or statistics based on protein structures (see the RCSB for the repository), segments of the protein sequence are tested for structural tendencies.  chaining these predictions together, initial protein folds are put together.  Once put together long term interactions can assemble a protein structure.
BTW that is not to say that Protein folding is solved - the solutions that come out often produce a structure that is really similar to the final structure, but often there are substantial differences.
Just looking at the individual sequence there are no simple rules to decide how the protein fold - ultimately molecular physics of the individual sequence determines where the fold will go.
This is incredibly terse, but it could get you started.  Study of protein without any helices or beta strands is a topic in itself - they can be treated the same way as above.  Then there are also proteins who do not have a single fold, but are dynamic and flop around all the time, or only have a shape when in contact with a surface of some kind.  So there's even more.

Thanks for this answer (very helpful).  You wrote:  "ultimately molecular physics of the individual sequence determines where the fold will go".  Might not the rules that I am inquiring about "simply" be the 'knowledge' of how to implement the principles of molecular physics based on the properties of each amino acid?
What leads me to think that something like this might be true is the fact that all proteins (in their vast variety of shapes and functions) are formed from just 20 different amino acids.

Yes - it really depends on what you call rules. If you call Newton's laws 'rules about how objects move' you could just call them rules. we could say "vanderWaals forces, Maxwell's equations, Hooke potentials and Newton's Laws" are the rules of protein folding, but its not much of a guideline.  Oh nuts i also forgot to mention that protein folding is not really solved.  I will put that in..

Disclaimer: This is an interesting question if I have understood what you are trying to ask. But unfortunately the case is that there are so many different cases its impossible to cover them here. Other answers talk about folding and modification, but these are still heavily dependant on the "2d" DNA sequence and aren't useful if all one has is a final protein, so I'll discuss the 'rules' of a final structure. This started as a comment and got too long!
In summary, no, there are not many examples in the grand scheme of things where rules at a protein level exist in any sort of grammatical way. Its all about 3D chemistry.
Protein Structure in relation to Function.
Functional areas in a protein are often made up of structures like alpha helices and beta sheets linked by very flexible looping regions. The way these structural elements are connected is generally different in every protein. However some motifs that perform similar tasks can be identified by their 3D shape and order of connection (which I think is what you're asking about). For example the OB motif (images and good starting point here) has a strict order that the beta sheets follow, whereas the helix is optional. Although this is a neat example of protein "grammar", its very much exceptional when motifs like this are identified.
No Obvious Rules.
This following answer is educated guessing, and other peoples comments would be helpful.
Proteins are much more complex than a 2 dimensional language like English or DNA. One way to think about why your question is difficult to answer is considering that protein biochemistry happens in 3D space whereas our other examples, language and DNA, operate linearly in a 2D line.
Any evidence of a linear ordering in a finished protein implies very simple folding and post-translational processing. Most biochemical tasks are not simple and require complex nuances in the enzymes' chemistry (which comes from 3D chemistry, not 2D sequence). DNA is complicated too, but like our language, it is designed to be simple and read quickly in a line. This means if a sequence wants to do something a bit more sophisticated, it needs a specific order. This isn't a problem in 3D space as there is a lot more to variation other than sequence.

"Proteins are much more complex than a 2 dimensional language like English or DNA."  Good point, but what are we to make of the fact that the initial formation of a protein takes place in a linear, 2-d chain of just 20 amino acids?  It certainly seems to start out in a language-like fashion (don't you think?).
If so, should not the question be what are the rules or principles which determine how the transformation is made from a 2-dimensional, language-like system to a 3-d dimensional, functional machine?

I'm going to assume that you mean "are there any rules for which amino acids can follow which amino acids in a protein?" The answer is no. In terms of a protein's chemistry, there is no restriction on the amino acid sequence.
However, not all amino acid sequences will fold into a definite 3D structure, and not all amino acid sequences will be soluble in water. For these reasons some amino acid sequences cannot be produced via the standard in vivo process (i.e. by a ribosome), but there's no reason they couldn't be produced through chemical synthesis.

I suppose you are not asking how does DNA code for mRNA which has codons (sets of 3 nucleic acids) when read in the correct reading frame (where 3 base pairs each are read beggining from the start codon) a ribosome then translates this into protein... theres a lot more details then what I said... that is called translation:
http://en.wikipedia.org/wiki/Translation_%28biology%29
Afterwords the protein is folded into a 3d shape
http://en.wikipedia.org/wiki/Folding_funnel
Other stuff (other than amino acids) can be added, like a a lipid for anchoring into the membrane (GPI anchor or prenylation) or sugar (glycosylation) amoung other things, this is called post translational modification.
http://en.wikipedia.org/wiki/Posttranslational_modification
if you are asking about the evolution of proteins, here is another article:
http://en.wikipedia.org/wiki/Protein_family
wikipedia can get pretty detailed, also there might not be a lot of pictures... lippincott's illustrated biochemistry has lots of great pictures... but it's a book for health science students, not very abstract/theoretical/philosophical so you won't get much on evolution of protein families among different life forms...
If you are asking which amino acids can go together and which stuff can't, I dunno, I'm not a biochemist...

I hope that I got what are you asking. You give the example of words, it's not good one. Look on the protein like a machine or maybe cupboard. You bought one in Ikea and now you need to follow the instruction to bring together all the elements. If you just paste together all the parts you will not get a working cupboard. What rules the parts of cupboard following? Physic.

Take for beginning the Bohr model of atom. If you want simpler example - planets in solar system. After that put 10 atoms together to from the simplest amino acid. What structure will they get? Bring near another amino acid. How will they interact together?

The rules comes from physics. And they are very very very very complected. To understand what structure some protein will get or how it will interact with another protein - you need to take all the atoms in the system and to know how they will act one with another. Only huge computers can calculate such things - and only the simplest of them.

Edit: answer to the comment:
Thats what so amazing in the nature. The evolution found the way to build all the body proteins just from approximately 20 amino acids. By the way that doesn't mean that there is just 20 a.c. There are more that 500. 240 Of them can be found free in nature and other only only as intermediates in metabolism. (http://onlinelibrary.wiley.com/doi/10.1002/anie.198308161/abstract)

If you want another example - take Lego. You have - lets say - 20 types of different peaces but you can make a lot of different things from them.

The nature must use a minimal amount of building blocks. This giving advantage in the evolution cause it is simpler. Look at the DNA. Its build just from 4 building blocks! And caring all the information of how to form entire body. Isn't it amazing? :)

I agree that the protein is a machine and I understand (thanks answers like yours) that the laws of physics are involved.
Nonetheless, there seems to me a crucial difference between man-made machines and protein machines.  The machines we make (including from IKEA) are not made from 20 fundamental parts which when put together and folded properly give me the end product I need.
But that is how proteins are made -- does that not suggest that there must be some intervening logic or system which mediates between the linking of the fundamental units and the functioning of the 3-d machine?

I posted an edit to my answer.

authors: Данило Омельченко


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Dreadnoughtus: Why are new taxa named using Dog Latin?
Once upon a time, binomial nomenclature was expected to follow Latin rules: the genus had to be a noun and the species had to be an adjective that agreed with the genus according to Latin rules of adjectival agreement with the noun modified by it. That’s why we have species names like sativus, sativa, and sativum seen again and again, the exact form depending on the genus’s gender.
So if knew a bit of Greek and Latin, you could figure out something about what binomials such as Stegosaurus armatus or Dodecatheon pulchellum might be about.
Enter 2014, and with it such new binomials as the ponderous Dreadnoughtus schrani.  That looks more like Dog Latin than Classical Latin: just tack a few Latinate-looking suffixes to words that cannot be decoded using any known roots from Greek or Latin.
When I first read about it, I honestly thought somebody was making a bad joke. It’s not like the Greeks and Romans never thought of fearing nothing; one might imagine a taxon built out of actual classical roots — perhaps like *Timendumnihil — would have been more universally understandable than the Dog-Latin form Dreadnoughtus we’ve been stuck with.
Is there no requirement that new taxa have classical forms?  Was there ever, and if so, when and why did this change?  Or, if there was not, then why did everybody seem to go along with the scheme for so long?

