133b - Water and Electrolyte Absorption Flashcards

1
Q

Which transporter do we use to absorb fructose?

A

GLUT5 (apical)

GLUT2 (basolateral)

  • Fructose cannot use the SGLT1 transporter
    • => Cannot pull in Na+
    • => Less hydrating
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2
Q

Why does gatorade hydrate you more than water?

(From an ion transport perspective)

A

The SGLT1 transporter is only active in the presence of both sodium and glucose (or galactose)

  • More sodium and sugar absorption = stronger gradient pulling water in
  • Cl- also plays a role
    • Na+ pulls Cl- in too
    • More ions = more gradient for water
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3
Q

Which protein drives water absorption in the intestine?

A

Na+/K+ ATPase

  • Pumps Na+ out through the basolateral membrane
  • Sets up a gradient for Na+ absorption
    • Via Na+/H+ exchange, SGLT1, ENaC, etc
  • H2O follows
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4
Q

Where in the GI tract are most fatty acids absorbed?

A

Distal ileum

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5
Q

How does K+ homeostasis differ in different parts of the colon?

A
  • Proximal colon = mostly secretion
  • Distal colon = mostly absorption

[Think about the logic of resorption, it needs to be further down to catch it as it is secreted]

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6
Q

How is chloride secretion regulated?

What is the significance?

A

CFTR channel opening is regulated by cAMP

  • Cl- is secreted through the CFTR channel
  • More cAMP = more Cl- secretion
  • Excess Cl- secretion = watery diarrhea
    • Cholera toxin -> increased cAMP -> watery diarrhea

[Cl- is high inside the cell, there is always a gradient to leave

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7
Q

In general, which ions are abosrbed in the small intestine and colon?

Which are secreted?

A
  • Absorbed
    • Na+, H2O
  • Secreted
    • HCO3-, H+
  • Cl- depends on action of CFTR
    • Regulated by cAMP
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8
Q

In the gut lumen, vitamin D3 upregulates the absorption of which two ions?

A

Calcium

Phosphorous

  • Vitamin D3 upregulates the transcription of proteins required for absorption
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9
Q

What protein is required for us to absorbe Ca2+ from the intestinal lumen?

A

Calcium Binding Protein (CBP)

  • Intracellular Ca2+ is low so there is a gradient for absorption
  • CBP helps neutralize the charge
    • CBP transcription is upregulated by vitamin D3
  • ATPase required to absorbe Ca2+ through the basolateral membrane
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