Function Rid body of nitrogenous wastes Regulate water, electrolyte, and acid-base balance of blood

Kidneys Not actually located in lower back  more central in the torso, extend from T 12 to L 3 vertebra Right kidney is lower than left due to being crowded by the liver A renal capsule encloses each kidney, giving them a glistening appearance when fresh Adipose capsule – surrounds each kidney and helps hold it in place against the muscles of the trunk wall

Kidneys Renal cortex – lighter, outer region Renal medulla – darker, central region Renal pyramid – triangular sections of renal medulla, separated by renal columns Calyces – cup shaped areas that collect urine, which drains into the renal pelvis, then to the ureter, which leads to the bladder

Nephrons Over a million in each kidney Two main structures: a glomerulus, which is a knot of capillaries, and a renal tubule Bowman’s capsule = cup-shaped end of renal tubule that surrounds glomerulus

Nephrons Glomerulus forms filtrate, essentially plasma without blood proteins  performs filtration, which is the removal of blood, proteins, and other large particles from urine Tubule cells perform reabsorption, where substances such as amino acids, glucose, water, and ions are removed from filtrate and returned to blood. Secretion helps get rid of substances like drugs, excess ions, etc., which helps maintain the acid-base balance in blood.

Urine Clear, yellow, and usually acidic, but the pH can vary widely Usually contains nitrogenous wastes, water, and various ions (sodium and potassium especially) Usually does not contain glucose, blood proteins, blood, pus (WBCs), bile If these are present in urine, it could be an indication of a serious health problem Sugar could indicate diabetes, bile could indicate liver disease, blood could indicate trauma to urinary tract, pus could indicate a urinary tract infection, etc.

Ureters Slender tubes (25-30 cm long) that run from kidney to bladder Carry urine Smooth muscle layers contract to help propel urine to the bladder by peristalsis Kidney stones – extremely concentrated urine becomes uric acid salt crystals  when they pass through the ureter and are squeezed by the ureter wall, it causes excruciating pain Urine is prevented from flowing backwards by small, valvelike folds of bladder mucosa that flap over the ureter openings

Urinary Bladder Smooth, collapsible, muscular sac that stores urine temporarily 3 openings – 2 ureters and urethra, which carries urine outside of body  Internal and external sphincters – one at each end of urethra As urine accumulates, the bladder expands and rises  muscle wall thins to allow it to store more urine without substantially increasing its internal pressure Micturition = voiding or emptying the bladder Incontinence = inability to voluntarily control external sphincter  release of urine Urinary retention = bladder is unable to expel urine, usually occurs after surgery with general anesthesia