Renin-Angiotensin-Aldosterone System Flashcards
Blood volume regulation
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
How long does BP regulation by kidney take
24-48 hours
Functions of the kidney
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
How much of cardiac output does the kidney receive
20% of cardiac output
What percentage of blood fluid that enters the glomerulus is filtered
20% of plasma
What percentage of plasma filtered into the renal tubule is reclaimed
99%
How are afferent arteriole cells specialised
Modified SM cells referred to as granular/juxtaglomerular cells
Responsible for hormone Renin secretion
Renin
Hormone release the juxtaglomerular/glomerular cells that regulates blood pressure
3 Stimuli for renin release
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)
Mechanism of Renin
Angiotensin Converting Enzyme (ACE) converts Angiotensin I into angiotensin II
Where is angiotnensin II made
It can be made in various tissues that contain all elements to make angiotensin II locally (e.g. heart, blood vessels, perivascular fat)
Actions of angiotensin II
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
Actions of vasopressin in CV system
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)
Action of Aldosterone
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
What does a decrease in blood flow to the kidney lead to
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