S4) Blood Pressure and The Kidney

Question 1

What is the formula for calculating blood pressure?

Answer 1

mean arterial BP = CO x TPR

Question 2

What is the formula for calculating cardiac output?

Answer 2

CO = SV x HR

Question 3

Explain the 2 actions which allow for the short term regulation of blood pressure

Answer 3

Baro-receptor reflex:

• Adjust sympathetic and parasympathetic inputs to the heart to alter CO
• Adjust sympathetic input to blood vessels to alter TPR

Question 4

Describe the long term regulation of blood pressure

Answer 4

Neurohormonal response to affect salt and water balance

Question 5

Identify 4 processes which act on the kidney to regulate blood pressure

Answer 5

• Renin-angiotensin-aldosterone system
• Sympathetic nervous system
• Prostaglandins
• ADH

Question 6

Describe the events which occur in RAAS

Answer 6

Question 7

Identify 3 factors which stimulate renin release from the JGA cells in the kidney

Answer 7

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

Question 8

What are the direct effects of Angiotensin II on the kidney?

Answer 8

• Vasoconstriction of efferent arteriole (AA > EA)
• Enhances Na⁺ reabsorption at the PCT (stimulates Na-H exchanger in apical membrane)

Question 9

Angiotensin II stimulates aldosterone release from the adrenal cortex.

Identify 2 of its actions on the kidney

Answer 9

Acts on principal cells of collecting duct:

• Stimulate Na⁺ and water reabsorption by increasing expression of the apical Na⁺ channel (ENaC)
• Increases basolateral Na+ extrusion via Na/K/ATPase

Question 10

How does the sympathetic nervous system act on the kidney?

Answer 10

• Reduce renal blood flow (vasoconstriction of renal artery)
• Stimulates Na⁺ reabsorption (NHE3 & Na/K ATPase) in PCT
• Stimulates renin release from JGA

Question 11

In normal situations, prostaglandins have little effect.

Regardless, how does it act in RAAS?

Answer 11

• Vasodilates the afferent arteriole
• Enhances renin release

Question 12

What stimulates the release of prostaglandins?

Answer 12

Release stimulated by vasoconstrictors:

• Angiotensin II
• Noradrenaline
• ADH

Question 13

Prostaglandins and RAAS interact to stimulate each other.

What is the net effect of both of these substances?

Answer 13

• Systemic vasoconstriction
• Vasoconstriction of the efferent arteriole
• Vasodilation of afferent arteriole
• Preservation of GFR

Question 14

What is the main role of ADH?

Answer 14

• Increases water reabsorption in distal nephron (AQP2) in order to control plasma osmolarity through water retention
• Concentrated urine formed

Question 15

What stimulates the release of ADH?

Answer 15

• Plasma osmolarity
• Severe hypovolaemia

Question 16

ADH is also called arginine vasopressin.

Why is this?

Answer 16

ADH also causes vasoconstriction

Question 17

Atrial Natriuretic Peptide acts in the opposite direction of other neurohormonal regulators.

What are its 2 main actions?

Answer 17

• Causes vasodilation of afferent arteriole, increasing GFR
• Inhibits Na⁺ reabsorption especially in collecting duct, causing natriuresis

Question 18

What stimulates the release of ANP and what inhibits its release?

Answer 18

• Low circulating blood volume = inhibits ANP release
• High circulating blood volume = stimulates ANP release

Question 19

In terms of evolution, why is hypertension an anticipated problem?

Answer 19

• Mechanisms which increase/maintain BP are stronger than the mechanisms which reduce BP when it is too high
• Hence, volume depletion (dehydration or blood loss or sepsis) is more of a risk than hypertension

Question 20

What is hypertension?

Answer 20

Hypertension is a persistent increase in blood pressure

Question 21

Identify 2 pathological processes involving RAAS

Answer 21

• Secondary hypertension
• Secondary hyperaldosteronism (oedema)

Question 22

Identify 4 clinical conditions resulting in secondary hypertension

Answer 22

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

Question 23

Describe the pathophysiology of renovascular disease

Answer 23

• Renal artery stenosis
• 1/both kidneys affected
• Due to atheroma (75%) or fibromuscular dysplasia (25%)

Question 24

Identify 5 endocrine causes of hypertension

Answer 24

• Primary hyperaldosteronism (Conn’s syndrome)
• Cushing’s syndrome
• Liquorice
• Phaeochromocytoma
• Hyperthyroidism / Hypothyroidism

Question 25

What is apparent mineralocorticoid excess syndrome?

Answer 25

AME is a condition resulting in an excess amount of aldosterone and cortisol in the distal nephron of the kidney due to excessive liquorice ingestion

Question 26

What is oedema?

Answer 26

Oedema is the accumulation of excessive salt/water in the interstitium

Question 27

Identify 5 causes of generalised oedema

Answer 27

• Heart failure
• Chronic kidney disease
• Nephrotic disease
• Liver disease
• Pregnancy

Question 28

What is Chronic Kidney Disease?

Answer 28

• CKD is a condition leading to the inability to excrete excess salt and water due to reduced kidney function (↓ GFR)
• It results in hypertension and oedema

Question 29

Which 2 underlying processes lead to Nephrotic syndrome?

Answer 29

• Reduced oncotic pressure causing reduced perfusion pressure and activation of RAAS / SNS / ADH
• Alterations in sodium and water excretion due to reduced kidney function (hypertension & reduced GFR)

Question 30

Identify 3 symptoms of Nephrotic Syndrome

Answer 30

• Proteinuria > 350 mg/mmol (>3.5 g / 24 hr)
• Hypoalbuminaemia
• Oedema