Lecture 25: Mucosal Absorption-2 GI Blood Flow Flashcards
What are the different mechanisms in which Na+ is absorbed
Na+ co-transporter, Na/H exchanger, simple diffusion
How is K+ absorbed
Simple diffusion
How is Cl- absorbed
Simple diffusion, Na+ coupled
How is Ca2+ absorbed
Simple diffusion, active transport
How is Mg absorbed
Simple diffusion, active transport
How is Fe absorbed
Heme transporter, specific channel
What does vitamin absorption depend on
Solubility
What is the primary side of Na+ absorption
Small intestine
What is the function of the Na/H+ exchanger in small intestine
Acidify lumen, neutralize luminal HCO3-
Ca2+ is absorbed from GI tract via
Facilitated diffusion
At high concentrations of Ca2+ it is transported via
Paracellular diffusion
At low concentrations of Ca2+ it is transported via
Transceullular diffusion
The transport of calcium adjust for variations in ___
Diet
What are the 3 steps in transcellular transport of Ca2+ into duodenum
- Apical uptake of Ca2+ via electrochemical gradient
- Ca2+ binds calbindin which maintains low concentration. (Vit D increases expression of calbindin)
- Basolateral Na/Ca2+ exchanger pumps Ca2+ out
What increases the expression of calbindin
Vitamin D
At what concentration does Mg uptake happen paracellularly
High
At what concentration does intercellular transport of Mg occur
High
What transporters are involved in intercellular transport of Mg from apical side
TRP transporters
How is Mg transported on basolateral side
Secondary active Mg2+/Na+ exchanger
Absorption of nonheme iron exclusively occurs as ___
Fe2+
How does Fe2+ cross the apical membrane
DMT1 via H+ gradient (maintained by Na/H exchange)
Cytoplasmic Fe2+ binds __ for transit across the cell to basolateral membrane
Mobilferrin
Fe2+ exits basolateral membrane via
Ferroportin
___ promotes intestinal absorption and solubilization (Reduces Fe3+ to Fe2+)
Gastric acid
What is transferrin
Required for plasma transport of Fe
What is ferritin
Intracellular storage depot for Fe to be released in a controlled fashion
What are the fat soluble vitamins
A, D, E, and K
How are fat soluble vitamins absorbed
Solubilized and transported in Micelles, enter circulation in chylomicrons
What are the water soluble vitamins
B1, B2, B6, B12, C, biotin, folate, pantothenic acid
How are water soluble vitamins absorbed
Na+ dependent co-transport
B12 binds to ___ which protects it from digestion
Gastric intrinsic factor
What artery supplies the stomach, 1st part of duodenum, head, pancreas and liver
Celiac
What artery supplies the remainder of pancreas, gut through 2/3 transverse colon
Cranial mesenteric
What artery supplies distal colon and proximal rectum
Caudal mesenteric
The fraction of cardiac output to gut ___after meal
Increases
What vein collects blood from stomach, small and large intestines
Hepatic portal vein
Nutrient rich blood enters __, which regulates nutrient concentration
Liver
Blood runs through two capillary beds __ and ___ before it returns to heart
Mesenteric, portal
What drives blood through mesenteric and portal capillary beds
- Pressure in portal vein is slightly greater than that of hepatic sinusoids.
- Resistance in sinusoids in much lower
Postprandial hyperemia dependent on constituents of ingesta. __ and __ promote hyperemia
Bile acids and fats
How does increased resistance in the liver affect the intestine
Reduces blood flow, portal hypertension
Right heart insufficiency increases vena cava pressure which leads to ___blood flow to intestine
Decrease
How does SNS stimulation affect intestinal circulation resistance
Increases it
If there is subnormal blow flow to GI what happens to intestines
Can die, subnormal at tip of villus causing ischemia, tissue damage and cell death
Describe countercurrent exchange in the villus
Oxygen begins to diffuse from arterial to venous blood without reaching capillaries at tip of villus
Creates oxygen gradient from tip (low oxygen) to base (high oxygen)
How does low blood flow affect countercurrent exchange in villi
Further reduces amount of O2 getting to tip of villus can result in cell death
How does solute concentration in arterial blood change at the tip of villus if blood flow is low and transit time is prolonged
Solute concentration increases, trapping them near tip of villus
Consequences for nutrient absorption and water movement
Describe what happens during exercise induced heat stress
- Thermoregulatory mechanisms in effect
- Blood flow shunted from GI to skin
- If temperatures continue to rise and mechanism can’t compensate then will result in intestinal ischemia
- Release of endotoxins
- Systemic inflammatory response and coagulation cascade
- Multi-organ failure or death
What are some examples of short term adaptations of GI
- Modulation of membranous enzymatic set up
- Modulation of blood supply (metabolic demands, postprandial hyperemia)
- Increase absorptive SA(villi hypertrophy)
Mesenteric blood flow rates ___in response to metabolic demands during milk production
Increase
What GI adaptions are seen in a python after a meal
Lengthening of intestinal villi and rapdily decresse intestimal pH from 7 to 2
How do hibernating animals adapt their GI system
Reduce required rates of oxygen consumption
How does a patient with an irreversible intestinal injury (resection) undergo GI adaption
Remaining length of intestine will hypertrophic and increase absorptive capability. Villus hypertrophy
If the ileum is resected what happens to fat, bile salt and VitB 12 absorption
Decrease as ileum is main site
If the colon is resected what happens to VFA absorption
Decreases
How do you treat animals post intestinal resection
Give highly digestible foods, short, frequent feedings, water electrolytes, energy and protein
