Human urinary system comprises a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.
1. Kidneys : (a) There is pair of kidneys which are dark-red, bean shaped, each with a notch, the hilus on its inner side, (b) Blood vessels, lymph vessels, nerves and ureter enter or leave the kidney through the hilus. (c) They are situated in the anterior part of the abdominal cavity one on either side of the median line, (d) Last two pair of ribs (floating ribs) protect the kidneys, (e) The concave side of each kidney faces inwards and convex side outwards, (f) The right kidney is slightly lower than the left and
| the left kidney is a little nearer to the middle plane than the right, (g) The kidney is metanephric.
2. Ureters : (a) The ureter of each kidney leaves from the renal pelvis in the hilus region, (b) They are narrow, whitish, tubular structures, running backward along the abdominal wall to open into the urinary bladder, (c) Ureters are composed by transitional epithelium, (d) They carry urine from the kidneys to the urinary bladder.
3. Urinary bladder : (a) It lies in the pelvic cavity and is pear shaped, muscular, sac-like structure,
(b) Its inner lining is composed of transitional epithelium, (c) The muscular layer of the urinary bladder is well developed. The latter consists of three layers of smooth muscle-inner and outer layer of longitudinal fibres and middle layer of circular fibres, (d) Both the sympathetic and parasympathetic nervous systems innervate the urinary bladder, (e) Internally, the urinary bladder has a triangular area, the trigone, between the three openings-two openings through which the ureters enter the bladder and one opening through which the urethra leaves the-bladder, (f) The urinary bladder stores urine temporarily
4. Urethra: (a) It is a canal like structure which extends from the neck of the bladder and leads to exterior, (b) It opens by urethral orifice infront of vaginal aperture, (genital aperture), (c) In male, urethra is much longer opens out at the tip of the penis by urinogenital aperture, (d) Thus the urethra of male carries both urine and semen.