Histology of Bladder and Urinary Tract
Excretory passages except urethra have general structure of
- Mucosa
- muscularis
- adventitia (or serosa)
Mucosa has exceptional transitional epithelium composed of thickened plaques
- transitional epithelium impermeable to salts and water
- ability to become thicker and flatter as urinary bladder stretched
- in un-distended bladder plaques fold inward within apical membrane
- in distended bladder plaques reinserted into apical membrane
No submucosa or muscularis mucosae present
Tubular portions surrounded by two layers of smooth muscle
- inner, longitudinal layer
- outer, circular layer
- more random arrangement of muscle fibre orientation in bladder
Terminal portions of ureters run in bladder wall
- as bladder distends with urine, ureters compressed
- this prevents backflow of urine and spread of infection towards kidneys
Bladder supplied by both sympathetic and parasympathetic nerves
- sympathetic fibres probably innervate blood vessels in bladder wall
- parasympathetic fibres end in ganglia in muscle bundles, are efferent
fibres of micturition reflex
Urethra divided into three portions in male
- prostatic urethra (3-4 cm)
- lined with transitional epithelium
- membranous urethra (1 cm)
- passes through pelvic and urogenital diaphragms of body wall
- to corpus cavernosum
- transitional epithelium ends here - often described as stratified or
pseudostratified columnar
- muscles of pelvic and urogenital diaphragm form external (voluntary)
sphincter of urethra
- penile urethra (15 cm)
- lined with pseudostratified columnar epithelium
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