L25: Mucosal Absorption II Flashcards
where is the primary sites of Na+ absorption
small intestine
main mathod of sodium absorption
co-transporters
Calcium is absorbed from the GI tract by _______ diffusion
facilitated
High calcium concentration causes low _________ diffusion
paracellular
-low Ca diets stimulate traanscellular transport
what is Calbindin
Ca-binding protein, stimulated by vitamin D
what are the 3 steps of active Ca transport in the duodenum
- apical uptake via Ca channel driven by electrochemical gradient
- Ca binds to calbindin - a carrier protein for Ca; maintains a low concentration of free Ca inside the cell
- Basolateral Ca pump and a Na-Ca exchanger extrude Ca into lateral space
why would a Vit D deficiency affect the uptake of calcium
Vit D increases the expression of calbindin
calbindin is a needed carrier protein for Ca
magnesium uptake happens ________at high _______ concentration
paracellulary
Mg
Intracellular transport of Mg occurs at ______ Mg concentrations and involves ______ transporters on the apical side
normal
TRP
at the basolateral side of the membrane, Mg absorption is via ________
secondary active trasnport mechanism through a Mg/Na exchanger
the amount of iron ingested is _____ compared to the amount absorbed
greater
the absorption of nonheme iron occurs almost exclusively as _____ which crosses the duodenal apical membrane through ________
Fe2+
DMT1, Driven by a H+ gradient which is maintained by Na-H exchange
what maintains the H+ gradient required for DMT1 transporter
Na-H exchange
what happens to heme after it enters the enterocyte
heme oxygenase released Fe3+ which is then reduced to Fe2+
how does Fe2+ exit the enterocyte
through basolateral ferroportin
intracellular iron storage depot that releases iron in a controlled fashion
Ferritin
how are lipid soluble vitamins processed
same manner as dietary lipid
B12 binds to gastric _________ which protects it from digestion
intrinsic factor (parietal cells)
what artery supplies the stomach, the 1st part of the duodenum, the head of the pancreas and the liver
celiac artery
what artery supplies the remainder of the pancreas and the gut through the first 2/3rd of the transverse colon
cranial mesenteric artery
what artery supplies the distal colon and proximal rectum
caudal mesenteric artery
where does the hepatic portal vein collect blood from
stomach, small intestine, some of the large intestine
blood from the hepatic portal vein runs through two capillary beds, the ________ and ______, before returning to the heart
mesenteric and portal
what drives blood through the mesenteric and portal capillary beds
pressure in portal vein is slightly higher than in hepatic sinusoids
sinusoids of liver are large, so resistance is low
venous outflow of liver goes into thoracic vena cava
this causes hepatic hemodynamic; small changes in pressure have have large effects on fluid exchange
the magnitude of postprandial hyperemia depends on…
increased resistance in the liver reduces blood flow from the ______
intestine
(portal hypertension)
right heart insufficiency increases vena cava pressure, leading to _____ blood flow from the ______
reduced, intestine
sympathetic stimulation causes a _________ in intestinal circulation
an increased resistance
if bloow flow is low and transit time prolongs, _____ may die
intestine
subnormal blood flow at the tip of the villus causes _____ and _____
ischemia and tissue damage, can lead to cell death (necrosis)
arterial supply to the inestinal villus enters the villus at…
the base and carries blood to its tip
what type of blood flow occurs in the intestinal villi and what effect does this have
antiparallel (Countercurrent) blood flow: arterial vessels and venules are parallel
leaves tip of villi to be susceptible to anoxic damage
O2 begins to diffuse from arterial to venous blood before reaching the capillaries at the tip of the villis; creates as O2 gradient from the tip (low O2) to the base (high O2)
gradient is strong when blood flow is low –> anoxic damage at tip of villus due to prematures O2 exchange at the nase
solutes enter the inestersitial space and venules at the ____ of the villus and transfer back from venules through interstitium into arterioles at the ______
tip
base
what increases the amount of blood at the tip of villi
solue concentration in arterial blood
what are the short term adaptations of the GI tract
- modulation of membraneous enzymatic set up
- modulation of blood supply - adjustments to metabolic demands, postprandial hyperemia
- increase its absorptive SA; villi hypertrophy
mesenteric blood flow rates increase in response to ….
metabolic demands
ex-milk production
how does the Burmese python rapidly modulate gut activity with a meal
- rapid postprandial increase in SA
- increase in plasma concentrations of: CCK, neurotensin, glucagon, insulin, glucose-dependent insulinotropic peptide
