The Male Reproductive System - Accessory Ducts

Accessory Ducts:

• The accessory ducts associated with the male reproductive system include rete testis, vasa efferentia, epididymis, and vas deferens.
• The accessory ducts transport the sperms released from the seminiferous tubules to the outside through urethra.
  Seminiferous tubules unite to form straight tubules ⇒ open into rete testis (irregular cavities) ⇒ Vasa efferentia (series of fine tubules that conduct sperms) ⇒ epididymis (stores sperms temporarily) ⇒ vas deferens ⇒ join with a duct from seminal vesicle to form ⇒ opens into urethra ⇒ urethral meatus (external opening).

1) Rete testis:

• The seminiferous tubules of each lobule converge to form a tubulus rectus that conveys the sperms into the rete testis.
• The rete testis is a tubular network on the posterior side of the testis from where vasa efferentia arise.

2) Vasa efferentia: 

• Rete testis fuse to from 10 to 20 efferent ductules called vasa efferentia or ductuli efferentes. These ductules come out from the upper dorsal (posterior) surface of the testis and open into common tubules, which get highly coiled to form epididymis or ductus epididymis. 

3) Epididymis: 

• The epididymis is a single highly coiled tube (about 20 ft) that temporarily stores the spermatozoa and they undergo physiological maturation and acquire increased motility and fertilizing capacity.
• Each epididymis is attached to the posterolateral side of the testis.
• It is divided into three parts: 
  

1. Head or Caput epididymis: At the anterior end of the testis epididymis is called caput epididymis, which receives the sperms from rete testis by several fine, ciliated ductules called vas efferentia.
2. Body or Corpus epididymis: The middle part of the epididymis is known as corpus epididymis.
3. Tail or Cauda epididymis: The posterior end of the epididymis is called cauda epididymis.

• In the head of the epididymis, the semen is concentrated by reabsorption of the fluid secreted by the seminiferous tubules. The sperm matures, becomes motile and physiologically active to fertilize the egg. As from here, sperms pass down in the tail of the epididymis where they are stored for a while before entering the vas deferens. Epididymis by its peristalic and segmenting contractions pushes the sperms into the vas deferens. Spermatozoa are produced continuously whether ejaculation takes place or not. If not ejaculated, they are reabsorbed. 
  
  
• Functions of Epididymis:  
  i) Serves as a duct for the passage of sperms from the testis to vas deferens.
  ii) Stores sperms prior to ejaculation. Storage in the epididymis makes the sperms motile and mature. 

4) Vas Deferens: 

• Vas Deferens run upward and enters into the abdominal cavity. From the tail of epididymis arises a partially coiled, long tube called, the vas deferens.
• It is about 40 cm in length slightly coiled in the beginning but becomes straight as it enters the abdominal cavity through the inguinal canal.
• From here it passes over the urinary bladder and joints the duct of the seminal vesicle to form the ejaculatory duct. Near its end, vas deferens dilates to form a spindle like an ampulla for the temporary storage of sperms.

5) Urethra:  

• Urethra arises from the urinary bladder and joins the ejaculatory duct to form the urinogenital canal as it carries urine as well as sperms and secretions of seminal vesicles, prostate gland, and Cowper's gland.
• It originates from the urinary bladder and extends through the penis by an external opening called urethral meatus.
• It is 20 cm long and passes through the penis.
• It consists of three regions - prostatic urethra where prostate gland opens, membranous urethra at the urogenital diaphragm, and the spongy penile urethra that passes through penis.
• The urethra has two sphincters - an internal sphincter of smooth muscle fibres at its beginning and an external sphincter of striated muscles fibres around the membranous part.

6) Ejaculatory Duct:  

• It is about 2 cm long Thin-walled tube.
• They are formed by the union of ducts from seminal vesicle and vas deferens.
• The ejaculatory ducts of the two sides after passing through the prostate gland open into the urethra.
• They carry sperms mixed up with secretion of seminal vesicle.