Gastrointestinal hormones

Early studies on the motility and secretory activity of the gastrointestinal tract indicated that control was not only by the autonomic nervous system but also by a series of gastrointestinal hormones whose release is stimulated when specific hormones reach particular loci in the tract.

Gastrointestinal hormones are chemical messengers that are implicated by many aspects of physiological functions of the gastrointestinal tract, including the regulation of secretion, absorption and digestion, and gut motility.

Gastrointestinal hormones are a large family of peptides and are secreted by endocrine cells that are widely distributes throughout the gastrointestinal mucosa and pancreas. Hormones were originally identifies by four primary actions.
Sccretin: stimulates secretion of HCO3 and H2O
Gastrin: stimulates gastric secretion of acid
Cholecystokinin: contract gallblader
Pancreozymin: stimulates pancreatic secretion of enzymes

And as of today there are more than 50 gut hormones genes and a multitude of bioactive peptides, which makes the gut as the largest endocrine organ of the body.

The gastrointestinal hormones are synthesized in various segments of the gastrointestinal tract but only gastrin appears to be present in the stomach of healthy individuals. The remaining hormones are present in greatest amounts in the duodenum and jejunum, with tapering expression of cholecystokinin and secretin into the ileum in addition.
Gastrointestinal hormones

Vitamins synthesis by intestinal bacteria

Although, by definition, vitamins required by man cannot be synthesized within the tissues, it is important to note that bacteria within the gut can synthesis many of the vitamins required by man. The human intestinal bacteria can synthesize vitamin K, a member of the naphtoquinone family.

Vitamin K2 also called menaquinone also is a product of metabolism of most bacteria including the normal intestinal bacteria of most higher animal species. The vitamin K bacterial reactions occur, in part, in the ileum, where the menaquinone is absorbed.

Among bacteria involve in synthesizing vitamin K are: Bacteroides spp., Eg. Lenta, Propionibacterium spp., Veillonella spp., staphylococci, enterococci enterobacteria.

Most of the vitamin B12 (cyanocobalamin) required by humans comes indirectly from the meat and milk of ruminants. The synthesis of B12 is ruminant is exclusively bacterial origin. It appears most of the bacterially formed B12 I human occurs in the large bowel. It was demonstrated that E. coli, Bifidobacterium spp., Veillonella spp., Fusobacterium spp., Eurobacterium spp., and Clostridium spp., among the bacteria that synthesized B12 in the small intestine.

Folic acid and thiamine B complex vitamins are also synthesized by bacteria in the intestinal tract. Other vitamins synthesized by intestinal bacteria are:
*Biotin
*Folic acid (B2)
*Pantothenic acid (B5)
*Niacin (B3)
*(Pyridoxine) B6
Vitamins synthesis by intestinal bacteria

What is gastrointestinal tract (GI)?

The digestive system includes the gastrointestinal tract, which starts at the mouth, where food and fluids are taken into the body and ends at the anus, where the final waste products are eliminated in the feces.

The gastrointestinal tract consists of all structures derived from the primitive gut tube and distal to the esophagus.

As such the gastrointestinal tract includes the stomach, small intestine, large intestine and those accessory structures that have formed from that part of the gut (liver, gallbladder, pancreas, hepatopancreatic duct, anal tonsils).

The accessory organs contribute needed materials for the breakdown and processing of the food entering the system.

The gastrointestinal tract (GI) is bordered by a layer of epithelial cells (with glands) sitting on a lamina propria (or basement membrane), comprising the mucosa and adjacent to the sub-mucosa, which is penetrated by blood capillaries, lymphatics and nerves.

Beneath the mucosa and sub-mucosa are two layers of smooth muscle, lying in longitudinal and transverse directions, to allow contractions and peristalsis,

The stomach contains the same tissue layers as are found in the esophagus, small intestine and colon, with some important variations in the secretions and structure of the mucosa layer.

The surface of the mucosa is a layer of simple columnar epithelial cells called surface mucous cells.

The mucosa contains a lamina propria (areolar connective tissue) and a muscularis mucosae (smooth muscle).
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Within the stomach, but particularly in the small intestine, the surface area of the mucosa is greatly increased. The mucosal and sub-mucosal layer is folded into microscopic villi on the surface of larger folds or ridges.

The main functions of the gastrointestinal system consist of digestion and absorption.
What is gastrointestinal tract (GI)?