Digestive System Physiology
The digestive system is an intricate system that can be disrupted by disease, diet and emotional stress. Cardiology is not a required rotation at OVC, but I picked it up nonetheless because it is one of my weakest subjects. The gallbladder is a small, pear-shaped organ located just posterior to the liver. In certain regions of the alimentary canal, the mucosa may perform one or all three of these functions. Essential Haematology 5e Essential. This is a tube that transfers food to the organs of digestion. Partially digested food starts to arrive in the small intestine as semi-liquid chyme , one hour after it is eaten.
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Other examples of malabsorption include defects of pancreatic secretion that result in maldigestion. Rarely, because of failure to digest lactose which, in large amounts, has a hyperosmotic effect , neonatal farm animals or pups may have diarrhea while they are being fed milk. Reduced secretion of digestive enzymes at the surface of villous tip cells is characteristic of epitheliotropic viral infections recognized in farm animals. The ability of the GI tract to digest food depends on its motor and secretory functions and, in herbivores, on the activity of the microflora of the forestomachs of ruminants, or of the cecum and colon of horses and pigs.
The flora of ruminants can digest cellulose; ferment carbohydrates to volatile fatty acids; and convert nitrogenous substances to ammonia, amino acids, and protein. In certain circumstances, the activity of the flora can be suppressed to the point that digestion becomes abnormal or ceases. Incorrect diet, prolonged starvation or inappetence, and hyperacidity as occurs in engorgement on grain all impair microbial digestion.
The bacteria, yeasts, and protozoa also may be adversely affected by the oral administration of drugs that are antimicrobial or that drastically alter the pH of rumen contents. Signs of GI disease include excessive salivation, diarrhea, constipation or scant feces, vomiting, regurgitation, GI tract hemorrhage, abdominal pain and distention, tenesmus, shock and dehydration, and suboptimal performance. The location and nature of the lesions that cause malfunction often can be determined by recognition and analysis of the clinical findings.
In addition, abnormalities of prehension, mastication, and swallowing usually are associated with diseases of the oral mucosa, teeth, mandible or other bony structures of the head, pharynx, or esophagus. Vomiting is most common in single-stomached animals and usually is due to gastroenteritis or nonalimentary disease eg, uremia, pyometra, endocrine disease. The vomitus in a dog or cat with a bleeding lesion gastric ulcer or neoplasm may contain frank blood or have the appearance of coffee grounds.
Horses and rabbits do not vomit. Regurgitation may signify disease of the oropharynx or esophagus and is not accompanied by the premonitory signs seen with vomiting. Large-volume, fluid diarrhea usually is associated with hypersecretion eg, in enterotoxigenic colibacillosis in newborn calves or with malabsorptive osmotic effects. Blood and fibrinous casts in the feces indicate a hemorrhagic, fibrinonecrotic enteritis of the small or large intestine, eg, bovine viral diarrhea, coccidiosis, salmonellosis, or swine dysentery.
Black, tarry feces melena indicate hemorrhage in the stomach or upper part of the small intestine. Tenesmus of GI origin usually is associated with inflammatory disease of the rectum and anus. Small amounts of soft feces may indicate a partial obstruction of the intestines. Abdominal distention can result from accumulation of gas, fluid, or ingesta, usually due to hypomotility functional obstruction, adynamic paralytic ileus or to a physical obstruction eg, foreign body or intussusception.
Distention may, of course, result from something as direct as overeating. A sudden onset of severe abdominal distention in an adult ruminant usually is due to ruminal tympany.
Ballottement and succussion may reveal fluid-splashing sounds when the rumen or bowel is filled with fluid. Varying degrees of dehydration and acid-base and electrolyte imbalance, which may lead to shock, are seen when large quantities of fluid are lost eg, in diarrhea or sequestered in intestinal obstruction or in gastric or abomasal volvulus.
