question: During development, how does the body know to put the organs in their specific locations?
comment: There are a bunch of hormones released during development that progressively specialise the cells in that area depending on the signals the cells get. These hormones switch on certain genes in the DNA that tell the cell what it needs to become. These exist along a gradient and it's known as 'patterning'. In early development, the hormones are produced by a small collection of cells that tell the embryo what part is going to become the head and tail end of the body in the future. As the body continues to develop, the collection of hormones change and become more specialised and may only exist in certain regions. Using some of your examples, the heart knows where to go because there are various hormones all spread on a gradient. Maybe 3 developmental hormones are at their strongest concentration at the center of the chest, which then switches on the genes in these cells that allow them to specialise as cardiac muscle fibers.
passages: Skeletal tissues are generally placed directly on the grid but softer tissues like glands or skin are first placed on rafts, which are then kept on the grids.
  
  The grids themselves are placed in a culture chamber filled with fluid medium up to the grid; the chamber is supplied with a mixture of O and CO to meet the high O requirements of adult mammalian organs. A modification of the original grid method is widely used to study the growth and differentiation of adult and embryonic tissues.
  
  Section::::Uses.
   The digestive system starts to develop from the third week and by the twelfth week, the organs have correctly positioned themselves.
  
  Section::::Development of organs and organ systems.:Respiratory system.
   Gesell observed that maturational development always unfolds in fixed sequences: an embryo's heart is always the first organ to develop, then the central nervous system (the brain and spinal cord), followed by the peripheral organs. After birth, babies first gain control over their lips and tongues, then their eye movements, followed by control over their neck, shoulders, arms, hands, fingers, legs, and feet. There is a genetic cephalocaudal (head-to-foot) trend in both prenatal and postnatal development.
   Organogenesis is the development of the organs that begins during the third to eighth week, and continues until birth. Sometimes full development, as in the lungs, continues after birth. Different organs take part in the development of the many organ systems of the body.
  
  Section::::Development of organs and organ systems.:Blood.
   All major structures are already formed in the fetus, but they continue to grow and develop. Since the precursors of all the major organs are created by this time, the fetal period is described both by organ and by a list of changes by weeks of gestational age.
  
  Because the precursors of the organs are now formed, the fetus is not as sensitive to damage from environmental exposure as the embryo was. Instead, toxic exposure often causes physiological abnormalities or minor congenital malformation.
  
  Section::::Development of the fetus.:Development of organ systems.
   Two-thirds of all vertex presentations are LOA, possibly because of the asymmetry created by the descending colon that is on the left side of the pelvis .
  
  Section::::Diagnosis.
  
  Usually performing the Leopold maneuvers will demonstrate the presentation and possibly the position of the fetus. Ultrasound examination delivers the precise diagnosis and may indicate possible causes of a malpresentation. On vaginal examination, the leading part of the fetus becomes identifiable after the amniotic sac has been broken and the head is descending in the pelvis.
  
  Section::::Management.
   Section::::Organs produced by the germ layers.
  
  The endoderm is the inner most germ layer of the embryo which gives rise to gastrointestinal and respiratory organs by forming epithelial linings and organs such as the liver, lungs, and pancreas. The mesoderm or middle germ layer of the embryo will form the blood, heart, kidney, muscles, and connective tissues. The ectoderm or outermost germ layer of the developing embryo forms epidermis, the brain, and the nervous system.
  
