RAAS – Glug Glug Glug…

When I teach endocrinology students our unit on the adrenal gland cortical hormones, I always post a PowerPoint slide which depicts a Wikipedia image of the renin-aldosterone-angiotensin-system (RAAS).

Renin-angiotensin-aldosterone_system
This image is licensed CC-BY-SA 3.0 by A. Rad. Accessed on 12/4/17.

Its author does an elegant job of elaborating angiotensin II’s targets and responses, which include increases in sympathetic nervous system activity, tubular Na+ reabsorption and K+ excretion and H2O retention, adrenal cortex release of aldosterone, arteriolar vasoconstriction with a concomitant increase in blood pressure, and posterior pituitary release of ADH (arginine vasopressin) leading to reabsorption of H2O by the collecting duct. Overall there is an increase in the perfusion of the juxtaglomerular apparatus (JGA), which offers the negative feedback signal to reduce renin output by the JGA.

I point out to students this elegant, multiple-organ defense of falling blood pressure: the kidney (for renin release), liver, lung, adrenal cortex, hypothalamus (for both CRH and ADH), and kidney (for elevated perfusion) is all automatic. But when I show diagrams from multiple sources, including texts, I offer this question, “What is missing from these images?” I do prompt them with a clue about loss of perspiration during  workouts, but the ‘lights don’t go on’ until I reveal a PowerPoint shape with this on it, “Glug, glug, glug” – then they smile …. because they realize that drinking fluids provides the fastest return from hypovolemia…

Be thorough. Connect the dots.


Post comes from Robert S. Rawding, Ph.D., Professor in the Department of Biology at Gannon University in Erie, PA.

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