Urethra - Overview

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The urethra connects the urinary bladder (depicted in Chapter 5. Urinary System, Urinary Bladder) to the external orifice at the tip of the glans, the end of the penis. The urethra of the male mouse consists of a membranous portion and a penile portion. The membranous urethra extends from the neck of the urinary bladder to the pelvic girdle. Near the bladder on the dorsal wall of the membranous urethra is the colliculus seminalis, where the vas deferens, prostate glands, seminal vesicles, and ampullary glands enter the urethra. Before its transition into the penile urethra, the membranous urethra forms the urethral diverticulum, where the bulbourethral glands open into the urethra. The seminal colliculus is lined by low columnar epithelium, the rest of the membranous urethra by urinary epithelium (transitional epithelium or urothelium). The remaining layers of the membranous urethra include a mucosa, a well-vascularized lamina propria, a layer of small mucous urethral glands opening into the membranous urethra, and a muscularis of skeletal muscle. The penile urethra is surrounded by the tissues of the penis and is lined with urinary epithelium. The penile urethra has no glands and and its lamina propria is fibrous. The external orifice of the urethra is lined by stratified squamous epithelium. In Chapter 5. Urinary System, the female urethra is described.

The micrographs depict the membranous male urethra (for a detailed view of the penile urethra, see Penis 40X). The 4X micrograph is a longitudinal section of the membranous male urethra showing its wide lumen. The 10X micrograph presents the layer of urethral glands surrounding the urethra. The alveoli that form the urethral glands, including their oval basal nuclei, are shown in detail in the 20X and 40X micrographs. The 40X micrograph also displays details of the urinary epithelium.