Editing Anatomy and Physiology (section)

== Renal and Urinary System ==

The '''nephron''' is the functional unit; each kidney has about one million. Blood enters the glomerulus through the afferent arteriole and leaves through the narrower efferent arteriole, creating the hydrostatic pressure that drives filtration. Filtrate passes to the proximal convoluted tubule (where most reabsorption occurs), the loop of Henle (which concentrates urine), the distal convoluted tubule (site of aldosterone action on sodium and potassium), and the collecting duct (site of ADH action on water).

Kidney functions: excretion of nitrogenous wastes, regulation of fluid volume and electrolytes, acid-base regulation by excreting hydrogen ions and reabsorbing bicarbonate, blood pressure regulation through renin, erythropoietin production, and activation of vitamin D.

Typical adult reference values: blood urea nitrogen about 10 to 20 mg/dL, serum creatinine about 0.6 to 1.2 mg/dL. Creatinine is the more specific indicator of kidney function because blood urea nitrogen also rises with dehydration, high protein intake, and gastrointestinal bleeding.

Adequate urine output in an adult is at least 30 mL per hour.

'''Nursing application:'''
* The kidney is the long-term regulator of both blood pressure and acid-base balance, so kidney failure produces hypertension, metabolic acidosis, hyperkalemia, fluid overload, anemia, and hypocalcemia with hyperphosphatemia. Each of these follows from a function listed above.
* Urine output below 30 mL per hour is reported promptly; it signals inadequate renal perfusion.
* Nephrotoxic exposures include aminoglycosides, nonsteroidal anti-inflammatory drugs, and iodinated contrast media. Hydration and monitoring of creatinine are protective.
* The bladder holds roughly 300 to 500 mL before a strong urge to void; urinary retention with overflow incontinence is a common postoperative and post-anesthesia problem.