I'm not a latinologist, but I don't think new words have been added to latin or (classical) greek in a long time. This creates a limited vocabulary, and new taxa may not fit the classical vocabulary. Additionally, classical languages are no longer widely taught, so the average person may have more exposure to pseudo latin than to real latin. Pseudo latin may also be more easily understood by the lay audience than real latin.

There is an International Commission on Zoological Nomenclature, to which submissions for new organisms' names is strongly recomended. The discoverer does have some leeway within this system if there is no Latin name that well-describes this species. Your example is one of many.
Chapter 31, for example, clearly states:

31.1.1. A species-group name, if a noun in the genitive case formed from a personal name that is Latin, or from a modern personal name that is or has been latinized, is to be formed in accordance with the rules of Latin grammar.

Examples. Margaret, if latinized to Margarita or Margaretha, gives the genitives margaritae or margarethae; similarly Nicolaus Poda, even though the name of a man, if accepted as a Latin name, gives podae; Victor and Hercules, if accepted as Latin names, give victoris and herculis; the name of Plinius, a Roman, even though anglicized to Pliny, gives plinii; Fabricius and Sartorius, if treated as Latin names, give fabricii and sartorii, but if treated as modern names give fabriciusi and sartoriusi; Cuvier, if latinized to Cuvierius, gives cuvierii.

31.1.2. A species-group name, if a noun in the genitive case (see Article 11.9.1.3) formed directly from a modern personal name, is to be formed by adding to the stem of that name -i if the personal name is that of a man, -orum if of men or of man (men) and woman (women) together, -ae if of a woman, and -arum if of women; the stem of such a name is determined by the action of the original author when forming the genitive.

Example. Under this provision, the species-group names podai from Poda, victori from Victor, and cuvieri from Cuvier are admissible. The names puckridgei and puckridgi may be formed from Puckridge.

Similar rules apply for genus and family names.
Since your example was a new genus and species, it didn't "fit" into previous categories (in the future, if and when similar discoveries are made that shed light on the genus' relation to others, the name can and will be changed accordingly, with or without the authors' approval).

According to the research team that discovered the taxon, the genus name Dreadnoughtus "alludes to the gigantic body size of the (which presumably rendered healthy adult individuals nearly impervious to attack)" and to the two dreadnought battleships of the Argentine Navy, the ARA Rivadavia and ARA Moreno. Thus, the genus name also honors the country (Argentina) in which Dreadnoughtus schrani was discovered. The name of the type species, schrani, was given in recognition of the American entrepreneur Adam Schran for his financial support of the project. - Wikipedia

A "good" or "useful" taxon is commonly taken to be one that reflects evolutionary relationships. Since this one does not, in a few decades, this name may well be gone.

Brava for a well-documented answer! I hadn’t realized that it might get its name revised that easily.  And your genitive mention reminded me of last year’s new orchid species in an existing genus,  Lophiaris silverarum — “of the Silveras” in the genitive plural -arum.

Names get revised all the time, especially now with the ability to determine relationships genetically.I feel bad for pathologists, who must face the reclassification of bacteria regularly, it seems.


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Are there any known health benefits / risks from milliampere current (0.1-2 mA) on forehead?
This is about devices like that sold by foc.us that allows user to apply a small current on a specific part of the forehead.
For the sake of this question I use the foc.us "gamer" model as example. This device has:

a headset with two (moist)electrodes that are positioned on the forehead
a controller unit that is used to apply a (selectable) current between 0.1mA - 2.0mA through the electrodes

[Update:] the electrodes have a surface area of 35mm x 35mm (they are 12mm thick).
According to information received from the company this device is a "micro current signal generator" and can be operated in "tDCS" mode (I am not sure what "tDCS" means). The device has a timer so that it can be set to provide this current between 1 - 40 minutes.
They sell this device with an (explicit or implicit) claim that is helps the wearer improve their ability to focus (on, for example, a game that the wearer is playing).
Are there any known health benefits (such as improved ability to focus) or dangers (damage on the nerve system?) from applying a current on the forehead?

Interesting question!
You ask 3 questions if I am correct:

What is tDCS;
What are the adverse effects of tDCS (at 0.1 - 2 mA);
What are the health benefits (enhanced focus);

I will answer your questions one by one:
(1) What is tDCS: tDCS devices are TransCranial Direct Current Stimulation (tDCS) devices. They send direct current through (trans) the skin and skull (cranial) to the brain.
(2) Adverse effects: EDITED: A review by one of the leaders in the field (Nitsche et al. Transcranial direct current stimulation: State of the art 2008; Brain Stim. (1) 206-23) mentions that current densities between 0.029 and 0.08 mA/cm2 are regularly applied in humans, with session durations of up to 40 min. Side effects are summarized in Table 1 in the cited review. Side effects are mostly nonexistent, though quite a few studies report some itching or tingling sensations under the electrode surface. Very rarely headaches or more serious side effects are reported. The authors predict that the limits will probably increase in the coming years (i.e., after 2008).
A more recent review, however, mentions a slightly lower upper limit of regularly applied current densities, namely 0.066 mA/cm2 in humans, using stimulation times of up to 20 min.
The highest upper safe current limit I could find is mentioned in a 2009 paper by Bikson et al. that mentions 0.14 mA/cm2 based on animal data.
Note that it is not current level per se that determines safety, it is the density of the current that matters. Moreover, the duration of stimulation will be an important factor to take into account.
To go back to your device: in case of 3.5 x 3.5 cm square electrodes (i.e., 12 cm2) as mentioned in the question, the current level range (0.1 - 2 mA) represents a current density range of 0.008 - 0.16 mA/cm2. However, I skimmed the website and they mention 3 cm square sponges or 3.5 cm diameter circular sponges, which brings the upper limit to 0.22 and 0.28 mA/cm2, respectively. The website says the device can be used up to 40 min.
In all, based on this literature review on tDCS and despite the company claiming their device is safe, I would conclude the upper limit of 2 mA not advisable, as its assciated current density exceeds the upper limits that I was able to find (Note, my answer is by no means a comprehensive review on safety of tDCS !). Dependent on the exact electrode surface you could calculate your own safety limit based upon the references cited.
(3) tDCS and enhanced focus: Health benefits in terms of ability to focus: I searched Google Scholar using the search term "TransCranial Direct Current Stimulation attention", which yielded no useful hits.
Another way to go for your focus question is to look at what cortex is situated underneath the 'forehead' that is stimulated by this device. Basically it is the prefrontal cortex:

Stimulating the prefrontal cortex reportedly increases working memory (Fregni et al., 2005) and motor learning (Nitsche et al., 2003). Working memory basically allows a person to use acquired information (let's say seconds or perhaps minutes ago) in subsequent tasks. Motor learning is essentially training of motor skills. Both motor learning and working memory are essential in gaming(!). However, one should carefully read the cited articles (and perhaps related ones, I gave just a few) in terms of effect size, electrode placement and stimulus conditions (including, but not limited to: current level, stimulus duration, stimulus waveforms, stimulus frequency, session duration etc.) to extrapolate their findings onto your device.

