Lecture 8 - Blood pressure in the kidney

Question 1

How does hypotension affect the kidney

Answer 1

1. Reduced blood flow to the kidney detected by low pressure baroreceptors
2. Interpreted as a reduction in ECF
3. The macula densa cells release prostaglandins which cause the afferent arteriole to dilate (tubuloglomerular feedback system).
4. More Na+ , Cl- and water is retained via RAAS and the myogenic response.
5. Increase renal blood flow

Question 2

Main responses to hypotension in the kidney

Answer 2

RAAS
Sympathetic NS
Prostaglandins
ADH

Question 3

RAAS

Answer 3

1. Liver produces angiotensinogen which is converted to angiotensin I by renin which is produced by the granular cells of the kidney and released in response to hypotension.
2. Ang I is converted to ang II by the angiotensin converting enzyme (ACE) in lungs.
3. Ang II acts on the adrenal gland to release aldosterone (steroid hormone)
4. Aldosterone acts on the collecting ducts to retain water, increasing BP.

Question 4

ACE inhibitors

Answer 4

Inhibits ACE therefore less angiotensin I is converted to angiotensin II

Can cause dry cough due to bradykinin accumulation

Question 5

Statins

Answer 5

Inhibit the effects of angiotensin II so less aldosterone is produced.

Question 6

Spironolactone

Answer 6

Inhibits the effect of aldosterone in DCT

Inhibits ROMK in PCT

Question 7

Sympathetic NS control of hypotension

Answer 7

Hypotension detected by baroreceptors

• Beta 1 adrenergic nerve stimulates renin release which stimulates RAAS. (slow)
• Decreased SAN threshold therefore increased HR
• Increased myocardial contractility which increases stroke volume
• Vasoconstriction which increases TPR

Question 8

Aldosterone

Answer 8

Produced by the zona glomerulosa of the adrenal gland
Steroid hormone

1. In the DCT, aldosterone stimulates the Na+/K+ pump in the principal cells.
2. More Na+ is reabsorbed and thus water is reabsorbed too
3. More K+ is secreted therefore there is a risk of hypokalaemia.

Question 9

Conditions that reduce perfusion pressure with ECF volume intact

Answer 9

Heart failure
Liver cirrhosis
Nephrotic syndrome
Renal artery stenosis

Question 10

Renal response to hypertension

Answer 10

1. Increased kidney perfusion
2. Decrease in aldosterone secretion and ANP released.
3. Decrease in ECF volume
4. Decreased BP

Question 11

Oedema

Answer 11

Excessive secretion of fluid in the interstitium.

Can be caused by excess salt and water retention by the kidney

Question 12

Secondary hypertension

Answer 12

Renal artery stenosis
Coarctation of the aorta
Primary hyperaldosteronism (Conn’s syndrome)
Cushing’s syndrome

Question 13

3 mechanisms that releases renin from the kidney

Answer 13

1. Direct sympathetic stimulation of the JGA
2. Reduced renal blood flow detected by baroreceptors in the JGA
3. Reduced NaCl to the macula densa cells

Question 14

Angiotensin II

Answer 14

Increases synpathetic activity
Increases reabsorption of Na+ and water retention
Stimulates the adrenal glands to release aldosterone from the zona glomerulosa
Arterioriole vasoconstriction - increase TPR
Increases the secretion of ADH from the pituitary gland posterior lobe

Question 15

What does aldosterone stimulate?

Answer 15

DCT:

• Upregulation of Na+/K+ pump on the basolateral membrane
• Upregulates Na/Cl cotransporter
• Stimulates secretion of K+ into the tubule

Collecting duct::

• Upregulates Na+ channels in the collecting duct and colon
• Stimulates H+ secretion in the collecting duct

Question 16

What stimulates ADH release?

Answer 16

Angiotensin II

Blood osmotic pressure increases

Question 17

ADH

Answer 17

Antidiuretic hormone (vasopressin)
Increases expression of aquaporin channels in the collecting duct 
More water is reabsorbed

Question 18

Sepsis and oedema

Answer 18

Dysregulated immune response to an infection that causes damage to the host.

Leaky capillaries - decrease in blood pressure as more fluid lost to the interstitium

Triggers compensatory mechanisms, water and sodium retention which increases ECF and BP

Still leaky so more leaks - oedematous

Question 19

BP and natriuresis

Answer 19

As BP increases sodium excretion increases and more water is excreted.

If hypertensive for a long time, a new set point is made and a higher blood pressure is required to excrete the same amount of sodium.

Question 20

Renal artery stenosis

Answer 20

1. Reduced renal perfusion perceived as low ECF and hypotension
2. Less Na+ and Cl- delivery to the DCT which is detected by the macula densa cells
3. Release prostaglandins which causes afferent arteriole dilation

4, Increased sympathetic activity stimulates RAAS