SUPPLEMENTARY: 1
Seminal Vesicle (LP)


The seminal vesicles are blind ending diverticula of the vasa deferentia lying on the posterior aspect of the bladder. Each is a convoluted tube about 15 cm long which is coiled and folded on itself. The coils adhere to each other where they come into contact. The lumen is therefore seen several times in one plane of section. It was thought at one time, that the seminal vesicles were storage organs for sperm, but it has been shown in humans that sperm are stored only in the epididymis. The seminal vesicles produce a viscous, slightly yellowish secretion, rich in nutrients which makes up about 70% of the volume of the seminal fluid.



The walls of the seminal vesicles consist of inner and outer layers of smooth muscle and an external layer of connective tissue containing many elastic fibres. The lining epithelium consists of tall columnar cells. The height of the epithelium and its secretory activity are dependant on testosterone secretion.

The epithelium is thrown up into a series of thin folds which increase the surface area of the lining epithelium and allow the organ to distend with secretion. Irregular purple and pink masses of secretion can be seen in the lumen.



The fluid secreted by the seminal vesicles contains abundant fructose, prostaglandins, amino acids, citric acid and ascorbic acid. Fructose is the major metabolic substrate of sperm. At orgasm, in response to sympathetic stimulation, the muscular wall of the seminal vesicles contract to propel the fluid from the lumen of the vesicles into the ejaculatory ducts which are the terminal portions of the vasa deferentia. The right and left ejaculatory ducts pass through the substance of the prostate to join the prostatic urethra at the prostatic utricle.

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