Digestion and Absorption of Macronutrients - Anatomy and Physiology
- Which transporter moves monosaccharides out of the enterocyte into the blood?
- GLUT2 on the basolateral membrane, by facilitated diffusion.
- What are the main products of triglyceride digestion by pancreatic lipase?
- Monoglycerides and free fatty acids.
- Inside enterocytes, absorbed lipids are reassembled into triglycerides and packaged into what particles, which enter which vessels?
- Chylomicrons, which leave by exocytosis and enter the lacteals (lymphatic capillaries) rather than blood capillaries.
- In what forms are dietary proteins absorbed by enterocytes?
- As free amino acids and as dipeptides and tripeptides; most small peptides are hydrolyzed to amino acids inside the cell.
- How is fructose absorbed across the apical membrane of enterocytes?
- By facilitated diffusion through GLUT5. It does not require Na+.
- What converts inactive pepsinogen into pepsin in the stomach?
- Hydrochloric acid (low pH), after which pepsin also activates more pepsinogen autocatalytically.
- Which enzyme begins the chemical digestion of starch in the mouth?
- Salivary amylase. Pancreatic amylase continues starch digestion in the small intestine.
- Which transporter moves glucose and galactose across the apical membrane of intestinal enterocytes?
- SGLT1, a secondary active transporter that couples their uptake to Na+ moving down its gradient.
- Which brush border enzyme activates trypsinogen in the duodenum?
- Enteropeptidase (enterokinase). The trypsin it produces then activates the other pancreatic proteases.
- A person lacking lactase drinks milk and develops bloating and diarrhea. What causes these symptoms?
- Undigested lactose stays in the lumen, drawing water in osmotically, and colonic bacteria ferment it, producing gas.
- Which brush border enzyme hydrolyzes lactose, and what are the products?
- Lactase, which splits lactose into glucose and galactose.
- How do bile salts aid fat digestion?
- They emulsify large fat globules into small droplets, increasing the surface area for lipase, and form micelles that carry lipid products to the enterocytes.