Abdominal pain is due to stretching or inflammation of the serosal surfaces of abdominal viscera or the peritoneum; it may be acute or subacute, and its manifestation varies among species. In horses, acute abdominal pain is common see Colic in Horses. Subacute pain is more common in cattle and is characterized by reluctance to move and by grunting with each respiration or deep palpation of the abdomen. Abdominal pain in dogs and cats may be acute or subacute and is characterized by whining, meowing, and abnormal postures eg, outstretched forelimbs, the sternum on the floor, and the hindlimbs raised.
Abdominal pain may be difficult to localize to a particular viscus or organ within the abdomen. A complete, accurate history and routine clinical examination can often determine the diagnosis. In outbreaks of GI tract disease in farm animals, the history and epidemiologic findings are of prime importance. In small animals, travel history or other details such as recent adoption from a shelter or recent kenneling or exposure to other animals in dog parks might give clinical suspicion to certain infectious diseases.
The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch. Whilst the muscularis externa is similar throughout the entire gastrointestinal tract, an exception is the stomach which has an additional inner oblique muscular layer to aid with grinding and mixing of food.
The muscularis externa of the stomach is composed of the inner oblique layer, middle circular layer and outer longitudinal layer. Between the circular and longitudinal muscle layers is the myenteric plexus. Activity is initiated by the pacemaker cells, myenteric interstitial cells of Cajal.
The gut has intrinsic peristaltic activity basal electrical rhythm due to its self-contained enteric nervous system. The rate can be modulated by the rest of the autonomic nervous system. The coordinated contractions of these layers is called peristalsis and propels the food through the tract. Food in the GI tract is called a bolus ball of food from the mouth down to the stomach. After the stomach, the food is partially digested and semi-liquid, and is referred to as chyme.
In the large intestine the remaining semi-solid substance is referred to as faeces. The outermost layer of the gastrointestinal tract consists of several layers of connective tissue. Intraperitoneal parts of the GI tract are covered with serosa. These include most of the stomach , first part of the duodenum , all of the small intestine , caecum and appendix , transverse colon , sigmoid colon and rectum.
In these sections of the gut there is clear boundary between the gut and the surrounding tissue. 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 Human gastrointestinal tract. For other uses, see Guts disambiguation. The chyme arrives in the intestines having been released from the stomach through the opening of the pyloric sphincter. The resulting alkaline fluid mix neutralises the gastric acid which would damage the lining of the intestine. The mucus component lubricates the walls of the intestine.
When the digested food particles are reduced enough in size and composition, they can be absorbed by the intestinal wall and carried to the bloodstream. The first receptacle for this chyme is the duodenal bulb. From here it passes into the first of the three sections of the small intestine, the duodenum.
The next section is the jejunum and the third is the ileum. The duodenum is the first and shortest section of the small intestine. It is a hollow, jointed C-shaped tube connecting the stomach to the jejunum. It starts at the duodenal bulb and ends at the suspensory muscle of duodenum.
The attachment of the suspensory muscle to the diaphragm is thought to help the passage of food by making a wider angle at its attachment. Most food digestion takes place in the small intestine. Segmentation contractions act to mix and move the chyme more slowly in the small intestine allowing more time for absorption and these continue in the large intestine. In the duodenum, pancreatic lipase is secreted together with a co-enzyme , colipase to further digest the fat content of the chyme.
From this breakdown, smaller particles of emulsified fats called chylomicrons are produced. There are also digestive cells called enterocytes lining the intestines the majority being in the small intestine. They are unusual cells in that they have villi on their surface which in turn have innumerable microvilli on their surface. All these villi make for a greater surface area, not only for the absorption of chyme but also for its further digestion by large numbers of digestive enzymes present on the microvilli.
The chylomicrons are small enough to pass through the enterocyte villi and into their lymph capillaries called lacteals. A milky fluid called chyle , consisting mainly of the emulsified fats of the chylomicrons, results from the absorbed mix with the lymph in the lacteals. The suspensory muscle marks the end of the duodenum and the division between the upper gastrointestinal tract and the lower GI tract. The digestive tract continues as the jejunum which continues as the ileum.
