L20 - Digestive physiology

• Where does digestion mostly occur in the human body?

  Small intestine
• What is the role of enzymes in digestion?

  They hydrolyze larger molecules into monomers
• What are the steps involved in the absorption of molecules in the intestine?

  Enter cells, move to interstitial fluid, diffuse into capillaries
• What is simple diffusion?

  Passive process across membrane
• What type of molecules undergo facilitated diffusion?

  Polar molecules via channels or carrier proteins
• What is primary active transport?

  Movement using energy directly
• What is secondary active transport?

  Cotransport carriers move molecules against gradient
• What enzyme begins carbohydrate digestion in the mouth?

  Salivary amylase
• What does pancreatic amylase do in the small intestine?

  Continues digestion of sugars into disaccharides
• What are brush border enzymes responsible for?

  Completing digestion of sugars into monosaccharides
• What does sucrase break down?

  Sucrose into fructose and glucose
• How are glucose and galactose absorbed in the intestine?

  Na+-dependent secondary active transport
• What role does Na+-K+ ATPase play in absorption?

  Maintains Na+ gradient for glucose transport
• How is fructose absorbed in the intestine?

  Facilitated diffusion
• What initiates protein digestion in the stomach?

  Pepsin secreted by chief cells
• What do pancreatic proteases do in the small intestine?

  Break down proteins into smaller pieces
• What are the names of some pancreatic proteases?

  Trypsin, chymotrypsin, carboxypeptidase B
• What do brush border peptidases do?

  Break polypeptides into di- and tripeptides
• How are di- and tripeptides absorbed in the intestine?

  H+-dependent secondary active transport
• What happens to amino acids inside absorptive cells?

  They are digested to single amino acids
• Where does lipid digestion primarily occur?

  Small intestine
• What is the first step in lipid digestion?

  Emulsification of lipids with bile salts
• What do pancreatic lipases do?

  Break down triglycerides to monoglycerides and fatty acids
• What are micelles?

  Groups of monoglycerides and fatty acids with bile salts
• How do fatty acids and monoglycerides enter absorptive cells?

  By simple diffusion from micelles
• What happens to monoglycerides and fatty acids inside absorptive cells?

  They are converted back to triglycerides
• What are chylomicrons?

  Triglycerides combined with cholesterol and proteins
• How do chylomicrons enter the lymphatic system?

  Via exocytosis into interstitial fluid
• What do pancreatic nucleases break down?

  Nucleic acids into nucleotide monomers
• What do nucleosidases and phosphatases do?

  Break down nucleotides into free bases, sugars, and phosphates
• How are breakdown products of nucleic acids absorbed?

  Actively transported by special carriers
• What are vitamins?

  Organic cofactors that help with metabolism
• How are water-soluble vitamins absorbed?

  By specific active or passive transporters
• How is vitamin B12 absorbed?

  Bound by intrinsic factor and absorbed by endocytosis
• How are fat-soluble vitamins absorbed?

  Carried by micelles and absorbed by simple diffusion
• How are vitamins K and B7 made available for absorption?

  Through bacterial metabolism in the large intestine
• How are most electrolytes absorbed in the small intestine?

  Via active transport along the entire length
• Where are calcium and iron mainly absorbed?

  In the duodenum
• How much chyme enters the small intestine daily?

  ~9 L
• How much water is reabsorbed in the small intestine?

  ~90% of the water in chyme