Epididymis


Epididymis
Epididymis
Illu testis surface.jpg
1: Epididymis
2: Head of epididymis
3: Lobules of epididymis
4: Body of epididymis
5: Tail of epididymis
6: Duct of epididymis
7: Deferent duct (ductus deferens or vas deferens)
Gray1148.png
The right testis, exposed by laying open the tunica vaginalis.
Gray's subject #258 1242
Vein Pampiniform plexus
Precursor Wolffian duct
MeSH Epididymis

The epididymis (play /ɛpɨˈdɪdɨmɪs/; plural: epididymides /ɛpɨˌdɪdɨˈmdz/) is part of the male reproductive system and is present in all male amniotes. It is a narrow, tightly-coiled tube connecting the efferent ducts from the rear of each testicle to its vas deferens. A similar, but probably non-homologous, structure is found in cartilaginous fishes.

Contents

Regions

The epididymis can be divided into three main regions

  • The head (Caput). The head of the epididymis receives spermatozoa via the efferent ducts of the mediastinum of the testis. It is characterized histologically by a thin myoepithelium. The concentration of the sperm here is dilute.
  • The body (Corpus)
  • The tail (Cauda). This has a thicker myoepithelium than the head region, as it is involved in absorbing fluid to make the sperm more concentrated.

In reptiles, there is an additional canal between the testis and the head of the epididymis, which receives the various efferent ducts. This is, however, absent in all birds and mammals.[1]

Histology

The epididymis is covered by a two layered pseudostratified epithelium. The epithelium is separated by a basement membrane from the connective tissue wall which has smooth muscle cells. The major cell types in the epithelium are:

  • Principal cells: columnar cells that, with the basal cells, form the majority of the epithelium. These cells cells extend from the lumen to the basal lamina,[2] They also have non-motile stereocilia, which are long and branching in the head region and shorter in the tail region.[2] They also secrete carnitine, sialic acid, glycoproteins, and glycerylphosphorylcholine into the lumen.
  • Basal cells: shorter, pyramid-shaped cells which contact the basal lamina but taper off before their apical surfaces reach the lumen.[2] These are thought to be undifferentiated precursors of principal cells.[2]
  • Apical cells: predominantly found in the head region[2]
  • Clear cells: predominant in the tail region[2]
  • Intraepithelial lymphocytes: distributed throughout the tissue.[2]

Role in storage of sperm and ejaculant

Spermatozoa formed in the testis enter the caput epididymis, progress to the corpus, and finally reach the cauda region, where they are stored. Sperm entering the caput epididymis are incomplete - they lack the ability to swim forward (motility) and to fertilize an egg. During their transit in the epididymis, sperm undergo maturation processes necessary for them to acquire these functions.[3] Final maturation is completed in the female reproductive tract (capacitation).

During ejaculation, sperm flow from the lower portion of the epididymis (which functions as a storage reservoir). They have not been activated by products from the prostate gland, and they are unable to swim, but are transported via the peristaltic action of muscle layers within the vas deferens, and are mixed with the diluting fluids of the seminal vesicles and other accessory glands prior to ejaculation (forming semen).

The epithelial cells of the epididymis possesses numerous apical modifications that are often referred to as stereocilia, as under the light microscope they look like cilia. However, as electron microscopy has revealed them to be structurally and functionally more similar to microvilli, some now refer to them as stereovilli.[4]

Pathology

An inflammation of the epididymis is called epididymitis. It is much more common than orchitis.

Embryology and vestigial structures

A Gartner's duct is a homologous remnant in the female.

In the embryo, the epididymis develops from tissue that once formed the mesonephros, a primitive kidney found in many aquatic vertebrates. Persistence of the cranial end of the mesonephric duct will leave behind a remnant called the appendix of the epididymis. In addition, some mesonephric tubules can persist as the paradidymis, a small body caudal to the efferent ductules.

Epididymectomy

Epididymectomy is the surgical removal of the epididymis sometimes performed for Post-Vasectomy Pain Syndrome.

Gallery

Notes

  1. ^ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 394–395. ISBN 0-03-910284-X. 
  2. ^ a b c d e f g Kierszenbaum, Abraham L. (2002). Histology and cell biology : an introduction to pathology. St. Louis [u.a.]: Mosby. pp. 556. ISBN 0-323-01639-1. 
  3. ^ Jones R (1999). "To store or mature spermatozoa? The primary role of the epididymis". Int J Androl 22 (2): 57–67. doi:10.1046/j.1365-2605.1999.00151.x. PMID 10194636.  abstract
  4. ^ Ross, Michael H.; Pawlina, Wojciech (2011). Histology: A Text and Atlas. Lippincott Williams & Wilkins. pp. 110–112. ISBN 978-0-7817-7200-6. 

External links



Wikimedia Foundation. 2010.

Look at other dictionaries:

  • epididymis — c.1600, fleshy mass at the back of the testicles (jocularly called a taint), Mod.L., lit. that which is on the testicles, from Gk. epididymis, a word probably coined by Greek anatomist Herophilus (c.300 B.C.E.) from epi on (see EPI (Cf. epi )) +… …   Etymology dictionary

  • Epididymis — Ep i*did y*mis, n. [NL., fr. Gr. ?; epi upon + ? testicle.] (Anat.) An oblong vermiform mass on the dorsal side of the testicle, composed of numerous convolutions of the excretory duct of that organ. {Ep i*did y*mal}, a. [1913 Webster] || …   The Collaborative International Dictionary of English

  • Epididymis — (gr.), Nebenhode, s.u. Genitalien. Epididymītis, deren Entzündung …   Pierer's Universal-Lexikon

  • Epididymis — (griech.), der Nebenhoden; Epididymitis, Entzündung des Nebenhodens …   Meyers Großes Konversations-Lexikon

  • Epididymis — Epididymis, griech., Nebenhode …   Herders Conversations-Lexikon

  • Epididymis — ⇒ Nebenhoden …   Deutsch wörterbuch der biologie

  • epididymis — [ep΄ə did′i mis] n. pl. epididymides [ep΄ədi dim′i dēz΄] [ModL < Gr < epi , upon + didymoi, testicles, orig. pl. of didymos, double, redupl. of duo, TWO] a long, oval shaped structure attached to the rear upper surface of each testicle,… …   English World dictionary

  • Epididymis — A structure within the scrotum attached to the backside of the testis. The epididymis is a coiled segment of the spermatic ducts that serves to store, mature and transport spermatozoa between the testis and the vas (the vas deferens). * * * An… …   Medical dictionary

  • Epididymis — Hoden und Nebenhoden: 2 Nebenhodenkopf    (Caput epididymidis) 4 Nebenhodenkörper    (Corpus epididymidis) 5 Nebenhodenschwanz    (Cauda epididymidis) …   Deutsch Wikipedia

  • epididymis — Convoluted tubule connecting the vas efferens, that comes from the seminiferous tubules of the mammalian testis, to the vas deferens. Maturation and storage of sperm occur in the epididymis …   Dictionary of molecular biology


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.