Thank you for a detailed answer. I updated the original question with the electrode measurements.

@x457812 : Please read my revised answer. I added stuff and especially sub-answer (2) is extensively revisited as the electrode size changes things considerably

Very nice, thank you for the extra work on the answer.


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Taste of salt water
I had a question relating to chemistry and biology, so please tell me if this is suited better for the Chemistry website.
My question was, if water dissolves salt by separating the two ions, the Na+ ion and the Cl - ion, then why do we still taste salt in the water? The ions in the salt are still separated, so wouldn't the water not taste like salt?
(Any help on fixing this question would be appreciated)

We taste things in solution, either in liquids, in saliva, or a combination of both. Salt also separates into ions in the saliva on our tongues, the water in our mashed potatoes, the juice on our steaks, etc. If our tongue was perfectly dry, salt would not taste salty (nor would it "dissolve" on our tongues, as it does). That's what we are tasting: salt in solution as water, Na+ and Cl-. Like seawater.

Perception of saltiness is because of the sodium ion. At concentrations ≤ 100mM, sodium ions elicit a taste response pathway which is inhibited by a small molecule called amiloride. Other monovalent cations do not elicit this "amiloride-sensitive" response.
At higher concentrations sodium ions elicit a non-amiloride sensitive response; other ions like K+ also elicit this response.
The Epithelial sodium channel — ENaC, is responsible for sodium taste perception (amiloride sensitve) and there are distinct population of taste receptor cells that express this channel (Chandrashekar et al., 2010).
So other sodium salts like NaNO3 would also taste salty (the anions can surely have some role in the difference of taste)


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IgA complement activation
Recently, I have been reading Janeway's immunobiology and had a question on immunoglobin A. I read that IgA activates the complement pathway using the Fab fragment of the IgA. How does IgA do that? I can't seem to find an information on that in  the book or online.

@anongoodnurse 4th edition.. in Fig 3.20 on pg 102, it mentions that alternative complement pathway activated by Fab for IgA1

In the 2011 edition, compliment activation is discussed beginning in Ch. 10.

Oh, the 4th editions is very old. Even the NIH bookshelf has the 5th edition. Can you link the figure from the NIH edition so we know which one you are talking about?

@Chris in the 5th edition, the figure is 4.16

I found some reports on it (like reference 1) but there is an oddly little amount of publications on this topic. then I found this review in Mucosal Immunology (reference 2, interesting to read) which doubts this activation. It says:

Interaction with complement
IgA lacks the residues identified in the Fc regions of IgG or IgM that
  bind to C1q, and consequently IgA does not activate the classical
  complement pathway. Although several papers have reported activation
  of the alternate pathway by heat-aggregated, denatured, or
  recombinantly generated IgA, this seems to be essentially artifactual,
  and intact native IgA antibodies complexed with antigen inhibit
  complement activation induced by IgG or IgM antibodies. This
  effect is also replicated by Fabα fragments generated by cleavage of
  IgA1 antibodies with IgA1 protease. It is telling that mixed
  aggregates of heat-denatured IgG and IgA activate the alternate
  pathway in proportion to the content of IgG, and that C3b becomes
  covalently linked to the IgG heavy chains, not to IgA. Intriguing
  reports that IgA antibodies promote complement-dependent lysis or
  opsonization of encapsulated bacteria probably also arise from
  facilitation of alternate pathway activation by bacterial
  polysaccharides

It names three papers to underline this (which are number 45-47 in the reference list of the article), which can be found as references 3-5. So the question here is not only how the mechanism looks like, but also if this is real or an artefact.
References:

Activation of complement by human serum IgA, secretory IgA and IgA1
fragments.
Structure and function relationships in IgA
Anti-inflammatory activity of human IgA antibodies and their Fabα
fragments: inhibition of IgG-mediated complement activation
IgA blocks IgM and IgG-initiated immune lysis by separate molecular
mechanisms.
Activity of human IgG and IgA subclasses in immune defense against
Neisseria meningitidis serogroup B.

Janeway says much the same thing in different words. IgA is a very minor player in compliment activation, and even then, only in certain situations.

Roos et al (Journal of Immunology, 2001, reference below) suggests that IgA binds MBL, and activates complement by facilitating the lectin binding pathway for complement activation rather than being a major player in the alternate pathway.
Another group of researchers (Daha et al, in Nephrology Dialysis Transplantation, 2006) discusses a potential fourth method for complement activation, as well as describing IgA nephropathy as a result of both alternate- and lectin-activated complement activity. (second reference)
http://www.jimmunol.org/content/167/5/2861.full
http://ndt.oxfordjournals.org/content/21/12/3374.full.pdf

Your third paragraph is slightly confusing. "Has this been discredited?" and then you provide two sources. Are you asking if those articles have been discredited, in which case that should not be part of an answer but should be raised as your own question? Please try to rephrase to make the intention of your answer clear. Thank you.

I think you're right, AML--I decided just to remove the third paragraph entirely, and let the research articles I quoted speak for themselves.


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What's the worst that can happen from too much sleep deprivation? Can you die?
It is well known that sleep deprivation causes considerable discomfort in humans (and has even used as a form of torture), but nevertheless there have been people who went through protracted sleep deprivation, apparently with no long term consequence.
I've noticed that sleep deprivation seems to trigger an intense sense of "this is bad for me" - yet given the apparent lack of ill effects (beyond the obvious) I cannot say whether this is merely anxiety over discomfort, as opposed to a genuine perception of physiological damage.
What if you were to go without sleep for as long as possible, despite the discomfort? Is it possible to commit suicide in this way (and what would be the cause of death)? Would you fail because you eventually ignore whatever stimulus was preventing sleep, and sleep anyway? Would artificially counteracting the temporary debilitating physiological effects (such as loss of body temperature) allow you to survive sleep deprivation of arbitrary length?

yes, you can die!

I heard something on the radio the other day that mentioned studies on rats that eventually died after sleep deprivation, but it took some effort to keep them awake that long, can't remember the reference. IACUC probably wouldn't approve it today.

@user137 There are in fact several such studies (for rats, they usually rotate them into shallow water which forces the rats to wake up and move). The first problem is that these are in rats (or rats, flies, etc) and I am asking about humans. The second problem is that I haven't been able to figure out how exactly it is that these rats die: Do they just drop dead, or do they fall into such deep sleep that they are unable to wake up even as they drown in the water?

I believe one of Michael Jackson's causes of death was lack of sleep - that's why his doctor was sedating him. Trouble was, anesthesia isn't the same as sleep. Sorry, don't have a ref ATM, which is why this is a comment

@Superbest the rats die from hypothermia. Sleep deprivation increases the organism's need for energy. At first, sleep deprived animals overeat, but at some time, they cannot compensate and die. After the metabolism has reached the point of no return, you can even let the rats sleep and they will die soon nevertheless. See the popular science book Sleep thieves for a nice summary of the studies.

The short answer is: Yes.
Fatal familial insomnia is a genetically passed down disease that at some random point in a carriers life will suddenly stop them from sleeping, ever, they die within 7 to 18 months
I know you did not ask about the disease, but it shows (even without illegal war tests) that it will kill you eventually, even in humans.
I believe in humans without the disease a complete lack of sleep may kill them within weeks, but who knows? maybe it was the drug.

Eventually your brain will start to break down and malfunction.

