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**.