Long Term Control of Blood Pressure

Question 1

What is the role of the kidney in the long term control of blood pressure?

Answer 1

Regulating plasma volume and therefore blood pressure

Question 2

Where is renin produces?

Answer 2

From the JUXTAGLOMERULAR (granule cells) of the kidney

Question 3

What triggers renin production

Answer 3

• Activation of sympathetic nerves to the juxtaglomerular apparatus
• Decreased distension of afferent arterioles (the “renal baroreflex”)
• Decreased delivery of Na+/Cl- through the tubule

Question 4

What does renin do?

Answer 4

• Converts inactive angiotensinogen to angiotensin I
• Which is in turn converted by angiotensin converting enzyme to angiotensin II

Question 5

What does angiotensin II do?

Answer 5

Stimulates release of aldosterone from the adrenal cortex
- Increases Na+ reabsorption in the loop of Henle
- Therefore reduces diuresis and increases plasma volume
Increases release of ADH from the pituitary
- Increases water permeability of the collecting duct
- Therefore reduces diuresis and increases plasma volume
- And increases sense of thirst
Is a vasoconstrictor
- Therefore increases TPR
i.e. this is a negative feedback system
- Multiple mechanisms detect any decrease in MAP
- Stimulates release of renin
- This evokes multiple mechanisms which increase MAP

Question 6

Where is the ANTIDIURETIC HORMONE produced?

Answer 6

• Synthesised in the hypothalamus
• Released from the posterior pituitary

Question 7

What triggers ADH release?

Answer 7

• A decrease in blood volume (as sensed by cardiopulmonary baroreceptors and relayed via medullary cardiovascular centres)
• An increase in osmolarity of interstitial fluid (as sensed by osmoreceptors in the hypothalamus)
• Circulating angiotensin II (triggered by the renin-angiotensin-aldosterone system)

WHICH ARE ALL SIGNS OF LOW PLASMA VOLUME AND/OR MAP

i.e. this is another negative feedback system
- Multiple mechanisms detect any decrease in MAP
- Stimulates release of ADH
- This evokes multiple mechanisms which increase MAP

Question 8

Where are ATRIAL NATRIURETIC PEPTIDE and BRAIN NATRIURETIC PEPTIDE produced?

Answer 8

Produced in and released from myocardial cells in the atria and (despite the name), the ventricles respectively

Question 9

What triggers ANP and BNP release?

Answer 9

Increased distension of the atria and ventricles

Question 10

What do ANP and BNP do?

Answer 10

• Increase excretion of Na+ (natriuresis)
• Inhibit the release of renin
• Act on medullary CV centres to reduce MAP

i.e. this is yet another negative feedback system
- A mechanism detects any increase in MAP
- Stimulates release of ANP and BNP
- This evokes multiple mechanisms which reduce MAP