Chronic poor sleep puts us at increased risk for serious medical conditions, such as obesity, heart disease, and diabetes. During sleep, our bodies secrete hormones that help control appetite, metabolism, and glucose processing. Poor sleep can lead to an increase in the body's production of cortisol, also known as the stress hormone. In addition, skimping on sleep seems to throw other body hormones out of whack. Less insulin is released after you eat, and this along with the increased cortisol may lead to too much glucose in the bloodstream and thus an increased risk for type 2 diabetes.

At 24 Hours: Impaired Coordination, Memory, and Judgment
At 36 Hours: Physical Health Starts to Be Negatively Impacted
At 48 Hours: Microsleeps and Disorientation
At 72 Hours: Major Cognitive Deficits and Hallucinations
After even longer, your brain deteriorates and eventually you will die.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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awakening effects of light
I tried reading by light from a neighbouring room and felt sleepier than if my own lights were on.
Is there a formula for the intensity of light vs physiological preparation for sleep(calcium, melatonin)? Or is there a threshold intensity below which the body goes to "sleepy mode"?

I don't believe either is the reason. Back in the day of early man, the different intensity levels of light was used as a signal to our body's "master clock" to tell us when it was time to go to sleep. So to simply put it, when exposed to less intense light, such as artificial light, its picked up as the dimmer, less intense, light akin to when historically we would be getting ready to go to sleep.

There are new studies that are challenging this hypothesis, but there is some degree of speculation when trying to work out biochemical reactions of our prehistoric ancestors and how those genes affect us today.

It appears that short wavelength light (that is light around the blue and purple end of the electromagnetic spectrum) does have a significant effect on melatonin levels and the 'alerting response'.

Exposure to 2 h of monochromatic light at 460 nm in the late evening induced a significantly greater melatonin suppression than occurred with 550-nm monochromatic ligh - See more at: http://press.endocrine.org/doi/abs/10.1210/jc.2004-0957#sthash.feusLJf4.dpuf

Note that 450nm wavelength light is blue and 550nm light is yellow.
Interestingly, there is some evidence that occular photoreceptors (being neither rods nor cones) play a role in setting the circadian clock. These researchers hypothesize that retinal ganglion cells (nerve cells) are photo-receactive and play a role in regulating the circadian clock via innervation of the hypothalamus in the central nervous system.

Light synchronizes mammalian circadian rhythms with environmental time by modulating retinal input to the circadian pacemaker—the suprachiasmatic nucleus (SCN) of the hypothalamus. Such photic entrainment requires neither rods nor cones, the only known retinal photoreceptors. Here, we show that retinal ganglion cells innervating the SCN are intrinsically photosensitive. Unlike other ganglion cells, they depolarized in response to light even when all synaptic input from rods and cones was blocked. - Science 8 February 2002:
  Vol. 295 no. 5557 pp. 1070-1073
  DOI: 10.1126/science.1067262   http://www.sciencemag.org/content/295/5557/1070.short

So, while there is no 'formula' per-se, we might conclude that higher energy wavelengths (that is shorter wavelengths near blue and purple) are more effective in suppressing melatonin and more effecting in keeping you awake, as opposed to lower energy wavelengths like yellow and red.


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Production of processed Insulin in bacteria
Genetically-engineered bacteria are used to produce insulin in industry, but as far as I know, the bacteria can produce only proinsulin. Why is that? What happens in the human body in order to make functional insulin, that can't happen in some microorganisms? In the body proteases cut some at amino acids, and cleave the polypeptide while other enzymes create disulfide bonds.  Why is there no bacteria in the industry that can do the same? It's not possible for some reason or in other words — can such a bacterial strain not be engineered?

Have you read the Wikipedia article on Proinsulin? This has an explanation, can you say, which part of it you don't understand?

@Chris, yes. I don't see there answer to my question - why genetic-engineered bacteria could produce only proinsulin and not functional insulin? In the body proteases cut some amino acids, and then enzymes creating disulfide bonds. Why there is no bacteria in industry that can do the same? It's not possible for some reason?

Because insulin is held together by disulfide bonds, which are a pain the ass to properly form in a bacterial expression system. We tried to make bee venom PLA2, which has 5 disulfides, in e coli, and even following a published protocol for recovering the misfolded protein from inclusion bodies, unfolding it, refolding it with glutathione, our yield was terrible. Trying to mutate any of the cysteines ruined the refolding and all enzyme was inactive. Producing proinsulin is just easier at industrial scale.

@user137 Thank you! But why is it so hard to get right disulfide bonds in bacteria? Isn't it work of some enzyme?

@barbos The cytoplasm is a reducing environment, where disulfide bonds are likely to be reduced to free thiols. Disulfides survive better outside the cell. This is true for eukaryotes too, the proinsulin doesn't get converted to insulin until it's in a secretory vesicle, protected from the reducing environment.

@user137 this seems to be good enough for an answer to me

@rumtscho Answer is written. Made a comment initially because I don't really know the details behind industrial insulin production and someone from Eli Lilly or Norvo Nordisk would be better suited to answer it, but I don't think they would.

@user137 sure, details are always great. But a partial answer is still welcome, especially when it contains knowledge novel for the most readers. And I doubt that many of the site visitors have tried protein synthesis in bacteria, so something which might be everyday knowledge to you (that disulfide bonds don't work well) is likely to be valuable new information for many.

Insulin is processed from proinsulin by folding the peptide and forming 3 disulfide bonds before cleaving the peptide in 2 positions, leaving 2 peptide chains held in place by the disulfide bonds. This process is summarized in this image:

This only works because the peptide is packaged in a secretory vesicle during synthesis. This protects the peptide against the reductive environment of the cytoplasm, where glutathione is likely to reduce the disulfide bonds that hold insulin together.
When industrial insulin production moved from extracting the hormone from animal pancreases (pancreai?) to bacterial production of human recombinant insulin, glutathione was likely to cause a problem because simple protein production in bacteria just builds the protein in the cytoplasm, where glutathione is present. It is possible to export the protein into the periplasm during synthesis, similar to how proinsulin is moved into the endoplasmic reticulum during synthesis in human cells, but this can complicate protein purification (larger volumes of media, if protein is inside cells you can spin the cells down and work with a smaller volume).
Note that more recent methods use yeast to make insulin, potentially allowing production of actual insulin instead of proinsulin. And modern purification methods can extract insulin from animal sources that is just as good as recombinant sources.
I know from personal experience that it can be very hard to produce proteins with multiple disulfide bonds in bacteria. We attempted to produce mutants of bee venom PLA2 in E. coli, but the protein was misfolded and wound up in inclusion bodies. We purified the inclusion bodies, unfolded the proteins, then slowly refolded them by dialysing the protein in a glutathione solution. We aimed at making a protein with a free thiol for later chemical modification, but that free thiol just picked up a glutathione we couldn't remove without ruining enzyme activity.
Also please note that I am not fully aware of how insulin is made on the industrial scale and I could be wrong. That's why this was originally a comment.

As far as I know, the extraction from animals plays no role anymore - the process completey relies on production by GMO.

I think some poor countries still use animal insulin, the wikipedia page also says animal derived insulin is used for pets with diabetes. Probably cheaper to give cats and dogs cow insulin than to start full scale recombinant production of cat and dog insulin.

@user137, again thank you very much! You wrote about moving insulin to periplasm. So is it possible to pump hormone completely out of the bacteria? To the medium that it lives in. And we will get a final product - working insulin?

@Barbos Yes it should be possible to secrete it. B subtilis is often used for that purpose. Purification shouldn't be harder, just different.

