Regulation of Renal Function

By far, the most difficult aspect of renal physiology for students (and authors alike) is regulation of renal function. Neural signals, hormonal signals, and intrarenal chemical messengers combine to regulate the basic renal processes presented previously in a manner to help the kidneys meet the needs of the body. Unfortunately, our collective knowledge on much of this is, as yet, incomplete. Of necessity, much of the coverage in this textbook will attempt to draw an overview of renal function without an emphasis on nuance and detail that is more appropriate for advanced texts.
As with many organs, signals regulating the kidney arise from both neural and hormonal input. Neural signals originate in the sympathetic celiac plexus. Sympathetic signals exert major control over renal blood flow, glomerular filtration, and the release of vasoactive substances (the renin-angiotensin system, described later). Hormonal signals originate in the adrenal gland, pituitary gland, and heart. The adrenal cortex secretes the steroid hormones aldosterone and cortisol, and the adrenal medulla secretes the catecholamines epinephrine and norepinephrine. All of these hormones, but mainly aldosterone, are regulators of sodium and potassium excretion by the kidney. The pituitary gland secretes the hormone arginine vasopressin (also called ADH). ADH is a major regulator of water excretion, and via its influence on the renal vasculature and possible collecting-duct principal cells, probably sodium excretion as well. The heart secretes hormones, natriuretic peptides, that contribute to signaling increased excretion of sodium by the kidneys. The most difficult aspect of regulation lies in the realm of intrarenal chemical messengers (ie, messengers that originate in one part of the kidney and act in another part). It is clear that an array of substances (eg, nitric oxide, purinergic agonists, superoxide, various eicosanoids) influence basic renal processes, but, for the most part, the role of these substances is beyond the scope of this text.