Control of Blood Volume Flashcards

1
Q

What is responsible for the long term regulation of blood pressure?

A

Regulation of kidney function to control the body’s fluid volume

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2
Q

How do the kidneys control the body’s fluid volume?

A

Renal body-fluid feedback system:

  • when arterial pressure increases, urine output increases and vice versa
  • due to increased ECF increasing blood volume, cardiac output, and total peripheral resistance
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3
Q

What are the 2 determinants of the regulation of blood pressure?

A
  • renal output curve for salt and water

- level of salt and water intake

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4
Q

What effect does increasing water and salt intake on MABP graph?

A

If renal output for water and salt remained the same, then you would have a new equilibrium point and a new MABP

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5
Q

What is the equilibrium point for water and salt intake on MABP?

A

where MABP is maintained for long-term

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6
Q

Explain the effect modifying kidney function will have on MABP graph?

A
  • steeper slope of renal output, less increase in MABP for increase in water and salt intake
  • equilibrium point does not change much
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7
Q

Where is ADH released from?

A

Pituitary gland

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8
Q

What triggers the release of ADH?

A
  • increase in osmotic pressure (hypothalamic osmoreceptors)
  • hypovolaemia (decrease atrial baroreceptor firing rate)
  • hypotension (decrease in arterial baroreceptor firing to increase sympathetic activity)
  • angiotensin II
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9
Q

Explain the action of ADH

A
  • increases blood volume by increasing water permeability in renal collecting ducts and decreases urine output
  • in severe hypovolemic shock can cause reflex vasocontriction to increase total peripheral resistance
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10
Q

What is renin?

A

a proteolytic enzyme released from the kidneys

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11
Q

What triggers renin release?

A
  • sympathetic nerve activation (baroreceptor feedback)
  • renal artery hypotension
  • decreased sodium in distal tubules
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12
Q

Explain RAAS regulation of blood volume

A
  • blood volume decreases
  • baroreceptor rate decreases
  • signals MCVC centre
  • activates renal sympathetic nerves
  • increases kidney renin output
  • decreases urine formation
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13
Q

Explain RAAS regulation of blood pressure

A
  • decreased BP
  • renin release from juxtoglomerular cells
  • renin cleaves substrate to form angiontensin I
  • converted by enzyme in the lungs to angiotensin II
  • acts directly on kidneys to constrict renal arteries decreases blood flow
  • also causes release of aldosterone from adrenal glands to increase sodium and water reabsorption
  • also stimulates release of ADH
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14
Q

What is the atrial-natriuretic hormone

A

28 amino acid peptide stored in muscle cells of atria

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15
Q

What triggers the release of the atrial-natriuretic hormone?

A
  • stretch of the atria

- helps oppose effects of RAAS system and can help counteract volume overload

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16
Q

What is class 1 shock?

A

10-15% blood loss

17
Q

What is the immediate reflex response to hypovolemia?

A
  • baroreceptor reflex
  • SV and CO increases after loss but still less than before
  • HR increases
  • TPR increases
  • MABP is restored
18
Q

What is the later response to hypovolemia?

A
  • arteriolar constriction
  • decreased hydrostatic pressure in capillaries
  • favour fluid reabsorption to increase blood volume
  • temporary redistribution of pressure
19
Q

Treatment for severe hypovolemia?

A

fluid replacement:

  • resuscitation fluids: colloid and blood
  • fluid challenge algorithm
  • monitor central venous pressure
20
Q

What other factors affect blood pressure control?

A
  • cortex: conscious effects/emotions
  • nerves from cortex go to medullary CVC centre
  • time of day: hormones/cortical input
  • respiration: mechanical movements/chemoreceptors