The Urinary System - Structural Features

Written by docteam Tuesday, 15 June 2010 10:08

The urinary system is composed the kidneys, ureters, bladder, and urethra. The kidney are bean shaped organs, weighing about 200 g ,embedded in the back abdominal wall on either side of the vertebral column; through the hillus (or opening in the concave side of each organ) pass the renal artery and vein, lymphatic vessels, nerves, and ureter.

Cut longitudinally the kidney discloses two regions (an outer cortex and an inner medulla) and a cavity, or renal pelvis, from which the ureter is an outlet. Leading off the pelvis are a number of cup shaped recesses (calices), each calix enclosing the apex, or papilla, of a triangulas structure called the pyramid, each pyramid is composed of collecting tubules that open at the papilla.

The ureters are fibromuscular tubes, about 28 cm in length and 1.2 cm in diameter, that convey urine from the renal pelvis to the bladder. Situated immediately before the vagina in female and immediately before the rectum in the male, the urinary bladder is a tough, muscular sac. Leading urine from the bladder to the exterior is the urethra, a membranous tube about 3.5 cm in length in the female and about 20 cm in length in the male.

Urination is effected through contraction of the bladder musculature and relaxation of the sphincters guarding the opening into the urethra. The urge to urinate starts when about 250 ml of urine has accumulated in the bladder. When about 600 cc has accumulated, a sensation of pain may be aroused, and urination becomes urgent. Delaying urination until this point can have damaging effects, especially if it becomes a practice to do so.