@canadianer, thank you. I found just that article - http://link.springer.com/article/10.1007/s00253-003-1289-4. There is again production of proinsulin and not the working insulin. Maybe you can point me to the right source?

@Barbos I was only speaking hypothetically. Proinsulin processing is enzymatic, which complicates things.

So what, hypothetically, need to be dune? If I understand right - we can pump proinsulin to the periplasmic space, and it isn't a reducing environment, right? So the next step is to pump to the same area enzymes that will create a disulfide bonds. Am I right? Thank you!


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Why does renal artery stenosis lead to activation of Renin-Angiotensin system?
To my current understanding, stenosis or narrowing of the arteries would mean higher blood pressure, similar to atherosclerosis. So the Renin system should be suppressed to counter the high blood pressure. But..
I have read in a textbook that renal artery stenosis means lower blood flow in the kidney due to the narrowing of the artery. Thus the Renin system is activated to increase blood pressure.
So why does narrowing of the renal artery cause a decrease in blood pressure, and not increase?

Read your own question closely; the answer is right there. What purpose does the renin-angiotensin system serve normally? How is blood pressure determined at different places in the body? Why would a reduced blood pressure in the kidney elicit activation of renin-angiotensin system? How would that affect the rest of the body?

I understand how the renin-angiotensin system works. What I do not understand is why a stenosis in the renal artery leads to a decrease in blood pressure whereas atherosclerosis in other blood vessels leads to a increase in blood pressure. Aren't both narrowing of the blood vessels? So why the different outcomes?

So why does narrowing of the renal artery cause a decrease in blood pressure, and not increase?

It doesn't. It causes an increase.
If the blood flow to the kidney is decreased for any reason (for example, hemorrhage or dehydration), the kidney is one of the organs that will protect it's perfusion by causing an increase in BP through the renin-angiotensin-aldosterone system (RAAS).
Very briefly: decr. blood flow -> renin secretion by juxtaglomerular cells -> conversion of serum Angiotensinogen into Angiotensin I (+ ACE) -> Angiotensin II => elevated BP (by a host of mechanisms).
If there is renal artery stenosis, the kidney will try to compensate for this (locally) reduced blood flow by activating the RAAS. The kidney doesn't 'know' that the blood flow/pressure is only locally reduced. It will cause systemic hypertension as a way to increase it's blood flow.
Atherosclerosis is a whole different ball of wax.


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What triggers programmed cell death in humans (from outside the cell)?
What triggers programmed cell death in humans? Is it decided by the brain (for the entire body)? Or is it a local decision of a cell by its environment? Something else?
I realize that there might be different cases. But I'd like to get a general idea of where (and why, actually) does this happen.
EDIT
As linked to by a comment below - one type of cell-death (Necrosis) just "happens" to a cell. And perhaps there are other types that are decided by the cell.
What I'm asking about (and trying to understand more) is about the idea that cell-death might be initiated externally to the cell because it would be beneficial to the whole organism. Such as "the separation of fingers and toes" mentioned in Wikipedia  .   "Who" would initiate it? Are there examples of the CNS initiating it? Notifying the cell by nerves? By hormones? Are they initiated by neighboring cells? (And if so - what cells have the "clout" to send such signals?)
What I'm trying to understand is who decides when a cell dies in those cases where it's not the cell itself.

Have you read the wikipedia article on apoptosis? If not, please read it, then [edit] your question to narrow it down to a specific question about the process. As it stands now, this question is far too broad, as there are many different ways of triggering apoptosis, and many different pathways within the cell for effecting it.

@user133943 you should edit your question to specify that you mean regulated cell death (as it applies to development). As it is written, your question is too broad

The answer is, in part, it depends. Let's think of the PI3K/AKT pathway. Akt actively phosphorylates BAD which abrogates the Bax/Bak apoptosis pathway. RTK's at the plasma membrane activate this pathway when bound with survival factors. In the absence of survival factors, Akt would become dephosphorylated and you'd have a net movement toward apoptosis. In a particular form of cell death called anoikis, this could be as simple as detaching from the extracellular matrix. So anything that halts the binding of survival factors could play a role.
In the case of immune response, activated Tc cells can induce apoptosis by secreting pore-forming enzymes as well as enzymes that directly activate caspases. The Tc cells also express Fas on their membrance which is involved in the extrinsic apoptosis pathway. TNF (tumor necrosis factor) may also bind cell surface receptors as sort of a death factor, and push towards apoptosis.
These are just examples, some generic searches about apoptosis, necroptosis, entosis, and a myriad of other programmed death mechanisms will yield a very comprehensive overview.

Thank you. If I understand you correctly - the first type you mentioned is (very generally) - an example of cells having a built in mechanism to detect a condition (such as being detached from their natural surroundings) that warrants cell death. The second - more pertaining to my question - would be: the immune system. (Please feel free to correct me if I'm wrong.)

@user It's a very textbook answer, here's a review of some apoptotic regulation mediated by extracellular signaling. It's a complex response that may be regulated by paracrine, autocrine, neuronal signals in addition to cell-cell interaction. There's a bunch of different pathways that all differ in their mechanism of action.

One event that comes to mind is the use of radiation on cancer patients. Radiation is an external event that can trigger apoptosis in humans 1. When cancer patients receive radiation, the treatment is localized. The brain isn't telling the cells to die it is the radiation effects on the cell.

Ionizing radiation can also induce apoptosis via the generation of free radical oxygen species 2.

Free radical oxygen species does this by searching for an electrons in the molecular make up of the cell 3.


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Which fruit compounds affect the speed of fructose absorption?
Blood fructose levels are not regulated by insulin in the human body. This means that the body absorbs pure fructose very fast, and it raises the blood fructose levels rapidly.
Do fruits/ vegetation contain compounds, which help the digestive system to regulate the absorption of fructose? If so, what are they?

What do you mean by "fructose-regulating factors"? Hormones/substances which control the amount of fructose in the plants or something else?

Are there substances in fruits which help the body regulate fructose absorption?

Do you mean substances produced by the plants, for the humans/animals who eat the plants? If you don't mind me asking, what's in it for the plant?

@user8669 Please tell me, that this edit is valid, or did you mean something else?

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=919892&fileId=S0007114505001431

@Resonating as far as I remember digestion, this is a reasonable question. The speed of sugar absorption depends on the chyme contents, not just the percentage of sugar present in them. This is why the same food in different preparations has a different GI index, and although I don't remember if it applies to fructose as well, it's not too far fetched to ask if it applies, and what's the mechanism behind it. It doesn't matter what's the reason for the plant to contain whatever it contains. But I agree that the question as written is hard to understand, and possibly way too broad.

Drawing an analogy to other sugars, what would the absorption-regulating factors be for those sugars? General things like pH, salt content, etc or some specific signaling moecules?

@inf3rno Yes, this is exactly what I meant. Thank you very much for your edit.

Probably tannins inhibit the absorption of fructose, but that's just something I read in a post. Visit my link above, it claims, that eucalyptus leaf extract inhibits intestinal fructose absorption in rats, so that is one match. I don't have time to find more related articles, but ofc. there are compounds in fruits which makes them more healthy than processed food e.g. with corn syrup and other fructose containing components.

