question: Why is it needed for some medicine pills to be put into the anus? How does the body break down and absorb the medicine?
comment: Stomach acid can destroy some medicine. The lining of the lower intestine absorb the medicine without being damaged by acid .
passages: Rectal administration
  
  Rectal administration uses the rectum as a route of administration for medication and other fluids, which are absorbed by the rectum's blood vessels, and flow into the body's circulatory system, which distributes the drug to the body's organs and bodily systems.
   It is of importance in medicine as it can be affected in a number of diseases, including:
  
  BULLET::::- Crohn's disease
  
  BULLET::::- Tuberculosis
  
  BULLET::::- Lymphoma
  
  BULLET::::- Neuroendocrine tumours (carcinoid)
  
  Section::::Other animals.
  
  In veterinary anatomy, the ileum is distinguished from the jejunum by being that portion of the jejunoileum that is connected to the caecum by the ileocecal fold.
   BULLET::::- Palygorskite or attapulgite is a very absorbent clay, somewhat similar to bentonite. When used in medicine, it physically binds to acids and toxic substances in the stomach and digestive tract. For this reason, it has been used in several anti-diarrheal medications, but studies of such have since been rejected by the U.S. Food and Drug Administration as insufficient.
   Ileum
  
  The ileum is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum. Its main function is to absorb vitamin B, bile salts, and whatever products of digestion were not absorbed by the jejunum. 
   Section::::Function.:Neurotransmitters.
  
  The enteric nervous system makes use of over 30 different neurotransmitters, most similar to those of the CNS such as acetylcholine, dopamine, and serotonin. More than 90% of the body's serotonin lies in the gut; as well as about 50% of the body's dopamine, which is currently being studied to further our understanding of its utility in the brain.
  
  The heavily studied neuropeptide known as substance P is present in significant levels and may help facilitate the production of saliva, smooth muscle contractions, and other tissue responses.
  
  Section::::Function.:Neurotransmitters.:Receptors.
   There are three main sites where drug excretion occurs. The kidney is the most important site and it is where products are excreted through urine. Biliary excretion or fecal excretion is the process that initiates in the liver and passes through to the gut until the products are finally excreted along with waste products or feces. The last main method of excretion is through the lungs (e.g. anesthetic gases).
  
  Excretion of drugs by the kidney involves 3 main mechanisms:
  
  BULLET::::- Glomerular filtration of unbound drug.
   Enterics control the rate of drug release and determine where the drug will be released in the digestive tract. Materials used for enteric coatings include fatty acids, waxes, shellac, plastics, and plant fibers.
  
  Section::::Types.:Colors.
   Enteral administration is food or drug administration via the human gastrointestinal tract. This contrasts with parenteral nutrition or drug administration (Greek "para", "besides" + "enteros"), which occurs from routes outside the GI tract, such as intravenous routes. Enteral administration involves the esophagus, stomach, and small and large intestines (i.e., the gastrointestinal tract). Methods of administration include oral, sublingual (dissolving the drug under the tongue), and rectal. Parenteral administration is via a peripheral or central vein. In pharmacology, the route of drug administration is important because it affects drug metabolism, drug clearance, and thus dosage. The term is from Greek "enteros", "intestine".
   Section::::Function.
  
  The digestive tract is an important component of the body's immune system. In fact, the intestine possesses the largest mass of lymphoid tissue in the human body. The GALT is made up of several types of lymphoid tissue that store immune cells, such as T and B lymphocytes, that carry out attacks and defend against pathogens.
  
  New research indicates that GALT may continue to be a major site of HIV activity, even if drug treatment has reduced HIV count in the peripheral blood.
  
  Section::::Other animals.
   Often underlying medical conditions cause fecal impactions; these conditions should be treated to reduce the risk of future impactions. Many types of medications (most notably opioid pain medications, such as codeine) reduce motility of the colon, increasing the likelihood of fecal impactions. If possible, alternate medications should be prescribed that avoid the side effect of constipation.
   In the fetus the ileum is connected to the navel by the vitelline duct. In roughly 2−4% of humans, this duct fails to close during the first seven weeks after birth, leaving a remnant called Meckel's diverticulum.
  
  Section::::Function.
   Unlike many medicines, insulin cannot be taken orally at the present time. Like nearly all other proteins introduced into the gastrointestinal tract, it is reduced to fragments (single amino acid components), whereupon all activity is lost. There has been some research into ways to protect insulin from the digestive tract, so that it can be administered in a pill. So far this is entirely experimental.
  
  Section::::Methods of administration.:Subcutaneous.
   Section::::Routes of administration.:Suppository.
  
  Little research has been focused on the suppository (anal insertion) or pessary (vaginal insertion) methods of administration, also known as "plugging". These methods of administration are commonly carried out using an oral syringe. Heroin can be dissolved and withdrawn into an oral syringe which may then be lubricated and inserted into the anus or vagina before the plunger is pushed. The rectum or the vaginal canal is where the majority of the drug would likely be taken up, through the membranes lining their walls.
  
