Biol 1303 Digestive Functions of GI Organs Notes

Small intestines:




Villi:

,  Projections of intestinal mucosal cells that contain connective tissue, blood vessels, and
lymphatic vessels that aid in absorption (diffusion, passive and active transport) of
sugars, amino acids, lipids
 Lined with absorptive cells, secretory cells, endocrine cells
 Increase the surface area by 300–400% for absorption, while maintaining a small outer
surface for the organ
Digestive functions of the duodenum:
 Acidic chyme stimulates S cells to produce secretin
 Secretin stimulates pancreas to secrete pancreatic bicarbonate into duodenum
 Pancreatic juice neutralizes the acidic chyme
 Amino acids and fatty acids in chyme stimulate CCK cells to secrete cholecystokinin (CCK)
 CCK
 Increases pancreatic enzyme secretion
 Causes bile release from gallbladder
 Inhibits gastric emptying
Major hormones that control digestion:




Localized muscle movements in the small intestine:
 Segmentation
 Mixes secretions emptying into duodenum with chyme
 Stops when chyme reaches the ileum of the large intestine
 Peristalsis
 Moves chyme along length of small intestine as digestion and absorption occur
 Chyme remains in small intestine for a total of 3-5 hours
Liver secretions:
 Hepatocytes (liver cells) manufacture bile
 Bile salts
 Emulsify (break down) large lipid droplets into smaller ones = micelles
 Bile pigment
 Mainly the pigment bilirubin, derived from hemoglobin from worn-out red blood
cells
Liver functions in digestion:
 Processes many of the absorbed nutrients
 Hepatic portal vein transports nutrient rich venous blood to liver

,  Blood is distributed to hepatocytes through the hepatic sinusoids
 Hepatocytes extract and process nutrients
 Hepatocytes
 Combine simple carbohydrates to form glycogen
 Create lipids from glucose and amino acids
 Distribute amino acids to blood
 Break down excessive amino acids and worn-out proteins into glucose or
triglycerides
 After hepatocytes complete their work, blood drains from hepatic sinusoids to central
veins to hepatic vein to the inferior vena cava
Gallbladder secretion:
 Stores bile from liver
 CCK triggers bile release into duodenum of small intestine through common bile duct
Pancreas secretion:
 Pancreatic juice
 Secreted by pancreatic acinar cells
 Clear, colorless
 Flows into duodenum through pancreatic duct
 Composed of
 Water
 Sodium bicarbonate
 Neutralizes stomach acid
 Enzymes
 Pancreatic amylase
 Trypsin, chymotrypsin, carboxypeptidase
 Pancreatic lipase
 Ribonuclease, deoxyribonuclease
Pancreatic enzymes:
 Amylase
 Breaks down starches into sugars
 Trypsin, chymotrypsin, carboxypeptidase
 Break proteins down into amino acids
 Pancreatic lipase
 Breaks triglycerides into fatty acids
 Ribonuclease, deoxyribonuclease
 Break down nucleic acids
Liver, pancreas, and gallbladder functions: