e. Beneath the cortex is a reddish-brown area called the renal medulla. Within
the medulla are striated areas called the renal pyramids. Urine collecting tubules within
the pyramids cause the striated appearance.
f. The collecting tubules terminate at the pyramid's point, emptying the urine
into the renal pelvis. Along the edges of the renal pelvis are cup-like projections called
the minor and major calyces. Each minor calyx collects urine from the pyramid and
empties it into a major calyx. The major calyces empty into the renal pelvis.
The pelvis of each kidney is drained by a ureter, a muscular tube extending from
the hilum to the posterior portion of the urinary bladder. Ureters are smooth muscle
structures, and urine is passed through each ureter by peristalsis. Drop by drop, urine
passes into the bladder. Ureters are about 15 to 18 inches in length and about 1/5 inch
The urinary bladder, a muscular sac located in the lowest part of the abdominal
cavity, stores urine. Normally it holds 300 to 500 ml. The bladder is emptied by
contraction of its muscular walls that force urine out through the urethra.
The urethra is the tube that carries urine from the urinary bladder to the external
opening, the urinary meatus.
a. In the male, the urethra will vary in length. Including the portion within the
body, it is approximately 6 to 7 1/2 inches in length. It is divided into three areas: the
prostatic area, which passes through the prostate gland; the membranous area,
beneath the prostate; and the penile area, which passes through the penis.
b. The female urethra, about 1 1/2 inches long, extends from the bladder to the
meatus, which is located above the vaginal opening.
Urination is the discharge or voiding of urine. It is done by a contraction of the
bladder and relaxation of the sphincters. In the adult, the act of voiding, although
dependent on involuntary reflexes, is partly under voluntary control. Voluntary
contraction of abdominal muscles usually accompanies and aids urination.