Control of Blood Volume

Question 1

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

Answer 1

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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

• renal output curve for salt and water

- level of salt and water intake

Question 4

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

Answer 4

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

Question 5

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

Answer 5

where MABP is maintained for long-term

Question 6

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

Answer 6

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

Question 7

Where is ADH released from?

Answer 7

Pituitary gland

Question 8

What triggers the release of ADH?

Answer 8

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

Question 9

Explain the action of ADH

Answer 9

• 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

Question 10

What is renin?

Answer 10

a proteolytic enzyme released from the kidneys

Question 11

What triggers renin release?

Answer 11

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

Question 12

Explain RAAS regulation of blood volume

Answer 12

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

Question 13

Explain RAAS regulation of blood pressure

Answer 13

• 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

Question 14

What is the atrial-natriuretic hormone

Answer 14

28 amino acid peptide stored in muscle cells of atria

Question 15

What triggers the release of the atrial-natriuretic hormone?

Answer 15

• stretch of the atria

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

Question 16

What is class 1 shock?

Answer 16

10-15% blood loss

Question 17

What is the immediate reflex response to hypovolemia?

Answer 17

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

Question 18

What is the later response to hypovolemia?

Answer 18

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

Question 19

Treatment for severe hypovolemia?

Answer 19

fluid replacement:

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

Question 20

What other factors affect blood pressure control?

Answer 20

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