Renin-Angiotensin-Aldosterone System

Question 1

Blood volume regulation

Answer 1

Role of RAAS

When BP falls, there is an immediate activation of sensors located in major blood vessels and the heart (baroceptors)

They increase SNS outflow to produce immediate mechanisms to raise BP

Long-term restoration of BP is determined by kidney

Question 2

How long does BP regulation by kidney take

Answer 2

24-48 hours

Question 3

Functions of the kidney

Answer 3

Regulation of pH
Removing metabolic watse products
Production of hormones (e.g. erythropoeitin)
Activation of Vit D

Regulation of osmolarity

• Regulation of salt concentrations
• Regulation of extracellular fluid volume

Question 4

How much of cardiac output does the kidney receive

Answer 4

20% of cardiac output

Question 5

What percentage of blood fluid that enters the glomerulus is filtered

Answer 5

20% of plasma

Question 6

What percentage of plasma filtered into the renal tubule is reclaimed

Answer 6

99%

Question 7

How are afferent arteriole cells specialised

Answer 7

Modified SM cells referred to as granular/juxtaglomerular cells

Responsible for hormone Renin secretion

Question 8

Renin

Answer 8

Hormone release the juxtaglomerular/glomerular cells that regulates blood pressure

Question 9

3 Stimuli for renin release

Answer 9

Decreased renal perfusion pressure - less volume traveling to kidney (detected by granular cells)

Decrease NaCl concentration (detected at the macula densa)

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

Question 10

Mechanism of Renin

Answer 10

Angiotensin Converting Enzyme (ACE) converts Angiotensin I into angiotensin II

Question 11

Where is angiotnensin II made

Answer 11

It can be made in various tissues that contain all elements to make angiotensin II locally (e.g. heart, blood vessels, perivascular fat)

Question 12

Actions of angiotensin II

Answer 12

Potent vasoconstrictor - Increases peripheral resistance and hence BP (MAIN EFFECT/PURPOSE)

Enhances sympathetic nerve function

Increases release of aldosterone (adrenal gland)

Promotes Thirst

Release vasopressin (ADH)

Trophic effects in heart and blood vessels (Sustain hypertension, cardiac hypertrophy)

Increase in oxidative stress (endothelial cell damage)

**All its roles somehow serve to increase BP

Question 13

Actions of vasopressin in CV system

Answer 13

Direct vasoconstriction

Increases number of H2O channels in the distal tubules/collecting ducts of the kidney - increases fluid retension

Hence known as Anti-Diuretic Hormone (ADH)

Question 14

Action of Aldosterone

Answer 14

Increase expression of Na+ channels in Kidney tubules

Activates Na+/K+ pump (Retain 3 Na+ ions and lose 2 K+ ions)
Results in retention/rebasorption of Na+ (and water) in body

Draws fluid out of collecting duct to keep it in the body

Question 15

What does a decrease in blood flow to the kidney lead to

Answer 15

Important stimulus for renin release

Occurs with normal variations in fluid intake but also from pathological causes
- Decrease in cardiac output - heart failure
Granular cells not stretched as much; renin release, raise BP, higher afterload so heart has to work harder - Maladaptation

• Renal stenosis or aortic stenosis (narrowing); so less blood in kidney and renin released - Renin-induced hypertension
• Hypotensive shock

Question 16

Hypotensive shock

Answer 16

BP is below autoregulatory range for maintenance of cerebral and renal perfusion so consciousness is lost as brain is not getting enough oxygen and vital organ perfusion critically impaired

Question 17

Causes of hypotensive shock

Answer 17

Low BP can be due to low cardiac output (CO) and/or peripheral vasodilatation

1. Haemorrhagic shock - blood loss, low CO
2. Cardiogenic shock - MI causing loss of myocardial power
3. Endotoxic shock - bacterial toxins cause marked peripheral vasodilatation
4. Anaphylactic shock - allergic reaction, histamine release causes vasodilatation and increased capillary permeability allowing fluid to leak and get lost

Question 18

Calculate BP

Answer 18

Cardiac Output x TPR

Question 19

Discuss the RAAS during a haemmorage that causes hypotension

Answer 19