Mucosal Absorption I Flashcards
define absorption
process of translocating basic molecules from intestinal lumen through epithelium into vascular system
the end products of CHO and protein digestion are ___
hydrophilic
what’s the most important active transporter in GI?
Na/K ATPase
secondary active transport requires use of the ___ gradient
Na+
what types of transport is secondary active?
co-transport - aka ligands are on the same site
anti-porter/exchanger - ligands are on opposite sites
in secondary active co-transport, what happens once Na is bound to the transporter?
conformation change “delivers” ions and molecule into cell
which type of secondary active transport is SLUT GLUT?
co-transport
which type of secondary active transport is Na/H?
anti-porter/exchanger
Na/H transport creates the ___ gradient
H+
Na/K pump maintains ___ gradient
Na+
intracellular H+ is transported out by ___ antiport driven by which gradient?
Na/H
Na+ gradient
what is the teritiary active transport?
Cl/bicarb exchange
what does CA do?
catalyzes H+ and bicarb production
(tertiary active)
what are the three types of passive diffusion?
transcellular absorb
paracellular absorb
facilitated diffusion
what is transcellular absorption?
ions follow electrochemical gradient through ion channels in apical membrane
what is paracellular absorption?
ions follow electrochemical gradient and osmotic P through tight junctions
what is facilitated diffusion?
spontaneous passive diffusion of molecules/ions across membrane via specific transmembrane proteins
where are glc co-transporters located?
next to glycocalyx enzymes on apical membrane
how is fructose internalized?
facilitated diffusion
based on gradient
glc movement through basolateral space is driven by…
diffusion
water follows ___
SOLUTES
the concept of water following solutes is referred to as…
iso-osmolar absorption
what is used for oral rehydration therapy if the SI is still in tact?
SLUT GLUT - administer fluids with glc/electrolytes so slut glut gets put to use
SLUT GLUT stimulates water absorption by ___
solvent drag
what mechanism stays in tact in patients with D disorders?
SLUT GLUT solvent drag
CHO digestion/absorption pathophysiology is mostly due to ___ deficiency that ___ breakdown
enzyme
prevents breakdowns
what happens if you have unabsorbed CHO?
hold water osmolarity and cause osmotic D
what occurs at apical membrane regarding protein digestion? (what transporters)
aa co-transport (Na)
four co-transport - neutral aa, dibasic aa, dicarboxylic aa, imino/proline aa
peptide carrier (H transport)
peptides further digested by intracellular enzymes
what occurs at basolateral membrane regarding protein digestion?
release to extracellular space as free aa
facilitated diffusion
how does protein absorption occur during first 24hrs of life?
endocytosis of entire proteins and Ig’s
receptor mediated, unspecific
done via specialized enterocytes that disappear after ~24hrs
how does aminoaciduria develop?
develops from congenital defect in transport of specific aa
may still be able to do absorption of di/tri-peptides
what is cysinuria?
type of aminoaciduria
transporter for dibasic aa (cystine, lysine, arginine) is ABSENT from or reduced in gut/kidney
dibasic aa lost in urine/feces
can lead to cystine stones
what facilitates lipid digestion/absorption?
micelles
how does lipid absorption occur?
micelle comes close to enterocyte surface and contents diffuse into cell except for bile acids which remains in intestinal lumen
the concentration gradient ___ passive diffusion of micellar products
favors
how much ingested fat is removed by SI?
95%
what are the intracellular events of lipid absorption? (two paths)
lipids reassemble in cells (form triglyceride)
MONOGLYCERIDE ACYLATION PATH
PHOSPHATIDIC ACID PATH
chylomicrons
describe the monoglyceride acylation pathway of lipid intracellular absorption
2 mono + fatty acid acyl CoA = triglyceride
describe the phosphatidic acid pathway of lipid intracellular absorption
glycolysis -> P-glycerol or diOH-acetone P -> alpha-glycerolP -> triglycerides
what are chylomicrons?
core of triglyceride and cholesterol surrounded by phospholipase and apoproteins
aka transport vesicle for lipids in lacteals
what are lacteals?
lymphatic vessels of SI villi that absorb digested fats
water soluble chylomicrons ___ phospholipids, triglycerides, proteins
coat
describe the process of chylomicron assembling?
- fa, monoglyceride converts into triglycerides in ER
- cholesterol is re-esterified
- triglycerides ad cholesterol are packaged into chylomicrons
- apoproteins are embedded in chylomicrons
what are apoproteins?
structural components of lipoprotein particles
ligand for cell surface receptors
without apoproteins, large quantities of triglycerides would accumulate where?
enterocytes
what are the five lipoprotein vehicles?
chylomicrons
VLDL
IDL
LDL
HDL
chylomicrons are taken up by…
lacteals
where do lacteals drain?
into cisterna chyli (abdomen duct)
then thoracic duct
lastly, internal jugular vein
bile acids remain in the ___.
intestinal lumen
what happens regarding lipids if there is a lack of bile acids?
unable to digest fats
where is the bile acid transporter located and what is it called?
in ileum
Na-bile acid-cotransport
are bile acids recycled?
YES, returns to portal system
what is enterohepatic circulation?
refers to the process of bile acid recycling, storage, and release into SI lumen
bile acids are synthesized from ___ in the liver
cholesterol
which vein takes bile acids back to the liver?
portal vein
where do bile acids go if NOT recycled into the liver?
show up in blood plasma
are liver shunts acquired or congenital?
can be BOTH
how does a patient acquire a liver shunt?
liver disease
which species most likely gets extra-hepatic liver shunts?
small and toy breeds
which species most likely gets intra-hepatic liver shunts?
large breed dogs
what are body affects of liver shunts?
poor growth/development
neurologic changes
behavior change
increased thirst, frequent urination
V
accumulation of toxins and metabolic waste products can lead to HEPATIC ENCEPHALOPATHY
what is hepatic encephalopathy?
neurological disturbances in patients with liver dysfunction (shunt)
caused by effects on brain of substances that under normal circumstances are efficiently metabolized by liver
what does a bile acid test do?
liver function test
indicates degree of inflammation/damage
what does it mean if the bile acid test comes back normal?
low initial AND low 2hrs levels of bile acid
what does it mean if the bile acid test is elevated at rest?
bile acids remain in circulation
(shunt, liver disease, gallbladder issue, etc)
what does it mean if the bile acid test has normal resting level but elevated 2hrs levels?
bile acids are very slowly reabsorbed and escape into systemic circulation
