The male reproductive system consists of the following organs a pair of testes, a pair of epididymis, a pair of sperm duct (vasa deferentia; singular-, vas deferens), urethra, penis and accessory glands.
(i) Testes:
i. Testes (singular, testis) are the male gonads. A pair of testes are present in a human male.
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ii. In the embryonic stage, the testes are contained within abdomen. They descend down just before birth. Thus, testes are extra-abdominal. These are present in a thin pouch made up of skin and connective tissue called scrotal sac or scrotum. The scrotum is divided into right and left compartments by a muscular septum. One testis lies in each compartment.
iii. The high temperature of body does not allow maturation of sperms. Thus, the scrotum acts as thermoregulator, and it helps in maintaining the temperature at about 2-3 °C lower than the body temperature. This temperature is suitable for the development of sperms.
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Structure of Testes:
i. Each testis is encased in a capsule of white fibrous connective tissue called tunica albuginea.
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ii. Each testis has several highly coiled tubules called seminiferous tubules which are involved in the formation of spermatozoa. The process of formation of sperm is called spermatogenesis.
iii. Between the seminiferous tubules is the connective tissue, in which are present clumps of interstitial cells, also called Leydig cells These cells secrete the male sex hormone, testosterone. This hormone regulates the maintenance of primary and secondary sexual characteristics in males.
(ii) Epididymis:
It is a long tube about 6 m long, a highly coiled structure that remains attached to the testis and lies within the scrotal sac. It stores spermatozoa (sperms) and serves as a passage for their transport from the testis.
(iii) Vas Deferens (Sperm Ducts):
Each epididymis continues from its lower end as a vas deferens. It enters the abdominal cavity through the inguinal canal, passes over the urinary bladder and joins the duct of seminal vesicle to form the ejaculatory duct. The ejaculatory duct opens into the urethra. The inguinal canal allows the descent of the testes along with their ducts, nerves and blood vessels.
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Sometimes, because of high pressure in the abdomen, the intestine bulges into the scrotum through this inguinal canal and causes hernia.
(iv) Urethra:
The male urethra is about 15-20 cm in length and is differentiated into three parts an anterior prostatic part which passes through the prostate gland, a middle membranous part, and a posterior penile part which passes through the copulatory organ, the penis. The male urethra functions as a passage for both semen and urine.
(v) Penis:
Penis is the copulatory organ in males. It is a cylindrical, spongy, muscular and a highly vascular] organ. The urethra runs through it centrally and serves as a common passage for the exit of urine and semen. Hence, it is used as a passage to pass out urine and to deposit sperm in the female genital tract.
During sexual excitement, the spongy tissue gets filled-up with blood, making it erect and stiff. Externally, the penis is covered by skin. The tip of the penis is soft and highly sensitive. It is called glans penis. It is covered by a loose retractile fold of skin called prepuce.
(vi) Accessory Glands:
There are three accessory glands in males. These include—seminal vesicles, prostate gland and Cowper’s glands.
(1) Seminal Vesicles:
A pair of seminal vesicles are present at the base of the urinary bladder. The function of seminal vesicles is to allow transportation of sperms that descend from the testis and to secrete seminal fluid. The seminal fluid is a viscous fluid that provides nourishment to the sperms.
This secretion forms about 40-80 per cent of the ejaculate. Sperms get active when mixed with seminal fluid.
(2) Prostate Gland:
It surrounds the upper part of the urethra. It secretes alkaline fluid which is discharged into the urethra. This fluid keeps the sperms alive and helps them to swim vigorously.
(3) Cowper’s Glands or Bulbo-Urethral Glands:
These paired glands lie below the prostate gland and join the urethra at a short distance from that of the prostate gland. They secrete a white, viscous, alkaline secretion resembling mucous which acts as a lubricant.
Spermatozoa and Semen:
The spermatozoa are minute gametes produced by the testes in males. They are immotile when stored in the epididymis but get activated and motile by the secretions from the accessory reproductive glands in males. The secretions of various accessory glands along with sperms form the semen.
The sperms are released in millions. In one ejaculation about 200,000,000 (2 x 108) sperms are discharged. Sperms move with the speed of 2 mm/minute in female tract.
Structurally, a human sperm has three main parts head, neck and tail. The tip of a sperm is covered by a cap-like structure, acrosome, which helps the sperm to penetrate inside the egg during fertilization. Acrosome also releases one enzyme (hyaluronidase) which enables entry of sperm into egg by dissolving the wall of the egg. The structure of a human sperm.
The nucleus of the sperm contains genetic material which is transferred to egg and mixes with its nucleus during fertilization. The middle piece of sperm contains mitochondria which provide energy for sperm activation and sperm movement.