The jejunum, the midsection of the small intestine contains circular folds , flaps of doubled mucosal membrane which partially encircle and sometimes completely encircle the lumen of the intestine. These folds together with villi serve to increase the surface area of the jejunum enabling an increased absorption of digested sugars, amino acids and fatty acids into the bloodstream.
The circular folds also slow the passage of food giving more time for nutrients to be absorbed. The last part of the small intestine is the ileum. This also contains villi and vitamin B12 ; bile acids and any residue nutrients are absorbed here.
When the chyme is exhausted of its nutrients the remaining waste material changes into the semi-solids called feces, which pass to the large intestine, where bacteria in the gut flora further break down residual proteins and starches. The cecum is a pouch marking the division between the small intestine and the large intestine. At this junction there is a sphincter or valve, the ileocecal valve which slows the passage of chyme from the ileum, allowing further digestion. It is also the site of the appendix attachment.
In the large intestine ,  the passage of the digesting food in the colon is a lot slower, taking from 12 to 50 hours until it is removed by defecation. The colon mainly serves as a site for the fermentation of digestible matter by the gut flora. The time taken varies considerably between individuals. The remaining semi-solid waste is termed feces and is removed by the coordinated contractions of the intestinal walls, termed peristalsis , which propels the excreta forward to reach the rectum and exit via defecation from the anus.
The wall has an outer layer of longitudinal muscles, the taeniae coli , and an inner layer of circular muscles. The circular muscle keeps the material moving forward and also prevents any back flow of waste. Also of help in the action of peristalsis is the basal electrical rhythm that determines the frequency of contractions.
Most parts of the GI tract are covered with serous membranes and have a mesentery. Other more muscular parts are lined with adventitia. The digestive system is supplied by the celiac artery.
The celiac artery is the first major branch from the abdominal aorta , and is the only major artery that nourishes the digestive organs. There are three main divisions — the left gastric artery , the common hepatic artery and the splenic artery.
Most of the blood is returned to the liver via the portal venous system for further processing and detoxification before returning to the systemic circulation via the hepatic veins. The enteric nervous system consists of some one hundred million neurons  that are embedded in the peritoneum , the lining of the gastrointestinal tract extending from the esophagus to the anus. Parasympathetic innervation to the ascending colon is supplied by the vagus nerve. Sympathetic innervation is supplied by the splanchnic nerves that join the celiac ganglia.
Most of the digestive tract is innervated by the two large celiac ganglia, with the upper part of each ganglion joined by the greater splanchnic nerve and the lower parts joined by the lesser splanchnic nerve.
It is from these ganglia that many of the gastric plexuses arise. Early in embryonic development , the embryo has three germ layers and abuts a yolk sac.
During the second week of development, the embryo grows and begins to surround and envelop portions of this sac. The enveloped portions form the basis for the adult gastrointestinal tract. Sections of this foregut begin to differentiate into the organs of the gastrointestinal tract, such as the esophagus , stomach , and intestines.
During the fourth week of development, the stomach rotates. The stomach, originally lying in the midline of the embryo, rotates so that its body is on the left. This rotation also affects the part of the gastrointestinal tube immediately below the stomach, which will go on to become the duodenum. By the end of the fourth week, the developing duodenum begins to spout a small outpouching on its right side, the hepatic diverticulum , which will go on to become the biliary tree.
Just below this is a second outpouching, known as the cystic diverticulum , that will eventually develop into the gallbladder. Each part of the digestive system is subject to a wide range of disorders many of which can be congenital.
Mouth diseases can also be caused by pathogenic bacteria , viruses , fungi and as a side effect of some medications.
