What is digested in the large intestine

Transverse colon. This segment travels across the upper part of your abdomen, from right to left. Splenic flexure.

In the left upper side of your abdomen, your large intestine is located under your spleen. At this flexure, your large intestine turns downward. Descending colon. In the left side of your abdomen, your large intestine descends for about 5 inches. Rectosigmoid colon.

This part is about 5 inches long and leads into your rectum. This part of your large intestine stores stool. It's about 6 to 8 inches long and leads to your anal canal.

The hollow inside of your large intestine is known as the lumen. Its lining is called mucosa. It has special folds and projections to help it absorb nutrients. A layer of muscle muscularis propria supports the walls of your large intestine. Most of the bacteria that live in your body—and there are billions of them—live inside your large intestine.

These bacteria are important in digestion and in keeping your large intestine healthy. The good bacteria that live in your colon are called your normal flora. Diverticular bleeding may occur, as well as chronic injury to the small blood vessels next to the diverticula and colonic obstruction.

Inflammatory bowel disease IBD is uncontrolled inflammation and bowel injury in the large intestine resulting in severe discomfort, with symptoms such as abdominal cramps, bloating, gas, liquid motions and diarrhoea. Severe IBD may result in loss of appetite, loss of weight and iron deficiency anaemia. Today, there is evidence to suggest that the immune system overzealously attacks a microbial antigen on the gut lining Torres et al, Intestinal obstruction, a common complication, arises from swelling and formation of scar tissue, a thickening of the bowel wall and a narrowed intestinal passage strictures.

Perforation of the bowel may occur as a result of an abscess or fistula. Ulcerative colitis Ulcerative colitis is characterised by inflammation and ulceration in the lining of colon and rectum, and rectal urgency that can result in painful, bloody diarrhoea up to 20 times a day.

Perforation is a potential complication, since chronic inflammation and ulceration may weaken the intestine wall to such an extent that a hole may form. This is generally linked with toxic megacolon, an emergency condition where the colon loses all contractile function and gas builds up.

Perforation can result in life-threatening peritonitis. Appendicitis If the appendix becomes blocked it becomes inflamed, causing appendicitis. Obstruction causes a pressure build-up, which may compress the blood supply to the gut wall, resulting in ischaemic injury and bacterial infection. The classical symptom is acute pain beginning at the umbilicus and spreading to the right iliac fossa.

Nausea, vomiting and possibly fever may ensue. If this is not treated, the appendix may rupture, causing dangerous peritonitis and allowing bacterial infection to rapidly spread through the peritoneal cavity, potentially leading to death within hours. Appendicitis is one of the commonest causes of acute abdominal pain.

Colorectal cancer Colorectal cancer is the second most common cause of cancer death in the UK and may be signalled by constipation or diarrhoea, cramping, abdominal pain and rectal bleeding — which may be either visible or hidden in the faeces occult. Smoking, excessive alcohol consumption and a diet high in animal fat and proteins have been linked to an increased risk of colorectal cancer. Some studies suggest that increasing dietary fibre intake could reduce the risk Yang and Yu, Since most colon cancers arise from benign mucosal growths called polyps, prevention focuses on identifying these polyps.

Screening for occult faecal blood is currently offered every two years to people aged in most of the UK, although in Scotland it is offered from age 50 and Public England last year announced plans to extend its screening programme in stages to cover years of age PHE, Tagged with: Newly qualified nurses: systems of life.

Sign in or Register a new account to join the discussion. You are here: Gastroenterology. Gastrointestinal tract 5: the anatomy and functions of the large intestine. Abstract In the large intestine — the final section of the gastrointestinal tract — absorption of water and electrolytes takes place and colonic bacteria complete the process of chemical digestion. This article has been double-blind peer reviewed Scroll down to read the article or download a print-friendly PDF here if the PDF fails to fully download please try again using a different browser Click here to see other articles in this series.

Key points The large intestine comprises the caecum, colon, rectum, anal canal and anus Haustral and antiperistaltic contractions help it absorb water and electrolytes The large intestine is where faeces form from food residues, water and bodily by-products Mass movements push faeces towards the anus and create an urge to defecate Constipation can indicate serious physiological disturbance or disease. Also in this series Gastrointestinal tract 1: the mouth and oesophagus Gastrointestinal tract 2: the structure and function of the stomach Gastrointestinal tract 3: the duodenum, liver and pancreas Gastrointestinal tract 4: anatomy and role of the jejunum and ileum Gastrointestinal tract 6: the effects of gut microbiota on human health.

References Argnani F et al Hydrogen breath test for the diagnosis of lactose intolerance, is the routine sugar load the best one? World Journal of Gastroenterology ; 40, Gut ; 2, Peery AF et al Distribution and characteristics of colonic diverticula in a United States screening population.

Clinical Gastroenterology and Hepatology ; — Public Health England Bowel screening to start at Rusoke-Dierich O Damage caused by external factors. In: Rusoke-Dierich O. Diving Medicine. Though people can survive without gut flora, the microorganisms perform a host of useful functions, such as:. Bacterial flora : Escherichia coli, one of the many species of bacteria present in the human gut. Without gut flora, the human body would be unable to utilize some of the undigested carbohydrates it consumes.

