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Digestive Systems, Nutrition, and Metabolism > Intestinal Fluid and Electrolytes > Flashcards

Intestinal Fluid and Electrolytes Flashcards

1
Q

Name components of small intestine. Where does nutrient absorption occur? Secretions?

A

VIlli (the projections) and the crypts (the deep points). nutrient + electrolyte absorption occurs at the TIPS of the villi. Secretions occurs at the CRYPTS

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2
Q

Name components of large intestine. Where does nutrient absorption occur? Secretions?

A

Note: large intestine does not have villi, but it has “galnds” with crytps. Surfaces cells responsible for electrolyte absorption. Crypts responsible for electrolyte secretion

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3
Q

How much fluid runs through small intestine? How much meets the colon?

A

9L (Cardiac Output circulating blood volume is 5L…). Only 2 liters get to the colon. Means that the BULK of the activity of small intestine = absorption

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4
Q

Categorize tonocity of contents of duodenum

A

Isotonic, due to water and NaCL. This causes pH to go from acidic to neurtral/alkaline

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5
Q

Explain absorption within jejunum and ileum. What channel is responsible for the main absorption? Describe stool as it leaves ileum. Describe K movement. Describe Cl secretion.

A

Driven by absorption of Na and Cl uptake, which causes water uptake. This absorption is fostered by NHE/Cl-HCO3 parallel exchange. stool upon leaving ileum = alkaline. K movement = passive. Cl secretion is basal, thanks to CFTR in the intestinal crypts.

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6
Q

Describe ion and fluid handling of large intestine.

A
  1. Na, Cl reabsorbes
  2. K, HCO3 secreted (into lumen)
  3. Gets 2L of content volume from ileum, excretes 100mL
  4. MAX absorption capacity is 5L/day…safeguard for is small intestine sees too much content to absorb. Supersede this = diarrhea.
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7
Q

Cholera

A

Intestinal disease that leads to increased amounts of diarrhea. Hypokalemia, and impending death due to fluid loss and hypovolemia. Cholera works by causing a bowel obstruction, hindering content escape. Result: intestines secrete a tremendous amount of fluid to move the feces out.

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8
Q

What drives Na reabsorption? How does it work?

A
  1. Na/K pump, which works by creating low Na current 2. establishing NEGATIVE membrane potential (pumps 3 Na into basolateral side and 2 into luminal side…both Na/K pump (atpase) is on basolateral side).
  2. This allows Na to come through the luminal side. water follows the Na.
    Note: Water comes in through PARAcellular route.
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9
Q

List the mechs of Na absorption?

A
  1. Na/glucose and Na/amino acid transport (small intestine)
  2. Electroneutral Na-H exchange (NHE) (small intestine)
  3. Parallel Na-H and HCO3-Cl exchange (small intestine)
  4. Epithelial (ENaC) “electrogenic” sodium
    transport in the colon
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10
Q

Describe Na’s absorption in in small intestine, and how it leads to nutrient absorption. What kind of transport is this? How does the potential created lead to Cl absorption? What is the end result?

A

Post-prandial (after eating), Na absorption is coupled to meal absorption. Primary mech for Na absorption AFTER a meal Occurs in apical villus cells of PROXIMAL small intestine. This is a secondary active transport. it is NOT affected by cAMP or Ca current. It is ENTIRELY fostered by Na/K pump on basolateral side of enterocyte. Note that Na coming into basolateral side leads to negative potential in the lumen. If Cl is already in th eluman, Cl no longer wants to stay there. So it follows Na in too. This creates NaCl in the enterocyte. And now water can follow even more.

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11
Q

Describe job of NHE (Na-H exchange)…remember that it helped drive PepT1 activity.

A

Found in duodenum and jejunum WITHOUT HCO3-Cl exchanger. It brings Na into enterocyte by spitting H into lumen. Activated in presnce of HCO3. Still need Na/K on basolateral side.

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12
Q

Explain NHE/HCO3-Cl parralel exchange. THE MOST IMPORTANT ONE

A
  1. It is the primary Na transport in post-prandial period. Note that both NHE and HCO3-Cl or on the luminal (apical) side, Na/K is still on basolateral side. The setup allows for Na and Cl to be absorbed into enterocyte together.
  2. Fosters absortpion BETWEEN meals in ileum and LARGE intestine.
  3. It’s process is REDUCED by increased amounts of cAMP and Ca flow.
  4. It is increased by aldosterone (which only comes around in times of low bp, remember? aldosterone helps kidneys hold on to Na too, rememeber?) and decreased Ca.
  5. Net effect = absorption of NaCl into the enterocyte, even though they come in as separate ions. As a result of that, water follows through paracellular path.
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13
Q

result of increased cAMP activity in ileum/colon?

