Mucosal Digestion Flashcards
define digestion
breakdown of complex nutrient molecules
define absorption
transport of simple molecules across intestinal epithelium
simple molecules are absorbed through ___ membrane and are transferred through ___ membrane
apical
basolateral
maldigestion and malabsorption cause ___ symptoms but require ___ treatment approaches
similar symptoms
different Tx
a lot of enzymatic digestion and all absorption takes place on ___ of intestinal epithelium
surface
what are the barriers that nutrients must pass across before being taken up by blood or lymph?
unstirred layer
glycocalyx
cell membrane
enterocyte cytoplasm
basolateral membrane
intercellular space
basement of membrane
capillary/lymph membrane
a ___ surface facilitates membrane bound digestion and absorption
large
what are the four levels that surface is extended at in SI?
- GI elongation
- plica circulares (mucosal folds)
- villi (epithelial projections)
- brush border (microvilli)
what is glycocalyx?
layer formed by apical membrane covered in glycoproteins that are synthesized in enterocytes and transferred to apical surface
what makes up the mucosal barrier?
microvilli/glycocalyx
mucus
unstirred water
what is enteritis?
loss of function due to extreme SA reduction
what are the two phases of CHO digestion?
luminal
membranous
describe the luminal phase of CHO digestion
enzymes from salivary gland and pancreas
incomplete breakdown
describe the membranous breakdown of CHO digestion
brush border digestion
enzymes part of glycocalyx allow diffusion of nutrients through mucus layer before being broken down into monomers
where does luminal phase CHO digestion occur?
oral cavity, stomach, SI
explain the luminal phase of CHO digestion in oral cavity
a-amylase hydrolyzes starch to smaller polysaccharides
explain the luminal phase of CHO digestion in stomach
continues digestion
neutralized by acid when mixing
~40% starches convert to maltose
explain the luminal phase of CHO digestion in SI
pancreatic a-amylase (more powerful than saliva)
further breakdown
what are the products of starch from luminal phase?
amylose and amylopectin become di/tri-mers
explain the membranous phase of digestion of CHO
di/tri-meric sugars are broken down into monomers
final breakdown during membranous digestion occurs near site of absorption, which is…
apical membrane of absorptive cells
CHO polymers come as…
fiber, sugar, starch, glycogen
what is fiber?
vegetal origin
indigestible by mammals
beta-acetal bond between C1 and C4
digested by fermenting bacteria
what are sugars?
animal and vegetal origin
short molecules (sucrose, lactose)
what are starches?
vegetal origin
large molecules (a-acetal bond between C1 and C4
what is glycogen?
animal origin
large molecule
plant material provides…
fiber, sugar, starch
the polymers of fiber ___ be degraded by luminal or mucosal hydrolases in SI
CANNOT
what does fiber do when in GI tract?
fiber stays in lumen and provides bulk to feces
helps retain fluid and aids in passage
what does the rumen do to fiber?
converts to VFA
what are the two phases of protein digestion?
luminal
membranous
explain the luminal phase of protein digestion
breakdown to peptides and aa
starts in stomach by gastric enzymes and HCl
completed in duodenum by pancreatic enzymes
explain the membranous phase of protein digestion
further breakdown to aa
facilitated by peptidases in apical membrane of enterocytes
many protein enzymes are ___ for peptide bonds between specific types of aa
specific
what activates gastric pepsinogen?
HCl and pepsin
intestinal enzyme are released as ___
proenzymes
how is trypsinogen activated?
enterokinase/trypsin
what do endopeptides do?
cleave internal bonds
what do exopeptidases do?
cleave terminal residue of polymer chain
what do aminopeptidases do?
cleave N terminal residue
what do carboxypeptidases do?
cleave C terminal residues
in lipid digestion, triglycerides are hydrolyzed into…
monoglycerides and FFA
are fats water soluble?
NO
are lipolytic enzymes water soluble?
YES
lipids make a ___ portion of diet
large
fat digestion in oral cavity
minimal initial digestion
lipase
fat digestion in stomach
initial emulsification
fat globules liquify
lipid droplets
fat digestion in SI
emulsification is finalized
bile acids and phospholipids added
emulsified droplets are digested
pancreatic lipase and co-lipase produce free FA, monoglycerides
cholesterol esterase and phospholipase produce free FA, cholesterol, lyso phospholipid
which lipases produce free fa, monoglycerides?
cholesterol lipase
co-lipase
fat digestion in micelle formation
all digestion products surrounded by bile acids
what are the 4 steps of fat digestion in SI?
- emulsification by bile salts
- hydrolysis of triglycerides
- micelle formation
- micelle content absorbed in jejunum
what are primary bile acids?
synthesized by liver
some are conjugated with taurine or glycine in liver
what are secondary bile acids?
result of bacterial actions in colon
describe the emulsification by bile salts process
exposure to bile acids from liver/gallbladder and formation of bile encoated droplets
small droplets have triglycerides, cholesterol, esters, phospholipids
hydrophilic domains allow contact with lipase
what cooperates to access bile-coated droplets?
pancreatic lipase
co-lipase
describe hydrolysis of triglycerides
co-lipase clears bile constituents from area of surface to droplet
lipase hydrolyzes triglycerides producing FFA, monoglycerides
what are micelles?
small sized droplets containing FFA and bile acids
describe the process of micelle formation
products of hydrolytic lipid digestion combines with bile salts and phospholipids to form micelles in preparation for absorption
micelles act as lipid ___ and ___ lipid solubility in chyme
shuttles
increase solubility
micelle content can be absorbed in…
jejunum
nutritional differences between and within species are reflected by…
digestive intestinal activity
activities of digestive enzyme often ___ levels of substrate in diet
match
what is exocrine pancreas insufficiency (EPI)?
insufficient synthesis and secretion of enzymes from 90% of pancreas
caused by pancreatic acinar atrophy or tumor
what are symptoms of exocrine pancreas insufficiency?
anorexia, V, exercise intolerance, D, abdomen pain, dehydration
why does exocrine pancreas insufficiency cause D?
water follows solutes
why does exocrine pancreas insufficiency (EPI) anorexia and exercise tolerance?
insufficient breakdown of nutrients that prevents absorption
why does exocrine pancreas insufficiency (EPI) abdomen pain?
bacterial gas production and malfermentation in LI
why does exocrine pancreas insufficiency (EPI) cause V?
due to delayed gastric emptying
SI distension
bacterial toxins in LI
why does exocrine pancreas insufficiency (EPI) cause D?
osmotic D
why does exocrine pancreas insufficiency (EPI) cause dehydration?
insufficient water absorption in LI
since water follows solute (so stays in GI tract)
why does exocrine pancreas insufficiency (EPI) cause fever?
bacterial toxins, compromised immune defense
