Kidney Regulation of Blood Volume

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Kidney Regulation of Blood Volume

• A Homeostatic Mechanism

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Stimulus

• Lack of water (dehydration) concentrated
  blood.
• Cells that are sensitive to changes in blood
  water concentration (osmoreceptors) in
  hypothalamus detect this condition.

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Control Centre

• Posterior lobe of the pituitary gland releases
  the hormone antidiuretic hormone (ADH)
• Diuretics are chemicals that increase the flow
  of urine. ADH, being an antidiuretic does
  quite the opposite by inhibiting the flow of
  urine how does it do this ?

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Response ?

• ADH acts on the walls of the distal tubules and
  collecting duct within the kidney nephron to
  promote the reabsorption of H2O (antidiuresis)
  from the tubules back into the circulation
• This results in increasingly diluted blood.
• Note that the diluted blood is the negative
  feedback that signals the posterior pituitary to
  stop producing ADH

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Reverse this situation ...

• What would happen if the blood was too dilute?

• More concentrated or more dilute urine?
• More urine or less urine?

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Kidney Regulation of Blood pH

• Another Homeostatic Mechanism

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Control Center ?
Stimulus ?

• Low pH (high H)

• All tissues lining the nephron

Response ?

• H excreted in urine and HCO3 reabsorbed.

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Reverse this situation ...

• What would happen if the blood had an increased
  pH or low H

• More H excreted or reabsorbed?
• More HCO3- excreted or reabsorbed?

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Kidney Regulation of Salt concentration

• Another Homeostatic Mechanism

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Stimulus

• Low Na level in blood
• High K level in blood
• Reduced blood volume
• Stress
• Note that all of these are conditions that act
  against glomerular filtration low blood volume
  means low blood pressure and therefore poor
  filtration So ...

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Control Centre

• Juxtaglomerular apparatus secretes Renin
• Renin converts angiotensin I to angiotensin II
• Angiotensin II is a powerful vasoconstrictor
  that acts on the adrenal cortex to release the
  hormone aldosterone.

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Response ?

• Aldosterone acts on distal tubules to promote
  reabsorption of Na and H2O follows along with
  it.
• Blood volume returns to normal
• Blood pressure increases and along with it
  increased effectiveness of glomerular filtration.

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Reverse this situation ...

• What would happen if the blood had an increased
  Na, increased blood volume, or increased blood
  pressure?

• No release of aldosterone
• No Na reabsorption and thus
• No water reabsorption

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Question of the day ...
If you drank 1 liter of water do you expect the
salt concentration in urine to increase or
decrease? Why?
NaCl would decrease since secretion of
aldosterone would cause greater reabsorption of
Na from the distal tubule.