, 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:
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