volume regulation: blood pressure and the kidneys Flashcards
how is blood volume link to blood pressure ?
how is ECF volume sensed ?
describe RAAS
what is RAAS activated by ?
Reduced renal perfusion
Increased sympathetic activity
Both interpreted as a fall in blood volume
how is aldosterone secretion increased ?
RAAS
Increased plasma [K+]
how is renal Na excretion controlled ?
- Most filtered salt and water are reabsorbed in the proximal tubule (PT), with reabsorption increasing under RAAS activity.
- A smaller, variable fraction is reabsorbed in the distal tubule (DT) and collecting duct (CD).
- Na reabsorption and solute-free water reabsorption are regulated separately.
- Aldosterone increases Na reabsorption, raising plasma osmolarity, which is later adjusted by ADH-mediated water reabsorption.
- Although aldosterone regulates only a small fraction of Na reabsorption, minor adjustments can significantly impact total body Na levels.
what is the effect of aldosterone ?
Aldosterone effects on principal cells of the collecting duct (CD):
* Increases Na/K ATPase activity.
* Increases ENaC channel expression on the luminal membrane.
Leads to:
* Increased Na⁺ reabsorption.
* Increased K⁺ secretion.
* Can reduce urine Na⁺ concentration to as low as 1 mEq/L, making urine Na⁺ a key marker of volume status.
* Urine Na⁺ < 20 mEq/L suggests effective volume depletion (Faubel & Topf).
Effects of excess aldosterone:
* Hypokalemia (due to increased K⁺ secretion).
* Metabolic alkalosis (due to extra HCO₃⁻ production).
No significant hypernatremia:
* Volume expansion leads to water reabsorption.
* Pressure natriuresis counteracts Na⁺ retention in hypertension.
* Aldosterone effects on intercalated cells of CD:
* Increases H⁺ ATPase activity.
Leads to:
* Increased H⁺ secretion.
* Increased HCO₃⁻ reabsorption.
what is pressure natriuresis ?
If BP rises so does renal artery pressure
Kidney responds by increasing Na excretion
↓ ECFV
what is Liddle syndrome ?
Rare, genetic gain-of-function mutation in epithelial sodium channel (ENaC)
↑ renal Na retention
↑ECVF
↑ BP
Low renin
Low aldosterone
what is conns syndrome ?
Primary hyperaldosteronism
Often due to adenoma of adrenal cortex
↑ renal Na retention
↑ECVF
↑ BP
↓ plasma [K]
Low renin
High aldosterone
what is renal artery stenosis ?
Abnormal narrowing of the blood vessel
Reduced blood flow to stenotic kidney
Increased renin
what is Addison’s disease ?
Progressive failure of adrenal cortex
Insufficient cortisol
Insufficient aldosterone
Eventually adrenal crisis – fatal if not treated
Lack of cortisol and aldosterone
Hypotension
Hypovolemia
Hyperkalemia
Hyponatremia
