The large intestine is made up of the following parts:. Learn more about Intestine Transplant Disease States. Jan Blice Phone: Email: joanne. Renee Brown-Bakewell Phone: Email: renee. Children's Hospital's main campus is located in the Lawrenceville neighborhood. Our main hospital address is:. Pittsburgh, PA In addition to the main hospital, Children's has many convenient locations in other neighborhoods throughout the greater Pittsburgh region.
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Our Sites. Intestine Transplant. What Is the Small Intestine? The small intestine is made up of three segments, which form a passage from your stomach the opening between your stomach and small intestine is called the pylorus to your large intestine: Duodenum: This short section is the part of the small intestine that takes in semi-digested food from your stomach through the pylorus, and continues the digestion process.
The duodenum also uses bile from your gallbladder, liver, and pancreas to help digest food. Jejunum: The middle section of the small intestine carries food through rapidly, with wave-like muscle contractions, towards the ileum.
Ileum: This last section is the longest part of your small intestine. The ileum is where most of the nutrients from your food are absorbed before emptying into the large intestine. The transverse and sigmoid colon are tethered to the posterior abdominal wall by the mesocolon. Each year, approximately , Americans are diagnosed with colorectal cancer, and another 49, die from it, making it one of the most deadly malignancies.
People with a family history of colorectal cancer are at increased risk. Smoking, excessive alcohol consumption, and a diet high in animal fat and protein also increase the risk.
Despite popular opinion to the contrary, studies support the conclusion that dietary fiber and calcium do not reduce the risk of colorectal cancer. Colorectal cancer may be signaled by constipation or diarrhea, cramping, abdominal pain, and rectal bleeding. Bleeding from the rectum may be either obvious or occult hidden in feces.
Since most colon cancers arise from benign mucosal growths called polyps, cancer prevention is focused on identifying these polyps. The colonoscopy is both diagnostic and therapeutic. Colonoscopy not only allows identification of precancerous polyps, the procedure also enables them to be removed before they become malignant. Screening for fecal occult blood tests and colonoscopy is recommended for those over 50 years of age.
Food residue leaving the sigmoid colon enters the rectum in the pelvis, near the third sacral vertebra. The final These valves help separate the feces from gas to prevent the simultaneous passage of feces and gas. Finally, food residue reaches the last part of the large intestine, the anal canal , which is located in the perineum, completely outside of the abdominopelvic cavity.
This 3. The anal canal includes two sphincters. The internal anal sphincter is made of smooth muscle, and its contractions are involuntary.
The external anal sphincter is made of skeletal muscle, which is under voluntary control. Except when defecating, both usually remain closed. There are several notable differences between the walls of the large and small intestines. For example, few enzyme-secreting cells are found in the wall of the large intestine, and there are no circular folds or villi.
Other than in the anal canal, the mucosa of the colon is simple columnar epithelium made mostly of enterocytes absorptive cells and goblet cells.
In addition, the wall of the large intestine has far more intestinal glands, which contain a vast population of enterocytes and goblet cells. These goblet cells secrete mucus that eases the movement of feces and protects the intestine from the effects of the acids and gases produced by enteric bacteria.
The enterocytes absorb water and salts as well as vitamins produced by your intestinal bacteria. Figure 5. LM x Three features are unique to the large intestine: teniae coli, haustra, and epiploic appendages Figure 6.
The teniae coli are three bands of smooth muscle that make up the longitudinal muscle layer of the muscularis of the large intestine, except at its terminal end. Attached to the teniae coli are small, fat-filled sacs of visceral peritoneum called epiploic appendages. The purpose of these is unknown. Although the rectum and anal canal have neither teniae coli nor haustra, they do have well-developed layers of muscularis that create the strong contractions needed for defecation.
The stratified squamous epithelial mucosa of the anal canal connects to the skin on the outside of the anus. This mucosa varies considerably from that of the rest of the colon to accommodate the high level of abrasion as feces pass through.
Two superficial venous plexuses are found in the anal canal: one within the anal columns and one at the anus. Depressions between the anal columns, each called an anal sinus , secrete mucus that facilitates defecation.
The pectinate line or dentate line is a horizontal, jagged band that runs circumferentially just below the level of the anal sinuses, and represents the junction between the hindgut and external skin. The mucosa above this line is fairly insensitive, whereas the area below is very sensitive.
The resulting difference in pain threshold is due to the fact that the upper region is innervated by visceral sensory fibers, and the lower region is innervated by somatic sensory fibers. Most bacteria that enter the alimentary canal are killed by lysozyme, defensins, HCl, or protein-digesting enzymes. However, trillions of bacteria live within the large intestine and are referred to as the bacterial flora.
Most of the more than species of these bacteria are nonpathogenic commensal organisms that cause no harm as long as they stay in the gut lumen. In fact, many facilitate chemical digestion and absorption, and some synthesize certain vitamins, mainly biotin, pantothenic acid, and vitamin K. Some are linked to increased immune response. A refined system prevents these bacteria from crossing the mucosal barrier. Dendritic cells open the tight junctions between epithelial cells and extend probes into the lumen to evaluate the microbial antigens.
