L25: Mucosal Absorption II

Question 1

where is the primary sites of Na+ absorption

Answer 1

small intestine

Question 2

main mathod of sodium absorption

Answer 2

co-transporters

Question 3

Calcium is absorbed from the GI tract by _______ diffusion

Answer 3

facilitated

Question 4

High calcium concentration causes low _________ diffusion

Answer 4

paracellular
-low Ca diets stimulate traanscellular transport

Question 5

what is Calbindin

Answer 5

Ca-binding protein, stimulated by vitamin D

Question 6

what are the 3 steps of active Ca transport in the duodenum

Answer 6

1. apical uptake via Ca channel driven by electrochemical gradient
2. Ca binds to calbindin - a carrier protein for Ca; maintains a low concentration of free Ca inside the cell
3. Basolateral Ca pump and a Na-Ca exchanger extrude Ca into lateral space

Question 7

why would a Vit D deficiency affect the uptake of calcium

Answer 7

Vit D increases the expression of calbindin
calbindin is a needed carrier protein for Ca

Question 8

magnesium uptake happens ________at high _______ concentration

Answer 8

paracellulary
Mg

Question 9

Intracellular transport of Mg occurs at ______ Mg concentrations and involves ______ transporters on the apical side

Answer 9

normal
TRP

Question 10

at the basolateral side of the membrane, Mg absorption is via ________

Answer 10

secondary active trasnport mechanism through a Mg/Na exchanger

Question 11

the amount of iron ingested is _____ compared to the amount absorbed

Answer 11

greater

Question 12

the absorption of nonheme iron occurs almost exclusively as _____ which crosses the duodenal apical membrane through ________

Answer 12

Fe2+
DMT1, Driven by a H+ gradient which is maintained by Na-H exchange

Question 13

what maintains the H+ gradient required for DMT1 transporter

Answer 13

Na-H exchange

Question 14

what happens to heme after it enters the enterocyte

Answer 14

heme oxygenase released Fe3+ which is then reduced to Fe2+

Question 15

how does Fe2+ exit the enterocyte

Answer 15

through basolateral ferroportin

Question 16

intracellular iron storage depot that releases iron in a controlled fashion

Answer 16

Ferritin

Question 17

how are lipid soluble vitamins processed

Answer 17

same manner as dietary lipid

Question 18

B12 binds to gastric _________ which protects it from digestion

Answer 18

intrinsic factor (parietal cells)

Question 18

what artery supplies the stomach, the 1st part of the duodenum, the head of the pancreas and the liver

Answer 18

celiac artery

Question 19

what artery supplies the remainder of the pancreas and the gut through the first 2/3rd of the transverse colon

Answer 19

cranial mesenteric artery

Question 20

what artery supplies the distal colon and proximal rectum

Answer 20

caudal mesenteric artery

Question 21

where does the hepatic portal vein collect blood from

Answer 21

stomach, small intestine, some of the large intestine

Question 22

blood from the hepatic portal vein runs through two capillary beds, the ________ and ______, before returning to the heart

Answer 22

mesenteric and portal

Question 23

what drives blood through the mesenteric and portal capillary beds

Answer 23

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

Question 24

the magnitude of postprandial hyperemia depends on…

Question 25

increased resistance in the liver reduces blood flow from the ______

Answer 25

intestine
(portal hypertension)

Question 26

right heart insufficiency increases vena cava pressure, leading to _____ blood flow from the ______

Answer 26

reduced, intestine

Question 27

sympathetic stimulation causes a _________ in intestinal circulation

Answer 27

an increased resistance

Question 28

if bloow flow is low and transit time prolongs, _____ may die

Answer 28

intestine

Question 29

subnormal blood flow at the tip of the villus causes _____ and _____

Answer 29

ischemia and tissue damage, can lead to cell death (necrosis)

Question 30

arterial supply to the inestinal villus enters the villus at…

Answer 30

the base and carries blood to its tip

Question 31

what type of blood flow occurs in the intestinal villi and what effect does this have

Answer 31

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

Question 32

solutes enter the inestersitial space and venules at the ____ of the villus and transfer back from venules through interstitium into arterioles at the ______

Answer 32

tip
base

Question 33

what increases the amount of blood at the tip of villi

Answer 33

solue concentration in arterial blood

Question 34

what are the short term adaptations of the GI tract

Answer 34

• modulation of membraneous enzymatic set up
• modulation of blood supply - adjustments to metabolic demands, postprandial hyperemia
• increase its absorptive SA; villi hypertrophy

Question 35

mesenteric blood flow rates increase in response to ….

Answer 35

metabolic demands
ex-milk production

Question 36

how does the Burmese python rapidly modulate gut activity with a meal

Answer 36

• rapid postprandial increase in SA
• increase in plasma concentrations of: CCK, neurotensin, glucagon, insulin, glucose-dependent insulinotropic peptide