THE URINARY SYSTEM The urinary system is responsible for elimination of waste products of the body.
The urinary system is formed of the following: 2 kidneys 2 ureters Urinary bladder Urethra
The Kidneys Location: The kidneys are located in the posterior part of the abdominal cavity, one on either side of the vertebral column, behind the peritoneum (retroperitoneal). They extend obliquely from costal margin to just above iliac crest; opposite last thoracic and first 3 lumbar vertebrae (right kidney is slightly lower by about 1-2 cm than left).
Shape: the kidney is a reddish brown bean-shaped organ having 2 ends: Upper end: is related to the suprarenal gland. It is 1 inch from the median plane. Lower end: is rounded. It is 2 inch from the median plane 2 borders: Lateral border: convex Medial border: concave and presenting the hilum 2 surfaces: Anterior surface: irregular and related to abdominal organs Posterior surface: flat and related to the posterior abdominal wall Coverings: the kidney is surrounded by 3 coverings, which help to keep it in position: True renal capsule is an inner fibrous membrane, which invests the kidney. Perirenal fat: is a middle layer of fat, which surrounds both kidney and suprarenal gland. Fascial capsule is a thin, outer layer of fibrous connective tissue that surrounds each kidney and is derived from the fascia of the posterior abdominal wall.
Hilum: lies on the medial border of kidney. It gives passage for following structures (from anterior to posterior): Hilum: lies on the medial border of kidney. It gives passage for following structures (from anterior to posterior): Renal vein Renal vein Renal artery Renal artery Renal pelvis Renal pelvis Blood Supply: Each kidney is supplied by renal artery, which arises directly from abdominal aorta at level of 2nd lumbar vertebra. Renal veins collect blood from the kidneys and drain into inferior vena cava. The right renal vein is shorter than the left.
Relations: anteriorly, each kidney is related to the following structures: Relations: anteriorly, each kidney is related to the following structures: Right Kidney: Right suprarenal gland Liver 2 nd part of duodenum Right colic flexure Left Kidney: Left suprarenal gl. Stomach Pancreas Spleen Left colic flexure N.B.: the diaphragm separates the Lt. kidney from the last 2 ribs (11 th & 12 th ) and the Rt. kidney from last rib only (12th).
Section of Kidney: a longitudinal section in the kidney shows the following: Renal cortex: is outer portion of the kidney, which is granular reddish brown in appearance. It arches over the pyramids of the medulla and dips in between adjacent pyramids. These inward extensions of cortical substance are called the renal columns. Renal medulla: is darker in colour and consists of striated, cone- shaped masses called renal pyramids, which are about 5-11 in number. The base of each pyramid is directed towards the cortex, while its apex projects inwards toward the renal sinus (central cavity of the kidney) where it forms a papilla. Renal pelvis: the renal papillae are surrounded by trumpet-like tubes called minor calyces, which fuse together forming 2-3 major calyces. The later collect into the renal pelvis, which is a funnel-shaped sac that occupies the renal sinus and forms the upper expanded end of the ureter.
The ureters The ureters are muscular tubes, about 26 or 30 cm long, which convey urine from the kidneys to the urinary bladder. They lie behind the parietal peritoneum; each ureter descends along the posterior abdominal wall to the pelvic brim of its own side. After crossing the brim of the pelvis, they pass along the lateral wall of the pelvis and follow the downward and medial course along the pelvic floor to reach the urinary bladder. They enter the bladder by passing obliquely through its muscular wall. This part is called intramural part, which is cm. The obliquity of this part acts like a valve to prevent the reflux of urine from the U.B. to the ureter when the bladder is distended. Clinical note: Renal calculi may lodge at sites where lumen of ureter becomes relatively narrowed. The normal sites of constrictions in the ureter are:
The urinary bladder General features: The urinary bladder is a thick-walled muscular sac lies in the lower and anterior part of the pelvic cavity behind the symphysis pubis in both male and female (the size, shape and position dependent on age and amount of urine within it.
The urinary bladder is pyramidal in shape when empty. It has: Apex: is directed anteriorly Base (posterior surface): is related to In male: seminal vesicles and ampullae of vasae deferentia, which separate the bladder from the rectum. In female: is directly related to the anterior wall of the vagina. Superior surface: is related to In male: coils of small intestine. In female: anterior surface of the uterus. Inferolateral surfaces: are related to the side walls of the pelvis. Neck (inferior angle): is continuous with the beginning of the urethra in male and female, surrounding the internal urethral orifice. In male: it rests on the prostate. In female: it rests directly on the pelvic floor.
Urinary bladder in male Urinary bladder in female
Base of the urinary bladder in male
Interior of the urinary bladder: The mucosa of the bladder is thrown into folds, or rugae, when the bladder is empty. Trigone is a small triangular area in the floor of the bladder. Its anterior angle is formed by the internal opening of the urethra, and its posterolateral angles by the openings of the ureters. The musculature of the bladder is known as detrusor muscle; it is composed of an interwoven network of smooth muscle fibres.
Blood supply: Blood supply: Arterial: superior and inferior vesical arteries from internal iliac artery Arterial: superior and inferior vesical arteries from internal iliac artery Venous: veins drain into internal iliac vein from vesical plexus of veins. In the male, vesical plexus communicates with prostatic plexus of veins. Venous: veins drain into internal iliac vein from vesical plexus of veins. In the male, vesical plexus communicates with prostatic plexus of veins. Innervation: Innervation: Parasympathetic: preganglionic fibers arise from S2-4 synapse with postganglionic neurons in bladder wall via pelvic plexus motor to detrusor muscle & inhibitory to internal sphincter. Thus involved in micturation causes contraction of bladder wall and relaxation of sphincter. Parasympathetic: preganglionic fibers arise from S2-4 synapse with postganglionic neurons in bladder wall via pelvic plexus motor to detrusor muscle & inhibitory to internal sphincter. Thus involved in micturation causes contraction of bladder wall and relaxation of sphincter. Sympathetic: fibers arising from upper 2 lumbar nerves postganglionic fibers pass through hypogastric and pelvic plexuses inhibitory to detrusor muscle & motor to internal sphincter. Sympathetic: fibers arising from upper 2 lumbar nerves postganglionic fibers pass through hypogastric and pelvic plexuses inhibitory to detrusor muscle & motor to internal sphincter.
The urethra The urethra is the tube that conveys urine from the urinary bladder to the exterior. In males it has both an excretory and a reproductive function, but in females it is concerned only with excretion. Female Urethra: is shorter than the male. It is only 4 cm long. As it curves obliquely downwards and forward from the bladder, the posterior wall of the urethra is united firmly with the anterior wall of the vagina. The external orifice of the urethra is located directly in front of the vaginal opening. Male Urethra: The urethra is male consists of 3 parts: The prostatic urethra (2.5 cm) extends form the neck of the urinary bladder to the pelvic floor. During its course it is completely surrounded by the prostate gland. When this gland enlarges, as it commonly does in elderly men, it compresses at the prostatic urethra and interferes with the flow of urine. It is the most wide and dilatable part. Its posterior wall represents a median ridge “urethral crest” that forms a rounded elevation at its middle “colliculus seminalis The membranous urethra (1.5 cm) extends through the pelvic floor to the bulb of the penis. It narrowest and least dilatable part. A striated muscular sphincter surrounds this part of the urethra. The penile urethra (16 cm) traverses the corpus spongiosum of penis till the external urethral orifice.
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