A

NaCl absorption is blocked, and so is water uptake blockage. This leads to diarrhea. This is how these diseases happen.

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14
Q

What is job of epitehlial Na channel (ENaC)?

A
  1. works in distal colon.
  2. Na/K still on basolateral side, ENaC on apical side.
  3. Flow of Na through apical side is electrogenic (creates neg. potential in the lumen), fostering movement of other anions.
  4. Regulated by ALDOSTERONE, which increase activity of Na/K, ENaC efficiency/mobility/efficiency
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15
Q

Describe Cl absorption in proximal small intestine. cAMP dependent or independent?

A
  1. Passive Cl absorption is coupled to Na-nutrient absorption and ENaC.
  2. The negative potential created by Na enterocyte absorption on apical side creates negative potential. Cl can no longer stay there, and so follows Na in through apical side as well as paraccellular channels. Voltage dependent, cAMP INDEPENDENT
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16
Q

Describe solo apical Cl-HCO3 exchanger and how it mediates cl absorption.

A

Occurs in proximal colon. If more Cl is presented to the colon, then more HCO3 is spit out into the lumen.

17
Q

Describe NHE/Cl-HCO3 parallel exchange and it’s importance.

A
  1. It is the PRIMARY Cl transport in post-prandial period
  2. Ultimately, Cl flows in with Na, through 2 different channels.
  3. Occurs in distal ileum/colon.
18
Q 
What happens if patient Cl-HCO3 exchanger?
A child lacks the Cl-HCO3 exchanger and is
diagnosed with congenital chloridorrhea.
Predict the patient’s findings:
A. Diarrhea; normal acid base status
B. Constipation; normal acid base status
C. Diarrhea; metabolic alkalosis
D. Constipation; metabolic alkalosis
E. Diarrhea; metabolic acidosis
F. Constipation; metabolic acidosis
A

C. Diarrhea; metabolic alkalosis. note that despite Na’s absortpion, you still get diarrhea. note also that this is one of the rare times diarrhea causes metabolic alkalosis instead of the normal acidosis.

19
Q

Describe process of Cl secretion. Is Na involved? If so, how?

A
  1. Occurs at bottom of intestine (crypts), but its occurence is LOW.
  2. Note that when Cl moves back into the lumen, it creates net negative charge in the lumen, leading to Na following it through the apical, paracellular side
  3. Process leads to increased NaCl in lumen, and this increased water secretion.
    Note: Cl secretion into lumen intestine = water secretion into lumen intestine.
  4. NKCC channel supplies the Cl to be sent to apical side.
  5. CFTR allows Cl to be sent into lumen from apical side. If channel is screw up, stool is thick (“jelly”) in kiddie’s first stool
20
Q

What increases CFTR activity?

A

Secretogogues (cAMP or Ca current increases). Increases in cGMP causes this too.

21
Q

What would you expect in patients with constitutive increase in cAMP? What could cause this?

A

secretory diarrhea. Caused by bacterial exotoxins (E coli), hormones/neurotransmitters, or immune system products (histamine)

22
Q

How does cholera work?

A
  1. Cholera makes toxin that’s taken up by cell
  2. cAMP is produced, activating PKA
  3. CFTR is activated. CL is sent to lumen. Na follows. Water follows.
23
Q

What is an oral rehydration solution?

A

Has water with electrolyes and glucose and AA. Allows nutrient uptake through proximal intestine. This would then also allow Na and Cl uptake to maintain vascular volume. Helps in early stages of cholera. Note that it is not susceptible to cAMP activation…this is specific for proximal intestine.

24
Q

Describe role of K in small intestine. Explain Solvent drag.

A

K is passively absorbed by small intestine. “Solvent drag” entails the absorption of Na and Cl and water following. once this occurs there is an osmolarity imbalance on the basolateral side, so K follows the water too.

25
Q

Describe role of K in distal colon.

A

K is ACTIVELY absorbed through K/H exchanger.

26
Q

Describe regulation of K SECRETION into lumen

A
  1. K secretion occurs in colon
  2. Na/K up and NKCC both move K into enterocyte.
  3. K exits enterocyte into lumen via apical exit BK channel or K is recycled (go back out to basolateral side),
    Note: BK expression can increase, on apical side, making apical side more permeable to K. Would happen if K is higher in the body. Would also happen in cases of high amounts of K being presented to the colon. Happen in diarrhea patients.
27
Q

Another name for HCO3-CL exchanger

A

DRA

Digestive Systems, Nutrition, and Metabolism (20 decks)

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