The Urinary System

The urinary system is composed of two kidneys, two ureters, one urinary bladder and one urethra. The kidneys form the urine while the other parts; the ureters and the urethra are passageways and the bladder is storage site for the urine. The two kidneys as well as the two ureters are located retroperitoneally.

 

The Kidneys

         Each kidney is surrounded by three layers: the renal capsule to maintain the shape of the kidney, the adipose capsule for shock absorption and the renal fascia that anchors the kidney with the surrounding organs.

Renal hilum: deep fissure near the concave medial border through which the ureter, blood vessels, lymphatic vessels enter and exit the kidney.

Renal cortex: external reddish region of the kidney, divided into cortical and juxstamedullary zones.

Renal medulla: deep reddish-brown region of the kidney.

Renal pyramid: 8-18 pyramidal shaped structures forming the medulla, having wide base directed laterally and narrow rounded papillary directed medially.

Renal column: extensions of renal cortex between the renal pyramids.

Renal lobe: renal pyramid and the overlying area of renal cortex.

Minor calyx: cup-shaped structure receives the urine from the nephron in each lobe. Each minor calyx faces one pyramid.

Major calyx: cup-shaped structure receives the urine from the minor calyx. 3-4 are found in each kidney.

Renal pelvis: single large cavity collects the urine from the major calyces to drain in the ureter.

Nephron: the functional unit of the kidney, composed of renal corpuscle where the blood is filtered and the renal tubules where the filtered fluid is transferred.

Renal corpuscle: the filtration unit of the nephron composed of

Glomerulus: capillary network.

Glomerular capsule=Bowman's capsule: double-walled epithelial cup surrounding the glumerulus very well.

Proximal convoluted tubule: the nearest tube to the capsule.

Loop of Henle: extends into the renal medulla.

Distal convoluted tubule: the distant tube from the capsule.

Collecting duct: receives the filtered fluid from several distal convoluted tubules.

The ureters

·       Transportation of the urine from the kidney down to the urinary bladder.

·       Each one is 25-30 cm long curves medially and passes obliquely through the posterior walls of the urinary bladder.

·       Open at the internal ureteral openings into the urinary bladder.

The urinary bladder

·       Hollow distensible muscular organ situated in the pelvic cavity posterior to the pubic symphysis.

·       In male: anterior to the rectum directly.

·       In female: anterior to vagina inferior to uterus.

·       Trigone: smooth triangle at the floor of the urinary bladder, composed of the two posterior internal ureteral openings and one anterior internal urethral opening.

·       Micturition=urination: discharge of the urine from the urinary bladder.

The urethra

·       A tube like structure leading the urine to the exterior of the body by the external urethral orifice.

·       In female doesn't exceed 4cm length.

·       In male:* may reach 25 cm length.

                   *used also for semen discharge.                    

             *divided into 3 parts: the prostatic urethra (in prostate                           gland)

                                                      The membranous urethra (in perineum)

                                                      The spongy urethra (in the penis)