Yes they do. The answer is glucose.
Let's begin at the beginning: you eat a piece of fruit. The fruit contains many different kinds of sugars, including fructose and glucose. One of the immediate effects your digestion of this fruit has is to raise the levels in your blood of every type of sugar that was present, and the blood levels of many other types of nutrients as well. This has nothing to do with how well your body does/doesn't absorb fructose, it is simply a normal step in digestion.
Next, GLUT2 transporters in the insulin producing cells in your pancreas import glucose. This acts as a signal that tells those cells to start producing insulin. Insulin then diffuses around the body and produces myriad effects, including upregulation of GLUT4  activity across the body. These GLUT4 transporters are present on cells in many parts of your body and are what are responsible for taking up most of the glucose from your blood.
Now on to fructose. GLUT5 is the main fructose transporter. Just like GLUT4, GLUT5 activity is also regulated by insulin, but in a less quick and dramatic fashion than with GLUT4. Although there's a large body of work showing that GLUT5 does not respond quickly to insulin, recent work has shown that, for example, high levels of insulin lead to increased GLUT5 activity in skeletal muscle over a period of 24 hours.
So if what your trying to get at is some reason why eating an apple is better for you than chugging an equivalent volume of Auntie Jemimah's pure corn syrup, it's always going to be some reason like this where you have co-metabolism of several nutrients that tend to show up together in "natural" food. It is unlikely that there are any complex plant substances that would be primarily responsible for the health benefit of fresh fruit in general.

Dietary fibers and antioxidants (e.g. polyphenols) make fruits healthier in general, so your last paragraph is very wrong... Btw. the question was very specific about fructose absorption modifiers, which exist, e.g. eucalyptus leaf extract contains them: http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=919892&fileId=S0007114505001431

@inf3rno Your thing only really applies to fruit wrapped in Eucalyptus leaves. Unless you're claiming that the magical unidentified substance within eucalyptus leaf extract that is supposed to suppress adiposity is present in all fruits, which the authors certainly don't

We don't know what this "magical substance" is, so it might be there in fruits as well. Unless you have a proof about the opposite... ;-)

@inf3rno look up the teapot fallacy

The only problem here, that I don't want to answer this question, because I don't want to earn points with a question I edited. But as you wish...

-1, we have already talked about it why... :-) It took a while to write my own answer, I needed to do some research in the topic.

Do fruits/ vegetation contain compounds, which help the digestive
  system to regulate the absorption of fructose? If so, what are they?

Yes, many polyphenols (e.g. resveratrol, curcumin, quercetin, anthocyanins, phloretin, etc.) do this and much more. Each fruit and vegetable has its polyphenol composition. There are other beneficial fruit and vegetable compounds as well, but I'll talk only about polyphenols in the current post.
Sucrose is split by digestive enzymes (sucrase, glycoside hydrolase) in the small intestine into fructose and glucose. These enzymes are inhibited by polyphenols.
Glucose is transported by SGLT1, while fructose is transported by GLUT5 into enterocytes in the intestines. After that the cells transport these sugars with GLUT2 into the blood. Polypheonls can inhibit these transporters and decrease their expression.
Fructose and glucose is transported to the liver from the blood, with GLUT2, and they do nasty things in there. Fructose is more dangerous than glucose, because it is transformed without any regulation. It uses the same pathways as glucose and mostly fatty acids are created from it, which increase the blood VLDL, LDL, FFA level and cause insulin resistance. The byproducts are urate and free radicals, which cause hyperuricaemia and oxidative stress. Hyperuricaemia cause decreased NO levels (by counteracting with eNOS and reacting with NO directly), which cause increased blood pressure due to vasoconstriction. Hyperuricaemia damages the liver and the kidney too. Too high urate levels enhance LDL oxidation as well, which cause atherosclerosis. The free radicals deplete the antioxidants of the body and cause cancer. Polyphenols prevent atherosclerosis, restore NO levels, restore urate levels, scavenge free radicals, counteract with insulin resistance and prevent liver and kidney damage. So they can fix most of the problems fructose cause.
References:

The interactions of gallic acid and tannic acid with purified brush
  border sucrase (EC 3.2.1.48) from mouse intestine have been studied.
  These findings indicate that both gallic acid and tannic acid inhibit
  sucrase activity, which is pH dependent.

http://dx.doi.org/10.1042/BSR20090012

The effects of tea polyphenols on the sucrase activity are shown in
  Table .1. Among 10 compounds, esterified (gallated) polyphenols (ECg,
  EGCg, TF2A, TF2B, and TF3) were potent inhibitors.

http://dx.doi.org/10.1271/bbb.57.123

Quercetin reduced the effect of sucrase and maltase in the in vivo and
  in vitro treatments.

http://dx.doi.org/10.1016/j.nut.2011.01.008

In conclusion quercetin and its glycoside derivatives have alfa-glucosidase inhibitory activity and high peroxyl radical scavenging-linked antioxidant activity. The above benefits (anti-hyperglycemia and antioxidant activity) of quercetin and its glycoside derivatives taken together could support the evidence that diets rich in fruits and vegetables are associated with lower incidences of oxidation-linked diseases such as diabetes

Comparison of Antioxidant Potential and Rat intestinal alfa-Glucosidases inhibitory Activities of Quercetin, Rutin, and Isoquercetin - http://ijarnp.org/index.php/ijarnp/article/viewFile/41/41

Phloretin (Ph), which can be obtained from apples, apple juice, and cider, is a known inhibitor of the type II glucose transporter (GLUT2).

http://dx.doi.org/10.1002/mc.20480

The ATPase inhibitor quercetin, which inhibits tumor glycolysis, was shown to be a glucose transport inhibitor like the chemically related compound phloretin.

Preferential inhibition by quercetin of mitogen-stimulated thymocyte glucose transport. - http://www.ncbi.nlm.nih.gov/pubmed/220448

Glucosides of some other flavonoid classes such as naringenin-7-O-glucoside, genistein-7-O-glucoside and cyanidin-3,5-O-diglucoside were ineffective as well. Thus, dietary quercetin monoglucosides, for example, Q3G and Q4G, have an impact on intestinal nutrient transporters such as SGLT1 and related systems.

http://dx.doi.org/10.1079/BJN20041128

Excessive post-prandial glucose excursions are a risk factor for developing diabetes, associated with impaired glucose tolerance. One way to limit the excursion is to inhibit the activity of digestive enzymes for glucose production and of the transporters responsible for glucose absorption. Flavonols, theaflavins, gallate esters, 5-caffeoylqunic acid and proanthocyanidins inhibit α-amylase activity. Anthocyanidins and catechin oxidation products, such as theaflavins and theasinsensins, inhibit maltase; sucrase is less strongly inhibited but anthocyanidins seem somewhat effective. Lactase is inhibited by green tea catechins. Once produced in the gut by digestion, glucose is absorbed by SGLT1 and GLUT2 transporters, inhibited by flavonols and flavonol glycosides, phlorizin and green tea catechins.

http://dx.doi.org/10.1002/mnfr.201200511

In addition, curcumin suppressed glut2 expression by stimulating the activity of peroxisome proliferator-activated receptor-gamma (PPARγ) and de novo synthesis of glutathione. In conclusion, hyperglycemia stimulated HSC activation in vitro by increasing intracellular glucose, which was eliminated by curcumin by blocking the membrane translocation of GLUT2 and suppressing glut2 expression.

http://dx.doi.org/10.1016/j.mce.2010.12.028

This study investigated the effects of an anthocyanin-rich berry-extract on glucose uptake by human intestinal Caco-2 cells. Acute exposure (15 min) to berry extract (0.125%, w/v) significantly decreased both sodium-dependent (Total uptake) and sodium-independent (facilitated uptake) 3H-D-glucose uptake. In longer-term studies, SGLT1 mRNA and GLUT2 mRNA expression were reduced significantly. Polyphenols are known to interact directly with glucose transporters to regulate the rate of glucose absorption. Our in vitro data support this mechanism and also suggest that berry flavonoids may modulate post-prandial glycaemia by decreasing glucose transporter expression.

