L6: ECF 1 Flashcards
Na+ regulation responds primarily to changes in ***.
Blood volume, driven mainly by changes in blood pressure
What is the primary effector for Na+ regulation?
Renin-angiotensin-aldosterone system (RAAS)
When is RAAS activity increased?
When blood pressure decreases
Water regulation is responsive to changes in ** and **.
Osmolarity and volume of ECF
What does aldosterone do?
Stimulates Na+ reabsorption in the late distal tubule and collecting duct. Also stimulates K+ secretion.
-Na retention entails loss of K
What two things stimulate aldosterone release?
Increases in angiotensin II or plasma K+
What kind of receptor does aldosterone bind to?
Mineralcorticoid receptors in principal cells
What does the Aldo-MR complex stimulate?
Transcription resulting in up-regulation of epically ENaCs, apical K+ channels, Na+/K+ ATPase, mitochondrial metabolism, and H+ ATPase
What is aldosterone antagonized by?
Spironolactone
What is the primary control of aldosterone secretion?
Plasma AT II concentration
What does ATII do? (5)
1) Powerful vasoconstrictor
2) stimulates release of aldosterone
3) stimulates Na+/H+ exchange in the proximal nephron
4) stimulates thirst
5) increases salt retention and elevates arterial blood pressure
How do low levels of AT II affect GFR?
Low levels causes primarily vasoconstriction of the efferent arterioles. GFR is maintained or maybe increased
How do high levels of AT II affect GFR?
high levels have increased effects on afferent arterioles, which reduces glomerular filtration coefficient (Kf) at mesangial cells, and greatly reduces RBF. GFR decreases
What does AT II stimulate production of?
PGE2 and PGI2
What controls Angiotensin II levels?
Renin
What are the 3 components of renin release by the JGA?
1) intrarenal baroreceptors
2) macula dense
3) renal sympathetic nerves
How do intrarenal baroreceptors affect renin release?
Granular cells of the JGA respond to pressure in afferent arterioles. Renin release is inversely released to pressure in afferent arterioles.
How does the macula densa affect renin release?
Macula densa senses flow to distal tubule, renin is inversely related to GFR
How do renal sympathetic nerves affect renin release?
Stimulation of renal sympathetic nerves increase renin release via stimulation of B receptors
What converts angiotesinogen to angiotensin I?
Renin
What converts AT I to ATII?
Angiotensin Converting Enzyme (ACE)
What releases ANP and when?
The atria when pressures are high
What does ANP do?
- Increases GFR and the filtered load of NaCl (afferent arteriole becomes dilated and efferent becomes constricted)
- Decreases NaCl reabsorption by the collecting duct (directly inhibits secretion of renin and aldosterone, directly inhibits Na+ uptake by the medullary CD)
What is the most important hormone in regulating water balance?
ADH
Where is ADH released from and when?
From the pituitary when plasma osmolarity increases or plasma volume decreases
Does ADH affect NaCl excretion?
Not really
How does ADH restore hypovolemia?
- Increases CD permeability to water (water will leave CD to be reabsorbed)
- increases NKCC2 transporters in the LOH (increased gradient)
- increases permeability of inner medullary CD to urea
Where does aldosterone come from?
The adrenal cortex
What is normal body osmolarity?
290 mOsm/L
How does the body try to correct for a drop in plasma volume?
By increasing ADH to restore hypovolemia
What is osmolar clearance?
Th ml/min of blood plasma that is cleared of osmotically active particles
** calculated with clearance equation Cosm= Uosm(V)/Posm
What is normal Cosm?
1-2 mL/min
What does a reduced Cosm mean?
- there is a positive osmolar balance because it is not being cleared out (progression towards edema)
- May be caused by decreased GFR and increased aldosterone
What does an increased Cosm mean?
- There is “dumping” of osmolytes leading to a loss of ECF
- Diuretics, reduced aldosterone or any disease that reduces the ability of the kidney to reabsorb normally may cause this