  Section::::Adverse effects.
   The rectal route of administration is useful for patients with any digestive tract motility problem, such as dysphagia, ileus, or bowel obstruction, that would interfere with the progression of the medication through the tract. This often includes patients near the end of life (an estimated 1.65 million people are in hospice care in the US each year). Because using the rectal route enables a rapid, safe, and lower cost alternative to administration of medications, it may also facilitate the care of patients in long-term care or palliative care, or as an alternative to intravenous or subcutaneous medication delivery in other instances.
   Its function is to complete the process begun by pancreatic juice; the enzyme trypsin exists in pancreatic juice in the inactive form trypsinogen, it is activated by the intestinal enterokinase in intestinal juice. Trypsin can then activate other protease enzymes and catalyze the reaction pro-colipase → colipase. Colipase is necessary, along with bile salts, to enable lipase function. 
  
  Intestinal juice also contains hormones, digestive enzymes, mucus, substances to neutralize hydrochloric acid coming from the stomach and erepsin which further digests polypeptides into amino acids, completing protein digestion.
  
  Section::::Colonic crypts.
   Creatinine clearance is used as a measure of kidney functioning but it is only useful in cases where the drug is excreted in an unaltered form in the urine. The excretion of drugs from the kidney's nephrons has the same properties as that of any other organic solute: passive filtration, reabsorption and active secretion. In the latter phase the secretion of drugs is an active process that is subject to conditions relating to the saturability of the transported molecule and competition between substrates. Therefore, these are key sites where interactions between drugs could occur.
   Administration through the gastrointestinal tract is sometimes termed "enteral or enteric administration" (literally meaning 'through the intestines'). "Enteral/enteric administration" usually includes "oral" (through the mouth) and "rectal" (into the rectum) administration, in the sense that these are taken up by the intestines. However, uptake of drugs administered orally may also occur already in the stomach, and as such "gastrointestinal" (along the gastrointestinal tract) may be a more fitting term for this route of administration. Furthermore, some application locations often classified as "enteral", such as sublingual (under the tongue) and sublabial or buccal (between the cheek and gums/gingiva), are taken up in the proximal part of the gastrointestinal tract without reaching the intestines. Strictly enteral administration (directly into the intestines) can be used for systemic administration, as well as local (sometimes termed topical), such as in a contrast enema, whereby contrast media is infused into the intestines for imaging. However, for the purposes of classification based on location of effects, the term enteral is reserved for substances with systemic effects.
   The rectal route is an effective route of administration for many medications, especially those used at the end of life. The walls of the rectum absorb many medications quickly and effectively. Medications delivered to the distal one-third of the rectum at least partially avoid the "first pass effect" through the liver, which allows for greater bio-availability of many medications than that of the oral route. Rectal mucosa is highly vascularized tissue that allows for rapid and effective absorption of medications. A suppository is a solid dosage form that fits for rectal administration. In hospice care, a specialized rectal catheter, designed to provide comfortable and discreet administration of ongoing medications provides a practical way to deliver and retain liquid formulations in the distal rectum, giving health practitioners a way to leverage the established benefits of rectal administration.
   Section::::Functions.
  
  The barrier formed by the intestinal epithelium separates the external environment (the contents of the intestinal lumen) from the body and is the most extensive and important mucosal surface of body.
   Elimination (pharmacology)
  
  In pharmacology the elimination or excretion of a drug is understood to be any one of a number of processes by which a drug is eliminated (that is, cleared and excreted) from an organism either in an unaltered form (unbound molecules) or modified as a metabolite. The kidney is the main excretory organ although others exist such as the liver, the skin, the lungs or glandular structures, such as the salivary glands and the lacrimal glands. These organs or structures use specific routes to expel a drug from the body, these are termed elimination pathways:
  
  BULLET::::- Urine,
   Rectal venous plexus
  
  The rectal venous plexus (or hemorrhoidal plexus) surrounds the rectum, and communicates in front with the vesical venous plexus in the male, and the vaginal venous plexus in the female.
  
  A free communication between the portal and systemic venous systems is established through the rectal venous plexus. This allows administration of some medications normally given by mouth to be given rectally, while still bypassing first pass metabolism. Examples include rectal Diazepam and orally dissolving medications.
  
  Section::::Parts.
  
  It consists of two parts, an internal in the submucosa, and an external outside the muscular coat.
  
  Section::::Parts.:Internal plexus.
   The sublingual region underneath the front of the tongue is a location where the oral mucosa is very thin, and underlain by a plexus of veins. This is an ideal location for introducing certain medications to the body. The sublingual route takes advantage of the highly vascular quality of the oral cavity, and allows for the speedy application of medication into the cardiovascular system, bypassing the gastrointestinal tract.
  
  Section::::Digestive system.:Specialised organs and behaviours.:Teeth.
   Some drugs are inactive in the digestive tract, but this can be avoided if held between the upper lip and gum. This prevents the substances from getting swallowed with salivation, as would normally occur between the lower lip and gum, permitting slow release of the drug to prolong the duration of action.
   The colon is the last part of the digestive system. It extracts water and salt from solid wastes before they are eliminated from the body and is the site in which flora-aided (largely bacterial) fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a major role in absorption of foods and nutrients. About 1.5 litres or 45 ounces of water arrives in the colon each day.
   Jejunum
  
  The jejunum () is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds. Its lining is specialized for the absorption by enterocytes of small nutrient molecules which have been previously digested by enzymes in the duodenum.
  