Mouth diseases include tongue diseases and salivary gland diseases. A common gum disease in the mouth is gingivitis which is caused by bacteria in plaque. The most common viral infection of the mouth is gingivostomatitis caused by herpes simplex. A common fungal infection is candidiasis commonly known as thrush which affects the mucous membranes of the mouth. There are a number of esophageal diseases such as the development of Schatzki rings that can restrict the passageway, causing difficulties in swallowing.
They can also completely block the esophagus. Stomach diseases are often chronic conditions and include gastroparesis , gastritis , and peptic ulcers. A number of problems including malnutrition and anemia can arise from malabsorption , the abnormal absorption of nutrients in the GI tract. Malabsorption can have many causes ranging from infection , to enzyme deficiencies such as exocrine pancreatic insufficiency.
It can also arise as a result of other gastrointestinal diseases such as coeliac disease. Coeliac disease is an autoimmune disorder of the small intestine. This can cause vitamin deficiencies due to the improper absorption of nutrients in the small intestine. The small intestine can also be obstructed by a volvulus , a loop of intestine that becomes twisted enclosing its attached mesentery.
This can cause mesenteric ischemia if severe enough. A common disorder of the bowel is diverticulitis. Diverticula are small pouches that can form inside the bowel wall, which can become inflamed to give diverticulitis.
This disease can have complications if an inflamed diverticulum bursts and infection sets in. Any infection can spread further to the lining of the abdomen peritoneum and cause potentially fatal peritonitis.
Crohn's disease is a common chronic inflammatory bowel disease IBD , which can affect any part of the GI tract,  but it mostly starts in the terminal ileum. Ulcerative colitis an ulcerative form of colitis , is the other major inflammatory bowel disease which is restricted to the colon and rectum. Both of these IBDs can give an increased risk of the development of colorectal cancer.
Ulcerative coliltis is the most common of the IBDs . Irritable bowel syndrome IBS is the most common of the functional gastrointestinal disorders. These are idiopathic disorders that the Rome process has helped to define. Giardiasis is a disease of the small intestine caused by a protist parasite Giardia lamblia. This does not spread but remains confined to the lumen of the small intestine.
Giardiasis is the most common pathogenic parasitic infection in humans. There are diagnostic tools mostly involving the ingestion of barium sulphate to investigate disorders of the GI tract. Gestation can predispose for certain digestive disorders. Gestational diabetes can develop in the mother as a result of pregnancy and while this often presents with few symptoms it can lead to pre-eclampsia.
From Wikipedia, the free encyclopedia. Redirected from Digestive system. See also gastrointestinal tract. For digestive systems of non-human animals, see Digestion.
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Retrieved 12 June The New England Journal of Medicine, The Functional Gastrointestinal Disorders. Diagnosis, Pathophysiology and Treatment. Anatomy of the mouth. Vermilion border Frenulum of lower lip Labial commissure of mouth Philtrum.
Hard palate Soft palate Palatine raphe Incisive papilla. Parotid gland duct Submandibular gland duct Sublingual gland duct. Oropharynx fauces Plica semilunaris of the fauces Uvula Palatoglossal arch Palatopharyngeal arch Tonsillar fossa Palatine tonsil.
Anatomy of the gastrointestinal tract , excluding the mouth. Muscles Spaces peripharyngeal retropharyngeal parapharyngeal retrovisceral danger prevertebral Pterygomandibular raphe Pharyngeal raphe Buccopharyngeal fascia Pharyngobasilar fascia Piriform sinus. Sphincters upper lower glands. Suspensory muscle Major duodenal papilla Minor duodenal papilla Duodenojejunal flexure Brunner's glands. Ileocecal valve Peyer's patches Microfold cell.
Ascending colon Hepatic flexure Transverse colon Splenic flexure Descending colon Sigmoid colon Continuous taenia coli haustra epiploic appendix. Anatomy of the liver, pancreas and biliary tree. Physiology of the gastrointestinal system. Submucous plexus Myenteric plexus. Segmentation contractions Migrating motor complex Borborygmus Defecation.
Diseases of the digestive system primarily K20—K93 , —