9. Aldosterone and the RAAS Flashcards
What type of hormones is aldosterone? Where is it released from?
mineralocorticoid
zona glomerulosa cells
What effect does aldosterone have on BP?
Increases Na+ and water reabsorption in the kidneys… increases extracellular volume… increases arterial BP
How does aldosterone increase BP?
Acts at nuclear mineralocorticoid receptors in distal tubules and collecting duct cells of kidney nephrons:
- upregulates expression of basolateral Na+/K+ pump… pumps 3 Na+ ions out of cell into interstitial fluid (and 2 K+ ions in)… promotes conc. gradient allowing Na+ and water in blood (and K+ in urine)
- upregulates expression of epithelial Na+ channels (ENaCs) in collecting duct… promotes Na+ absorption
How is aldosterone transported in the blood?
steroid hormone = lipophilic - needs carrier protein
mainly serum ALBUMIN, to lesser extent TRANSCORTIN
How is the RAAS activated?
1- decrease in plasma Na+
2- decreased kidney perfusion
3- fall in BP or loss of blood volume (e.g. haemorrhage/dehydration)… sensed by carotid sinus baroRs… increased sympathetic tone to kidney
Cause juxtaglomerular cells of kindey nephrons to release renin into general circulation.
What are the effects of renin?
cleaves angiotensinogen (constitutively released by liver) to angiotensin I
What happens to angiotensin I?
cleaved by ACE (angiotensin-converting enzyme) to angiotensin II within lung capillaries
How does AngII act to increase BP?
- potent vasoconstrictor
- stimulates adrenal cortex release of aldosterone (which acts on nephron distal tubules and collecting ducts to increase Na+ and H20 reabsorption)
- stimulate ADH release from posterior pituitary
What are the actions of ADH?
induces translocation of aquaporin water channels in PM of collecting duct cells… more water reabsorption
What are the most widely used anti-hypertensive drugs acting on RAAS?
ACE inhibitors
