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GI Final > Fluid and Electrolyte Absorption DSA > Flashcards

Fluid and Electrolyte Absorption DSA Flashcards

1
Q

How much fluid do the small and large intestines absorb per day?

A

9 L/day

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2
Q

What causes diarrhea?

A

disturbances in the absorptive mechanisms that lead to excess fluid loss

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3
Q

What determines whether the fluid will move via paracellular or cellular route?

A

permeability of tight junctions

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4
Q

What is the resistance in the small intestine tight junctions and large intestine tight junctions?

A

small intestines: “leaky” tight junctions, low resistance permits PARACELLULAR movement

large intestines: “tight” tight junctions, high resistance permits CELLULAR movement

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5
Q

What is the major site for Na+ absorption?

A

jejunum

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6
Q

What transporters are on the apical membrane of the jejunum?

A

Na+ -monosaccharide cotransporters
Na+-amino acid cotransporters
Na+-H+ exchange

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7
Q

What is the source of H+ in the jejunum?

A

CO2+H2O H2CO3 H+ + HCO3-

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8
Q

How does Na+ leave the basolateral membrane in the jejunum?

A

Na+-K+ ATPase

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9
Q

What is the net electrolyte movement in the jejunum?

A

Na+ and HCO3- absorbed into blood

H+ excretion into lumen

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10
Q

What electrolytes are absorbed in the ileum?

A

Na+ and Cl-

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11
Q

What are the transport mechanisms on the apical membrane of the ileum?

A

Na+ -monosaccharide cotransporters (in)
Na+-amino acid cotransporters (in)
Na+(in)-H+(out) exchange
**HCO3- (out)/Cl- (in) exchange

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12
Q

What are the transport mechanisms on the basolateral membrane of the ileum?

A

Na+(to blood)/K+ (in) ATPase

Cl- transporter (to blood)

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13
Q

What is the net electrolyte movement of the ileum?

A

H+ and HCO3- secreted to lumen

Na+ and Cl- absorbed to blood

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14
Q

What channels are on the apical membrane of the colon?

A

Na+ channel (in) = absorption

K+ channel (out) = secretion

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15
Q

What induces the synthesis of Na+ channels?

A

aldosterone

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16
Q

What is the effect of aldosterone on colon epithelial cells?

A

increased synthesis of Na+ channels –> increased Na+ absorption –> increased K+ secretion due to increased Na+ pumped by the Na+ K+ ATPase

17
Q

What is the effect of the high flow rate of intestinal fluid in the colon during diarrhea?

A

causes increased colonic K+ secretion, resulting in increased K+ loss in feces and HYPOkalemia.

18
Q

What are the differences in function of the intestinal epithelial cells in the villi vs crypts?

A

villia - absorb fluid and electrolytes

crypts - secrete fluid and electrolytes

19
Q

What transport mechanisms are on the apical membrane of epithelial cells in the crypts of the intestine?

A

Cl- channels

20
Q

What are the transport mechanisms on the basolateral membrane of the epithelial cells in the crypts of the intestines?

A

Na+/K+ ATPase

Na+/K+/2Cl- cotransporter (in)

21
Q

What is the net electrolyte movement in the crypts?

A

Cl- secreted cellularly through Cl- channel

Na+ and H2O secreted paracellularly following Cl- transport

22
Q

Are the Cl- channels of the apical membrane of the crypts usually open or closed?

A

closed, except when responding to hormones and neurotransmitters from receptors on the basolateral membrane

23
Q

What hormones or neurotransmitters affect the Cl- channels on the apical membrane in the crypts?
-mechanism

A
  • ACh
  • VIP

through adenylyl cyclase generating cAMP –> open Cl- channels

24
Q

What happens in cholera?

A
  • adenylyl cyclase is maximally stimulated
  • Cl- channels in crypts are continuously open –> continuous secretion of NaCl and H2O
  • fluid secretion by crypt cells overwhelms the absorptive capacity of the intestinal villar cells
  • causes severe life-threatening diarrhea
25
Q

What does diarrhea cause?

LO3

A

Circulatory collapse

  • decreased ECF volume
  • decreased intravascular volume
  • decreased arterial pressure

Electrolyte (HCO3- and K+) loss

  • hyperchloremic metabolic acidosis with normal anion gap (greater loss of HCO3- compared to Cl-)
  • hypokalemia
26
Q

What system attempts to restore BP?

A

renin-angiotensin II-aldosterone system

-attempts will be futile if the volume of fluid lost from GI tract is too great or too rapid

27
Q

What are the main causes of diarrhea?

LO4

A
  • decreased surface area for absorption: infection and inflammation of SI
  • osmotic diarrhea: presence of nonabsorbable solutes in the lumen of intestins (lactase deficiency)
  • secretory diarrhea: excessive secretion of fluid by crypt cells (E coli, cholera toxin)
28
Q

How does lactase deficiency cause osmotic diarrhea?

LO 5

A
  • lactose is not digested to glucose and galactose (absorbable forms)
  • undigested lactose is not absobed and remains in lumen of intestine
  • retains water by remaining in lumen
  • bacteria in intestine may degrade lactose to more osmotically active solutes (compounding the problem)
29
Q

How does cholera toxin cause secretory diarrhea?

LO6

A
  1. cholera toxin enters intestinal crypt cells by crossing apical membrane
  2. A subunit of cholera toxin moves to basolateral membrane where it catalyzes ADP ribosylation of alpha s of Gs protein coupled to adenylyl cyclase
  3. ADP ribosylation of alpha s inhibits GTPase activity (GTP cannot be converted to GDP), so adenylyl cyclase is permanently activated
  4. cAMP levels remain high. Cl- channels in apical membrane are kept open.

Cl- secretion followed by Na+ secretion followed by H2O secretion, overwhelms absorptive villi of the SI and colon.

30
Q

What is a major advancement in treatment of diarrheal disease worldwide?

A

oral rehydration solution

-solution contains Na+, Cl-, and HCO3- which stimulate intestinal absorption of fluid and electrolytes

31
Q

What is the absoption/secretion function of the duodenum?

A

bring chyme to osmotic equilibrium with plasma

  • water absorbed from hypotonic solutions
  • water secreted/Na+ and Cl- absorbed from hypertonic solution

GI Final (15 decks)

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