Large Intestine

6 May 2021

The large intestine is the terminal part of the digestive tract. It is wider and shorter than the small intestine, approximately 1.5 meters long and twice the diameter. Its primary function is to finish the absorption of nutrients and water, synthesise certain vitamins ( B12, thiamin, and riboflavin and vitamin K), form faces, and eliminate the faces from the body. The large intestine runs from the appendix to the anus. It frames the small intestine on three sides and is divided into four main regions:

  • The cecum is the first part of the large intestine bordered by the ileocecal valve, which regulates chyme from the small intestine to the large intestine. The cecum is a suspended pouch inferior to the ileocecal valve in the lower, just right, of the midline area of the abdominal cavity. It is about 6 cm long and receives the ileum content, and continues the absorption of water and salt. The appendix attaches to the cecum and can act as a bacterial reservoir in illness to repopulate the enteric bacteria. The twisted anatomy of the cecum provides the right environment for the accumulation and multiplication of antic bacteria. The inner walls are lined with a thick mucous membrane, through which water and salts are absorbed. Under the lining is a deep layer of muscle tissue that creates a churning and kneeing motion. 
  • The colon, which blends seamlessly from the cecum, is the longest section of the large intestine. The colon first travels up the right side of the abdomen; this section is called the ascending colon. At the inferior surface of the liver, the colon bends to the midline to form the right colic flexure (hepatic flexure) and become the transverse colon; from this region on is defined as the hindgut. Food residue passing through the transverse colons travels across to the left side of the abalone, which dips slightly at midline before bending at the left colic flexure (splenic flexure) inferior to the spleen to pass down the descending colon, which lies at the posterior left side of the abdomen wall. The descending colon enters into the pelves and becomes the s-shaped sigmoid colon which extends first superiorly to the midline and then curves again in an inferior direction posteriorly to the bladder to become the rectum. The purpose of the colon is to lubricate waste products, absorb remaining fluids and salts, and store waste products until they are ready to be passed from the body. The dehydration of liquid materials from the small intestine mainly happens in the ascending and transverse regions of the colon, which forms into faecal mass (faeces). The inner walls of the colon consist of a mucous membrane, which absorbs fluids and secrets mucus for the lubrication of the waste material. There are two types of muscles in the deeper muscles layer of the colon. The circular muscles produce the mild churning and mixing motions of the intestine. The longitudinal muscles are the ones that create strong contractions that actually move the faeces. 
  • The Rectum is the penultimate segment of the digestive system. Faeces leaving the sigmoid colon enters the rectum just before discharge. The rectum is between 13 to 15 cm long and begins near the third sacral vertebra S3 and extends inferiorly, and follow the curvature of the anterior side of the sacrum and coccyx to the anus. There are three lateral bends segmented from the other by a  trio of internal traverse folds called rectal valves or the valves of Houston. The valves help support the rectal content by separating the faeces from gas. A sheath of longitudinal muscle surrounds the outside of the rectal wall that shortens the rectum's length when the surge to eliminate waste occurs due to sufficient pressure builds up within the dissented rectal cavity. 
  • The Anal Canal is the final part of the large intestine, located in their perineum, completely outside the abdominopelvic cavity. It is between 3.8 and 5 cm long and structurally opens to the exterior body at the anus. Within the anal canal, there are two sphincters. Superiorly, the internal anal sphincter makes up two-thirds of the canal and is made up of smooth muscle derived from the endoderm, which contracts involuntarily. Anteriorly, the external anal sphincter makes up one-third of the anal canal and is made of skeletal muscle derived from the ectoderm, under voluntary control. 

The Large Intestine

The Anal canal is related to the mouth and the hands through