Aldosterone: Regulating Nephron Activity Vincent Li

Basic Information• Steroid hormone secreted by the adrenal glands

(that sit atop the kidneys)• Acts on the distal tubules and collecting ducts of

nephrons, making them reabsorb more Na+ and water

Control & Homeostasis • Renin-angiotensin-aldosterone system (RAAS)• A drop in blood pressure or volume in the afferent

arteriole of the nephron causes the juxtaglomerular apparatus to release renin, an enzyme that initiates a chain of chemical reactions that ultimately yield a peptide called angiotensin II.

• Angiotensin II stimulates adrenal glands to release aldosterone, which causes distal tubules and collecting ducts to reabsorb more water and Na+, which increases blood pressure and volume.

Hyper-secretion and Hypo-secretion• Hyper-secretion of aldosterone can be caused by Bartter

Syndrome (defect in kidney’s ability to reabsorb sodium), a benign tumor nodule in the adrenal gland, or a low-sodium diet.

• Hyper-secretion can result in loss of too much potassium from the body, as aldosterone also functions in potassium reabsorption.

• Hypo-secretion of aldosterone can be caused by Addison’s Disease (damage to adrenal cortex from infections like tuberculosis or HIV, hemorrhage, or tumors reduce hormone release) or a high-sodium diet.

• Aldosterone also functions in maintaining blood pH by forcing H+ ions into urine. Hypo-secretion will decrease this effect and cause the blood to become more acidic.

Analogy• Take a colander (interior represents inside of the

nephron tubule). The holes represent the pores of the aquaporins lining the tubule of a nephron. Aldosterone makes the aquaporins more permeable to water and sodium ions – think of the holes of the colander getting larger to let more water leave.

Works Cited• "Addison's Disease: MedlinePlus Medical Encyclopedia." U.S

National Library of Medicine. U.S. National Library of Medicine. Web. 09 Feb. 2014. <http://www.nlm.nih.gov/medlineplus/ency/article/000378.htm>.

• "Aldosterone Blood Test: MedlinePlus Medical Encyclopedia." U.S National Library of Medicine. U.S. National Library of Medicine. Web. 11 Feb. 2014. <http://www.nlm.nih.gov/medlineplus/ency/article/003704.htm>.

• "Aldosterone." WebMD. WebMD, 10 July 2010. Web. 11 Feb. 2014. <http://www.webmd.com/a-to-z-guides/aldosterone>.

• "Bartter Syndrome: MedlinePlus Medical Encyclopedia." U.S National Library of Medicine. U.S. National Library of Medicine. Web. 11 Feb. 2014. <http://www.nlm.nih.gov/medlineplus/ency/article/000308.htm>.