Digestive System

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Appendicectomy Colectomy Colonic polypectomy Colostomy Hartmann's operation. The Division of Gastroenterology is studying and developing new treatments and therapies through more than 25 current research projects, including clinical trials and independent projects. The likeliest cause is an immune reaction the body has against its own intestinal tissue. In contrast, neither the left ventral nor left dorsal colons are attached directly to the body wall, allowing these portions of the colon to become displaced or twisted. These signs are seen on a seasonal basis and are synchronous with the emergence of large numbers of encysted larvae into the lumen of the large colon.

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Digestive System: Facts, Function & Diseases

This is why it is sometimes known as the 'graveyard of red blood cells'. A product of this digestion is the pigment bilirubin , which is sent to the liver and secreted in the bile. Another product is iron , which is used in the formation of new blood cells in the bone marrow. The liver is the second largest organ after the skin and is an accessory digestive gland which plays a role in the body's metabolism. The liver has many functions some of which are important to digestion.

The liver can detoxify various metabolites ; synthesise proteins and produce biochemicals needed for digestion. It regulates the storage of glycogen which it can form from glucose glycogenesis.

The liver can also synthesise glucose from certain amino acids. Its digestive functions are largely involved with the breaking down of carbohydrates. It also maintains protein metabolism in its synthesis and degradation. In lipid metabolism it synthesises cholesterol. Fats are also produced in the process of lipogenesis. The liver synthesises the bulk of lipoproteins.

The liver is located in the upper right quadrant of the abdomen and below the diaphragm to which it is attached at one part, This is to the right of the stomach and it overlies the gall bladder. The liver produces bile , an important alkaline compound which aids digestion. Bile acts partly as a surfactant which lowers the surface tension between either two liquids or a solid and a liquid and helps to emulsify the fats in the chyme.

Food fat is dispersed by the action of bile into smaller units called micelles. The breaking down into micelles creates a much larger surface area for the pancreatic enzyme, lipase to work on. Lipase digests the triglycerides which are broken down into two fatty acids and a monoglyceride.

These are then absorbed by villi on the intestinal wall. If fats are not absorbed in this way in the small intestine problems can arise later in the large intestine which is not equipped to absorb fats.

Bile also helps in the absorption of vitamin K from the diet. Bile is collected and delivered through the common hepatic duct. This duct joins with the cystic duct to connect in a common bile duct with the gallbladder. Bile is stored in the gallbladder for release when food is discharged into the duodenum and also after a few hours. The gallbladder is a hollow part of the biliary tract that sits just beneath the liver, with the gallbladder body resting in a small depression.

Bile flows from the liver through the bile ducts and into the gall bladder for storage. The bile is released in response to cholecystokinin CCK a peptide hormone released from the duodenum.

The production of CCK by endocrine cells of the duodenum is stimulated by the presence of fat in the duodenum. It is divided into three sections, a fundus, body and neck. The neck tapers and connects to the biliary tract via the cystic duct , which then joins the common hepatic duct to form the common bile duct.

At this junction is a mucosal fold called Hartmann's pouch , where gallstones commonly get stuck. The muscular layer of the body is of smooth muscle tissue that helps the gallbladder contract, so that it can discharge its bile into the bile duct. The gallbladder needs to store bile in a natural, semi-liquid form at all times. Hydrogen ions secreted from the inner lining of the gallbladder keep the bile acidic enough to prevent hardening.

To dilute the bile, water and electrolytes from the digestion system are added. Also, salts attach themselves to cholesterol molecules in the bile to keep them from crystallising. If there is too much cholesterol or bilirubin in the bile, or if the gallbladder doesn't empty properly the systems can fail. This is how gallstones form when a small piece of calcium gets coated with either cholesterol or bilirubin and the bile crystallises and forms a gallstone. The main purpose of the gallbladder is to store and release bile, or gall.

Bile is released into the small intestine in order to help in the digestion of fats by breaking down larger molecules into smaller ones. After the fat is absorbed, the bile is also absorbed and transported back to the liver for reuse. The pancreas is a major organ functioning as an accessory digestive gland in the digestive system.

It is both an endocrine gland and an exocrine gland. The endocrine part releases glucagon when the blood sugar is low; glucagon allows stored sugar to be broken down into glucose by the liver in order to re-balance the sugar levels. The pancreas produces and releases important digestive enzymes in the pancreatic juice that it delivers to the duodenum.

The pancreas lies below and at the back of the stomach. It connects to the duodenum via the pancreatic duct which it joins near to the bile duct's connection where both the bile and pancreatic juice can act on the chyme that is released from the stomach into the duodenum. Aqueous pancreatic secretions from pancreatic duct cells contain bicarbonate ions which are alkaline and help with the bile to neutralise the acidic chyme that is churned out by the stomach.

