Gastrointestinal tract

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By the same logic they are often toxic or harmful to the human body to varying degrees. They argued that ammonotely in Palestine Sunbirds was only 'apparent' because it was not a result of excessive excretion of ammonia, but rather the result of a reduction in excreted urate resulting from post-renal modification of urine. This is true for vegetables but for fish and meat, cooking tends to soften it to a degree, but then overcooking tends to toughen it up like leather well done steak being virtually inedible! You may need to experiment a little to find the optimum balance of number and size of bowel movements, stool solidity and extent of digestion. This in turn has an effect on one's digestion and rate of digestion, and hence appetite. Initially this felt very good after a 7 day raw blended vegetable cleanse - incurred huge and unhealthy weight loss I was asked if I had been in a concentration camp by one ex-colleague and I went back to needing very little sleep each night, but over a period of a few months, this feeling of wellbeing disappeared and I gradually had one cold after another, before coming down with the flu and never recovering into full blown CFS.


These parts of the tract have a mesentery. Retroperitoneal parts are covered with adventitia. They blend into the surrounding tissue and are fixed in position. For example, the retroperitoneal section of the duodenum usually passes through the transpyloric plane. These include the esophagus , pylorus of the stomach, distal duodenum , ascending colon , descending colon and anal canal.

In addition, the oral cavity has adventitia. Specific proteins expressed in the stomach and duodenum involved in defence include mucin proteins, such as mucin 6 and intelectin Finally, transit through the colon takes 12 to 50 hours with wide variation between individuals. The gastrointestinal tract forms an important part of the immune system. There are additional factors contributing to protection from pathogen invasion. For example, low pH ranging from 1 to 4 of the stomach is fatal for many microorganisms that enter it.

Beneficial bacteria also can contribute to the homeostasis of the gastrointestinal immune system. For example Clostridia , one of the most predominant bacterial groups in the GI tract, play an important role in influencing the dynamics of the gut's immune system. This is due to the production of short-chain fatty acids during the fermentation of plant-derived nutrients such as butyrate and propionate.

Basically, the butyrate induces the differentiation of Treg cells by enhancing histone H3 acetylation in the promoter and conserved non-coding sequence regions of the FOXP3 locus, thus regulating the T cells , resulting in the reduction of the inflammatory response and allergies.

The large intestine hosts several kinds of bacteria that can deal with molecules that the human body cannot otherwise break down. These bacteria also account for the production of gases at host-pathogen interface , inside our intestine this gas is released as flatulence when eliminated through the anus.

However the large intestine is mainly concerned with the absorption of water from digested material which is regulated by the hypothalamus and the re absorption of sodium , as well as any nutrients that may have escaped primary digestion in the ileum. Health-enhancing intestinal bacteria of the gut flora serve to prevent the overgrowth of potentially harmful bacteria in the gut.

These two types of bacteria compete for space and "food," as there are limited resources within the intestinal tract. Enzymes such as CYP3A4 , along with the antiporter activities, are also instrumental in the intestine's role of drug metabolism in the detoxification of antigens and xenobiotics.

There are many diseases and conditions that can affect the gastrointestinal system, including infections , inflammation and cancer. Various pathogens can cause gastroenteritis an inflammation of the stomach and small intestine. These can include those organisms that cause foodborne illnesses. Gastroenteritis is the most common disease of the GI tract. Diverticular disease is a condition that is very common in older people in industrialized countries. It usually affects the large intestine but has been known to affect the small intestine as well.

Diverticulosis occurs when pouches form on the intestinal wall. Once the pouches become inflamed it is known as diverticulitis. Inflammatory bowel disease is an inflammatory condition affecting the bowel walls, and includes the subtypes Crohn's disease and ulcerative colitis.

While Crohn's can affect the entire gastrointestinal tract, ulcerative colitis is limited to the large intestine. Crohn's disease is widely regarded as an autoimmune disease.

Although ulcerative colitis is often treated as though it were an autoimmune disease, there is no consensus that it actually is such. Functional gastrointestinal disorders the most common of which is irritable bowel syndrome. Functional constipation and chronic functional abdominal pain are other functional disorders of the intestine that have physiological causes, but do not have identifiable structural, chemical, or infectious pathologies.

Gastrointestinal surgery can often be performed in the outpatient setting. In the United States in , operations on the digestive system accounted for 3 of the 25 most common ambulatory surgery procedures and constituted 9.

Various methods of imaging the gastrointestinal tract include the upper and lower gastrointestinal series:. Animal intestines have multiple uses. From each species of livestock that is a source of milk , a corresponding rennet is obtained from the intestines of milk-fed calves. Pig and calf intestines are eaten, and pig intestines are used as sausage casings. Calf intestines supply calf-intestinal alkaline phosphatase CIP , and are used to make goldbeater's skin. Many birds and other animals have a specialised stomach in the digestive tract called a gizzard used for grinding up food.

