Notes
Epididymis, Ductus deferens, and Seminal Vesicle
Helpful Tip
Structures share common features: Each structure comprises a tube of smooth muscle lined with pseudostratified epithelium; upon sympathetic stimulation, the smooth muscle contracts to move spermatozoa or seminal fluid from the testis to the penile urethra. The epithelial layers comprise both basal and columnar cells.
Epididymis
- A long, coiled tube that stores developing sperm (and contributes a small amount of seminal fluid).
- Has a ring of smooth muscle; gradually thickens as the epididymis transitions to the ductus deferens.
- Epithelial lining comprises:
- Columnar (aka, principle) cells; they are tall and irregularly shaped, with stereocilia projecting into the lumen. The function of the sterocilia is contested, but they may increase surface area for reabsorption of fluid within the epididymis.
- The basal cells have spherical nuclei that are near the base of the epithelium.
- Clinical correlation: epididymitis is inflammation of the lining of the epididymis; it can be caused by bacterial infections, including sexually transmitted infections.
Ductus deferens (aka, vas deferens)
- Continuous with the epididymis; it ascends to enter the pelvis, then passes over the urinary bladder and ureter.
- Is a muscular tube that actively conducts sperm from the epididymis to the ejaculatory duct; this transport occurs during the emission phase of ejaculation.
- Three sublayers of smooth muscle:
- Inner longitudinal, intermediate circular, and outer longitudinal.
- These three layers provide the peristaltic contractions necessary to move sperm from the epididymis, into the body via the spermatic cord, and around the urinary bladder to reach the ejaculatory duct.
- Mucosal folds are covered in epithelia:
- Columnar cells with stereocilia.
- Basal cells rest on lamina propria.
- The mucosal folds allow for distention of the ductus deferens during ejaculation.
- Clinical Correlation: A vasectomy involves surgically sealing the ductus deferens closed so that sperm cannot pass into the ejaculatory ducts; special cells within the epididymis and ductus deferens phagocytose the sperm.
Seminal vesicle
- Contributes the majority of the total seminal plasma volume (~70%).
- It is a diverticulum of the ductus deferens; its cavities give it a honeycomb-like appearance.
- Connective tissue folds comprise an elastic lamina propria and secretory pseudostratified epithelia.
- Within the cytoplasm of the epithelia cells, lipid droplets give the glandular tissue a characteristic foamy appearance.
- Thick smooth muscle surrounds the mucosa; during emission, the smooth muscle contracts to drain the seminal vesicle fluid into the ejaculatory duct.
Images:
Histology (Mark Braun, MD, & Indiana University: http://medsci.indiana.edu/c602web/602/c602web/toc.htm; http://www.indiana.edu/~anat215/virtualscope2/start.htm)