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Module 104: Theme 1 > Salt and water transport and its control > Flashcards

Salt and water transport and its control Flashcards

1
Q

Transcellular

A

The movement of ions/ water through the cell between each membrane.

Transport establishes concentration gradients and can work against electrochemical gradients.

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2
Q

Paracellular

A

The movement of ions/water between cells in the interstitial space.

This transport it regulated by tight junctions and dictated mainly by an electrochemical gradient.

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3
Q

Tight junctions

A

Structure between cells in the intestinal epithelium.

Regulates the permeability of the intestines to water and solutes.

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4
Q

Primary active transport

A

ATP driven transcellular transport that moves ions against an electrochemical gradient.

Example: Na-ATPase

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5
Q

Secondary active transport

A

ATP driven transcelluar transport.

Co-transports ions.

Example:
Na-GLUC transporter

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6
Q

Na/K+ ATPase

A

Basolateral antiporter on enterocytes that drives Na+ absorption.

Na+ transport is against concentration gradient as Na+ is already low inside cell

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7
Q

Na+ coupled transport

A

Apical symporter on enterocytes.

Na/K-ATPase created an electrochemical gradient for Na+ to move into the cell.

Na+ brings glucose and amino acids as it moves into cell.

This causes the lumen to become more negative- driving Cl- absorption into the cell.

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8
Q

Na+/ H+ exchanger

A

Present on the luminar membrane of the enterocyte.

Drives Na+ absorption and H+ secretion.

Na/K-ATPase establishes gradient for this exchanger

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9
Q

HCO3-/ Cl- exchange

A

Present on the luminar membrane of the enterocyte.

Cl- movement into the cell is driven by increasing negativity of the lumen- caused by Na+ absorption.

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10
Q

Na/K/2Cl symporter

A

Present on the basolateral membrane of the enterocyte.

Drives electrochemical gradient for transport of Cl- into the lumen via the CFTR chloride channel.

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11
Q

CFTR chloride channel

A

Channel present on the luminar membrane of the enterocyte.

Allows flow of Cl- out of the cell into the lumen.

This channel is expressed most in the colon and ileum.

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12
Q

Water absorption

A 
Na+ is aborbed into the cell via:
Na coupled transport
Na/H+ exchanger.
- Then into the blood via 
Na/K-ATPase

Cl- is absorbed into the cell via Cl-/HCO3- exchanger.

This drives the paracellular transport of water into the blood- via tight junctions

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13
Q

Secretion of water

A

Cl- is secreted into the lumen via CFTR.

This drags and Na+ and H2O paracellularly across tight junctions into the lumen.

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14
Q

Jejunum ion transport

A

Contains Na+, Cl-, K+, HCO3- and water absorption.

  • Highest Na+ absorption (coupled)
  • Solvent drag the most important mechanism of transport.

Apical:

  • Na coupled with glucose, a.a and fructose
  • Na/H exchange

Basolateral:

  • Glucose, fructose and a,a channels.
  • K+ channels
  • Na/K- ATPase
  • Bicarbonate channel
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15
Q

Solvent drag

A

Water moves to obtain osmotic equilibrium.

This causes solvents to be pulled with water transport.

Occurs where right junctions are the leakiest (upper small intestines)

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16
Q

Ileum ions transport

A

Site has the highest absorption of NaCl

Mechanism are similar to jejunum transport.

Apical:

  • Na coupled
  • Na/H
  • HCO3/Cl

Basolateral:

  • Glucose, a.a and fructose channel.
  • K channel
  • Na/K
  • Cl channel
17
Q

Colon ion transport

A

Does not contain tight junctions for H2O absorption.

Apical:

  • Na+ channels
  • Na/H
  • Cl/HCO3

Basolateral:

  • K channel
  • Na/K-ATPase
18
Q

Aldosterone

A

Mineralocorticoid that increases the synthesis of Na+ channels.

Stimulates more K+ secretion into lumen.

Can cause hypokalemia.

19
Q

Oral rehydration therapy

A

Solution of glucose, sodium (salt) and amino acids.

The facilitates absorption of Na+ into the cell which also drives Cl- absorption.

20
Q

Cholera toxin on intestinal juice secretion

A

Toxin is secreted by Vibrio cholerae.
- stimulates excess production of cAMP in crypt cells.

This drives Cl- out of the cell as CFTR is regulated by cAMP.

This draws out Na+ and H2O paracellularly- can lead to dehydration through secretory diarrhea.

Treatment- oral rehydration therapy.

21
Q

Lactose intolerance

A

Lactase deficiency means that lactose is not broken down to release glucose.

Lactose drives water out paracellularly and causes osmotic diarrhea.

22
Q

Bacterial enterotoxins that cause secretory diarrhea

A

Cholera

Heat-liable E.coli

Salmonella

Campilobacter

Heat stable E.coli

Yersinia

23
Q

4 pathophysiological changes of transepithelial transport

A
  1. Stimulates of net fluid and electrolyte secretion.
  2. Mucosal destruction—-> Increased permeability
  3. Increased propulsive muscle contractions.
  4. Nutrient malabsorption
24
Q

Colon water and electrolyte absorption

A

Na+ enters cell on apical membrane:

  • Na+ channels
  • Na/H antiport

Na/K-ATPase drives Na+ entry into cells

K+ leaves into lumen via channels and is also absorbed in the blood.

Cl-/HCO3- exchange release bicarbonate to neutralise acid and removes Cl- from lumen.

NaCl- into cells creates osmotic gradient for transcellular water movement.

25
Q

Ion transport in Jejunum

  • Na+
  • K+
  • Cl-
  • HCO3-
A

Na- actively absorbed [ Na+/H+- ATPase]
- especially coupled transport with glucose, amino ands

K- passively absorbed through K+ channels when water is absorbed .

Cl- absorbed

HCO3- absorbed, so it can be secreted in ileum and colon.

26
Q

Ion transport in Ileum

  • Na+
  • K+
  • Cl-
  • HCO3-
A

Na- actively absorbed using sodium pump and coupled transport.

K- passively absorbed through channels

Cl- absorbed, some using exchange with HCO3-

HCO3- Secreted, some in exchange with Cl-

27
Q

Ion transport in colon

  • Na+
  • K+
  • Cl-
  • HCO3-
A

Na- Actively absorbed

K- secreted when concentration is <25 mM

Cl- absorbed, some in exchange for Cl-

HCO3- secreted, some in exchange for Cl-

Module 104: Theme 1 (18 decks)

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