The dendritic cells with antigens then travel to neighboring lymphoid follicles in the mucosa where T cells inspect for antigens. This process triggers an IgA-mediated response, if warranted, in the lumen that blocks the commensal organisms from infiltrating the mucosa and setting off a far greater, widespread systematic reaction.
The residue of chyme that enters the large intestine contains few nutrients except water, which is reabsorbed as the residue lingers in the large intestine, typically for 12 to 24 hours.
Thus, it may not surprise you that the large intestine can be completely removed without significantly affecting digestive functioning. For example, in severe cases of inflammatory bowel disease, the large intestine can be removed by a procedure known as a colectomy.
Often, a new fecal pouch can be crafted from the small intestine and sutured to the anus, but if not, an ileostomy can be created by bringing the distal ileum through the abdominal wall, allowing the watery chyme to be collected in a bag-like adhesive appliance.
In the large intestine, mechanical digestion begins when chyme moves from the ileum into the cecum, an activity regulated by the ileocecal sphincter. Right after you eat, peristalsis in the ileum forces chyme into the cecum. When the cecum is distended with chyme, contractions of the ileocecal sphincter strengthen. Once chyme enters the cecum, colon movements begin.
Mechanical digestion in the large intestine includes a combination of three types of movements. The presence of food residues in the colon stimulates a slow-moving haustral contraction. This type of movement involves sluggish segmentation, primarily in the transverse and descending colons.
When a haustrum is distended with chyme, its muscle contracts, pushing the residue into the next haustrum. These contractions occur about every 30 minutes, and each last about 1 minute. These movements also mix the food residue, which helps the large intestine absorb water. The second type of movement is peristalsis, which, in the large intestine, is slower than in the more proximal portions of the alimentary canal.
The third type is a mass movement. These strong waves start midway through the transverse colon and quickly force the contents toward the rectum. Mass movements usually occur three or four times per day, either while you eat or immediately afterward. Distension in the stomach and the breakdown products of digestion in the small intestine provoke the gastrocolic reflex , which increases motility, including mass movements, in the colon.
Fiber in the diet both softens the stool and increases the power of colonic contractions, optimizing the activities of the colon. Although the glands of the large intestine secrete mucus, they do not secrete digestive enzymes. Therefore, chemical digestion in the large intestine occurs exclusively because of bacteria in the lumen of the colon.
Through the process of saccharolytic fermentation , bacteria break down some of the remaining carbohydrates. This results in the discharge of hydrogen, carbon dioxide, and methane gases that create flatus gas in the colon; flatulence is excessive flatus.
Each day, up to mL of flatus is produced in the colon. More is produced when you eat foods such as beans, which are rich in otherwise indigestible sugars and complex carbohydrates like soluble dietary fiber. The small intestine absorbs about 90 percent of the water you ingest either as liquid or within solid food.
Feces is composed of undigested food residues, unabsorbed digested substances, millions of bacteria, old epithelial cells from the GI mucosa, inorganic salts, and enough water to let it pass smoothly out of the body. Of every mL 17 ounces of food residue that enters the cecum each day, about mL 5 ounces become feces. Feces are eliminated through contractions of the rectal muscles. The process of defecation begins when mass movements force feces from the colon into the rectum, stretching the rectal wall and provoking the defecation reflex, which eliminates feces from the rectum.
This parasympathetic reflex is mediated by the spinal cord. It contracts the sigmoid colon and rectum, relaxes the internal anal sphincter, and initially contracts the external anal sphincter. The presence of feces in the anal canal sends a signal to the brain, which gives you the choice of voluntarily opening the external anal sphincter defecating or keeping it temporarily closed.
If you decide to delay defecation, it takes a few seconds for the reflex contractions to stop and the rectal walls to relax. The next mass movement will trigger additional defecation reflexes until you defecate. The beginning portion of the small intestine the duodenum begins at the exit of the stomach pylorus and curves around the pancreas to end in the region of the left upper part of the abdominal cavity where it joins the jejunum.
The duodenum has an important anatomical feature which is the ampulla of Vater. This is the site at which the bile duct and pancreatic duct empty their contents into the small intestine which helps with digestion. The jejunum is the upper part of the small intestine and the ileum the lower part, though there is no clear delineation between the jejunum and ileum. The lining of the small intestinal mucosa is very highly specialized for maximizing digestion and absorption of nutrients.
The lining is highly folded to form microscopic finger-like projections called villi which increase the surface area to help with absorption. The lining also contains specialized groups of cells that produce chemicals which help digestion, provide immune defenses, and hormones that help to control coordination of digestive process of the intestine, gallbladder, and pancreas. An important anatomic feature of the small intestine is also its highly integrated nervous system which lies within the wall of the intestine this is called the enteric nervous system The enteric nervous system plays a very important role in coordinating much of the activities of the small intestine including its muscular activity of propulsion the moving of intestinal contents.
The small intestine is responsible for absorption of nutrients, salt, and water. On average, approximately nine liters of fluid enters the jejunum each day. The small intestine absorbs approximately seven liters, leaving only 1. Significant abnormalities of the small intestine therefore, are manifested by malabsorption of nutrients, and diarrhea.
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