2.1 Human reproductive system

. Human reproductive system The male reproductive system comprises of a pair of testes, accessory ducts, glands and external genitalia (Fig. . ) .

Testes are the primary male sex organs. They are a pair of ovoid bodies lying in the scrotum (Fig. . a) .

The scrotum is a sac of skin that hangs outside the abdominal cavity. Since viable sperms cannot be produced at normal body temperature, the scrotum is placed outside the abdominal cavity to provide a temperature - o C lower than the normal internal body temperature. Thus, the scrotum acts as a thermoregulator for spermatogenesis. Each testis is covered by an outermost fibrous tunica albuginea and is divided by septa into about - lobules each containing - highly coiled testicular tubules or seminiferous tubules.

These highly convoluted tubules which form percent of the testicular substance are the sites for sperm production. The stratified epithelium of the seminiferous tubule is made of two types of cells namely sertoli cells or nurse cells and spermatogonic cells or male germ cells. Sertoli cells are elongated and pyramidal and provide nourishment to the sperms till maturation. They also secrete inhibin , a hormone which is involved in the negative feedback control of sperm production.

Spermatogonic cells divide meiotically and differentiate to produce spermatozoa. Interstitial cells or Leydig cells are embedded in the soft connective tissue surrounding the seminiferous tubules. These cells are endocrine in nature and are Fig. .

Male reproductive system Human Reproduction characteristic features of the testes of mammals. It secretes androgens namely the testosterone hormone which initiates the process of spermatogenesis. Other immunologically competent cells are also present. The accessory ducts associated with the male reproductive system include rete testis, vasa efferentia, epididymis and vas deferens (Fig.

. b) . The seminiferous tubules of each lobule converge to form a tubulus rectus that conveys the sperms into the rete testis. The rete testis is a tubular network on the posterior side of the testis.

The sperms leave the rete testis and enter the epididymis through the vasa efferentia. The epididymis is a single highly coiled tube that temporarily stores the spermatozoa and they undergo physiological maturation and acquire increased motility and fertilizing capacity. The epididymis leads to the vas deferens and joins the duct of the seminal vesicle to form the ejaculatory duct which passes through the prostate and opens into the urethra. The urethra is the terminal portion of the male reproductive system and is used to convey both urine and semen at different times.

It originates from the urinary bladder and extends through the penis by an external opening called urethral meatus. The accessory glands of the male reproductive system include the paired seminal vesicles and bulbourethral glands also called Cowper’s gland and a single prostate gland . The seminal vesicles secrete an alkaline fluid called seminal plasma containing fructose sugar, ascorbic acid, prostaglandins and CRYPTORCHISM The failure of one or both testes to descend down into the scrotal sacs is known as cryptorchism (crypto – hidden + orchis – testicle). It occurs in – percent of new born males.

A surgical correction at a young age can rectify the defect, else these individuals may become sterile and are unable to produce viable sperms. Urinary bladder Seminal vesicle Prostate gland Vas deferens Bulbourethral gland Epididymis Glans penis Scrotum Testis Ureter Blood vessels and nerves Vas deferens Epididymis Rete testis Tunica albuginea Tubulus rectus Seminiferous tubule Vasa efferentia Fig. . (a) Diagrammatic view of the male reproductive system Fig.

. (b) Testis showing inner details Human Reproduction the external genitalia located in the pelvic region (Fig. . a) .

These parts along with the mammary glands are integrated structurally and functionally to support the process of ovulation, Fertilization, pregnancy, child birth and child care. Ovaries are the primary female sex organs that produce the female gamete, ovum. The ovaries are located one on each side of the lower abdomen. The ovary is an elliptical structure about - cm long.

Each ovary is covered by a thin cuboidal epithelium called the germinal epithelium which encloses the ovarian stroma . The stroma is differentiated as the outer cortex and inner medulla. Below the germinal epithelium is a dense connective tissue, the tunica albuginea . The cortex appears dense and granular due to the presence of ovarian follicles in various stages of development.

The medulla is a loose connective tissue with abundant blood vessels, lymphatic vessels and nerve fibres. The ovary remains attached to the pelvic wall and the uterus by an ovarian ligament called mesovarium . The fallopian tubes (uterine tubes or oviducts), uterus and vagina constitute the female accessory organs (Fig. .

b) . Each fallopian tube extends from the periphery of each ovary to the uterus. The proximal part of the fallopian tube bears a funnel shaped infundibulum . The edges of the infundibulum have many finger like projections called fimbriae a coagulating enzyme called vesiculase which enhances sperm motility.

The bulbourethral glands are inferior to the prostate and their secretions also help in the lubrication of the penis. The prostate encircles the urethra and is just below the urinary bladder and secretes a slightly acidic fluid that contains citrate, several enzymes and prostate specific antigens. Semen or seminal fluid is a milky white fluid which contains sperms and the seminal plasma (secreted from the seminal vesicles, prostate gland and the bulbourethal glands). The seminal fluid acts as a transport medium, provides nutrients, contains chemicals that protect and activate the sperms and also facilitate their movement.

The penis is the male external genitalia functioning as a copulatory organ. It is made of a special tissue that helps in the erection of penis to facilitate insemination. The enlarged end of the penis called glans penis is covered by a loose fold of skin called foreskin or prepuce. The female reproductive system is far more complex than the male because in addition to gamete formation, it has to nurture the developing foetus.

The female reproductive system consists of a pair of ovaries along with a pair of oviducts, uterus, cervix, vagina and