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Like rest of Gastrointestinal canal, Large Intestine is made of four tissue layers: innermost layer, known as mucosa, is made of simple columnar epithelial tissue. Mucosa of Large Intestine is smooth, lacking villi found Small Intestine. Many mucous glands secrete mucus into hollow lumen of Large Intestine to lubricate its surface and protect it from rough food particles. Surrounding mucosa is layer of blood vessels, nerves and connective tissue know as submucosa, which support other layers of large intestine. Muscularis Layer Surrounds Submucosa And Contains Many Layers Of Visceral Muscle Cells That Contract And Move Large Intestine. Continuous contraction of smooth muscle bands in muscles produces lumpy, pouch-like structures know as haustra in large Intestine. Finally, serosa forms outermost layer. Serosa is thin layer of simple squamous epithelial tissue that secretes watery serous fluid to lubricate surface of large Intestine, protecting it from friction between abdominal organs and surrounding muscles and bones of lower torso. Large Intestine Performs Vital Functions Of Converting Food Into Feces, Absorbing Essential Vitamins Produced By Gut Bacteria, And Reclaiming Water From Feces. Slurry Of Digested Food, Known As Chyme, Enters Large Intestine From Small Intestine Via Ileocecal Sphincter. Chyme passes through cecum where it is mixed with beneficial bacteria that have colonized large intestine throughout personas lifetime. Chyme is then slowly moves from one haustra to next through four regions of colon. Most of movement of chyme is achieved by slow waves of peristalsis over period of several hours, but colon can also be emptied quickly by stronger waves of mass peristalsis following large meal. While chyme moves through large intestine, bacteria digest substances in chyme that are not digestible by human digestive system. Bacterial fermentation converts chyme into and releases vitamins including vitamins K, B1, B2, B6, B12, and biotin. Vitamin K is exclusively produced by gut bacteria and is essential in proper clotting of blood. Gases such as carbon dioxide and methane are also produced as byproduct of bacterial fermentation and lead to flatulence, or gas passing through anus. Absorption of water by large intestine not only helps to condense and solidify feces, but also allows body to retain water to be used in other metabolic processes. Ions and nutrients released by gut bacteria and dissolve in water are also absorbed in large Intestine and used by body for metabolism. Dry, condensed fecal matter is finally stored in rectum and sigmoid colon until it can be eliminated from body through process of defecation.
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Digestion of proteins and carbohydrates, which partially occurs in stomach, is complete in small intestine with aid of intestinal and pancreatic juices. Lipids arrive in intestine largely undigested, so much of focus here is on lipid digestion, which is facilitated by bile and enzyme pancreatic lipase. Moreover, intestinal combines with pancreatic juice to provide liquid medium that facilitates absorption. Intestine Is Also Where Most Water Is Absorb, Via Osmosis. Small intestines absorptive cells also synthesize digestive enzymes and place them in plasma membranes of microvilli. This distinguishes small intestine from stomach; that is, enzymatic digestion occurs not only in lumen, but also on luminal surfaces of mucosal cells. For optimal chemical digestion, chyme must be delivered from stomach slowly and in small amounts. This is because chyme from stomach is typically hypertonic, and if large quantities were forced all at once into small intestine, resulting osmotic water loss from blood into intestinal lumen would result in potentially life-threatening low blood volume. In addition, continued digestion requires adjustment of low pH of stomach chyme, along with rigorous mixing of chyme with bile and pancreatic juices. Both processes take time, so pumping action of pylorus must be carefully controlled to prevent duodenum from being overwhelmed with chyme.
There are several differences between walls of large and small intestines. For example, few enzyme-secreting cells are found in wall of large intestine, and there are no circular folds or villi. Other than in anal canal, mucosa of colon is simple columnar epithelium made mostly of enterocytes and goblet cells. In addition, wall of large intestine has far more intestinal glands, which contain vast populations of enterocytes goblet cells. These goblet cells secrete mucus that eases movement of feces and protects intestine from effects of acids and gases produced by enteric bacteria. Enterocytes absorb water salts as well as vitamins produced by your intestinal bacteria.
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