The pancreas is also the main source of enzymes for the digestion of fats and proteins. Some of these are released in response to the production of CKK in the duodenum.

The enzymes that digest polysaccharides, by contrast, are primarily produced by the walls of the intestines. The cells are filled with secretory granules containing the precursor digestive enzymes.

The major proteases , the pancreatic enzymes which work on proteins, are trypsinogen and chymotrypsinogen. Elastase is also produced. Smaller amounts of lipase and amylase are secreted. The pancreas also secretes phospholipase A2 , lysophospholipase , and cholesterol esterase. The precursor zymogens , are inactive variants of the enzymes; which avoids the onset of pancreatitis caused by autodegradation.

Once released in the intestine, the enzyme enteropeptidase present in the intestinal mucosa activates trypsinogen by cleaving it to form trypsin; further cleavage results in chymotripsin. The lower gastrointestinal tract GI , includes the small intestine and all of the large intestine. The lower GI starts at the pyloric sphincter of the stomach and finishes at the anus.

The small intestine is subdivided into the duodenum , the jejunum and the ileum. The cecum marks the division between the small and large intestine. The large intestine includes the rectum and anal canal. Partially digested food starts to arrive in the small intestine as semi-liquid chyme , one hour after it is eaten. After two hours the stomach has emptied. In the small intestine, the pH becomes crucial; it needs to be finely balanced in order to activate digestive enzymes.

The chyme is very acidic, with a low pH, having been released from the stomach and needs to be made much more alkaline.

This is achieved in the duodenum by the addition of bile from the gall bladder combined with the bicarbonate secretions from the pancreatic duct and also from secretions of bicarbonate-rich mucus from duodenal glands known as Brunner's glands. 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 , [2] 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 [31] 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.

The pharynx, or throat, is a funnel-shaped tube connected to the posterior end of the mouth. The pharynx is responsible for the passing of masses of chewed food from the mouth to the esophagus. The pharynx also plays an important role in the respiratory system, as air from the nasal cavity passes through the pharynx on its way to the larynx and eventually the lungs. Because the pharynx serves two different functions, it contains a flap of tissue known as the epiglottis that acts as a switch to route food to the esophagus and air to the larynx.

It carries swallowed masses of chewed food along its length. At the inferior end of the esophagus is a muscular ring called the lower esophageal sphincter or cardiac sphincter. The function of this sphincter is to close of the end of the esophagus and trap food in the stomach. The stomach is a muscular sac that is located on the left side of the abdominal cavity, just inferior to the diaphragm. In an average person, the stomach is about the size of their two fists placed next to each other.

This major organ acts as a storage tank for food so that the body has time to digest large meals properly. The stomach also contains hydrochloric acid and digestive enzymes that continue the digestion of food that began in the mouth. It is located just inferior to the stomach and takes up most of the space in the abdominal cavity. The entire small intestine is coiled like a hose and the inside surface is full of many ridges and folds.

These folds are used to maximize the digestion of food and absorption of nutrients. The liver is a roughly triangular accessory organ of the digestive system located to the right of the stomach, just inferior to the diaphragm and superior to the small intestine.

The liver weighs about 3 pounds and is the second largest organ in the body. The liver has many different functions in the body, but the main function of the liver in digestion is the production of bile and its secretion into the small intestine.

The gallbladder is a small, pear-shaped organ located just posterior to the liver. The gallbladder is used to store and recycle excess bile from the small intestine so that it can be reused for the digestion of subsequent meals. The pancreas is a large gland located just inferior and posterior to the stomach.

The pancreas secretes digestive enzymes into the small intestine to complete the chemical digestion of foods. The large intestine is a long, thick tube about 2. It is located just inferior to the stomach and wraps around the superior and lateral border of the small intestine. Even the smell of food can generate saliva, which is secreted by the salivary glands in the mouth, contains an enzyme, salivary amylase, which breaks down starch.

Teeth, which are part of the skeletal system, play a key role in digestion. In carnivores, teeth are designed for killing and breaking down meat.

The BioDigital Human ]. Swallowing pushes chewed food into the esophagus, where it passes through the oropharynx and hypopharynx. At this point, food takes the form of a small round mass and digestion becomes involuntary.

A series of muscular contractions, called peristalsis, transports food through the rest of the system. After an hour or two of this process, a thick semi-liquid paste, called chyme, forms.

The next stop for the chyme is the small intestine, a foot 6-meter tube-shaped organ, where the majority of the absorption of nutrients occurs. The nutrients move into the bloodstream and are transported to the liver. The liver creates glycogen from sugars and carbohydrates to give the body energy and converts dietary proteins into new proteins needed by the blood system. The liver also breaks down unwanted chemicals, such as alcohol, which is detoxified and passed from the body as waste, the Cleveland Clinic noted.

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