http://dx.doi.org/10.1371/journal.pone.0078932

RES increased SIRT1 expression, but decreased the expression of GLUT5 and aldolase B in aortas from HFr-fed rats. These results suggest that RES contributes to the restoration of HFr-induced vascular dysfunction in rats, at least in part, by up-regulation of SIRT 1 and down-regulation of GLUT5 and aldolase B in the aorta. Moreover, RES may have a positive influence on vasculature by partly restoring the plasma arginine:ADMA ratio and leptin levels.

http://dx.doi.org/10.1139/cjpp-2014-0245

High dietary fructose intake: Sweet or bitter life? - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3158875/
A causal role for uric acid in fructose-induced metabolic syndrome - http://ajprenal.physiology.org/content/290/3/F625
Gut microbial adaptation to dietary consumption of fructose, artificial sweeteners and sugar alcohols: implications for host–microbe interactions contributing to obesity - http://www.drperlmutter.com/wp-content/uploads/2014/04/Payne-et-al-2012-Obesity-reviews.pdf
Early Life Exposure to Fructose and Offspring Phenotype: Implications for Long Term Metabolic Homeostasis - http://dx.doi.org/10.1155/2014/203474
Dietary fructose, salt absorption and hypertension in metabolic syndrome: towards a new paradigm - http://onlinelibrary.wiley.com/doi/10.1111/j.1748-1716.2010.02167.x/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false
Toward a Unifying Hypothesis of Metabolic Syndrome - http://pediatrics.aappublications.org/content/129/3/557.short
Uric acid transport and disease - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2877959/

The present study demonstrates that resveratrol is more effective than metformin in improving insulin sensitivity, and attenuating metabolic syndrome and hepatic oxidative stress in fructose-fed rats.

http://dx.doi.org/10.1016/j.phrs.2012.05.003

Quercetin supplementation improved some risk factors of cardiovascular disease, yet exerted slightly pro-inflammatory effects.

http://dx.doi.org/10.1016/j.numecd.2011.08.010

In conclusion, dietary HFCS causes vascular insulin resistance and endothelial dysfunction through attenuating IRS-1 and eNOS expressions as well as increasing iNOS in rats. Resveratrol has capability to recover HFCS-induced disturbances.

http://dx.doi.org/10.1016/j.fct.2013.07.026

The major flavonoid is Quercetin, which belongs to the class called flavonols and is mainly found in apples, tea, onions, nuts, berries, cauliflower, cabbage and many other foods. It exhibits a wide range of biological functions including anticarcenogenic, anti-inflammatory and antiviral; it also inhibits lipid peroxidation, platelet aggregation and capillary permeability. This review focuses on the main effects of Quercetin on obesity and diabetes.

Beneficial Effects of Quercetin on Obesity and Diabetes - http://benthamopen.com/tonutraj/articles/V004/189TONUTRAJ.pdf

These results indicate that resveratrol ameliorated FF A-induced insulin resistance by regulating mTOR and p70-S6K phosphorylation in skeletal muscle cells, through a mechanism involving sirtuins.

Attenuation of skeletal muscle FFA-induced insulin resistance by the polyphenol resveratrol. Elucidation of the mechanisms involved - https://dr.library.brocku.ca/handle/10464/2832

Resveratrol, trans-4-hydroxystilbene, pterostilbene, polydatin, and mulberroside A were found to have antihyperuricemic activities. The uricosuric and nephroprotective actions of resveratrol and its analogues were mediated by regulating renal organic ion transporters in hyperuricemic mice, supporting their beneficial effects for the prevention of hyperuricemia.

http://dx.doi.org/10.1002/mnfr.201100828

Adult male Wistar rats were treated with a normal or high-fat/sucrose diet (HFS) with or without Res for 13 weeks. HFS and in vitro treatment with high glucose increased hyperpermeability in rat aorta, heart, liver and kidney and cultured bovine aortic endothelial cells (BAECs), respectively, which was attenuated by Res treatment. Application of Res reversed the changes in eNOS and Cav-1 expressions in aorta and heart of rats fed HFS and in BAECs incubated with high glucose. Res stimulated the formation of NO inhibited by high glucose in BAECs.

http://dx.doi.org/10.1371/journal.pone.0113716

In summary, all 3 tea polyphenol extracts induced weight loss and anti-inflammatory and angiogenic effects, although the tissue content of polyphenols differed significantly.

http://dx.doi.org/10.3945/jn.114.191007

Blackcurrants and lingonberries, as either whole berries or nectars, optimize the postprandial metabolic responses to sucrose. The responses are consistent with delayed digestion of sucrose and consequent slower absorption of glucose.

http://dx.doi.org/10.3945/ajcn.112.042184

Resveratrol prevented the HFS-induced arterial wall inflammation and the accompanying increase in PWV. Dietary resveratrol may hold promise as a therapy to ameliorate increases in PWV.

http://dx.doi.org/10.1016/j.cmet.2014.04.018

Taken together the data suggest that dietary flavonoids exhibit three distinct modes of action with regard to cancer prevention, based on their hydroxyl and methoxy decoration: (1) inhibitors of CYP1 enzymatic activity, (2) CYP1 substrates and (3) substrates and inhibitors of CYP1 enzymes.

http://dx.doi.org/10.1016/j.bmc.2011.03.042

These data demonstrate that resveratrol inhibits CYP1A1 expression in vitro, and that it does this by preventing the binding of the AHR to promoter sequences that regulate CYP1A1 transcription. This activity may be an important part of the chemopreventive activity of resveratrol.

http://www.ncbi.nlm.nih.gov/pubmed/9865727

As a chemoprevention agent, resveratrol has been shown to inhibit tumor initiation, promotion, and progression, as well as inhibit the growth of cancerous cells through increased apoptosis and/or cell cycle blockage. Inflammatory processes are associated in the pathogenesis of many chronic diseases including heart disease and cancer. Resveratrol has been shown to reduce inflammation via inhibition of prostaglandin production, cyclooxygenase-2 activity, and nuclear factor-кB activity. In addition, the estrogenic activity of resveratrol may help prevent post-menopausal bone loss.

http://dx.doi.org/10.1111/j.1541-4337.2006.00001.x

These findings suggest that fructose-induced metabolic syndrome is attenuated by the polyphenol-rich fraction of amla.

http://dx.doi.org/10.1017/S0007114509991978

Man, your answrs are so long!

I'm unsure currently about the empirical data surrounding inhibition of GLUT5, but with regards to GLUT2, some data exists to point out flavonoids and phloretin as potential inhibitors found in diet. The following articles should provide some sort of starting point to dig a little deeper on the matter.
http://www.ncbi.nlm.nih.gov/pubmed/17699876
http://www.ncbi.nlm.nih.gov/pubmed/17172639

http://www.ncbi.nlm.nih.gov/pubmed/25392295 resveratrol reduces the expression of transporter genes.

authors: Полина Рябенкова


text:
How does the population fitness change after a change in mutation rate?
The mean population fitness as given by mutation load theory depends only on the genome-wide mutation rate ($U$). My question is: How many generations is needed to reach a new mutation load equilibrium after a change in $U$?

