The urinary system
The urinary system consists of the kidneys, ureters, urinary bladder, and urethra
– The kidneys remove from the blood the toxic waste products of protein metabolism (urea and uric acid), water and inorganic salts.
– The kidneys are reddish brown, bean-shaped organs, located on the posterior abdominal wall, one on each side of vertebral column behind the peritoneum opposite the last thoracic and the upper 2 or 3 lumber vertebrae. The left kidnev is sliahtlv higher. Each kidnev is about 4 inches long. 2 inches wide, and 1 inch thick.
– The kidneys are held in place by a capsule of fat.
– Each kidney has 2 surfaces (anterior and posterior). 2 borders (medial and lateral), and 2 poles (upper and lower).
– The anterior surface is related to different structures on both sides. The right kidney is related to the liver, duodenum, right colic flexure, and coils of small intestine. That of the left kidnev is related to the pancreas, spleen, stomach. Jejunum, and descending colon.
– The posterior surface is related on both sides lies to the muscles of the posterior abdominal wall.
– The lateral border is convex.
– The medial border is concave in the middle part where it presents a slit called the hilum that gives passage to the renal vessels anteriorly and the pelvis of the ureter posteriorly. The hilum lies at level of first lumbar vertebra.
– The upper pole on both sides is related to the corresponding suprarenal gland.
– The lower pole on each side is slightly above the iliac crest
– Each kidney contains more than one million unites called nephrons.
The ureter is a tube which actively propels the urine towards the urinary bladder by peristaltic contractions.
It is 10 inches long. Its upper end is dilated and divided into a number of calyces, (minor calyces receive the collecting ducts and join to form major calyces). The abdominal part passes behind peritoneum on the psoas major muscle. The pelvic part enters the pelvis and turns medially to enter the back of the urinary bladder.
The urinary bladder is a hollow muscular organ, located in the pelvic cavity behind the pubic bone. Its function is to store and to expel urine.
When fixed, it is a tri-sided pyramid with an apex anteriorly and a base posteriorly. The ureters pierce the
upper part of the base obliquely to prevent back flow of urine. The neck of the bladder is the lowest part and is continuous downwards with the urethra. The neck is surrounded by an involuntary smooth muscle sphincter, controlled b> autonomic nerves. The triangular area between the urethra and ureteric orifices is called the trigone.
It is the tube which extends from neck of the urinary bladder to the body surface at the external urethral orifice.
Male urethra: (Fig. 29)
It is about 20 cm long. It is divisible into 3 parts:
1. The prostatic urethra: is about 3 cm long and it is surrounded by the prostate gland. It receives the 2 ejaculatory ducts.
2. The membranous urethra: is the shortest part. It is 2 cm long and it is surrounded by striated muscle.
3. The penile urethra (or spongy urethra). It is about 15cm long. It traverses the corpus spongiosum of the penis till it opens at the external urethral orifice which is the narrowest point.
Female urethra: li is about 4 cm long and it lies anterior to the vagina.