Male Reproductive System: Structure and Function
Give an account of the male reproductive system in man?
In this article we will discuss about the male reproductive system:-(1) Definition, (2) Reproductive organs and it’s Structure and function.
Genital ducts and epididymis
*Bulbourethral Or the cowper’s gland.
Histology of testes
Reproduction in Man:
Human beings are unisexual and there is well marked sexual dimorphism between male and female.
Male Reproductive System:
The male reproductive system consists of a pair of testes, genital ducts, a penis and the accessory glands.
The male has a pair of testes located in the pouch like scrotum. The scrotum itself is divided into two scrotal sacs by an internal partition. Each scrotal sac contains one testis and communicates with the abdominal cavity by a narrow passage called inguinal canal. The testes develop inside the abdomen close to the kidneys and descend down into the scrotum before birth. This is because the scrotum provides a cooler environment necessary for spermatogenesis. This extra-abdominal position of the testes is well marked in most of the mammals, including man. However, platypus, whale, elephant and a few other mammals are exceptions to this where the testes are found in the abdomen. If the testes fails to descend into the scrotum and is retained in the abdomen, it results in a condition called cryptoorchism. A spermatic cord consisting of vas deferens, spermatic artery, vein and nerve arises from each testis. It travels through the inguinal canal and connects to the dorsal abdominal wall.
Genital ducts and epididymis:
A set of about 10-20 fine ducts called vasa efferentia arise from the rete testis and join together to form a common duct of about 6 meters called vas deferens. The vas deferens becomes highly convoluted to form a complex structure called epididymis. The epididymis is meant for the storage and maturation of the sperms. The sperms also gain motility and fertilizing power while passing through the epididymis.
The vas deferens leaves the base of epididymis and enters into the abdominal cavity. It joins the duct of the seminal vesicle of its side to form the ejaculatory duct. The ejaculatory duct of both the sides open into the urethra or the urinogenital canal. The urethra originates from the urinary bladder and travelling through the penis opens to the outside at the top of the penis.
The penis is the male copulatory organ. It is covered with a thin but loose skin. Its terminal sensitive part is called glans penis which bears the external urethral opening. The fold of skin covering the glans is called prepuce. Histologically, the penis is made up of three erectile cords of spongy tissue. Two of the cords which lie dorsally are called corpora cavernosa and the third one lying ventrally is called corpus spongiosum.The empty sinuses of the cords are filled with blood when erected. The urethra runs through the corpus spongiosum.
The glands associated with the male reproductive system are the
(i) Paired Seminal Vesicles
(ii) Unpaired Prostate Gland
(iii) The Paired Bulbourethral or The Cowper’s Gland.
There are two muscular, convoluted, pouch-like structures lying between the urinary bladder and rectum called seminal vesicles. Each vesicle leads into a short duct which joins the vas deferens. It secretes an alkaline, viscous fluid which forms the bulk of the semen. The seminal secretion is rich in fructose, Vit-C and mucous. It nourishes the sperm and contributes about 60% of the total volume of the semen.
It is a lobular compact gland. It lies below the urinary bladder surrounding the urethra and opens into the later by many small ducts. The ejaculatory duct runs through the prostate gland before opening into the urethra. It secretes a milky-white alkaline fluid at the time of seminal ejaculation which enhances the motility and fertility of the sperm by neutralizing the acidic secretions of the vas deferens and acidic vaginal secretions. In some men above 50 years of age, it begins to involute, grows larger causing urinary obstruction. necessitating its surgical removal.
Bulbourethral or Cowper’s gland:
A pair of small bulbourethral glands lie below the prostate and near the origin of urethra. They open into the urethra by fine ducts. During sexual excitement these glands secrete a transparent, alkaline, viscous fluid which has a lubricating action. It also neutralizes the acidity of the urethra and vagina.
Sexual intercourse or manipulation of the male external genitalia terminates with ejaculation of seminal fluid or semen. The volume of semen is 2.5-5 ml per ejaculation. On an average, 1 ml of semen contains about 100,000,000 of sperms. It is composed of the fluid and sperm from the vas deferens (10 %), fluid from the seminal vesicles (60 %), fluid from the prostate glands (30%) and small amount of mucous and other secretions from bulbourethral gland. The average pH of semen is about 7.5. The sperms can live for many weeks in the male genital ducts but once they are ejaculated in the semen, their maximal life span is 24-48 hrs (at normal body temperature). However, semen can be stored for many years below – 100°C.
Histology of Testes:
The testis is covered by a connective tissue capsule called tunica albuginea. A number of septa radiating from this capsule divide the interior of the testis into about 300 small lobules. Each lobule contains two or three highly coiled seminiferous tubules. Each seminiferous tubule is surrounded by connective tissue. Groups of specialized cells called interstitial cells orthe cells of Leydig are present in the connective tissue. They produce the male sex hormone the testosterone. Each seminiferous tubule is lined by a germinal epithelium covered externally by a thin basement membrane. The germinal cells of the epithedium produce sperms by the process of spermatogenesis. There are a number of very large sertoli cells which provide support and nourishment to the developing sperms. All the seminiferous tubules of the testis converge to open into a structure called rete testis which is a system of fine interconnected tubules.