S4.2 Blood Pressure & The Kidney

Question 1

How do you calculate mean arterial BP?

Answer 1

CO (SV x HR) x TPR

Question 2

Both short and long term regulation are needed for BP control. Describe short term

Answer 2

Baroreceptor reflex, BP control for acute changes.
Nerve endings in carotid sinus + aortic arch sensitive to stretch, increased arterial pressure increases stretch, increased firing of AP detected in medulla. Decreases sympathetic outflow so reduces HR, CO and TPR (bradycardia and vasodilatation). Vice versa for low BP.

Question 3

Both short and long term regulation are needed for BP control. Describe long term

Answer 3

Interaction of neuronal and hormonal responses which control Na+ balance and therefore ECV; RAAS, sympathetic NS, ADH, prostaglandins and natriuretic peptides.

Question 4

How does RAAS control BP?

Answer 4

Angiotensin 2 acts directly on blood vessels causing vasoconstriction, and directly on kidneys to stimulate sodium reabsorption increasing blood volume and hence CO and bp.
Angiotensin 2 interacts with adrenal cortex to release aldosterone which also causes Na reabsorption

Question 5

What factors stimulate renin release?

Answer 5

Reduced NaCl delivery to distal tubule

Reduced perfusion pressure in the kidney Sympathetic stimulation to JGA

Question 7

How does the sympathetic NS control BP?

Answer 7

SNS decreases renal blood flow by causing vasoconstriction, so Na excretion is decreased and BP increases.

Question 8

How does ADH control BP?

Answer 8

ADH increases water reabsorption, increasing BP

Question 9

How does ANP control BP?

Answer 9

Only one that decreases BP.
Acts via vasodilation of AA (increases blood flow and thus GFR), and inhibits sodium reabsorption which causes natriuresis.

Question 10

Define hypertension

Answer 10

A sustained increase in blood pressure with diastolic >90 mmHg or systolic >140 mmHg.

Question 11

Identify the 4 main secondary causes of hypertension

Answer 11

Renal-vascular disease: renal artery stenosis which activates RAAS

Coarctation of the aorta

Conn’s syndrome: aldosterone-secreting adenoma causing hypertension and hypokalaemia
Cushing’s syndrome: increased cortisol, acts on aldosterone receptors, sodium and water retention

Question 12

How do prostaglandins control BP?

Answer 12

Cause vasodilation of the afferent arteriole, so GFR increases and BP increases.
Produced by RAAS and SNS.
Enhance renin release