Basic Concepts of GIT

• GLIP is the only gastrointestinal hormone released by all three major foodstuffs (fats, proteins, and carbohydrates)

  1. Increase insulin secretion
  2. Decrease Gastric H+ secretion
• G cells produce gastrin in the stomach when protein hydrolysates and distension occurs this causes an increase in gastric acid secretion and stimulates gorwth of gastric mucosa
• I cells produce CCK, which is found in duodenum, when protein and lipid hydrolysates are present causing an

  1. increase in gall bladder contraction and relaxation of sphincter of oddi
  2. Increase in pancreatic enzyme secretion - HCO3-
  3. Growth of exocrine pancreas and bladder
  4. Inhibits gastric emptying
• S cell produce secretin, located in the duodenum, which is stimulated by acid thus

  1. increasing pancreatic and billary HCO3- secretion to neutralise the acid
  2. Decrease gastric H+ secretion
  3. Inhibits trophic effect of gastrin on gastric mucosa
• D cells produce somatostatin, located in the stomach, when there is excess acid this reduces gastrin release
• Enetrochromaffin cells produce serotonin in the entire GIT when there are toxins and lipid hydrolysates this increases intestinal motility and fluid secretion
• enterochromafin like cells produce histamin in the stomach which increases gastric acid secretion
• M cells produce motilin in the small intestine when fastin which increases the migrating motility complex
• Gastrin and CCK has identical terminal amino acid sequence which means both can be use for exocytosis
• Secretin and VIP have identical internal amino acid sequence
• Ghrelin and motilin have identical internal amino acid sequence
• Ach > Cholinergic nuerons

  1. Contraction of smooth muscle and Relxation of sphincter
  2. increase salivary secretion, gastric and pancreatic
• Norepinephrine > Adrenergic neurons

  1. relaxation of smooth muscle and contraction of sphincters
  2. Increase salivary secretion
• Vasoactive intestinal peptide (VIP) > Enteric Nervous System

  1. Relxation of smooth muscle
  2. Increase intestinal and Pancreatic sectrion
• Gastrin releasing peptide > Vagal neurons of gastric mucosa

  1. Increase gastric secretion
• Neuropeptide Y > Neurons of Enteric nervous system

  1. Decrease intestinal sectrion
  2. Relxation of smooth muscle
• Substance P > Cosecreted with Ach by Enteric nervous system

  1. Contraction of smooth muscle
  2. Increase salivary secretion
• 7th to 9th cranial nerve for salivary glands
• Vagi for the GIT except the distal portion of large bowel
• Pelvic nerves supply the distal portion of the large bowel