  Section::::Mechanism of organ formation.
   Certain signals set up the spatial pattern of expression of the Hox complex early in development. The Hox complex acts like a stamp, giving cells in each segment a long term positional value. The cell memory of a given positional value depends on two inputs, the first being the ability of many Hox proteins to autoactivate their own transcription, and the second derived from two large groups of transcriptional regulators: The Polycomb group and the Trithorax group. A defect in either of these regulators results in a pattern which is initially correct but is not maintained at later embryonic stages.
   "Barker's Hypothesis" is also known as "Fetal Programming Hypothesis". The word "programming" illustrates the idea that during critical periods in early fetal development, there are persisting changes in the body structure and function that are caused by environmental stimuli. This relates to the concept of developmental plasticity where our genes can express different ranges of physiological or morphological states in response to the environmental conditions during fetal development.
   In the adult patient, a curved array transducer with center frequencies of 3–6 MHz is used, while the pediatric patient should be examined with a linear array transducer with higher center frequencies. Artifacts of the lowest ribs always shadow the upper poles of the kidneys. However, the whole kidney can be examined during either normal respiration or breath hold, as the kidney will follow the diaphragm and change position accordingly.
   Given the ancient origin of most vertebrate organs, researchers have looked for model systems, where organs have evolved more recently, and ideally have evolved multiple times independently. An outstanding model for this kind of research is the placenta, which has evolved more than 100 times independently in vertebrates, has evolved relatively recently in some lineages, and exists in intermediate forms in extant taxa. Studies on the evolution of the placenta have identified a variety of genetic and physiological processes that contribute to the origin and evolution of organs, these include the re-purposing of existing animal tissues, the acquisition of new functional properties by these tissues, and novel interactions of distinct tissue types.
   Epidemiologist David Barker was the earliest proponent of the theory of fetal origins of adult disease, prompting the theory to be denoted as "Barker's hypothesis". In 1986, Barker published findings proposing a direct link between prenatal nutrition and late-onset coronary heart disease. He had noticed that the poorest areas of England were the same areas with the highest rates of heart disease, unearthing the predictive relationship between low birth weight and adult disease. His findings were met with criticism, mainly because at the time heart disease was considered to be predominantly determined by lifestyle and genetic factors. Since Barker's initial findings, the results have been replicated in diverse populations of Europe, Asia, North American, Africa, and Australia. In explanation of such findings, Barker suggests that fetuses learn to adapt to the environment they expect to enter into once outside of the womb. Essentially, all transmissions entering the placenta act as "postcards" giving the fetus clues as to the outside world, preparing its physiology appropriately. This can be an adaptive mechanism, when fetal conditions accurately represent the world of birth; alternatively, it can be a harmful mechanism, when fetal conditions of plenitude or scarcity do not match the world of birth and the child has been physiologically predisposed to inhabit an environment where expected resources are drastically different from reality.
   Section::::Structure.:Organ systems.
  
  Two or more organs working together in the execution of a specific body function form an organ system, also called a biological system or body system. The functions of organ systems often share significant overlap. For instance, the nervous and endocrine system both operate via a shared organ, the hypothalamus. For this reason, the two systems are combined and studied as the neuroendocrine system. The same is true for the musculoskeletal system because of the relationship between the muscular and skeletal systems.
   During organogenesis, molecular and cellular interactions between germ layers, combined with the cells' developmental potential, or competence to respond, prompt the further differentiation of organ-specific cell types. For example, in neurogenesis, a subpopulation of ectoderm cells is set aside to become the brain, spinal cord, and peripheral nerves. Modern developmental biology is extensively probing the molecular basis for every type of organogenesis, including angiogenesis (formation of new blood vessels from pre-existing ones), chondrogenesis (cartilage), myogenesis (muscle), osteogenesis (bone), and many others.
  
  Section::::Development.:Plant embryos.
   The critical role of echocardiography in prenatal diagnosis is evident, and both the accuracy and safety of the test are now well established. The structures in these images are small, however, and random movements of the fetus make for a challenging and time-consuming examination. Despite these factors, fetal echocardiography has provided clinicians with earlier diagnosis of heart disease and a better understanding of fetal hemodynamics.
   The human nervous system develops from a small, specialized plate of cells on the surface of the embryo. Early in development, this plate of cells forms the neural tube, a narrow sheath that closes between the third and fourth weeks of pregnancy to form the brain and spinal cord of the embryo. Four main processes are responsible for the development of the nervous system: cell proliferation, the process in which nerve cells divide to form new generations of cells; cell migration, the process in which nerve cells move from their place of origin to the place where they will remain for life; cell differentiation, the process during which cells acquire individual characteristics; and cell death, a natural process in which cells die.
   A study published in 2016, suggests that all sacral autonomic output may be sympathetic; indicating that the rectum, bladder and reproductive organs may only be innervated by the sympathetic nervous system. This suggestion is based on detailed analysis of 15 phenotypic and ontogenetic factors differentiating sympathetic from parasympathetic neurons in the mouse. Assuming that the reported findings most likely applies to other mammals as well, this novel perspective suggests a simplified, bipartite architecture of the autonomic nervous system, in which the parasympathetic nervous system receives input from cranial nerves exclusively and the sympathetic nervous system from thoracic to sacral spinal nerves.
   Another mechanism that determines the cell fate is regional determination (see Regional specification). As implied by the name, this specification occurs based on where within the embryo the cell is positioned, it is also known as positional value. This was first observed when mesoderm was taken from the prospective thigh region of a chick embryo, was grafted onto the wing region and did not transform to wing tissue, but instead into toe tissue.
  
