Chapter 14: Digestion

Which transporter do glucose, galactose, and fructose leave intestinal cell from?

Glut2

fructose diffuses across the membrane through which transporter?

Glut5

sucrose

a disaccharide consisting of glucose and fructose. It's digested by sucrase

alpha-amylase

a pancreatic enzyme that digests starch. it cleaves the alpha-1,4 bonds of starch but not the alpha-1,6.

polysacch. are cleaved into monosacch. by what?

alpha-amylase (comes from the pancreas)

protein absorption

amino acids and di- and tripeptides are absorbed into the intestinal cells by specific transporters. Free amino acids are then released into the blood stream through antiporters for use by other tissues--> sent to liver.

bile salts

amphipathic molecules synthesized from cholesterol in the liver and secreted from the gall bladder in response to cholecystokinin. they go into lipid droplets to make triacylglycerols more readily digested.

pepsinogen--> pepsin

autocatalysis at low pH (very slowly)

why can't zymogens release digestive enzymes everywhere?

because proteases are deadly for cell. only want them active in specific places.

what are the products of cleaved starch by amylase?

di- and trisaccharides, maltose, maltrotriose, and limit dextrin.

lactose

digested by lactase to form glucose and galactose

hydrolases

digestive enzymes that cleave their substrates by the addition of water. *all digestive enzymes are hydrolases

alpha-dextrinase

digests limit dextrin into simple sugars.

peptidases

enzymes that are attached to the external surfaces of intestinal cells. these enzymes cleave the oligopeptides into amino acids and di- and tripeptides that can be transported into intestinal cell

lipases

enzymes that degrade triacylglycerides into free fatty acids and monoacylglycerols

FATP

fatty acid transport ptotein. once fatty acids and MAG enter cell through FABP, they carry them to the smooth ER where triacylglycerols are made.

which transporter transports the fatty acids and MAG into the intestinal cells?

fatty-acid-binding protein (FABP)

what happens in mouth in terms of digestion?

food is chewed which makes more surface area of the food so when it gets to stomach it mixes better with pepsin. saliva contains Na+, K+, Cl-, and HCO3- and mucoproteins and amylase-- all helps begin break down.

what are the final digestion pdts?

free fatty acids and monoacylglycerols. they are carried in michelles to the plasma membrane of intestinal epithelial cells where they get absorbed.

michelle

globular structures formed by small lipids in aqueous solutions. carries digestion products to intestinal cells to be absorbed

gluten

gluten refers to the protein in wheat, rye, and barley. all glutens are rich in proline and glutamine and are resistant to complete digestion by pepsin and the pancreatic proteases.

prilosec

irreversible inhibitor of H+/K+ pump.

what does pancreas do when it responds to presence of CCK?

it releases a host of digestive enzymes into the intestine where the digestion of proteins continues and the digestion of lipids and carbs begins.

lipids (triacylglycerides) are converted into fatty acids by what?

lipases which are secreted by the pancreas

what all works to digest to form monosaccharides?

maltase, sucrose, lactase, glucosidase, and dextrinase

emulsion

mixture of lipid droplets and water

pancreatic proteases hydrolyze the proteins into small fragments called what?

oligopeptides

trypsin activates what?

other zymogens.

protein digestion

proteins broken down by enzymes secreted by the pancreas. peptidases which are associated with intestinal cells further digest proteins.

proteins are digested to amino acids by what?

proteolytic enzymes (proteases) which are secreted by the stomach and pancreas

H+/K+ ATPase (pump)

pumps H+ into stomach in exchange for K+ at expense of ATP hydrolysis

pancreatic zymogens are produced and released where?

the intestine

what happens as food enters intestine from stomach?

the low pH of food stimulates the cells of small intestine to release the hormone secretin which promotes release of bicarbonate from pancreatic cells which neutralize pH of food.

zymogens (or proenzymes)

these are digestive enzymes secreted as inactive forms (exception of alpha amylase). before their secretion, they exist in granules near the cell membrane. granules fuse with membrane and spill their content into the lumen of intestine.

chylomicrons

they are made up of 98% triacylglycerols with the proteins and phospholipids on surface. this is a very stable particle andis released into the lymph system into the blood.

lipids

they must be degraded into fatty acids. they are NOT soluble in water. In the stomach, grinding/mixing converts lipids into an emulsion

how do cholesterol-lowering medications work?

they remove bile salts since they are made from cholesterol.

digestion: stomach

this is where protein digestion begins. proteins are denatured by the acidic environment with pH of 1-2. the proteolytic enzyme pepsin begins protein degredation. secretin is used to help neutralize acid.

transporters

transport amino acids and di- and tripeptides into an intestinal cell. there are at least 7 different transporters, each being specific to a group of amino acids. mutations in transporters can cause diseases (ex: hartnup disease)

protease activates what?

trypsin

when is zymogen activated?

when a part of the inactive precursor is proteolytically cleaved and the enzyme enteropeptidase is secreted by the epithelial cells of the small intestine, activates pancreatic zymogen trypsinogen to form trypsin, which in turn activates the remaining pancreatic zymogens.

what is needed to pull K+ into stomach while H+ leaves stomach?

ATP

glucose and galactose are transported into cells with accompany of Na+ through which transporter?

SGLT

gluten sensitivity

celiac disease: intestinal inflammatory disorder that's triggered in susceptible individuals by proteins in wheat, rye, and barley. The pain comes from the inflammatory response to gluten-derived peptides.

what are human's primary source of carbs?

starch

polypeptide products of pepsin digestion

stimulate release of CCK

secretin

stimulated by low pH of food, released from intestinal cells. promotes release of sodium bicarbonate from pancreatic cells

Cholecystokinin (CCK)

stimulated by polypeptide pdts of pepsin digestion. released from intestinal cells. stimulates release of digestive enzymes from pancreas.

sodium bicarbonate

stimulated by release of secretin. released from pancreatic cells. helps neutralize pH of food.

pepsin

stomach enzyme. it is secreted as a zymogen called pepsinogen which has a small amount of enzyme activity and can activate itself to some degree in an acidic environment.

where are maltase, alpha-glucosidase, and alpha-dextrinase located at?

surface of intestinal lining.