digestion & absorption Flashcards
digestion of carbs
amylase: produced by salivary glands + pancreas; released in mouth + small intestines
- catalyses breakdown of polysaccharides (starch) into disaccharides (maltose) by hydrolysing glycosidic bonds
membrane-bound disaccharidases:
- catalyses breakdown of disachharides into monosaccharides by hydrolysis of glycosidic bonds
digestion of proteins
endopeptidases - hydrolyse peptide bonds between AAs in the middle of polymer chains
exopeptidases - hydrolyse peptide bonds between AAs at the ends of polymer chains
dipeptidases - hydrolyse peptide bonds between 2 AAs in a disaccharide
absorption of glucose & AAs
Na+ actively transported out of epithelial cell into the blood via Na-K pump against its conc grad.
- this reduces conc of Na+ in epithelial cell, creating a new conc gradient, allowing Na+ to diffuse from the ileum into the epithelial cell down this new conc grad via a cotransporter protein
- protein also carries glucose/AAs with the Na+ into the cell against its own conc grad
- conc of glucose/AAs inside the cell increases
- so glucose/AAs can eventually diffuse out the cell into the blood via FD through a channel protein
digestion & absorption of lipids
bile salts: produced in liver; stored in gall bladder; and delivered to small intestines by bile ducts
- emulsify lipids into small fat droplets (micelles), to provide a larger SA for rapid hydrolysis by lipase
lipase: produced by pancreas; released into small intestines
- hydrolyses ester bonds in lipids to form monoglycerides + FAs
- these stick together w bile salts to form micelles
micelles deliver monoglycerides + FAs to epithelial cells of lumen so they can diffuse through the membrane
- need to modified back to triglycerides in golgi body + ER to be used in the body
- these triglycerides combine w proteins to form chylomicrons
- these are released from the epithelial cell via exocytosis + absrobed into the lacteal + eventually drained into the capillaries
