URINARY SYSTEM Lecturer Dr.Firdous M.Jaafar Department of anatomy/histology section Lecture 3
Objectives 1- Describe the structure of the urinary bladder, 2- Describe the structure of the ureters, bladder, and urethra.
Urinary bladder
Urinary bladder The wall of the bladder consists of three layers: 1- Mucosa: It is the inner layer, composed of transitional epith. and lamina propria. In an empty bladder, the transitional epith. is 5-6 cells in thickness, the superficial cells are rounded and bulge into the lumen, while in full bladder epithelium will stretch and superficial cells become squamous.
Urinary bladder
Transitional epithelium of empty bladder Urinary bladder The superficial cells of the transitional epithelium have a special membrane of thick plates separated by narrow bands of thinner membrane that are responsible for the osmotic barrier between urine and tissue fluids.
Urinary bladder
Plates of the surface transitional cells Urinary bladder 2-Muscular layer: Thick layer that runs in every direction, without distinct orientation. At the bladder neck(origin of urethra), the muscular layer will arrange in three layers: a- Inner longitudinal layer: it will become circular distal to the bladder neck and surrounds the prostatic urethra in the male, and external meatus of the female, forming the true involuntary urethral sphincter. b- Middle circular layer: it ends at the bladder neck. c- Outer longitudinal layer: continues to the end of the prostate in male, and the external urethral meatus in female.
Urinary bladder 3- Adventitia: Loose connective tissue rich in blood vessels, except the upper part of the bladder which is covered by serosa(because it is an intra peritoneal part).
Medical application Cystitis, or inflammation of the bladder mucosa, is the most frequent problem involving this organ. Such inflammation is common during urinary tract infections, but it can also be caused by immunodeficiency, urinary catheterization, radiation, or chemotherapy.
Ureter The wall consists of three layers: 1- Mucosa: similar to that of the urinary bladder. 2- Muscular layer: it has a helical arrangement, then near the bladder, it will become two layers; an inner longitudinal and outer circular. When the ureter pass through the wall of the bladder, the muscles will become longitudinal only. The ureter pass obliquely through the bladder forming a valve to prevent the back-flow of urine. In addition, there is a flap of bladder mucosal membrane act as a valve. 3- Adventitia: loose connective tissue.
Ureter Ureter
Medical application A common problem involving the ureters is their obstruction by renal calculi (kidney stones) formed in the renal pelvis or calyces, usually from calcium salts (oxalate or phosphate) or uric acid. Most kidney stones are asymptomatic, but movement of stones from the renal pelvis into the ureter can cause extreme pain on the affected side of the body.
Medical appliation Bacterial infections of the urinary tract can lead to inflammation of the renal pelvis and calyces, or pyelonephritis. In acute pyelonephritis bacteria often move from one or more minor calyx into the associated renal papilla, causing accumulation of neutrophils in the collecting ducts.
Urethra It is a tube that carries urine to the outside. Male urethra: 1- prostatic urethra: lined by transitional epith. 2- membranous urethra: lined by stratified or pseudostratified columnar epit. It is surrounded by voluntary urethral sphincter. 3- penile urethra: lined by simple columnar or pseudostratified columnar epith. Which will change into stratified squamous distally.
Male urethra
Urethra Female urethra: Short tube; about 4-5cm long, lined by pseudostratified epith., and near the external orifice, it becomes stratified sequamous epith. The middle portion is surrounded by the external voluntary sphincter.
Female urethra