Testis
The male reproductive organs of man include the sperm producing organs, the conducting tubes and some glands associated with the tubes. The most important male reproductive organ is the testis. It is called the primary sexual organ of male. We will see a little later how the testis produces sperms. For the present, let us examine its location in the body and the duct arising out of this organ. When a male child is born, the testis can be found to be located in a sac like structure between the two thighs. This sac is called the scrotal sac or scrotum. But the testis is formed in the abdominal cavity. Before the birth of a male child, the testis descends into the scrotal sac through a narrow passage which is known as the inguinal canal. The scrotal sac is rather a loose sac which can elongate and contract depending upon the body and external temperatures.
There are two testes which are somewhat oval in shape. Each testis is covered by a fibrous tissue called tunica albuginea. From each testis arise a number of very fine tubules, the vasa effferentia which open into a wider tube which is somewhat curved like a horseshoe. This horseshoe shaped structure is called the epididymis. In fact, the convolutions of the 6-metre long canal make up the epididymis.
Epididymis
Epididymis receives sperms from the testis through the vasa efferntia. From the posterior part of epididymis arises another duct which is 25cm long. This duct is known as the vas deferens. The starting point of vas deferens is the epididymis but its end point is the seminal vesicle. The vas deferens runs forward and passes through the inguinal canal to enter the abdominal cavity. The vas deferens runs interiorly up to the urinary bladder from where it takes a sharp turn and runs downward to open into an elongated sac called seminal vesicle. Sperms are stored in the seminal vesicle.
Seminal vesicle
It can be seen at the base of the urinary bladder. For each testis, there is one vas deferens and one seminal vesicle. The function of seminal vesicle is to store the sperms that have come from the testis and to secrete seminal fluid. A small duct of the seminal vesicle and the vas deferens unite to form short ejaculatory duct which passes through the prostate gland.
Prostate gland
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It surrounds the commencement of urethra. The two ejaculatory ducts also open at the commencement of the urethra. Prostate gland has a large number of groups of cells called follicles. These follicles communicate with the urethra through a dozen small ducts. The urethra in the region of prostate gland is called prostatic urethra. About 2.f cm from the prostatic urethra, towards the lower region, there are tow bulbo-urethral glands. Their ducts open into the urethra. Bulbo-urethral glands are also called Cowper’s gland (named after a British surgeon, William Cowper). The urethra passes down through an organ called penis.
Penis
Penis is a tubular organ. It is composed of two masses of tissue. A narrow tube, called urethra, passes through the penis. When blood vessels of the penis dilate upon stimulation called the glands. The fold of skin which covers the penis ids called prepuce.
Sperm
Sperm is a haploid cell in which four different parts can be recognized: middle piece, tall. The head contains the haploid nucleus. The neck bears centriole. The middle piece has compact mitochondria. The tail is like a cilium or flagellum, which beats in a characteristic manner so as to provide locomotion to the sperm as a whole.
What is semen? For one thing, this is a fluid which contains sperms. There may be 100 million sperms in 1 ml of the semen. The semen may also be called seminal fluid. If we filter out all the sperms from the seminal fluid, the remaining fluid is called seminal plasma. This seminal plasma is a mixture of the secretions from seminal vesicle, prostate gland, and bulbo-urethral gland. When a person is vasectomised (i.e., when his vas deferens is tied by thread so as to prevent the sperms form passing beyond the epididymis), he can ejaculate the seminal plasma but this will not have sperms in it.
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When the semen is discharged in the vagina during coitus, the sperms begin climbing up the vaginal wall and gradually ascend towards the uterus and finally reach the upper parts of the two fallopian tubes. But only one sperm enters the ovum, if the latter is incidentally present there. Vast majority of sperms die while climbing up the fallopian tube because of some reason or the other. Sperms can move up or travel at the rate of 100 um per second. When does sperm enter the ovum? There is no definite time for it. But sperms can remain alive in the fallopian tube for about 12 hours. In this span of time, if a sperm can meet the ovum, it is likely to enter the ovum. This is call fertilization.