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Physiology III > Lecture 25: Mucosal Absorption-2 GI Blood Flow > Flashcards

Lecture 25: Mucosal Absorption-2 GI Blood Flow Flashcards

1
Q

What are the different mechanisms in which Na+ is absorbed

A

Na+ co-transporter, Na/H exchanger, simple diffusion

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2
Q

How is K+ absorbed

A

Simple diffusion

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3
Q

How is Cl- absorbed

A

Simple diffusion, Na+ coupled

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4
Q

How is Ca2+ absorbed

A

Simple diffusion, active transport

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5
Q

How is Mg absorbed

A

Simple diffusion, active transport

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6
Q

How is Fe absorbed

A

Heme transporter, specific channel

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7
Q

What does vitamin absorption depend on

A

Solubility

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8
Q

What is the primary side of Na+ absorption

A

Small intestine

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9
Q

What is the function of the Na/H+ exchanger in small intestine

A

Acidify lumen, neutralize luminal HCO3-

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10
Q

Ca2+ is absorbed from GI tract via

A

Facilitated diffusion

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11
Q

At high concentrations of Ca2+ it is transported via

A

Paracellular diffusion

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12
Q

At low concentrations of Ca2+ it is transported via

A

Transceullular diffusion

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13
Q

The transport of calcium adjust for variations in ___

A

Diet

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14
Q

What are the 3 steps in transcellular transport of Ca2+ into duodenum

A
  1. Apical uptake of Ca2+ via electrochemical gradient
  2. Ca2+ binds calbindin which maintains low concentration. (Vit D increases expression of calbindin)
  3. Basolateral Na/Ca2+ exchanger pumps Ca2+ out
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15
Q

What increases the expression of calbindin

A

Vitamin D

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16
Q

At what concentration does Mg uptake happen paracellularly

A

High

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17
Q

At what concentration does intercellular transport of Mg occur

A

High

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18
Q

What transporters are involved in intercellular transport of Mg from apical side

A

TRP transporters

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19
Q

How is Mg transported on basolateral side

A

Secondary active Mg2+/Na+ exchanger

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20
Q

Absorption of nonheme iron exclusively occurs as ___

A

Fe2+

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21
Q

How does Fe2+ cross the apical membrane

A

DMT1 via H+ gradient (maintained by Na/H exchange)

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22
Q

Cytoplasmic Fe2+ binds __ for transit across the cell to basolateral membrane

A

Mobilferrin

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23
Q

Fe2+ exits basolateral membrane via

A

Ferroportin

24
Q

___ promotes intestinal absorption and solubilization (Reduces Fe3+ to Fe2+)

A

Gastric acid

25
Q

What is transferrin

A

Required for plasma transport of Fe

26
Q

What is ferritin

A

Intracellular storage depot for Fe to be released in a controlled fashion

27
Q

What are the fat soluble vitamins

A

A, D, E, and K

28
Q

How are fat soluble vitamins absorbed

A

Solubilized and transported in Micelles, enter circulation in chylomicrons

29
Q

What are the water soluble vitamins

A

B1, B2, B6, B12, C, biotin, folate, pantothenic acid

30
Q

How are water soluble vitamins absorbed

A

Na+ dependent co-transport

31
Q

B12 binds to ___ which protects it from digestion

A

Gastric intrinsic factor

32
Q

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

A

Celiac

33
Q

What artery supplies the remainder of pancreas, gut through 2/3 transverse colon

A

Cranial mesenteric

34
Q

What artery supplies distal colon and proximal rectum

A

Caudal mesenteric

35
Q

The fraction of cardiac output to gut ___after meal

A

Increases

36
Q

What vein collects blood from stomach, small and large intestines

A

Hepatic portal vein

37
Q

Nutrient rich blood enters __, which regulates nutrient concentration

A

Liver

38
Q

Blood runs through two capillary beds __ and ___ before it returns to heart

A

Mesenteric, portal

39
Q

What drives blood through mesenteric and portal capillary beds

A
  1. Pressure in portal vein is slightly greater than that of hepatic sinusoids.
  2. Resistance in sinusoids in much lower
40
Q

Postprandial hyperemia dependent on constituents of ingesta. __ and __ promote hyperemia

A

Bile acids and fats

41
Q

How does increased resistance in the liver affect the intestine

A

Reduces blood flow, portal hypertension

42
Q

Right heart insufficiency increases vena cava pressure which leads to ___blood flow to intestine

A

Decrease

43
Q

How does SNS stimulation affect intestinal circulation resistance

A

Increases it

44
Q

If there is subnormal blow flow to GI what happens to intestines

A

Can die, subnormal at tip of villus causing ischemia, tissue damage and cell death

45
Q

Describe countercurrent exchange in the villus

A

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)

46
Q

How does low blood flow affect countercurrent exchange in villi

A

Further reduces amount of O2 getting to tip of villus can result in cell death

47
Q

How does solute concentration in arterial blood change at the tip of villus if blood flow is low and transit time is prolonged

A

Solute concentration increases, trapping them near tip of villus

Consequences for nutrient absorption and water movement

48
Q

Describe what happens during exercise induced heat stress

A
  1. Thermoregulatory mechanisms in effect
  2. Blood flow shunted from GI to skin
  3. If temperatures continue to rise and mechanism can’t compensate then will result in intestinal ischemia
  4. Release of endotoxins
  5. Systemic inflammatory response and coagulation cascade
  6. Multi-organ failure or death
49
Q

What are some examples of short term adaptations of GI

A
  1. Modulation of membranous enzymatic set up
  2. Modulation of blood supply (metabolic demands, postprandial hyperemia)
  3. Increase absorptive SA(villi hypertrophy)
50
Q

Mesenteric blood flow rates ___in response to metabolic demands during milk production

A

Increase

51
Q

What GI adaptions are seen in a python after a meal

A

Lengthening of intestinal villi and rapdily decresse intestimal pH from 7 to 2

52
Q

How do hibernating animals adapt their GI system

A

Reduce required rates of oxygen consumption

53
Q

How does a patient with an irreversible intestinal injury (resection) undergo GI adaption

A

Remaining length of intestine will hypertrophic and increase absorptive capability. Villus hypertrophy

54
Q

If the ileum is resected what happens to fat, bile salt and VitB 12 absorption

A

Decrease as ileum is main site

55
Q

If the colon is resected what happens to VFA absorption

A

Decreases

56
Q

How do you treat animals post intestinal resection

A

Give highly digestible foods, short, frequent feedings, water electrolytes, energy and protein

Physiology III (34 decks)

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