Blood Pressure & Urine

[scaredpremed12345]

How is the sympathetic nervous system supposed to decreases urine output? If sympathetic system releases hormones that cause an increase in blood pressure and wouldn't that blood pressure increase cause an increase in glomerular filtration which increases urine output? Isn't this contradictory?

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[treeclimbingmonkey]

Yes you are right although one may assume that glomerular filtration rate to increase, it is important to considered one of the main functions of kidneys. Reabsorption!!! Furthermore, the release of hormones such as aldosterone (via the renin-angiotensin pathway) and ADH (from anterior pituitary) would cause the reabsorption of water and salts in the collecting duct and distal convoluted tubule which would increase the blood pressure (due to increased plasma osmolality) once the fight or flight hormone norepinephrine is released systemically. Thus, in this way urine output would decrease due to reabsorption of water and salts by the body to function in the "fight or flight" state.
Hope that helps!

AK Lectures - Autonomic Nervous System (Sympathetic and Parasympathetic)