Another feature not found in the human but found in a range of other animals is the crop. In birds this is found as a pouch alongside the esophagus. Other animals including amphibians , birds , reptiles , and egg-laying mammals have a major difference in their GI tract in that it ends in a cloaca and not an anus.

From Wikipedia, the free encyclopedia. Redirected from Digestive tract. For other uses, see Guts disambiguation. Esophagus , Stomach , and duodenum. Development of the digestive system. Duct of gland outside tract 7: Gland in mucosa 8: Glands in submucosa Meissner's submucosal plexus Areolar connective tissue Auerbach's myenteric plexus Oral mucosa and Gastric mucosa.

Serous membrane and Adventitia. This section discusses related diseases, medical associations with the gastrointestinal tract, and use in surgery. Gastrointestinal disease and Gastroenterology.

Ruminant and Methanogens in digestive tract of ruminants. This article uses anatomical terminology; for an overview, see Anatomical terminology. Invertebrate Zoology 7 ed. Surgical and Radiologic Anatomy.

Factor in achieving total enteroscopy? H; Fava, F; Hermes, G. M; Hold, G; Quraishi, M. G; Hart, A A new clinical frontier". The Neglected Endocrine Organ". Introduction to Behavioral Endocrinology. Retrieved 2 September Oxford textbook of medicine: Retrieved 1 July Mitchell; illustrations by Richard; Richardson, Paul Gray's anatomy for students 3rd ed.

Human Embryology and Developmental Biology 3rd ed. Histology and cell biology: From Bench Side to Bedside. Small intestine transit time in the normal small bowel study. American Journal of Roentgenology ; 3: Colonic Transit Study Technique and Interpretation: Scandinavian Journal of Gastroenterology. Key Regulators of Immune Homeostasis and Inflammation".

The American Journal of Pathology. Current Opinion in Gastroenterology. Influence on innate and acquired immunity". World Journal of Gastroenterology. Science of everyday things: The Journal of Biological Chemistry. Agency for Healthcare Research and Quality. Journal of Clinical Investigation. Retrieved 19 May Human systems and organs.

Fibrous joint Cartilaginous joint Synovial joint. Water balance requires the input matches output. Most birds can obtain water directly by drinking. Birds can also obtain water via the foods they ingest. For example, carnivores ingest animal tissue that is primarily water, frugivores consume fruits containing water, and the nectar consumed by nectarivores is, of course, largely water.

In the Sonoran Desert of the southwestern United States and northwestern Mexico, a cactus plant saguaro, Carnegiea gigantean appears to be an important source of water for several species of birds Wolf and de Rio Even foods that seemingly contain little water can serve as a water source because water is produced as a by-product of cellular metabolism. This metabolic water can be of particular importance to birds in arid environments Williams The amount of water formed during fuel oxidation depends on a variety of factors, including metabolic rate and fuel type carbohydrates, fats, or proteins; Schmidt-Nielsen How do birds drink?

Within each of these two main categories, however, there are several kinds of mechanisms. For example, water is taken into the mouth by scooping water with the lower beak in cockatoos Cacatuinae. Mallards drink using a complex interplay of capillary action and pressure changes in different areas of the mouth. Among the suction drinkers, parakeets ladle water with the tip of the tongue and some parrots drink with a suctioning action. Pigeons and doves, on the other hand, use a "double-suction mechanism" in which capillary action is responsible for bringing water between the slightly gaping tips of the beak and then the tongue acts as a piston to pump the water into the pharyngeal cavity.

Drinking by a Bengalese Finch. Water runs between the beak tips as a result of adhesion and capillary action. The bill then tips up and that, along with tongue movements, moves water into the pharynx Heidweiller and Zweers Mourning Dove drinking notice that doves don't have to tip their heads up like most other birds.

The role of bird kidneys Figure 1 , like the kidneys of other vertebrates is filtration, excretion or secretion, and absorption. They filter water and some substances from blood, such as waste products of metabolism and ions, that are voided in the urine. Kidneys also play an important role in conserving water and reabsorbing needed substances like glucose. The urinary organs of birds consist of paired kidneys and the ureters Figure 2 , which transport urine to the urodeum of the cloaca.

Avian kidneys are divided into units called lobules. Each lobule has a cortex outer area and medulla or medullary cone; Figure 3. Urine is carried from the avian kidneys to the cloaca and, specifically, the middle section called the urodeum by the ureters Figure from McSweeney and Stoskopf Image from Sherwood et al.

Lobule of an avian kidney. The medullary cones include the loops of Henle and collecting ducts of nephrons plus a number of capillaries called the vasa recta. The avian renal medulla is cone shaped because the number of loops of Henle decreases toward the apex of the medullary cones. The functional unit of the kidney is the nephron. Avian kidneys have two kinds of nephrons. A reptilian-type, with no loops of Henle are located in the cortex, and a mammalian-type with long or intermediate length loops, are located in the medulla Figure 4.

