Question

Answer the following question.

Explain the following parts of male reproductive system along with labelled diagram showing these parts- Testis, vasa deferentia, epididymis, seminal vesicle, prostate gland and penis.

Answer 1

The male reproductive system consists of the following:
i. Primary sex organs (Gonads): Testes
ii. Accessory organs: Accessory ducts and accessory glands
iii. External genitalia: Scrotum and Penis

i. Primary sex organs: Testes

Testes are a pair of primary sex organs which are mesodermal in origin. They are located outside the abdomen in a pouch called scrotum, i.e. extra-abdominal in position. Testes develop in the abdominal cavity (early foetal life) and later descend into the scrotal sac through a passage called inguinal canal. They are suspended in the scrotal sac by the spermatic cord. Testes are connected to the wall of scrotum by a short fibromuscular band called gubernaculum.
They are oval in shape, about 4 to 5 cm long, 2 to 3 cm wide, and 3 cm thick.
The outermost covering of the testis is formed of a dense fibrous membrane called tunica albuginea.

ii. Accessory sex organs:

It includes accessory ducts, accessory glands.

a. Accessory ducts:

1. Rete testis:
The seminiferous tubules of the testis at the posterior surface form a network of tubules called rete testis. The rete testis opens into vasa efferentia. 2. Vasa efferentia:
Vasa efferentia are 12-20 fine tubules arising from the rete testis and join to the epididymis. They carry sperms from the testis and open into the epididymis.
3. Epididymis:
It is a long and highly coiled tube which is differentiated into an upper caput-, middle corpus- and lower cauda epididymis. The sperms undergo maturation in the epididymis.

4. Vasa deferens:
The vas deferens travels up to the abdominal cavity and loops over the ureter to open into the urethra. Vas deferens join the seminal vesicle to form ejaculatory duct.

5. Ejaculatory ducts:
The ejaculatory duct passes through the prostate gland and opens into the urethra.

6. Urethra:
The urethra provides a common passage for the urine and semen and hence is also called urinogenital duct. In males the urethra is long and extends through the penis. It opens to the outside by an opening called the urethral meatus or urethral orifice.

b. Accessory glands:

1. Seminal vesicles:
These are a pair of small fibromuscular pouches present on the posterior side of the urinary bladder. They secrete a seminal fluid (alkaline) containing citric acid, fructose, fibrinogen, and prostaglandins. About 60% of the total volume of semen is made up of seminal fluid. Fructose provides energy to sperms for swimming, while fibrinogen helps in coagulation of semen after ejaculation for quick propulsion into the vagina. The prostaglandins stimulate reverse peristalsis in vagina and uterus aiding the faster movement of sperms towards the egg in the female body.

2. Prostate gland:
Prostate gland consists of 20 to 30 lobes and is located under the urinary bladder. It surrounds the urethra. It releases a milky white, alkaline fluid called prostatic fluid into the urethra. Prostatic fluid forms about 30% of the total volume of semen. It contains citric acid, acid phosphatase and various other enzymes.
The acid phosphatase protects the sperm from the acidic environment of the vagina.

3. Cowper’s glands:
Cowper’s glands are also known as bulbourethral glands. These are pea-sized and lie on either side of membranous urethra. They secrete a viscous, alkaline, mucous like fluid which acts as a lubricant during copulation.
Semen: It is the viscous, alkaline and milky fluid (pH 7.2 to 7.7) ejaculated by the male reproductive system. Generally, 2.5 to 4.0 ml of semen is given out during a single ejaculation and it contains about 400 million sperms. Semen contains secretion of the epididymis and the accessory glands for nourishing (fructose), neutralizing acidity (Ca++, bicarbonates), activation for movement (prostaglandins).

iii. External genitalia:

a. Penis:
The penis is the male copulatory organ. It is cylindrical and muscular with three bundles of erectile tissue: a pair of postero-lateral tissue called corpora cavernosa and a median corpus spongiosum. The swollen tip of the penis is called glans penis. It is covered by a loose fold of skin called foreskin or prepuce.

b. Scrotum:
It is a loose pouch of pigmented skin lying behind the penis and is divided into a right and left scrotal sac by a septum of tunica dartos made of smooth muscle fibres. The foetal testes are guided into and retained in the scrotum by a short fibro muscular band called gubernaculum. The testes remain suspended in scrotum by a spermatic chord.
The failure of the testis to descend into the scrotum is called cryptorchidism which also results in sterility.
The cremaster and dartos muscles of scrotum help in drawing testes close or away from the body. This helps in maintaining the temperature of the testis 2-3 0C lower than the normal body temperature, necessary for spermatogenesis.