RAAS System

Question 1

Renin-Angiotensin-Aldosterone-System (RAAS)

Answer 1

RENIN :
- enzyme that is released by renal juxtaglomerular cells in response to reduced renal perfusion

Reduced renal perfusion > RENIN released

Other Factors that stimulate Renin release:
> Hyponatraemia
> Sympathetic nerve stimulation

Renin hydrolyses conversion of ANGIOTENSINOGEN to ANGIOTENSIN I

ANGIOTENSIN I:
- converted to ANGIOTENSIN II by angiotensin-converting enzyme (ACE) in the lungs

Functions of ANGIOTENSIN II: = VASOCONSTRICTION OF VASCULAR SMOOTH MUSCLE

• increases BP > vasoconstriction of efferent arteriole of glomerulus
• increases filtration fraction (FF) to preserve GFR (FF = GFR/Plasma flow)
• stimulates THIRST (via hypothalamus)
• stimulates ALDOSTERONE and ADH release
• increases proximal tubule Na+/H+ activity

ALDOSTERONE: released by zona glomerulosa in response to

1) Angiotensin II
2) Potassium
3) ACTH

in DCT > causes RETENTION OF Na+ in exchange for K+/H+

Question 2

ALDOSTERONE

Answer 2

• Increases absorption of Na+ by renal tubules
• Increases excretion of K+ by renal tubules

= Increased Na+ and Decreased K+ in ECF
Increased Na+ > Fluid Retention > Increases Blood Pressure

Excess Aldosterone:

• Hypokalaemia > muscle weakness
• Alkalosis (exchange of Na+ for H+)
• HTN

Aldosterone Deficiency:

• Hyperkalaemia > HF
• Hyponatraemia
• Hypoglycaemia

Aldosterone is responsible for 90% of mineralocorticoid activity
Produced in bona glomerulosa (outermost layer) of adrenal gland

Question 3

RENIN

Answer 3

Secreted by juxtaglomerular cells and hydrolyses Angiotensinogen to produce Angiotensin

Factors stimulating Renin secretion:

• Decrease BP - hypotension causing reduced renal perfusion
• Decrease Na+ - hyponatraemia
• Symptomatic nerve stimulation
• Catecholamines eg adrenaline
• Erect posture

Factors reducing renin secretion: Drugs, Beta-blockers, NSAIDs