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63 Cards in this Set

  • Front
  • Back
Why does your nutrients need to be digested?
macro-nutrients exist as large polymers that can not be efficiently absorbed w/o digestion
What is an explanation of passive immunity or food allergies?
intact proteins and larger peptides can be absorbed, but only to a certain extent.
How is food digested in the mouth?
a-amylase: digests starch enzymes
lingual lipase: digests TAGs

There is NO protein digestion
How is food digested in the stomach?
pH 1-2
What is pepsinogen?
it is the inactive form of pepsin--it is activated by acid
What does HCL do?
kills microorganisms
denatures proteins to make them susceptible to proteolytic digestion
activates pepsinogen
Where is the site of synthesis of digestive enzymes/zymogens?
Where are the enzymes of the pancreas delivered and what do they attack?
duodenum and attack dietary proteins and lipids
What are some examples of enzymes that the pancreas secretes and what do they do?
a-amylase (hydrolase cleaving starch)
pancreatic lipase (needs to bind cofactor to become active)
NaHCO3 (to neutralize acid)
How does a-amylase become active? pancreatic lipase?
a-amylase is secreted as an active enzyme

pancreatic lipase needs to bind a cofactor to become active (it is not a zymogen)
How does the liver and gallbladder aid digestion?
secrete/store bile acids (which emulsify aggregated lipids)
What role does bile acids play in protein or carbohydrate digestion?
No role
What role does the small intestines play in digestion?
completes the conversion of carbs and proteins into absorbable, lower-molecular weight species

It also deals with bulf absorption of products of macro-nutrient digestion
Where are the enzymes in the small intestines?
anchored to the luminal surface of the enterocytes
In what form do carbs have to be inorder to be absorbed?
monosaccharides (glu, fru, gal)
What are the major dietary carbs?
Starch (plant polysaccharide)
Sucrose (disaccharide, table sugar, gluctose-fructose)
Lactose (disaccharide, milk sugar, galactose-glucose)
Name the two forms of starches?
amylose (1,4)
amylopectin (1,6)
What carbohydrate bonds are broken during oral digestion?
non-terminal a 1,4 linkages
What limits digestion in the mouth
higher pH---proteins aren't denatured
Starch is broken into what compounds in the intestinal phase?
a-limit dextrins
free glucose
heterogenous mix
What are two non-digestible polysaccharides?
dietary fiber (mainly from plants)
Why isn't cellulose digested?
glucosidic bonds in the cellulose are B-linked (our enzymes are a-specific)
At the luminal surface of the small intestines (enterocytes) what are carbohaydrates converted into?
What catalyzes the conversion of oligosaccharides into monosaccharides?
glycosidases formed by enterocytes
Uptake of glucose and galactose require what?
Na+/glucose cotransporter (symporter) used Na+ as a driving force

Binding of Na+ increases the affinity for glucose/galactose
Is the uptake of Glucose and galactose against or with the concentration gradient?
against (therefore requires energy)

secondary active transport which uses Na+/K+ ATPase for the energy
How is ATP hydrolyzed during the uptake of monosaccharides?
ATP is secondarily hydrolyzed by ATPase in order to maintain Na+ gradient (NOT by glucose carrier protein)
Fructose uses what type of transport to enter the enterocytes?
facilitated diffusion (flows down the concentration gradient)
Once inside the enterocytes, how does the monosaccharide enter the cirrculation?
facilitated diffusion carriers
Name some clinical problems that lead to carbohydrate absorption.
loss of pancreatic function
damage to the intestinal epithelial surface
transporter deficiencies or defects
digestive enzyme defects (lactase deficiency)
What are some characteristics of primary lactase non-persistence?
common amoung non-white populations
lactase activity declines with age
may tolerate small amounts of milk
Name some types of lactase deficiencies.
1.Primary lactase non-persistence
2. inherited (congenital)lacase deficiency (rare)
3.sucrase/isomaltase deficiency (rare)

enzymes 2, 3 are formed from common precursor
What are the symptoms of lactase deficiency?
1. produce gas and other osmotically active products
2. diarrhea
3. flatulence
4. cramps

failure to digest leads to increased nutients for organisms in the GI track
What is the goal of protein digestion?
convert proteins into free AA and small peptides that can be absorbed
What are zymogens and why are they important?
it is a form of enzyme regulation that is important in digestion and blood clotting
Are zymogens involved in carbohydrate digestion?
What are the suffix and prefix of zymogens?
suffix: ogen
prefix: pro
Where does protein digestion start and with what?
started by pepsins in the stomach
What activates pepsin and is pepsin essential?
It is auto-activated by acid conditions and activated pepsin cleaves other pepsinogen molecules

Pepsin is not essential
Where is the bulk of protein digestion and what does it produce?
small intestines and it produces free AA and small peptides
What are the two protease types that come from the pancreas? And what do they digest?
Endoproteases (trypsin, chymotrypsin, elastase) - internal/non-terminal peptide bond
exoproteases (carobxypeptidase) - terminal AA residues
What initiates the activation of zymogens? And what does it convert?
enteropeptidase converts trypsinogen to trypsin

Trypsin then activates more trypsinogen and other zymogens
What are some conditions that may cause clinical problems with protein digestion?
transporter defects
What are two types of transporter defects with protein transport?
hartnup disease
What are symptoms of hartnup disease?
red, scaly rash (similar to pellegra)
neurologic impairment (ataxia)
Niacin deficiency (Trp is converted to niacin)
What is Hartnup disease?
defect in transport of large neutral aromatic AA

Example: tryptophan
What is Cystinuria?
defect in the transporter that catalyzes re-uptake of several AA (cystine) in kidney
What are some symptoms of Cystinuria?
failure to absorb water(concentration in urine)
precipitates out as kidney stones
Which is more common Cystinuria or Hartnup disease?
Why does pancreatitis occur?
trypsin inhibitor protein is overwhelmed when duct is blocked
What is the most prevalent dietary lipid? And how must it be converted in order to be absorbed?
TAGs (triacylglyerols)

It must be converted to 2 fatty acids and 2 monoacylglycerol
What are most lipids digested by? And what is the name of the enzyme that digests lipids in the mouth?
Mouth: lingual lipase
Most digestion is due to pancreatic lipase
What is Colipase and what activates it?
Trypsin cleaves colipase in order for it to bind to pancreatic lipase (to activate it)
What are some special problems with lipid digestion and how are they avoided?
lipids are not water soluble and tend to form large droplets BUT bile acids act as detergents to form micelles
What are some other dietary lipids and how are they digested?
phospholipids:phospholipase A2(secreted as zymogen

Cholesteryl esters:cholesteryl ester hydrolase (secreted as active enzyme)
What are TAGs?
esters of glycerol and 3 fatty acids (mainly C16, C18)
What is re-esterification? And where does it occur?
Conversion of 2-monoacylglycerol and long chain fatty acids back to TAGs

This happens inside the enterocyte
What are TAGs packaged into and what hydrolyzes them?
TAGs are packaged into Chylomicrons and hydrolyzed by lipoprotein lipase in the capillary walls
Chylomicrons travel where?
secreted into lymph and then into blood
What happens to FA with <12 AAs?
They are not good substrates and are released into enterohepatic circulation and absorbed by the liver
What happens if there isn't any pancreatic enzymes released?
fat malabsorption and steatorrhea
What happens if there is a deficient production of bile acids?
keeps insoluble cholesterol and phospholipids soluble= gallstones
What is the principle mechanism for elimination of cholesterol from the body?
conversion of cholesterol bile acids and secretions of bile acids into lumen of intestine.