What Does the Small Intestine Do?

The little intestine is a tubular structure within the abdominal cavity that carries the food in good continuation with the stomach up to the colon from where the large intestine carries it to the rectum and out of the body via the anus. The main function of this harmonium is to aid in digestion .

How big is the small intestine?

As a person grows the small intestine increases 20 times in duration from about 200 cm in a newborn to about 6 megabyte in an adult. The duration of the little intestine is approximated by three times the distance of the baby, or height of the child or adult .
The duodenum is about 25 centimeter ( 10 inches ) long ; the jejunum is about 2.5 m ( 8 feet ) long and the ileum is about 3.6 m ( 12 feet ) long .

Anatomy of the small intestine

The belittled intestine begins with the duodenum. The duodenum begins at the duodenal bulb and goes around the heading of the pancreas and ends as it returns to the peritoneal cavity at the ligament of Treitz. The peritoneal cavity is a thin membrane cavity that covers the organs within the abdomen with some exceptions.

The end of the small intestine is suspended within the peritoneal cavity by a slender, broad-based mesentery that is attached to the posterior abdominal wall. This allows free movement of the small intestine within the abdominal pit .
After the duodenum comes the next 40 % of the mobile small intestine called the jejunum. The remaining 60 % is the ileum .
The jejunum occupies the bequeath upper parcel of the abdomen while the ileum is positioned in the right slope and upper contribution of the pelvis .
The inside walls of the small intestine show mucosal folds. These are called the fold circulares. The fold are more numerous in the early jejunum and reduce in numbers in the late share and are wholly absent in the ileum .
Absorption takes place via primary cell type of the epithelial layer. Goblet cells, located throughout the epithelial layer, secrete mucus that helps protect the epithelial layer from digestion .
Enteroendocrine cells secrete hormones into blood vessels that penetrate each villus. Paneth cells, located in the epithelial layer facing the intestinal crypts, secrete lysozyme, an enzyme that destroys bacteria. An inner core of lamina propria ( connective tissues ) contains blood capillaries and small lymphatic capillaries called lacteals .
Enteroendocrine cell
Enteroendocrine cell
The submucosa under the mucous membrane contains Brunner ‘s ( duodenal ) glands, found merely in the submucosa of the duodenum. It secretes an alkaline mucus that neutralizes the gastric acid in the incoming chyme .
Aggregates of lymphoid follicles are scattered throughout the little intestine but are found in highest concentration within the ileum, where they are designated Peyer ‘s patches. These are more big among children and infants. The small intestine ends at the ileocecal valve that leads it to the colon. The ileocecal valve provides a barrier to the back stream of the colonic irrigation contents into the small intestine .
The wall of the belittled intestine and colon is composed of four layers : mucous membrane ( or mucous membrane ), submucosa, muscularis ( or muscularis propria ), and tunic ( or serous membrane ).

Functions of the small intestine

The small intestine is the depart of the intestines where 90 % of the digestion and concentration of food occurs, the other 10 % taking place in the stomach and large intestine. The chief function of the small intestine is absorption of nutrients and minerals from food .
Digestion involves two distinct parts. The first is mechanical digestion by chewing, grinding, churning and mixing that takes place in the sass and the stomach. The second separate of digestion is the chemical digestion that uses enzyme, bile acids etc. in order to break down food material into a phase that can then be absorbed, then assimilated into the tissues of the body. Chemical digestion occurs in the little intestine ( and, to a lesser extent, besides in some other part of the gastrointestinal tract .

Digestion of proteins

Proteins, peptides and amino acids are acted upon by enzymes such as trypsin and chymotrypsin, secreted by the pancreas. This breaks them down to smaller peptides. Chemical breakdown begins in the stomach and continues until the bombastic intestine .

Digestion of lipids

enzyme, like lipases secreted from the pancreas, act on fats and lipids in diet. This breaks the triglycerides into free fatso acids and monoglycerides. It is helped by bile salts secreted by the liver and the resentment bladder. The lipase is soluble in water but the fatso triglycerides are not. The bile salts hold the triglycerides in the watery environment until the lipase can break them into the smaller parts that can enter the intestinal villus for absorption .

Digestion of carbohydrates

Carbohydrates are broken down to childlike sugars and monosaccharides like glucose. pancreatic amylase breaks down some carbohydrates to oligosaccharides as well. Some carbohydrates and fibers pass undigested to the large intestine where they may, depending on their type, be bedraggled by intestinal bacteria .

Absorption in the small intestines

once broken down the nutrients are absorbed by the inner walls of the small intestine into the lineage pour. The nutrients are rendered small enough so that they may pass, or “ be transported ”, across the epithelial cells of the gastrointestinal tract. The nutrients are absorbed by processes of simple/passive diffusion, facilitated diffusion, elementary active transport, or secondary active conveyance .
The humble intestine is good for assimilation since it has a big inner surface area. This is formed due to the fold circulares which project many bantam finger-like structures of tissue called villus. The individual epithelial cells besides have finger-like projections, which are called known as microvilli .
For transport, nutrients normally rely upon :

  • Lipids – undergo passive or simple diffusion
  • Short-chain fatty acids – diffusion
  • Amino acids – primary active transport
  • Glucose – secondary active transport
  • Fructose – facilitated diffusion

other absorbed substances in the small intestines include :


Most of the body of water in ingested food and beverages is absorbed by osmosis .
approximately 80 % is absorbed by the small intestine, 10 % by the big intestine and the remaining 10 % excreted in the faeces .


Of these sodium is absorbed by dispersion and active transport. Chloride ( Cl- ) is absorbed passively along with sodium or actively transported. Iodine ( I- ) and Nitrate ( NO3- ) can passively follow Na+ ions or are absorbed actively. calcium ions ( Ca2+ ) are absorbed actively in a process stimulated by calcitriol ( active form of Vitamin D ). Iron ions ( Fe2+ and Fe3+ ), Potassium ions ( K+ ), Magnesium ions ( Mg2+ ) and Phospate ions ( PO43- ) are absorbed by active transport mechanisms.

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Vitamins and minerals

Vitamins including fat soluble ones ( Vitamins A, D, E and K ) are absorbed together with dietary fats. Water soluble vitamins like vitamins B and C are absorbed by diffusion. Vitamin B12 combined with intrinsic component ( from the stomach ) is absorbed by active voice transport .
Of these iron is absorbed in the duodenum, most are absorbed in the jejunum and Vitamin B12 and bile salts are absorbed in the by and by separate of the ileum .

Disorders of the small intestine

Some of the disorders of the little intestine include :

  • Obstruction of the small intestine. This may occur due to external pressure, masses in the lumen (foreign bodies, bezoar, gallstones), paralytic ileus, Crohn’s disease, Celiac disease, Carcinoid, Meckel’s Diverticulum, Gastric dumping syndrome, inguinal hernia, intussuseption, mesenteric ischemia etc.
  • Infections including Giardiasis, Ascariasis, Tropical sprue, Tape worm infestation etc.
  • Small intestine cancer

Further Reading

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Category : Health

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