Following is an article were they perform the kind of calculations I am interested in:
Let $U$ be the genome-wide mutation rate, $\delta U$ a change (between two time steps) in the genome-wide mutation rate and $s$ the mutational effect (effect on fitness) of a given mutation. In Agrawal and Whitlock (2012), page 13 (or 127 in the journal), $3^{rd}$ paragraph, the authors say:

[After a change in $U$,] it can take a long time to approach mutation-selection balance. For example, if the mutation rate is increased by $\delta U = 1$ deleterious mutation per genome per generation, then it would take ∼120 generations for fitness to decline 80% of its expected amount if s = 0.01. However, by obtaining a time series of data, one could infer the equilibrium load after tens or hundreds of generations even if equilibrium is not reached

How were these ~120 generations estimated/calculated?


text:
Survival curve in early humans
The survival curve/function describes the probability of a given individual to survive to age $x$. In humans, today's survival function is very much influenced by medicine. This leads me to wonder what the survival function looked like before modern medicine. Typically I wonder what the survival function looked like during the paleolithic age.
What did the survival function looked like during the paleolithic age?
Why did the survival function looked like that? What were the major causes of mortality for males and for females?

I posted an answer based on the same info as the answer here, since those papers can be useful for this question as well.

To obtain a full survival curve (basically a full life table) you would need to make quite a number of assumptions, since the data for paleolithic societies is scattered and probably biased. This is however not a field I know well, but I can point you to one recent paper (White, 2014) that explores how the ratio of young and old individuals in a population relates to demographic rates, using agent-based models. Using such a model you can obtain smooth survival curves and also explore how different assumptions will affect the survival curves.
There are also data from recent or current hunter-gatherer societies that can be used to approximate what the survival curves looked like during the paleolithic. For instance,  Hewlett (1991) (pdf here) has compiled survival rate data for individual hunter-gatherer societies (along with other demographic rates and data from other types of pre-industrial societies). The child mortality rate (deaths before age 15) often lie in the range 40-50% in active (mobile) and sedentary hunter-gatherer societies, with an infant mortality rate usually between 10-30% (death before 12 months of age). This indicates a fairly steep survival curve, which is the reason why the average age of paleolithic people is often estimated to ~25 years. This doesn't mean that most people died around the age of 25, just that the distribution of ages was very skewed and non-normal. Many died young, but people that survived to adulthood could become much older than 25.


text:
Miscarriage in early humans
Today, about 10 to 20 percent of known pregnancy end in miscarriage. Pregnancy is a biological process that has been very well studied by medicine. As a result, modern medicine helps a lot to prevent miscarriages and to prevent death of pregnant women.
What was the percentage of pregnancy ending in miscarriage before modern medicine? Typically, what was the percentage pregnancy ending in miscarriage in early Homo sapiens, during the paleolithic age?

Would it change your question if you knew that modern medicine can actually do very little to prevent miscarriages? Because there is actually very little modern medicine can do to prevent miscarriages. Death in childbirth? We've got that nearly covered. Healthier babies? Got that covered to a fair degree as well. But nope on the miscarriages.

Yes, that would indeed already be a nice insight. I assumed that modern medicine had an important impact but I actually had no idea. You can totally write an answer inspired by how modern medicine "fail" to prevent miscarriage.

@anongoodnurse - My guess is this would make an awesome answer, as the data on 2.5 million - 12k years ago is likely to be small or non-existent.

@anongoodnurse What about diet and overall health status? Doesn't this affect miscarriages rates? Even if this isn't only dependent on modern medicine and direct measures to specifically decrease miscarriage rates, I would still expect miscarriage rates to differ between modern humans and paleolithic people. But I'm only speculating and could definitely be mistaken.

@fileunderwater - nutrition affects age of menarche and number of ovulatory (vs. anovulatory) cycles, but it's not known to prevent miscarriages.

@anongoodnurse Ok good to know and you are probably right about this. See comment under your answer for further ideas on infection and miscarriage rates.

Pregnancy is a biological process that has been very well studied by medicine. As a result, modern medicine helps a lot to prevent miscarriages and to prevent death of pregnant women.

While the latter clause is correct (maternal - and infant - mortality is reduced with medical care), the former is not.
Miscarriages have been a problem as far back as recorded history. The written record includes medicinal recipes to prevent miscarriages. The problem then, as now, is that it just can't be done very well.
From a 2000 Obstetrics journal article:

Human reproduction is extraordinarily wasteful. The reasons for this have taxed all of the contributors to this book. As we move into the 21st century it is sobering to reflect on the fact that we have failed to harness the power of the evolving revolution in molecular medical biology to answer the fundamental question: why is the fate of a fertilized egg so hazardous and so unsuccessful? The following account summarizes our limited knowledge of the epidemiology of miscarriage and then moves on to consider some of the medical causes of miscarriage...

Miscarriage is difficult to study, and the causes difficult to establish, so the literature showing that any interventions help (antibiotics, bed rest, supplements, etc.) is not plentiful. Smoking seems to have a deleterious effect on pregnancy. How this relates to early populations is a matter of conjecture.
Some good studies do exist, however. One good study in the New England Journal of Medicine followed an ideal group: women who had no history of infertility, who were trying to become pregnant.
Of 221 couples followed for 6 months, a total of 199 pregnancies were detected, of which 126 ended in live birth (therefore a 37% miscarriage rate). Because of the methodology, failure of blastocysts to implant could not be measured. The findings of this study were supported by others (31%), etc.: early loss increased when implantation occurred later than 10 days after ovulation. While the authors were hopeful ("There may be opportunities to increase fertility by extending the time during which implantation can occur."), they were also realistic ("Such interventions should be approached cautiously, however, because they may have unintended consequences with respect to the quality of surviving embryos.") Basically, you can't fool around too much with Mother Nature in this realm.
Has modern medicine been able to change this rate? Not really. Even with IVF, where thousands of dollars are spent trying to preserve a single pregnancy (certainly not the norm), miscarriage is common. The best way to increase the viability of IVF pregnancy is to select better oocytes, embryos, etc. In other words, maternal factors remain refractory to manipulation.
Even things obstetricians long took for gospel (for example, bedrest with pre-eclampsia) have little evidence of benefit to the fetus.
The literature is vast in this area (reproduction is an important field to study). I can write a book on how little can be manipulated on average (I will consider spending thousands of dollars on one pregnancy not average), but it wouldn't sell. What does sell are false claims, this one being as good as any claimed today:

To prevent miscarrying or if one that is apt to miscarrie goe a journey let her take this powder morning and evening whilst shee journeys: Take of Dragons Blood the weight of a silver two-pence, a dram of red corrall powdered, the weight of 2 barly corns of Ambergrease, Besar ye weight of 3 barly corns, mix all these together and keep them close stoped in little vial glasse when you use take as much of it as lie upon a penny in a little clary water at nighte when you goe to bed, and in ye morning fasting and sleep after it to use it till you are out of danger.

From what I've heard, some infections during pregnancy, such as Rubella, can cause miscarriage. In the case of Rubella, this is now part of standard vaccination programmes, which should have decreased miscarriage rates. WebMD: causes of miscarriage also mentions Rubella, along with some other causes of miscarriage, some of which are prevented/treated by modern medicine (also see this WHO page). However, this is not my area and I'm only relying on secondary sources.

@fileunderwater - I did mention smoking. As for rubella, it's still not uncommon (though it's much better) but there are plenty of things that have come along to replace it as new causes of miscarriage. I'm not saying in no way are we better off; we are. But in the case of miscarriages, not by much. You can point to a number of things, such as cervical cerclage to prevent preterm delivery, but that doesn't help reduce miscarriages; it only helps the fetus to mature a bit more in occasional cases of preterm deliveries. A book can be written, but it probably won't be, and not by me.