Digestion Flashcards
salivary alpha-amylase
cleaves a(1-4) bonds of starch and glycogen in the mouth.
Inhibited in the acidic stomach lumen
Lingual Lipase
Released with siliva in the mouth with lipolytic activity continuing through to the stomach
Hydrolyzes long-chain triglycerides into partial glycerides and free fatty acids.
Act mainly on medium chain fatty acids.
7 common pancreatic inactive proteases/proteins that are proteolytically activated by Trypsin
trypsinogen, chymotrypsinogen, proelstase, two procarboxypeptidases, procolipase, prophospholipase A2.
Gastrin
leads to release of gastric acid from parietal cells into the lumen of the stomach.
secreted from G cells at the bottom of the gastric gland.
First phase of digestion
Digestion in the mouth: Salivary alpha amylase and lingual lipase secreated in saliva to break down starch and fats.
Second phase of digestion
Digestion in the stomach: Alpha amylase inactivated, lingual lipase still active. gastric lipase active. pepsinogen activated to pepsin.
Denaturing of DNA/RNA
Degradation of proteins and TAGs
Third Phase of Digestion
Intestinal digestion: release of secretin and cholecystokinin (CCK)
Neutrilization of pH in duodenum
secreation of bile salts and pancreatic enzymes (alpha amylase, phospholipase A2, trypsinogen)
trypsin activates enzymes for protein and lipid digestion,
Absorption of proteins, lipids, and sugars in intestinal lumen.
Secretin
Released in the presence of high proton concentration
Secretion of water and bicarb from the pancreas.
Inhibits to a certain degree the release of chyme from the stomach which allows time for neutralization of the present chyme
Cholecystokinin
activates secretion of bile from the gallbladder
inhibits gastric motility
activates enteropeptidase in duodenum
activates secretion of pancreatic enzymes
Bile Salts
Glycine or taurine (formed from cysteine in the liver) are conjugated with bile acids. Conjugated bile acids are often named bile salts
Released by the liver into the bile (95% taken up again via the enterohepatic circulation as Secondary bile acids)
•transport of free cholesterol in bile from the liver to
the duodenum
- emulsification of dietary lipids for digestion by pancreatic enzymes
- uptake of products of lipid digestion into intestinal mucosal cells
Pancreatic Lipase
Digestion of dietary triacylglycerols, needs emulsification of lipids performed by conjugated bile salts.
forms 2-monoacylglycerol that is absorbed in the intestinal lumen.
colipase
Anchors pancreatic lipase on the lipid droplet
Chylomicrons
lipid transport from intestinal cell to lymph/blood circ. monolayer lipid membrane filled with: TAGs formed inside the cell fat-soluble Vitamins Cholesterol esters
SGLT
Glucose/glactose transporter into cell lumen
Amino acid transport
Using Na pump
Medium Chain Fatty acids in Digestion
released from intestinal mucosal cells directly as free fatty acids into the portal vein and reach the liver.
milk is a good source, allows the rapid uptake into the liver for energy metabolism.
TAGs with medium-chain fatty acids can be degraded by lingual and gastric lipase which do not need bile salts for activity
Pepsin
Pepsin acts mainly as endopeptidase, which means that it cleaves proteins from the inside and leads to smaller proteins and peptides
Formed from pepsinogen secreted by cheif cells. pepsinogen is activated to pepsin by acid catalyzed cleavage from HCl or by already active pepsin.
Pancreatic alpha-amylase
cleaves dietary polysaccharides to disaccharides in the duodenum
cleaves alpha (1-4) linkages of sugars
Enteropeptidase
Synthesized by cells of the duodenum, with the purpose that it is not in contact with zymogens of the pancreas until these zymogens reach the intestines.
Cleaves trypsinogen to trypsin (an irreversible activation by proteolytic cleavage)
Phospholipase A2
Cleaves glycerophospholipids and releases the fatty acyl group.
It forms a free fatty acid and a lyso-phospholipid, both molecules have detergent character and can now be used to emulsify dietary lipids.
Apo b48
Marks chylomicrons for transport into lymph
Trypsin cleavage of proteins
After Arg or Lys residues
long, narrow binding pocket
Chymotrypsin cleavage of proteins
After bulky (Met, Leu) and aromatic (Phe, Tyr, Trp) residues
wide, large binding pocket
Elastase cleavage of proteins
After Ala, Gly, Ser
Small binding pocket
Carboxypeptidase cleavage of proteins
Cleave from carboxyl-end
Ala Leu, Ile, Val, Arg, Lys