Nephrons filter the blood plasma to eliminate waste products, but, in doing so, must not lose needed materials like glucose or too much water. Blood enters nephrons via small arteries called afferent arterioles Figure 5. This blood enters the glomerulus a collection of capillaries; Figure 6 under high pressure and 'filters' through the walls of the capillaries and the walls of a surrounding structure called a capsule. The filtrate that moves from the glomerular capsule into the proximal tubules is basically plasma without protein the protein molecules are too large.

That filtrate, therefore, contains lots of important substances. In the proximal convoluted tubules, those needed substances such as vitamins and glucose are reabsorbed into the the blood Figure 7. Nephron components mammalian type nephron shown: Plasma is filtered from the glomerular capillaries into the glomerular capsule. Filtrate then travels through the tubules and loop of Henle before entering the collecting duct. Glomeruli of an Anna's Hummingbird. Reabsorption of materials from the proximal convoluted tubule back into the blood.

Other than mammals, birds are the only vertebrates that conserve body water by producing urine osmotically more concentrated than the plasma from which it is derived. However, the ability of birds to concentrate urine is limited compared to mammals. Typically, water-deprived birds produce urine that is 1.

This 'concentrating capacity' resides within the medullary cones. Solutes sodium chloride, or NaCl are actively transported out the ascending limb of the Loop of Henle Figure 8 , where they become concentrated in the medulla medullary cones. When urine passes throughout the osmotic gradient in the medulla, water leaves the tubules by osmosis and the urine become concentrated. Because only the looped nephrons contribute to the intramedullary osmotic gradient, the presence of loopless nephrons may limit the ability of the kidneys to produce hyperosmotic urine.

Thus, the concentrating ability of avian kidneys is more limited than in mammals. This reduced capacity of avian kidneys to concentrate urine compared to mammals means that more water accompanies the solutes that travel from the kidneys through ureters to the cloaca. Water-deprived birds do have a mechanism for reducing the amount of water leaving the kidneys.

In response to dehydration, the pituitary gland releases more of a hormone called arginine vasotocin AVT into the blood. In the kidneys, AVT causes a reduction in the glomerular filtration rate the rate at which plasma filters from the glomeruli into the glomerular capsule; Figure 8 so less water moves from the blood into the kidney tubules. In addition, AVT increases the permeability of the walls of collected ducts to water by opening protein water channels called aquaporins Figure 8.

As the collecting ducts become more permeable, more water moves by osmosis out of the collecting ducts because of the higher solute concentration in the medullary cones and can be reabsorbed by kidney capillaries. Studies to date suggest that the extent to which AVT can reduce urine production and water loss varies among species, but, in general, AVT is less effective in conserving water than the mammalian equivalent antidiuretic hormone, or ADH; Nishimura and Fan Therefore, water-deprived birds tend to produce more urine, and lose more water from the kidneys, than would a similar-sized water-deprived mammal.

A proposed model for urine concentration in the mammalian-type nephron of birds showing transport of NaCl and water in various nephron segments. Left , NaCl is actively exported out of the thick ascending limb TAL and some re-enters the descending limbs DLs by simple diffusion but, despite the resulting high solute concentration, water does not follow because the membrane is not permeable to water.

Loops of Henle exhibit some variation in length and more NaCl is transported out of the longer loops of Henle so the osmotic gradient is greatest near the end of the medullary. AVT arginine vasotocin is a hormone that helps birds conserve water by reducing the glomerular filtration rate the rate at which plasma moves from glomeruli in the glomerular capsules and by increasing the permeability of collecting ducts to water by opening protein water channels called aquaporins; AQP Figure from Nishimura and Fan Nasal respiratory turbinates are complex, epithelially lined structures in nearly all birds and mammals that act as intermittent countercurrent heat exchangers during respiration.

Respiratory turbinates also allow birds to conserve water by helping to 'dehumidify' air during exhalation. During inhalation top , ambient air passes over the respiratory turbinates and is warmed to body temperature. As a result, air is saturated with water vapor, and the turbinates are cooled by evaporative water loss.

During exhalation bottom , warm air from the lungs returns through the nasal passage and is cooled as it passes over the turbinate surfaces. This results in a substantial reduction in the moisture and heat contained in exhaled air. This graph depicts water vapor added to inhaled air shaded arrow and water condensate recovered from exhaled air open arrow. Hillenius and Ruben Birds that feed on nectar can consume a huge amount of fluid compared to their body weight. And the more dilute the nectar, the higher the volumes ingested.

