Digestion

Question 1

overview digestion of proteins

Answer 1

digested into AA by proteolytic enzymes (proteases) secreted by stomach and pancreas

Question 2

overview digestion of carbs

Answer 2

cleaves to monosaccharides by a-amylase secreted by saliva and pancreas

Question 3

overview digestion of lipids

Answer 3

converted into fatty acids by lipases secreted by pancreas

Question 4

how do digestive enzymes work?

Answer 4

most digestive enzymes are hydrolases; they cleave by adding a molecule of water

Question 5

digestive enzyme secretion

Answer 5

• digestive enzymes are secreted as inactive forms (zymogens or proenzymes)
• proteolytic cleavage activates next set of enzymes

prior to secretion, zymogens exist in granulas near the cell mmebrane

the granules fuse with the CM and expel their contents in the intestine lumen

Question 6

pepsin synthesis, zymogen, activator

Answer 6

• site of synthesis: stomach
• zymogen: pepsinogen
• activator: self activates in low pH

Question 7

chymotrypsin synthesis, zymogen, activator

Answer 7

• site of synthesis: pancreas
• zymogen: chymotrypsinogen
• activator: trypsin

Question 8

trypsin synthesis, zymogen, activator

Answer 8

• site of synthesis: pancreas
• zymogen: trypsinogen
• activator: enteropeptidase (on small int epithelial cells)

Question 9

elastase synthesis, zymogen, activator

Answer 9

• site of synthesis: pancreas
• zymogen: proelastase
• activator: trypsin

Question 10

what is the only enzyme secreted already active/not as a zymogen?

Answer 10

a-amylase; secreted by saliva and pancrease in its active form

Question 11

what is the main digestive function of mastication?

Answer 11

inc SA > easier for enzymes to bind

Question 12

role of saliva in digestion

Answer 12

• contains mucoproteins that homogenize food and provide excess lubrication to swallow
• contains a-amylase > cleaves a-1,4-glycosidic bonds

Question 13

protein digestion in the stomach

Answer 13

• proteins are denatured by acidic (1-2 pH) stomach by breaking ionic and H bonds
• proteolytic enzyme pepsin breaks proteins into smaller fragments

Question 14

stomach acid mechanics

Answer 14

• gastric proton pump (H-K-ATPase) located on cells lining stomach
• pumps protons into stomach in exchange for K (w cost of ATP hydrolysis)

Question 15

digestion in the small intestine

Answer 15

• low pH from stom stim small int cells to release hormone secretin
• secretin promotes release of sodium bicarb from pancreas to neautralize
• polypeptide products of pepsin from stomach stim release of cholecystokinin (CCK) by intestinal cells
• pancreas responds to CCK > releases cascade of digestive enzymes into intestine to continue protein digestion and start digestion of lipids and carbs

Question 16

final stage of protein digestion

Answer 16

• pancreatic proteases hydrolyze proteins > oligopeptides
• peptidases (attached to ext surfaces of int cells) cleave oligopeptides > AA and di- and tri-peptides that can be transported into int cells via transporters (7 types)
• AA released into blood stream by antiporters for use within body

Question 17

carbs must be broken into ____ for absorption/use in the body

Answer 17

carbs must be broken into > disaccharides then > monosaccharides (glucose, fructose, galactose) for absorption/use

Question 18

carb breakdown in small intestine

Answer 18

• a-amylase cleaves a-1,4 bonds but NOT a-1,6 > breaks down to di- and tri-saccharides
• maltose and maltotriose and limit dextrin (not digestible by a-amylase due to a-1,6 bonds)
• a-glucosidease digests rest except dextrin which is broken down by a-dextrinase (both on surfaces of intestinal cells)

Question 19

makeup, source, and digestion of: sucrose

Answer 19

• sucrose = glucose + fructose
• from veggies
• digested by sucrase on surface of intestinal cell

Question 20

makeup, source, and digestion of: lactose

Answer 20

• lactose = glucose + galactose
• in milk
• digested by lactase on surface of intestinal cell

Question 21

transport of monosaccarides into intestinal cell

Answer 21

glucose + galactose move from lumen through cell via secondary active transport with Na-glucose linked transporter (SGLT)

fructose trasported via GLUT5

GLUT2 releases all 3 out of cell and into blood

Question 22

where does lipid digestion begin?

Answer 22

stomach (kind of); they are ingested in triacylglycerol form and must get to fatty form for intestinal absorption

lipids are prepped in stomach via grinding and mixing action for making an emulsion (like salad dressing)

Question 23

lipid digestion in small int

Answer 23

once lipids move to small int, emulsification is enhanced with bile salts

binding bile salts to lipid droplets makes them more soluble

lipases (pancreatic enzymes) then break triacylglycerols to free fatty acids and monoacylglycerol which are carried in micelles to plasma membrane of int epithelial cells where they’re absorbed

Question 24

what are bile salts

Answer 24

amphipathic molecules that come from cholesterol; made in liver and secreted by gallbladder in response to CCK

Question 25

what are micelles and what stimulates their formation

Answer 25

carry final products of lipid digestion to intestinal epithelial cell PM for absorption; helps move fatty molecule in water filled area

globular and formed by small lipids where the polar heads are outward facing and fatty tails are facing inwards

bile salts stim their formation

Question 26

lipid / fatty acid absorption

Answer 26

• transported into int cells by fatty acid binding protein (FABP)
• moved to smooth ER via fatty acid transport proteins (FATP)
• triaglycerols resynthesized from FA and monoacylglycertol > associated with proteins > small amount of phospholipid and cholesterol formed in lumen of smooth ER
• > all moved into bloodstream and lymph system via chylomicrons (TAG)