Regulation of Volume

Question 1

Which receptors detect pressure?

Answer 1

• Baroreceptors

Question 2

Where are low pressure baroreceptors found (3)?

Answer 2

• Atria
• Right ventricle
• Pulmonary vasculature

Question 3

Where are high pressure baroreceptors found (3)?

Answer 3

• Carotid sinus
• Aortic arch
• Juxtaglomerular apparatus

Question 4

What is the response to a decrease in pressure of a low pressure side baroreceptor (3 steps)?

Answer 4

1. Reduced baroreceptor firing
2. Signal through afferent fibres to the brainstem
3. Stimulate sympathetic activity & ADH release

Question 5

What is the response to an increase in pressure of a low pressure side baroreceptor (2 steps)?

Answer 5

1. Atrial stretch
2. ANP, BNP released

Question 6

What is the response to a decrease in pressure of a high pressure side baroreceptor (3 steps)?

Answer 6

1. Reduced baroreceptor firing
2. Signal through afferent fibres to the brainstem
3. Stimulate sympathetic activity & ADH released AND JGA cells release renin

Question 7

Which brainstem centre regulates blood pressure?

Answer 7

• Cardio-regulatory centre

Question 8

What is the tonic frequency of baroreceptor firing rate?

Answer 8

• Baroreceptor firing of receptors which tonically suppress sympathetic activity

Question 9

What happens due to reduced baroreceptor firing?

Answer 9

• There is an upregulation in sympathetic activity & ADH release

Question 10

What happens to the heart rate and stroke volume in response to reduced baroreceptor firing?

Answer 10

• Increases (SAN and ventricular cardiomyocytes have sympathetic post-ganglionic neurones)

Question 11

Which peptides are released in response to high blood pressure (2)?

Answer 11

• ANP & BNP
  
  • ​Synthesised in response to atrial stretch

Question 12

What is ANP?

Answer 12

• A small peptide synthesised within the atria (In addition to BNP)

Question 13

When is ANP released?

Answer 13

• In response to atrial stretch due to high blood pressure, and circulates in blood where it binds to complementary receptors

Question 14

What effect occurs by ANP stimulation (3)?

Answer 14

• Vasodilation to reduce blood pressure (renal and systemic vessels)
• Inhibition sodium reabsorption in the distal nephron
• Inhibits renin & aldosterone release

Question 15

What is the overall effect from ANP stimulation?

Answer 15

• Reduces blood pressure

Question 16

What effect does ANP have on ADH?

Answer 16

• Suppresses the release of ADH

Question 17

Which enzyme is activated in response to ANP?

Answer 17

• Protein kinase G

Question 18

What is volume expansion?

Answer 18

• An increase in plasma sodium → increasing blood pressure & ECF volume

Question 19

Which ion determines ECF volume?

Answer 19

• Sodium (Na⁺)

Question 20

What effect does volume reduction have on BP?

Answer 20

• Volume reduction
  
  • Increased sympathetic activity:
    
    • Afferent arteriolar contraction
    • Reduced GFR
    • Increased Na⁺ uptake in the PCT / Increased renin / Increased angiotensin & aldosterone
      
      • Increased ADH

The above lead to:

1. Increased Na⁺ reuptake in PCT, DCT & CT
2. Increased H₂O reabsorption (water reabsortpion requires an osmotic gradient)
3. Decreased excretion H₂O &Na⁺
4. Increased ECF volume
5. Increased BP

Question 21

What effect does volume expansion have on BP?

Answer 21

• Volume expansion
  
  • Reduced sympathetic activity:
    
    • Afferent arteriolar dilation
    • Increased GFR
    • Decreased Na⁺ uptake in the PCT / Decreased renin / Decreased angiotensin & aldosterone
  • Increased ANP
    
    • Decreased renin
      
      • Increased GFR
      • Decreased ADH

The above lead to:

1. Decreased Na⁺ reuptake in PCT, DCT & CT
2. Decreased H₂O reabsorption (water reabsortpion requires an osmotic gradient)
3. Increased excretion H₂O &Na⁺
4. Decreased ECF volume
5. Decreased BP

Question 22

Practice Questions

Identify A

Answer 22

ANP

Question 23

Practice Questions

What is the effect of increased A on GFR?

Answer 23

It increases the GFR (by relaxing the SMCs in the afferent arteriole)

Question 24

Practice Questions

What is B and how does it change in response to volume expansion?

Answer 24

Angiotensin I and it reduces

Question 25

Practice Questions

How do the levels of renin change?

Answer 25

Renin levels go down (because of the reduction in sympathetic activity).

Question 26

Practice Questions

What is C?

Answer 26

ADH OR vasopressin

Question 27

Practice Questions

What proteins does C affect to alter water reabsorption and how does it affect these proteins?

Answer 27

C causes the aquaporins in the cells of the collecting duct to translocate from the cytoplasm to the cell wall increasing the permeability to water (in this context there is a reduction in C so a reduction in water permeability).

Question 28

Practice Questions

Identify D?

Answer 28

Aldosterone

Question 29

Practice Questions

How does Angiotensin II affect the production of D?

Answer 29

It causes an increase in the expression of aldosterone synthase (which is required for the last 2 steps of the conversion of cholesterol to aldosterone).

Question 30

Practice Questions

How does D affect water reabsorption?

Answer 30

D increases water reabsorption by increasing the permeability of the principal cells to sodium (for information but not required for the answer it increases the expression of ENaC, the Na/KATPase and proteins that increase their activity so increases Na reabsorption).

Question 31

Practice Questions

The excretion of which major ions/molecules is altered to correct the volume expansion and how is it affected?

Answer 31

Sodium and water and their reabsorption is reduced to correct the volume expansion.