  Section::::Modes of specification.:Syncytial specification.
   In Pretzel syndrome, part of the LYK5 gene is missing, which leads to a complete loss of this signaling function. The LYK5 gene has an important role in normal organ development. Defective organ development that begins during the earliest stages of pregnancy is not treatable and leads to a variety of medical problems throughout life.
  
  Section::::Treatment.
   The course of GVA fibers from organs in the pelvis, in general, depends on the organ's position relative to the pelvic pain line. An organ, or part of an organ, in the pelvis is said to be "above the pelvic pain line" if it is in contact with the peritoneum, except in the case of the large intestine, where the pelvic pain line is said to be located in the middle of the sigmoid colon. GVA fibers from structures above the pain line follow the course of the sympathetic efferent fibers, and GVA fibers from structures below the pain line follow the course of the parasympathetic efferents. Pain from the latter fibers is less likely to be consciously experienced.
   All of these cardiovascular system changes result in the adaptation from fetal circulation patterns to an adult circulation pattern. During this transition, some types of congenital heart disease that were not symptomatic "in utero" during fetal circulation will present with cyanosis or respiratory signs.
  
  Manifestations: When the newborn cries, there is a reversal of blood flow through the foramen ovale which causes the newborn to appear mildly cyanotic in the first few days of life. 
   Cephalization is a characteristic feature of the Bilateria, a large group containing the majority of animal phyla. These have the ability to move, using muscles, and a body plan with a front end that encounters stimuli first as the animal moves forwards, and accordingly has evolved to contain many of the body's sense organs, able to detect light, chemicals, and often sound. There is often also a collection of nerve cells able to process the information from these sense organs, forming a brain in several phyla and one or more ganglia in others.
  
  Section::::Bilateria.:Acoela.
   Large segmental hemangiomas of the head and neck can be associated with a disorder called PHACES syndrome. Large segmental hemangiomas over the lumbar spine can be associated with dysraphism, renal, and urogenital problems in association with a disorder called LUMBAR syndrome. Multiple cutaneous hemangiomas in infants may be an indicator for liver hemangiomas. Screening for liver involvement is often recommended in infants with five or more skin hemangiomas.
  
  Section::::Causes.
   Chung's work researching cardiomyopathies describes metabolic causes, identify genetic modifiers of disease progression in children and infants with the hypertrophic cardiomyopathy and novel genes for infantile cardiomyopathy.
  
  Section::::Research contributions.:Spinal Muscular Atrophy.
  
  One of Chung's contributions within the field of genetics involves her role in the development of screenings and treatment for spinal muscular atrophy (SMA),especially in newborns. Chung worked as a part of a team to develop a new screening and intervention process for infants with spinal muscular atrophy, with a pilot study conducted with a population of infants in New York identifying and successfully treating one infant with SMA.
   Section::::Genetics.
  
  This condition is very rare; its prevalence is unknown. Mutations in the GLI3 gene cause Pallister–Hall syndrome. The "GLI3" gene provides instructions for making a protein that controls gene expression, which is a process that regulates whether genes are turned on or off in particular cells. By interacting with certain genes at specific times during development, the GLI3 protein plays a role in the normal shaping (patterning) of many organs and tissues before birth. Defects in the same gene also cause Greig cephalopolysyndactyly syndrome.
  
raw_presuppositions: The body puts organs in certain spots.
raw_corrections: The body sends hormones that slowly change cells into the required organ.