Some types of gut flora have enzymes that human cells lack for breaking down certain polysaccharides. Carbohydrates that need bacterial assistance for digestion include:. Bacteria turn the carbohydrates they ferment into short-chain fatty acids SCFAs by a form of fermentation called saccharolytic fermentation.

These SCFAs include acetic acid, propionic acid, and butyric acid. SCFAs can be used by host cells as a major source of useful energy and nutrients for humans. They also help the body absorb essential dietary minerals such as calcium, magnesium, and iron. Evidence indicates that bacteria enhance the absorption and storage of lipids and produce and aid the absorption of needed vitamins, such as vitamin K.

After the food has been passed through the small intestine, it enters the large intestine. Within the large intestine, digestion is retained long enough to allow fermentation via gut bacteria that break down some of the substances that remain after processing in the small intestine.

Some of the breakdown products are absorbed. In humans, these include most complex saccharides at most, three disaccharides are digestible by humans. The large intestine houses over species of bacteria that perform a variety of functions.

Undigested polysaccharides fiber are metabolized into short-chain fatty acids by bacteria in the large intestine and get absorbed by passive diffusion. The bicarbonate that the large intestine secretes helps to neutralize the increased acidity from the formation of fatty acids. Intestinal bacteria also produce large amounts of vitamins, especially vitamin K and biotin a B vitamin , which are absorbed into the blood.

Although this source of vitamins provides only a small part of the daily requirement, it makes a significant contribution when dietary vitamin intake is low. An individual that depends on absorption of vitamins formed by bacteria in the large intestine may become vitamin-deficient if treated with antibiotics that inhibit other species of bacteria while targeting the disease-causing bacteria.

Other bacterial products include gas flatus —a mixture of nitrogen and carbon dioxide, with small amounts of the gases hydrogen, methane, and hydrogen sulphide. The bacterial fermentation of undigested polysaccharides produces these gases. Intestinal flora are also essential for the development of certain tissues, including the cecum and lymphatics. The large intestine absorbs water from the chyme and stores feces until it can be defecated.

Food products that cannot go through the villi, such as cellulose dietary fiber , are mixed with other waste products from the body and become hard and concentrated feces.

The feces is stored in the rectum for a certain period and then the stored feces is eliminated from the body due to the contraction and relaxation of the anus. The exit of this waste material is regulated by the anal sphincter.

Defecation is a combination of voluntary and involuntary processes that create enough force to remove waste material from the digestive system.

Constipation is uncomfortable, but it may be a signal that your diet is deficient in fibrous foods eat more fruits and vegetables and that you are not drinking enough water, so laxatives are generally not the best way to treat it. For the adult human, the process of defecation is normally a combination of both voluntary and involuntary processes that create enough force to remove waste material from the digestive system.

The rectal ampulla acts as a temporary storage facility for the unneeded material. As additional fecal material enters the rectum, the rectal walls expand. A sufficient increase in fecal material in the rectum causes the stretch receptors from the nervous system, located in the rectal walls, to trigger the contraction of rectal muscles, the relaxation of the internal anal sphincter, and an initial contraction of the skeletal muscle of the external sphincter.

The relaxation of the internal anal sphincter causes a signal to be sent to the brain indicating an urge to defecate. Defecation reflex : The conscious and parasympathetic pathways of the defecation reflex.

If this urge is not acted upon, the material in the rectum is often returned to the colon by reverse peristalsis where more water is absorbed, thus temporarily reducing pressure and stretching within the rectum. The additional fecal material is stored in the colon until the next mass peristaltic movement of the transverse and descending colon. If defecation is delayed for a prolonged period, the fecal matter may harden and autolyze, resulting in constipation.

Once the voluntary signal to defecate is sent back from the brain, the final phase begins. The abdominal muscles contract straining , causing the intra-abdominal pressure to increase. The perineal wall is lowered and causes the anorectal angle to decrease from 90 degrees to less than 15 degrees almost straight , and the external anal sphincter relaxes.

The rectum now contracts and shortens in peristaltic waves, thus forcing fecal material out of the rectum and down through the anal canal. The internal and external anal sphincters, along with the puborectalis muscle, allow the feces to be passed by pulling the anus up and over the exiting feces in shortening and contracting actions. Most of the movement of chyme is achieved by slow waves of peristalsis over a period of several hours, but the colon can also be emptied quickly by stronger waves of mass peristalsis following a large meal.

While chyme moves through the large intestine, bacteria digest substances in the chyme that are not digestible by the human digestive system. Bacterial fermentation converts the chyme into feces and releases vitamins including vitamins K, B1, B2, B6, B12, and biotin.

Vitamin K is almost exclusively produced by the gut bacteria and is essential in the proper clotting of blood. Gases such as carbon dioxide and methane are also produced as a byproduct of bacterial fermentation and lead to flatulence, or gas passed through the anus.