Osmolality and water regulation Flashcards
Draw the RAAS system
What causes the liver to release angiotensinogen
GC
Thyroid hormones
Oestrogen
Angiotensin 2
Inflammation
Renin trigggered by
Macula densa
Hypotension
B1
Angiotensin 2 actions
Thirst
Aldosterone and ADH
Drives Na/Cl absorption
Increased SNS repsonsiveness
Direct vasoconstriction in peripheral vessels
Mesangial cell contraction
Efferent and afferent arteriole constriction
Where is aldosterone released from
zona glomerulosa of the adrenal galnd
What stimulates aldosterone secretion
Hihg potassium
AT2
ACTH
How does aldosterone act 3
◦ Increasing sodium reabsorption and potassium secretion in the principal cells of the collecting duct
‣ Increased Na/K exchange basolaterally (induces protein synthesis)
‣ Increased Na facilitated diffusion and K+ facilitated diffusion channels into the apical/luminal membrane
◦ Has effects at all exocrine glands (sweat/salivary) and gut to increase Na reabsorption
◦ K+/H+ exchange in intercalated cells (hydrogen ion secretion)
What is the main determinant of total Na reabsorption
Aldosterone
ADH comes from
Posterior pituitary
ADH release is controlled by
◦ Baroreceptors - fall in plasma volume is detected by cardiac atrial receptors which reduce their afferent firming related to the hypothalamus promoting ADH release (a 5-10% loss of blood volume is required for this to occur) —> it shifts the normal set point for ADH release so lower osmolarity is tolerated as water contributes more to blood volume
◦ Osmoreceptors - hypothalamus senses changed osmotic pressure (a rise promotes ADH secretion) - sensing 2-3% change with 280 mosm/kg as their baseline
What does ADH cause 4
◦ Increases water permeability of the collecting duct luminal membrane promoting medullary water reabsorption
‣ Inserts protein channels (via cAMP mechanism) into the luminal membrane
◦ Increases urea reabsorption in the inner medullary collecting ducts maintaining contribution of urea to high medullary osmolality
◦ Increases potassium excretion by the cortical collecting duct and sodium reabsorption
◦ At high concentrations = vasoconstrictor reducing renal blood flow and GFR
ANP or ANF is secreted from where
Stretched atria and great veins
What is the action of ANP 3
◦ Increases GFR by dilating afferent arteriole but constricting the efferent arteriole (higher filtration pressure and coefficient)
◦ Inhibits renin and aldosterone e release —> increased sodium and water rexcretion
◦ Directly inhibits sodium reabsorption in the collecting ducts
Renin half life
80 minutes
Renin is found where
◦ stored by the granular cells of the juxtaglomerular apparatus, which lies close to the glomerulus and distal tubule
What gives negative feedback to renin release
AT2
What is the rate limiting step to RAAS
renin
Half life of angiotensin 2
2 minutes
Cleaved by angiotensinases - tissue peptidases
What hormones odes the kidney not produce but have actions in the kidney
ADH
Aldosterone
ANP
PTH
Calcitonin
Triggers for sympathetic nervous system activation
hypotension, hypovolemia, descending central stimuli (emotion), hypoglycaemia
Sensors that activate the sympathetic nervous system
various baroreceptors in the carotid sinus, aorta and atria and descending input from cortex
What is the efferent supply to the SNS
sympathetic nervous system (medulla, spinal cord, sympathetic ganglia) - descneding from the rostral ventrolateral medulla via intermediolateral column of the spinal cord
◦ Adrenal glands are innervated by the greater splanchnic nerve - T5-T9
‣ Pre-ganglionic fibres project to the medulla - cholinergic fibres - T7-9
What is the nerve supplying the adrenal chramffin cells?
sympathetic nervous system (medulla, spinal cord, sympathetic ganglia) - descneding from the rostral ventrolateral medulla via intermediolateral column of the spinal cord
◦ Adrenal glands are innervated by the greater splanchnic nerve - T5-T9
‣ Pre-ganglionic fibres project to the medulla - cholinergic fibres - T7-9
What is the trigger for the RAAS system to be activated?
SNS activation due to stress, hypotension
Renal hypoperfusion
Salt depletion via juxtamedullary feedback
What is the origin of renin? Location and precurser molecule
- 37kDa enzyme synthesied in juxtaglomerular cells of the renal cortex
◦ Prorenin precurser is cleaved
◦ Renin remains in storage vesicles of JG cells
◦ Release and serum concentration the rate limiting step
Renin is synthesised in stimulation or released from storage upon stimulation?
- 37kDa enzyme synthesied in juxtaglomerular cells of the renal cortex
◦ Prorenin precurser is cleaved
◦ Renin remains in storage vesicles of JG cells
◦ Release and serum concentration the rate limiting step
What is the rate limiting step to renin production
- 37kDa enzyme synthesied in juxtaglomerular cells of the renal cortex
◦ Prorenin precurser is cleaved
◦ Renin remains in storage vesicles of JG cells
◦ Release and serum concentration the rate limiting step
Where does angiotensinogen come from? What happens once it is metabolised?
◦ Large protein
◦ Majority cleaved to create angiotensin 1
◦ byproduct appears useless
What is angiotensin 1? What action does it have? What is it metabolised by?
- Angiotensin 1 - inert decapeptide
◦ Minimal physiological activity - stimulates catecholamine release when in high concentration
◦ Metabolised by ACE
ACE enzyme is where? What does it do?
◦ Angiotensin 1 breakdown to angiotensin 2
◦ Bradykinin metabolism
◦ In lung tissue or on endothelia in general
What type fo molecule is angiotensin 2
Octapeptide
Describe the half life of angiotensin 2? Where is it metabolised?
◦ Short lived molecule degraded rapidly by endothelial angiotensinases with a half life of 30 seconds
How does systemic hypotension activate the RAAS system?
- Baroreceptor response to low BP stimulate sympathetic nervous system –> beta 1 receptor stimulation on JG cells –> renin release (both ciruclating and direct stimulation)
◦ Then, via increasing intracellular cAMP, protein kinase A mediates the degranulation of renin-containing cells. In fact, anything that ends up increasing cAMP (prostaglandin I2 and E2, milrinone, theophylline) will also produce this effect
How does renal hypoperfusion translate to RAAS system activation?
- Renal perfusion pressure related - unclear mechanism/potentially JG cells - MAP of 85 the threshold for renin release
What is the pressure threshold for renin release
- Renal perfusion pressure related - unclear mechanism/potentially JG cells - MAP of 85 the threshold for renin release
Describe how salt depletion leads to renin release
- Decreased salt intake produces the release of renin
* The macula densa is implicated with juxtaglomerular cells releasing renin
What are the 6 actions of angiotensin 2
◦ Actions
‣ Potent vasoconstrictor - binds to Gq PCR facilitating IP3 mediated increase in IC calcium and vasoconstriction
* 2x as potent as noradrenaline
‣ Increased sensitivity to catecholamines
‣ Stimulating the release of vasopressin
‣ Stimulating the release of aldosterone
‣ Increased Na+/H+ exchange in the proximal tubules, thus sodium retention and acid excretion
‣ Increased sensation of thirst
◦ Summary actions
‣ Increase BV via water and sodium retention
‣ Increased acid excretion
‣ Increase blood pressure via increased PVR