RAAS Flashcards
What does RAAS stand for
Renin-Angiotensin-Aldosterone System
What is the role of RAAS
Essential for regulation of blood pressure and fluid balance
What are the hormones of the RAAS system
Renin
Angiotensin II
Aldosterone
What is RAAS primarily regulated by
Renal blood flow
What is the first stage of RAAS
Renin release
Where is renin released
Granular cells of the juxtaglomerular apparatus (JGA)
What are the 3 factors which result in the release of renin
- reduced sodium delivery to the distal convoluted tubules
- reduced perfusion pressure in the kidney
- sympathetic stimulation of juxtaglomerular apparatus
How is reduced sodium delivery to the distal convoluted tubules detected
By macula densa cells
How is reduced perfusion pressure in the kidney detected
By baroreceptors in the afferent arteriole
How is sympathetic stimulation of juxtaglomerular apparatus completed
Via B1 adrenoreceptors
What is the release of renin inhibited by
Atrial natriuretic peptide
When is ANP released
Stretch in the atria in response to increased blood pressure
What is angiotensinogen
Precursor protein produced in the liver
How is angiotensin I formed
Angiotensinogen cleaved by renin
How is angiotensin II formed
Angiotensin I converted by angiotensin converting enzyme (ACE)
Mainly occurs in the lungs where ACE is produced by vascular endothelial cells
How does angiotensin II exert its action
By binding to various receptors throughout the body
What receptors does angiotensin II bind to
One of two G-protein coupled receptors
AT1 and AT2 receptors
Where does most angiotensin II bind to
AT1 receptor
In the adrenal cortex what is the action of angiotensin II
Stimulates release of aldosterone
In the hypothalamus what is the action of angiotensin II
Increase thirst sensation
- increase fluid consumption
- raises circulating volume = increase BP
Stimulates anti-diuretic hormone (ADH) release ( posterior pituitary gland)
- production of more concentrated urine
- reduce loss of fluid
In the kidney what is the main action of angiotensin II
Stimulates NA+ reabsorption
In the arterioles what is the main action of angiotensin II
Vasoconstriction
In the sympathetic nervous system what is the main action of angiotensin II
Increased release of noradrenaline (fight or flight)
- increase cardiac output
- vasoconstriction of arterioles
- release of renin
What are the areas of the kidney that angiotensin II targets
Renal artery and afferent arteriole
Efferent arteriole
Mesangial cells
Proximal convoluted tubule
Describe the affect of angiotensin II on the renal artery and afferent arteriole
Vasoconstriction
Describe the affect of angiotensin II on the efferent arteriole
Vasoconstriction (greater than the afferent arteriole)
Describe the affect of angiotensin II on the mesangial cells
Contraction, leading to a decreased filtration rate
Describe the affect of angiotensin II on the proximal convoluted tubule
Increased Na+ reabsorption
What does angiotensin also play an important role in
Tubuloglomerular feedback
Helps maintain a stable GFR
What does angiotensin II act on to stimulate the release of aldosterone
Adrenal cortex
Describe aldosterone
Mineralocorticoid
Steroid hormone released from the zona glomerulosa of the adrenal cortex
What does aldosterone act on
Principal cells of the collecting ducts in the nephron
What is the action of aldosterone
Increases expression of apical epithelial Na+ channels to reabsorb urinary sodium
What can aldosterone cause
Increased levels can cause reduced levels of potassium in blood due to increased activity of sodium/potassium pump
What is ADH also known as
Vasopressin
What is ADH secreted by
Posterior pituitary gland
What controls the release of ADH
Changes in plasma osmotic pressure and volume status
Other factors
- exercise
- angiotensin II
- emotional state e.g. pain
What is ADH release inhibited by
ANP
ADH
What would a fall in plasma volume cause
Would be an increase in plasma sodium concentration = increase in osmolarity
Water moves down its concentration gradient into the plasma
Stimulates osmoreceptors to control
Increases release of ADH
ADH
What would an increase in plasma volume cause
Reduce plasma osmolarity
Osmoreceptors cells would expand - water moves down its concentration gradient out of the plasma
Decrease release of ADH
Where are signals for ADH sent
Afferent signals from hypothalamus to posterior pituitary
Where does ADH act
Distal convoluted tubule
Collecting ducts
How does ADH act
Increased plasma osmolarity
Through G-protein coupled receptors to increase insertion of Aquaporin-2 channels to the apical membrane of the DCT and CD cells
Describe ACEi (inhibitors)
Inhibit action of angiotensin converting enzyme so reduce levels of angiotensin II in the body
- decreased arteriolar resistance
- decreased arteriolar vasoconstriction
- decreased cardiac output
- reduces potassium excretion in the kidneys
