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Journey into the small intestine

by Martina Buccoliero, Ludovica Costa, Carlo Navone, Claudia Parola, Virginia Valfrè

Ludovica Costa

on 31 March 2013

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Transcript of Journey into the small intestine

Introduction Chemical digestion Absorption of nutrients Functions of the small intestine The duodenum From the duodenal bulb to the ligament of Treitz
Most of the chemical digestion occurs in the duodenum duodenum duodenal
bulb The breakdown occurs by means of bile and pancreatic digestive enzymes, which enter the duodenum through the common bile duct and pancreatic duct The jejunum Most of the absorption of nutrients occurs in the jejunum Its inner walls are covered with the mucous membrane, which comprises two kinds
of folds: Plicae circulares Permanent folds of mucous membrane Rugae temporary features which allow for contraction and distension of the intestinal wall Structure of the small intestine The ileum ileum Third and final portion of the small intestine. It ends with the ileocecal valve.
The absorption of nutrients and other digestive products is completed. Vitamin B12 and bile salts are absorbed. The cells in the ileum's wall secrete protease and carbohydrase enzymes, which aid further breakdown of fats and carbohydrates.
The unabsorbed material subsequently passes on to the large intestine. The small intestine reacts to the presence of food by producing the CCK hormone ----> stimulates the arrival of digestive enzymes secreted by the pancreas:
1) protease (comprises trypsin and chymotrypsin)
2) lipase
3) carbohydrase (comprises sucrase and maltase)
Hormone secretin causes sodium bicarbonate to be released, because it neutralizes the harmful potential of gastric acid. Chemical digestion consists of the breakdown of ingested foods into simpler compounds that can be absorbed and fruitfully exploited by the body Proteins are broken down into peptides and amino acids by proteases such as trypsin and chymotrypsin.
Lipids are degraded into fatty acids and glycerol by lipases and bile salts.

Sugar is broken down into monosaccharides (glucose and fructose) by sucrase.
Starch is broken down into maltose molecules, subsequently split into simpler glucose molecules by maltase.

Fiber remains undigested Process by which the nutrients and minerals found in the digested food are absorbed by the the inner walls of the small intestine into the bloodstream Absorption occurs by means of two main different processes:
1) Passive transport ----> when two areas have a different concentration gradient, diffusion proceeds until the difference has been eliminated; it involves the movement of substances from an area of higher concentration to that of lower concentration.
2) Active transport ----> involves the movement of substances against the concentration gradient of the areas in which active transport occurs. Villi and microvilli Villi = tiny finger-like projections protruding from the plicae circulares and the mucous membrane. Structure of villi
Enclosed by a layer of epithelial cells, which
are held together by tight junctions, and are
covered with smaller projections called microvilli.
Core of the villi ----> capillaries and lymphatic
vessels called lacteals

Functions of villi
Increase the surface over which absorption occurs. Thus absorption is
Absorption of nutrients ----> epithelial cells transport the nutrients
into the villi. Amino acids and simple sugars enter the capillaries, while the dietary fats are collected in the lacteals. The circulatory and lymphatic system then transport them to other parts of the body where they are needed. The movement of plicae circulares causes the food to move foreward. The contraction and relaxation of the intestinal tract propagate in a wave (peristalsis) and cause the food to advance. transverse section of the ileum Digestible carbohydrates The small intestine consists of a narrow, coiled tube located in the lower part of the abdominal cavity.
The small intestine is the name given to a portion of the
gastrointestinal tract, which is preceded by the stomach and followed
by the large intestine.
It may vary greatly in length; its average length in an adult
is about 6-7 m, and its diameter measures approximately 3 cm.
It is supported by the mesentery membrane, which
consists of a double layer of peritoneum tissue. A journey into the small intestine
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