INTRODUCTION :
As you are aware, humans are sexually reproducing and viviparous. The reproductive events in humans include formation of gametes (gametogenesis), i.e., sperms in males and ovum in females, transfer of sperms into the female genital tract (insemination) and fusion of male and female gametes (fertilisation) leading to formation of zygote. This is followed by formation and development of blastocyst and its attachment to the uterine wall (implantation),embryonic development (gestation) and delivery of the baby (parturition). You have learnt that these reproductive events occur after puberty. There are remarkable differences between the reproductive events in the male and in the female, for example, sperm formation continues even in old men, but formation of ovum ceases in women around the age of fifty years. Let us examine the male and
female reproductive systems in human.
THE MALE REPRODUCTIVE SYSTEM :
The male reproductive system is located in the pelvis region. It includes a pair of testes alongwith accessory ducts, glands and the external genitalia. testes are situated outside the abdominal cavity within a pouch called scrotum. The scrotum helps in maintaining the low temperature of the testes (2–2.5o C lower than the normal internal body temperature) necessary for spermatogenesis. In adults, each
testis is oval in shape, with a length of about 4 to 5 cm and a width of about 2 to 3 cm. The testis is covered by a dense covering. Each
testis has about 250 compartments called testicular lobules. Each lobule contains one to
three highly coiled seminiferous tubules in which sperms are produced. Each seminiferous tubule is lined on its inside by two types
of cells called male germcells (spermatogonia) and Sertoli cells.The male germ cells
undergo meiotic divisions finally leading to sperm formation, while Sertoli cells provide nutrition to the germ cells. The regions outside the seminiferous tubules called interstitial spaces, contain small blood vessels and interstitial cells or Leydig cells. Leydig
cells synthesise and secrete testicular hormones called androgens. Other immunologically competent cells are also present. The male sex accessory ducts include rete testis, vasa efferentia, epididymis and vas deferens. The seminiferous tubules of
the testis open into the vasa efferentia through rete testis. The vasa efferentia leave the testis and open into epididymis located along the posterior surface of each testis. The epididymis leads to vas deferens that ascends to the
abdomen and loops over the urinary bladder. It receives a duct from seminal vesicle and opens into urethra as the ejaculatory duct. These
ducts store and transport the sperms from the testis to the outside through urethra. The urethra originates from the urinary bladder and extends through the penis to its external opening called urethral meatus.
The penis is the male external genitalia. It is made up of special tissue that helps in erection of the penis to facilitate insemination.The enlarged end of penis called the glans penis is covered by a loose fold of skin called foreskin.
The male accessory glands include paired seminal vesicles, a prostate and paired bulbourethral glands. Secretions of these
glands constitute the seminal plasma which is rich in fructose, calcium and certain enzymes. The secretions of bulbourethral glands also helps in the lubrication of the penis.
THE FEMALE REPRODUCTIVE SYSTEM :
The female reproductive system consists of a pair of ovaries alongwith a pair of oviducts, uterus, cervix, vagina and the external genitalia located in pelvic region.These parts of the system alongwith a pair of the mammary glands are integrated structurally and functionally to support the processes of ovulation, fertilisation, pregnancy, birth and child care. Ovaries are the primary female sex organs that produce the female gamete (ovum) and several steroid hormones (ovarian hormones).The ovaries are located one on each side of the lower abdomen. Each ovary is about 2 to 4 cm in length and is connected to
the pelvic wall and uterus by ligaments. Each ovary is covered by a thin epithelium which encloses the ovarian stroma. The stroma is divided into two zones – a peripheral cortex and an inner medulla.oviducts (fallopian tubes), uterus and vagina constitute the female
accessory ducts. Each fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the uterus, the part closer
to the ovary is the funnel-shaped infundibulum. The edges of the
Infundibulum possess finger-like projections called fimbriae, which help in collection of the ovum after ovulation. The infundibulum leads to a wider part of the oviduct called ampulla. The last part of the oviduct, isthmus has
a narrow lumen and it joins the uterus.
The uterus is single and it is also called womb. The shape of the uterus is like an inverted pear. It is supported by ligaments attached to the pelvic wall. The uterus opens into vagina through a narrow cervix. The cavity of the cervix is called cervical canal which alongwith vagina forms the birth canal. The wall of the uterus has three layers of tissue. The
external thin membranous perimetrium, middle thick layer of smooth muscle, myometrium and inner glandular layer called endometrium that
lines the uterine cavity. The endometrium undergoes cyclical changes during menstrual cycle while the myometrium exhibits strong contraction during delivery of the baby.
The female external genitalia include mons pubis, labia majora, labia minora, hymen and clitoris . Mons pubis is a cushion of fatty
tissue covered by skin and pubic hair. The labia majora are fleshy folds of tissue, which extend down from the mons pubis and surround the vaginal opening. The labia minora are paired folds of tissue under the labia majora.
The opening of the vagina is often covered partially by a membrane called hymen. The clitoris is a tiny finger-like structure which lies at the upper junction of the two labia minora above the urethral opening. The hymen is
often torn during the first coitus (intercourse). However, it can also be brokenby a sudden fall or jolt, insertion of a vaginal tampon tampon, active participation in some sports like horseback riding, cycling, etc. In some women the hymen persists even after coitus. In fact, the presence or absence of hymen is not
a reliable indicator of virginity or sexual experience.
A functional mammary gland is characteristic of all female mammals.the mammary glands are paired structures (breasts)that contain glandular tissue and variable amount of fat.the glandular tissue of each breast is divided into 15-20 mammary lobes containing clusteres of cells called alveoli. The cell secrete milk, which is stored in the cavities (lumans) of alveoli. the alveoli open into mammary tubules.the tubules of each lobe join to form a mammary duct. several mammary ducts join to form a wider mammary ducts join to form a wider mammary ampulla which is connected to lactiferous duct. through which milk is sucked out.
GAMETOGENESIS :
The primary sex organs -the testes in the males and the ovaries in the females -produce gametes, i.e sperms and females -producegametes, i.e sperms and ovum. respectively, by the process called gametogenesis. in testis, the inmature male germ cells (spermarogoina)produce sperms by spermaticgenesis that begins at puberty.the spermarogoina. (Sing . spermatogonium) present on the inside wall of seminiferous tubules multiply by mitotic division and increase in numbers. each spermatogonium is diploid and contains 46 chromosomes. some of the spermatogonia is diploid and contains primary spermatocytes. Periodically undergo meiosis. A primary spermatocytes completes the first meiotic division (reduction division) leading to formation of two equal, haploid cells called secondary spermatocytes. which have only 23 chromosomes each. the secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids What would be the
number of chromosome in the spermatids?
The spermatids are transformed into
spermatozoa (sperms) by the process called
spermiogenesis. After spermiogenesis,
sperm heads become embedded in the
Sertoli cells, and are finally released from
the seminiferous tubules by the process
called spermiation.
Spermatogenesis starts at the age of
puberty due to significant increase in the
secretion of gonadotropin releasing hormone
(GnRH). This, if you recall, is a hypothalamic hormone. The increased levels of GnRH then acts at the anterior pituitary gland and
