Blood Pressure and the Kidney Flashcards
How is blood pressure regulated short term?
Baroreceptor reflex - adjust sympathetic and parasympathetic inputs to the heart to alter cardiac output and adjust sympathetic input to peripheral resistance vessels to alter TPR
How is blood pressure regulated in the long term?
Neurohormonal response to affect salt and water balance
What factors stimulate renin release?
1) Reduced NaCl delivery to distal tubule
2) Reduce perfusion pressure in the kidney (detected by baroreceptors in afferent arteriole)
3) Sympathetic stimulation to JGA
What cells release renin?
Granular cells of juxtaglomerular apparatus
What cells detect decreased NaCl delivery?
Macula densa cells
Outline the RAAS
Decreased renal perfusion stimulates the release of renin which cleaves angiotensinogen to angiotensin I.
ACE from lungs cleaves angiotensin I into angiotensin II
Angiotensin II stimulates release of aldosterone secretion from adrenal gland
Angiotensin II increases tubular NaCl reabsoprtion, increases sympathetic activity and causes arteriolar vasoconstriction
What are the actions of angiotensin II on the kidney?
1) Vasoconstriction of afferent and efferent arterioles (efferent>afferent)
2) Enhances Na+ reabsorption at the PCT by stimulating NHE on the apical membrane
3) Causes release of aldosterone
What are the actions of aldosterone?
Acts on the principal cells of the collecting ducts
Stimulates Na+ and therefore water reabsorption
Activates apical ENaC channel and K+ channels
Increases basolateral Na+ extrusion via Na+K+ATPase
How does aldosterone lead to increased water retention?
Increases expression of ENaC and Na+K+ATPase in the principal cells of the collecting duct
What do high levels of sympathetic stimulation do to renal blood flow?
Reduces renal flow
- Vasoconstriction of arterioles
- Decreases GFR
What does the sympathetic nervous system do to the apical NHE in PCT?
Activates it
What effect do prostaglandins have on renal arterioles?
Vasodilation of the afferent arteriole (not efferent)
What is the main role of ADH?
Formation of concentrated urine by retaining water to control plasma osmolarity
What stimulates ADH release?
Increases in plasma osmolarity or severe hypovolaemia
What are the 2 major actions of ANP?
1) Causes vasodilation (systemic circulation and afferent arteriole - increases GFR)
2) Inhibits Na+ reabsorption especially in collecting duct causing natriuresis
If there is renal artery stenosis, what happens to the levels of renin released?
They increase as there is reduced renal blood flow
How can renal artery stenosis lead to hypertension?
Reduced blood flow to kidney -> increased renin -> increased angiotensin II -> vasoconstriction (increased TPR means raised BP) -> increased aldosterone means increased blood volume
In primary aldosteronism, how would the levels of renin compare to the levels of aldosterone?
Renin wouldn’t increase
Aldosterone levels high
