Male Reproductive System

We will study Male Reproductive System. The purpose of this system is to get new version of human system. This new version is created by two partners. Here we will study male parts participating in reproduction.

Let us have a look at structures involved in the reproduction. (Fig. 1)

The scrotum is a sac like structure with two testicles, one on each side. Testicles have 200 – 300 seminiferous tubules which are connected to epididymis. The epididymis is a mass like structure attached to the upper part of testis. In its further course, epididymis increases in diameter and is named as ductus deferens or vas deferens. The main function of vas deferens is the storage of sperms. The vas deferens is muscular tube, about 46 cm. which ends in ejaculatory duct by joining the corresponding seminal vesicle. Seminal vesicle is a sac like structure joining ampulla of vas deferens.  Ampulla is a dilated portion of the vas deferens. The ejaculatory duct terminates in urethra which passes through penis.

Functional Aspects of Male Reproductive system

The scrotum is a muscular organ which lies outside the body. This is because the spermatogenesis needs temperature little lower than body. Exposure to cold causes contraction of muscles by which testes remain close to body and relatively heated surrounding exposure to warm reverse the process.

The testis is partially covered by tunica vaginalis. Tunica vaginalis is a sac with visceral and parietal layer. Hydrocele is a clinical condition, wherein collection of serous fluid occurs in tunica vaginalis. Internal to tunica vaginalis there is a tunica albuginea, a fibrous tissue which extends inwards, forming septa that divide the testis into compartments called lobules. Each lobule contains 1 to 3 tightly coiled tubules called seminiferous tubule where sperms are produced.

Spermatogenesis

During development of embryo primordial germ cells enters into testis and differentiate into spermatogonia.  The spermatogenesis occurs at puberty, as a result of stimulation by anterior pituitary through production of gonadotropic hormone. It consists of development of sperms from spermatogonia through various stages. Besides hormone from anterior pituitary, several hormones like LH, FSH, testosterone and oestrogen play a role in spermatogenesis e.g. testosterone is essential for growth and division of testicular germinal cells.

After puberty, increasing amounts of testosterone secretion causes development of secondary sexual characteristics that we notice in boys. e.g. distribution of hairs, effect on voice, muscles development. It also causes enlargement of testes, scrotum and penis. Every day about 300 million of sperm are produced.

Major parts of sperm are head and tail. (Fig. 3)

Head contains nucleus with 23 chromosomes. Over the nucleus there is a cap like vesicles filled with enzymes that help a sperm to penetrate oocyte.

After spermatogenesis sperm reside in seminiferous tubules. They are subsequently released into epididymis. Functionally epididymis is a site of sperm maturation, the process by which sperms acquire motility and ability to fertilize an ovum. This occurs over a period 14 days. After that, sperm is propelled into vas deferens by peristaltic contractions of its smooth muscles.

Act of Coition

Erection

The sexual act consists of stimulation, erection, emission and resolution. Parasympathetic fibres from the sacral portion of spinal cord, stimulated by visual, auditory, tactile and  even by thoughts, cause sexual stimulation. These parasympathetic fibres produce and release nitric oxide in walls of arterioles supplying penis. Nitric oxide in turn causes increased blood flow and widening of blood sinuses resulting in an erection.

Emission

When sexual stimulation becomes extremely intense, the reflex centres of spinal cord present in thoraco-lumbar region are stimulated. This results in sending impulses to genital organs through hypogastric and pelvic sympathetic nerve plexus. This leads to contraction of vas deferens and ampulla (fig.1), which causes expulsion of sperm into the internal urethra. Then contractions of muscular coat of the prostate gland occur followed by contraction of seminal vesicles causes expulsion of prostatic and seminal fluid into urethra forcing the sperm forward. This fluid mixes in internal urethra with mucus secreted by bulbourethral gland, to form semen which is alkaline in nature.

Nocturnal emission

It involves erection and ejaculation during sleep. It is a normal process and common at adolescent period.

Ejaculation When internal urethra, filled with semen, send signals through pudendal nerve to sacral region of spinal cord, these sensory signals further excite rhythmical contraction of the internal genital organs. It increases pressure in both erectile tissue of penis and urethra resulting into expulsion of semen into vagina. After ejaculation, the process of erection seizes within 1 or 2 minutes, called as resolution.