11) Tubular secretion, which seems to be important for removal of substances not already in the filtrate, is essentially reabsorption in reverse.

12) Urine moves down the ureters into the bladder due to gravitational pull alone.

13) The internal urethral sphincter is involuntary.

14) The urethra, which carries urine exiting the bladder by peristalsis, is typically shorter in females than in males.

15) The involuntary internal urethral sphincter is composed of skeletal muscle.

16) The fluid stored inside cells is referred to as extracellular fluid (ECF).

17) Excess blood plasma in the bloodstream initiates the thirst mechanism to restore fluid balance.

18) Antidiuretic hormone (ADH) causes increased water loss through the urine.

19) The most important trigger for aldosterone release is the renin-angiotensin mechanism, mediated by the renal tubules.

20) A person with arterial blood pH above 7.45 is said to have acidosis.

21) Carbon dioxide is most commonly transported as the bicarbonate ion in the blood.

22) When blood pH becomes too acidic, the tubule cells of the kidneys excrete bicarbonate ions and retain hydrogen ions.

23) Sexually transmitted infections (STIs) are primarily infections of the reproductive tracts but may also cause urinary tract infections.

24) Incontinence is often the final outcome of the urinary system during the aging process.