GIT

• Digestion and absorption of food

  Nutritive substances, vitamins, minerals, fluids for the utilization of the body
• Nutritive substances and their digestive enzymes

  • Carbohydrates: Mouth - ptyalin or salivary amylase for starch digestion, Small intestines - pancreatic amylase for CHO digestion; sucrase and lactase for CHO absorption
  • Proteins and nucleic acids: Stomach - pepsin, gelatinase, Small intestines - proteolytic enzymes (from the pancreas and intestinal), Mucosa - trypsin, chymotrypsin, elastase, endopeptidases
  • Lipids: Duodenum - pancreatic lipase, pancreatic esterase, bile salts (liver)
• Nerve supply


  • Autonomic nervous system, Parasympathetic activity increases the activity of intestinal smooth muscle, Sympathetic activity decreases intestinal smooth muscle activity; causes sphincter to contract
• Major networks of nerve fiber

  • Myenteric nerve plexus (Auerbach’s plexus) - between the outer longitudinal and middle circular muscle layers, Submucous plexus (Meissner’s plexus) - between the middle circular layer and the mucosa
• Gastrointestinal hormones


  • Gastrin: stimulates gastric acid and pepsin secretion, stimulates growth of gastric mucosa, causes contraction of the gastroesophageal junction, stimulates calcitonin secretion, stimulates secretion of glucagon and insulin after a protein meal; Cholecystokinin - Pancreozymin: produces contraction of the gall bladder, increases the secretion of pancreatic juice rich in enzymes, increases insulin secretion, produces contraction of pyloric sphincter; Secretin: causes the secretion of watery, alkaline pancreatic juice, decreases gastric acid secretion, inhibits gastric emptying and enhances the motility of small intestines and colon, augments the contraction of pyloric sphincter
• Activities of Pharynx


  Pharyngeal stage of deglutition, Moves bolus from oropharynx to laryngopharynx and into the esophagus, Closes air passageways
• Activities of Esophagus


  Esophageal stage of deglutition, Permits entry of bolus from larynx into the esophagus, Pushes bolus down
• Activities of Pharynx


  1. Pharyngeal stage of deglutition

  2. Moves bolus from oropharynx to laryngopharynx and into the esophagus

  3. Closes air passageways
• Activities of Esophagus


  1. Esophageal stage of deglutition

  2. Permits entry of bolus from larynx into the esophagus

  3. Pushes bolus down in the course of esophagus

  4. Permits entry of bolus into the stomach

  5. Has mucus for smooth passage of bolus
• Pancreas


  1. Produces 1200-1500 mL of pancreatic juice consisting of water, salts, sodium bicarbonate, and enzymes

  2. Sodium bicarbonate buffers the acidic gastric juices

  3. Enzymes in pancreatic juice include PANCREATIC AMYLASE, trypsin, chymotrypsin, carboxypeptidase, elastase, pancreatic lipase, ribonuclease, and deoxyribonuclease
• Liver


  1. Hepatocytes secrete 800-1000ml of bile per day

  2. Bile consists mostly of water, bile acids, bile salts, cholesterol, lecithin, bile pigments, and several ions

  3. Bile salts have an important role in emulsification
• Liver functions


  • Carbohydrate metabolism
  • Lipid metabolism
  • Protein metabolism
  • Processing of drugs and hormones
  • Excretion of bilirubin
  • Synthesis of bile salts
  • Storage of glycogen, vitamins (ADEK), minerals
  • Phagocytosis: rbc wbc and bacteria
• Small intestine


  1. The major events of digestion and absorption happen in the small intestine

  2. Divided into 3 regions: duodenum, jejunum, ileum

  3. Types of movements: segmentations and migrating motility complexes
• Large intestine activities


  1. Breaks down undigested carbohydrates, proteins, and amino acids into products that can be expelled in feces

  2. Mucosa maintains water balance, solidifies feces, absorbs some vitamins and ions

  3. Elimination of feces from the rectum is called defecation