Although the birds derive nutrients and energy from nectar, they have to get rid of the large amounts of water taken in. Failing to do so can have devastating consequences. Palestine Sunbirds have somehow overcome the problems of life on liquid diet, so McWhorter et al.

In the kidney, water is filtered out of blood by specialized structures called glomeruli, and some of the eliminated water is later reabsorbed in the nephron and collecting duct. The researchers set out to test how these processes respond to water intake in Palestine Sunbirds.

Although following the birds around and measuring their nectar intake is difficult, McWhorter and his colleagues came up with an ingenious solution to the problem. They discovered that the birds adjust the amount they consume according to the concentration of sucrose solutions they are fed: In this way, the team could vary the bird's water intake and measure the rates of renal filtration and reabsorption.

McWhorter explained that when the team began investigating this nectarivorous bird's approach to fluid management, it was thought that renal filtration changes according to water status; decreasing in response to water shortage, but increasing only moderately as the birds take on water. But this was based on ideas developed for birds that do not regularly cope with a large intake of water. McWhorter and his team also knew that when the birds are on dilute diets, water is shunted through the gut without being absorbed.

So, how would Palestine Sunbirds' kidneys cope? The team found that renal filtration is not exceptionally sensitive to water loading in sunbirds; it increased only slightly in response to a dramatic decrease in sucrose concentration. On the other hand, the fractional water reabsorption - a measure of the proportion of the eliminated water that is reabsorbed by the kidney - dropped significantly when the birds were on the most dilute diet.

The sunbirds' kidney responds to the elevated water levels by decreasing reabsorption, rather than by raising the filtration rate. The team also found that the glucose and osmotic concentrations in the final excreted fluids were significantly lower than those in the ureteral fluids released by the kidney. Because the gut and urinary tracts of birds join at the cloaca, the researchers conjecture that the dietary water that shunts through the gut might have diluted the ureteral fluids. They conclude that Palestine Sunbirds deal with large amounts of water intake by not absorbing it in the first place.

From an economical standpoint this makes sense, as eliminating water by increasing renal filtration rate can be energetically costly for birds. Sugar and other metabolites lost during filtration may only be retained by reabsorption, possibly overwhelming the kidney's ability to prevent solute loss. But how the gut could absorb nutrients without taking in dietary water is still a mystery, as the two processes normally come hand in hand Click on the photo to check out Peter Jones' website.

Sunbirds and other birds feeding on nectar from aloe erythrina Erythrina livingstoniana flowers. An important part of the diet of all birds is protein. Proteins are composed of subunits called amino acids, and those amino acids are sometimes used as a source of energy or are converted into fats or carbohydrates. When amino acids are used for energy or converted to fats or carbohydrates, the amine NH 2 group must be removed.

These amine groups are toxic and must be eliminated. Some organisms excrete these nitrogenous wastes as ammonia e. Birds and reptiles excrete these wastes primarily as uric acid. Although excreting nitrogenous wastes as uric acid has its advantages e. Molecular structure of a typical amino acid, ammonia, urea, and uric acid. The homeostasis of fluid and ions in birds involves several organ systems Figure 10 and is a more complex phenomenon than in other vertebrates. In birds, the kidneys and lower gastrointestinal tract cloaca, rectum, and ceca are involved in the regulation of extracellular fluid composition.

Many birds also have functional salt glands see below. Osmoregulatory organs of birds Hughes As noted above, the avian kidney has a limited capacity for the conservation of body water and electrolytes via elimination of hyperosmotic urine.

This low capacity to concentrate urine is not a liability because urine formed by the kidneys travels along the ureters into the cloaca Figure From there, it may move by retrograde peristalsis into the lower intestine colon and cecae. Fluid from the upper gastrointestinal tract also enters the cloaca.

Therefore, the cloaca receives an influx of water from the kidneys and the small intestine. The influx of water into the cloaca can be reabsorbed through the epithelium of the lower intestinal tract to maintain hydration. In the lower intestine and cecae, water and sodium chloride are reclaimed by the process of sodium-linked water reabsorption Figure In other words, positively-charged sodium ions are actively transported out of the intestine and negatively-charged chloride ions follow.

Water then follows by osmosis. Uric acid is, as a result, concentrated and excreted as a relatively dry mixture with feces Hildebrandt Diagram of the cloaca and lower intestine of a domestic chicken Gallus gallus. Initially, the solutes in the urine cause water to move by osmosis out of the surrounding tissues and into the coprodeum the section of the cloaca adjacent to the colon or large intestine. After being transported by peristalsis into the colon, however, NaCl is transported out of the colon and water follows the concentration gradient osmosis and is reabsorbed Laverty and Skadhauge The predominate form in which nitrogen is excreted by birds uric acid requires little water for excretion because it isn't very soluble in water.

However, it does require a significant amount of protein to maintain it in a colloidal suspension in the urine i.