Session 4 - BP and the Kidney

Question 1

How is mean arterial blood pressure calculated?

Answer 1

1/3 systolic + 2/3 diastolic BP

Question 2

Where are baroreceptors found in the body?

Answer 2

Aortic arch

Carotid sinus

Question 3

How is RAAS activated at the kidney?

Answer 3

Renin released at juxta-glomerular apparatus by granular cells in response to:

• Reduced NaCl delivery to distal tubule (macula densa)
• Reduced perfusion pressure in kidney (detected by baroreceptors at afferent arteriole)
• Sympathetic stimulation to JGA >renin release.

Question 4

How does the RAAS system increase blood pressure?

Answer 4

Find RAAS diagram and try to draw out!

Question 5

What actions does angiotensin II have at the kidney?

Answer 5

• Vasoconstriction of efferent and afferent arterioles (more effect on efferent)
• Enhanced Na+ reabsorption at PCT (stimulates Na-H exchanger in apical)
• Stimulate aldosterone release (adrenal cortex) : (affects principle cells of CD)
• Stimulate ADH release from post. pituitary (Stimulate aquaporins in CD)

Question 6

What are the actions of aldosterone on the kidney?

Answer 6

• Acts on Principal cells of collecting duct.
• Stimulating Na+, thus water reabsorption.
• Activates apical ENaC (and apical K+ channel)
• Increases basolateral Na+ extrusion via Na/K ATPase.

Question 7

In which ways does the sympathetic nervous system stimulate the kidneys?

Answer 7

• High levels of SNS stimulation reduce renal blood flow.

- Vasoconstriction of arterioles,

Question 8

What causes prostaglandin release at the nephron, what affect does this have?

Answer 8

Release stimulated by:
- Angiotensin II
- Noradrenaline
- Anti-diuretic hormone
Locally released, causing vasodilation of afferent arteriole (very local effect).
Also enhance renin release.

Question 9

How does antidiuretic hormone cause increase in blood pressure?

Answer 9

Increases water reabsorption in the distal nephron, via aquaporin channels (AQP2).

Question 10

What stimulates the release of ADH?

Answer 10

Increase in Plasma osmolality (detected a hypothalamus).

Severe hypovolaemia.

Question 11

What are the main actions of Atrial natriuretic peptide?

Answer 11

1. Vasodilation (systemic & afferent arteriole of glomerulus - >GFR)
2. Inhibits Na+ reabsorption especially in collecting duct. > Loss of sodium.

Question 12

How does ANP reduce blood pressure?

Answer 12

Its action opposes that of the RAAS system.

feedback to Adrenal glands, and inhibits renin secretion

Question 13

What is hypertension?

Answer 13

Persistent increase in blood pressure.

Question 14

How is hypertension clinically diagnosed?

Answer 14

Three readings of blood pressure above 140/90.

or 135/85 for 24 hour home monitoring device

Question 15

Which diseases can cause secondary hypertension?

Answer 15

Renovascular hypertension.
Coarctation of the aorta.
Primary hyperaldosteronism (Conn’s Syndrome)
Cushing’s syndrome.

Question 16

What are the two main types of Renovascular disease?

Answer 16

75% are Atheroma.
Fibromuscular dysplasia (FMD) = a non-atherosclerotic, non-inflammatory disease of the blood vessels that causes abnormal growth within the wall of an artery. (commonly renal/ carotid)

Question 17

What are the differences caused in unilateral vs bilateral renal artery stenosis?

Answer 17

Unilateral
- Increased RAAS from kidney on stenotic side.
- Causes hypertension, but healthy kidney can compensate and increase Na (and H20) excretion.
(no fluid overload!)

Bilateral
- Both stenotic vessels, so both kidneys have reduced GFR.
- This decrease in GFR will mean impaired Na and water secretion, thus increased Arterial BP.
- This increase BP will mean RAAS is actually inhibited (maybe due to ANP?), as there is no normal kidney to remove excess. This means angiotensin levels will be low or normal.
(There is hypertension, and can be oedema)

Question 18

What is coarctation of the aorta?

Answer 18

A congenital narrowing of the aorta (usually where the ductus arteriosus joined the aorta)

Question 19

How can an aortic coarctation be diagnosed?

Answer 19

Radioradial pulse delay, or radiofemoral delay.

Dependent on which two arteries there is a delay in can give an idea of the location of the coarctation

Question 20

What are some main endocrine causes of hypertension?

Answer 20

• Primary hyperaldosteronism (Conn’s syndrome) e.g. adrenal hyperplasia/ adenoma.
• Cushing’s syndrome

Question 21

What would circulating levels of Renin and Angiotensin II be in Primary hyperaldosteronism.

Answer 21

Low

aldosterone would cause high Na+ and water reabsorption, increasing BP, inhibting RAAS