renal hormones Flashcards
Describe the renin angiotensin system
- Renin cleaves angiotensinogen/renin substrate
- Angiotensin I (decapeptide) is acted on by ACE into
-
Angiotensin II, which binds
- AT1 receptors: does most of the work
- AT2 receptors: works most during fetal development
What activates the renin-angiotensin system?
What suppresses it?
- Activated by:
- Extracellular fluid volume depletion –> decreased arterial pressure
- Sodium depletion
- Stress/trauma
- Inhibited by:
- Extracellular fluid volume expansion
- Sodium repletion
The roles of the RAS system
Conservation of extracellular fluid volume
Maintenance of extracellular fluid volume
Maintenance of arterial blood pressure
Where is renin synthesized?
Juxtaglomerular cells (modified smooth muscle cells) lining the terminal portion of afferent arteriole.
Path of renin after synthesis
After synthesis by juxtaglomerular cells in teh afferent arteriole,
- 1/2 goes through the glomerulus and out the renal vein into general circulation where it does its work (lots of ACE in lung)
- 1/2 gets released into the kidney’s interstitial environment, where it will work on the angiotensinogen from proximal tubule
Where is the of ACE outside of the kidney?
Where is it inside the kidney?
Outside the kidney, most ACE is in the lungs
Inside the kidney, ACE is on the basolateral side of the proximal tubule cells
What is the rate limiting step for activation of the RAS system?
The amount of renin synthesized by the JG cells
To stimulate JG cells to release renin, either ___ has to decrease or ___ has to increase.
Cytosolic Ca2+ decreases
cAMP increases
Baroreceptor mechanism of regulating renin secretion
- Increased mean arterial pressure will activate stretch receptors on the JG cell membrane.
- Opens Ca2+ channels on the membrane so Ca2+ enters the JG cells.
- Increased [Ca2+]JG cells suppresses renin secretion
Thus, low mean arterial pressure would increase renin secretion.
Sympathetic system of regulating renin
- Increased sympathetics –> norepinephrine
- Norepinephrine will bind B1 receptors on JG cells to increase [cAMP]
- cAMP increases renin secretion
Macula densa mechanism of regulating renin secretion
- Increased NaCl delivery to the macula densa
- Macula densa releases Prostaglandin E2
- PGE2 inhibits renin secretion from JG cells.
Which would increase renin secretion (click all that apply)?
- Increased Ca++ conc in the JG cells
- Increased NaCl delivery to the macula densa
- Increased activity of the sympathetic nervous sytem
- Decreased cAMP in the JG cells
Increased sympathetics
Major actions of angiotensin II
-
Kidney.
- Reduce RBF
- Increase absolute reabsorption.
- Adrenal. Aldosterone
- Vascular. Vasoconstrictor
- Heart. Increased contractility
- Intestine. NaCl & H2O reabsorption
-
CNS.
- Thirst & salty appetite
- ADH release
- Sympathetics
- PNS. Adrenergic transmission (release more norepinephrine from sympathetics)
Whe macula densa NaCl delivery goes up, renin secretion goes __
down
Angiotensin II on the kidney (3)
- *Vasoconstrictor of the efferent arteriole –> decreases renal blood flow & maintains GFR*
-
Decreases Kf(reduces GFR a lil)
- Contraction of the intraglomerular mesangial cells reduces the surface area for filtration.
- Decreases proximal & distal tubule NaCl & H2O reabsorption