KP - 08 Secretory Function of Alimentary Tract

• Various alimentary tract hormones have specific roles in digestion.
• Hormones play a general role in the control of GI motility and secretions.
• A gland in the submucosa of the duodenum, known as the gastric mucosa, is the main function of secreting an alkaline-based mucus.
• The gastric, pancreatic, liver, small intestine, and large intestine secrete various substances.
• The large intestine secretes crypts of Lieberkuhn, which contain goblet cells that secrete mucous, and no intestinal villi.
• Gastric secretion consists of gastric tubular glands, oxyntic glands, Pylori c glands, parietal cells, chief (peptic) cells, delta cells, ECL cells, mucous cells, G cells, and mucous cells.
• Bile secretion, which is produced by the liver, has functions such as emulsifying fat or detergent function and absorption of fatty acids, monoglycerides, cholesterol, and other lipids from the intestinal tract.
• The small intestine secretes Brunner’s glands, which secrete alkaline mucus for irritation of duodenal mucosa, and crypts of Lieberkuhn, which contain goblet cells that secrete mucous, enterocytes that secrete water and electrolytes, and enterocytes that contain digestive enzymes (carbohydrases, proteases, lipases) for when absorbing food.
• The pancreas secretes protein-digesting enzymes such as trypsin, chymotrypsin, and carboxypolypeptidase, and carbohydrate-digesting enzymes like amylase.
• The secretory functions of the alimentary tract include the production of hormones that control GI motility and secretions.
• Secretory function of the alimentary tract involves the work of glands such as goblet cells and mucous gland which secrete mucous for protection and lubrication.
• Digestion involves the work of pits, which are invaginations into the submucosa, where enzymes are secreted.
• Vasoactive intestinal peptide (VIP) is secreted from the upper part of the intestine, and relaxes smooth muscles in the blood vessels and gut wall, increasing secretions of H20 and electrolytes.
• Motilin is secreted from M-cells in the upper part of the small intestine, the stomach, and the small intestine, and increases GI motility (gastric and intestinal), including migratory motor complexes (interdigestive myoelectric complexes).
• Somatostatin is secreted from Delta-cells in the upper part of the small intestine, the pancreas, and the gallbladder, and acts as a universal inhibitor, inhibiting GI motility and secretion of hormones, enzymes, bile.
• Gastrin is a hormone secreted from the stomach.
• Secretin is secreted from S-cells in the upper part of the small intestine, the exocrine pancreas, and the bile system, and increases secretion of H20 and HCO3- to the duodenum to neutralize acid secreted by the stomach.
• Glucose-dependent insulinotropic peptide (GIP) / Gastric inhibitory peptide (GIP) is secreted from K-cells in the upper part of the intestine, and inhibits insulin secretion, increasing gastric secretions and motility.
• GI Hormones are peptides (strings of amino acid) or peptide derivatives, mostly secreted from the upper part of the small intestine.
• Cholecystokinin, Secretin, Vasoactive intestinal peptide (VIP), Glucose - dependent insulinotropic peptide (GIP) / Gastric inhibitory peptide (GIP), Motilin, Somatostatin, Gastrin all inhibit gastric motility and secretions, except gastrin which increases gastric motility and secretions.
• Gastrin is secreted from G-cells in the Gastric antrum and small intestine, and increases peristalsis and secretions.
• Cholecystokinin is secreted from I-cells in the upper part of the small intestine, the exocrine pancreas, and the gall bladder, and increases secretion of digestive enzymes, bile, and to the duodenum.
• Enterogastrone is any hormone secreted by the duodenum.
• The oxyntic gland, a deep tubular gland in the stomach, is responsible for acid and pepsinogen secretion.
• Complex glands such as the salivary glands, pancreas, and liver secrete enzymes.
• The gastric, pancreatic, liver, small intestine, and large intestine secrete substances at different speeds.
• Neural control and hormonal control are two main categories of control of GI motility and secretions.
• Mechanical digestion, which involves the motility of the GI tract, and chemical digestion, which involves the secretion of enzymes, are two aspects of digestion.
• The gastric, pancreatic, liver, small intestine, and large intestine secrete various substances.
• By the end of this lecture, students will be able to identify the two main categories of glands in the alimentary tract.
• GI hormones are involved in the control of GI motility and secretions.
• Students will be able to state the secretory functions of the alimentary tract.
• The enteric nervous system, parasympathetic autonomic nervous system, and sympathetic autonomic nervous system are parts of the neural control of GI motility and secretions.
• Students will be able to describe the specific roles of various alimentary tract hormones in digestion.
• Pause and stretch are techniques used in digestion.
• Students will be able to describe the general role of hormones in control of GI motility and secretions.