Plasma, Filtrate and Urine Compositions

Neural Regulation

Kidneys are richly supplied by sympathetic fibers.
Strong stimulation (exercise or hemorrhage)–afferent arterioles are constricted.
Urine output is reduced, and more blood is available for other organs.

Hormonal Regulation

Angiotensin II constricts afferents and efferents, diminishing GFR.
Atrial Natriuretic Peptide relaxes mesangial cells, increasing capillary surface area and GFR.
ANP is secreted in response to stretch of the cardiac atria.

Tubular Reabsorption and Secretion

Much of the filtrate is reabsorbed
Especially water, glucose, amino acids, and ions
Secretion helps to mange pH and rid the body of toxic and foreign substances.