Renin-angiotensin-aldosterone system

Question 1

What is the renin-angiotensin-aldosterone system (RAAS)?

Answer 1

Hormone system that controls blood presssure and fluid/electrolyte balance

Comprises of 3 hormones : renin, angiotensin II, aldosterone

Primarily regulated by renal blood flow

Question 2

What are the functions of the kidneys?

Answer 2

Regulation of blood pH /osmolarity/ion conc/extracellular fluid volume
Removing metabolic waste products from the blood
Produce hormone such as EPO
Activation of vit D

Question 3

How much of the blood plasma gets filtered at the glomerulus ?

Answer 3

20%

The remaining 80% leave via the efferent arteriole unfiltered

Question 4

What are the stimuli for renin release?

Answer 4

Decreased blood flow to kidneys (detected by granular cells in the afferent and efferent arterioles) due to CHF and renal/aortic stenosis

Decreased NaCl conc (detected at macula densa - collection of specialized epithelial cells in the distal convoluted tubule)

Increased sympathetic nerve activity (via activation of beta-1 adrenoceptors)

Question 5

Describe the action of renin

Answer 5

Enzyme that converts angiotensin (plasma protein made by liver) into angiotensin 1

Question 6

Action of angiotensin converting enzyme (ACE)

Answer 6

Converts angiotensin I to angiotensin II

Some tissue can make angiotensin II without needing ACE (e.g heart, blood vessel, perivascular fat)

Question 7

Function of angiotensin II

Answer 7

Potent vasoconstrictor - increases BP 
Enhances sympathetic nerve fucntion 
Increases release of aldosterone 
Promotes thirst 
Release ADH 
Sustains hypertension and cardiac hypertrophy 
Increase in endothelial cell damage

Question 8

Function of aldosterone

Answer 8

Increases expression of Na+ channels
Activates Na+/K+ Pump
Retention of Na and water in body

Question 9

What is hypotension shock? Causes

Answer 9

When blood pressure falls below auto regulatory range for maintenance of cerebral and renal perfusion
Consciousness is lost and vital organ perfusion is critically impaired

Causes - haemorrhagic shock, cardio genie shock (MI), endotoxin shock (bacterial infection), anaphylactic shock

Question 10

Plasma potassium and RAAS

Answer 10

Hypokalaemia is a typical symptom of overactivation of the RAAS