Class 12 CBSE Biology Chapter 3 Human Reproduction Part-2
FEMALE REPRODUCTIVE SYSTEM :
Click here for Male Reproductive System
NCERT SOLUTION Human Reproduction
The female reproductive system consists of a pair of ovaries, a pair of oviducts, a uterus, a vagina, external genitalia, and a pair of mammary glands.
OVARY The ovaries produce the female gamete (ovum) and some steroid hormones (ovarian hormones). Each ovary is a compact or solid organ, consisting of an outer cortex and inner medulla. The stroma of the cortical region is composed of spindle-shaped fibroblasts. A poorly delineated dense connective tissue layer, the tunica albuginea, covers the cortex, giving it a whitish appearance. Located outside the tunica albuginea, the germinal epithelium, formed of simple squamous or cuboidal epithelial cells, covers the surface of the ovary. The ovaries are attached to the abdominal wall by an ovarian ligament called mesovarium.
Follicles are specialized structures in which oocyte growth and meiosis I occur. Ovarian follicles in different stages of development are embedded in the stroma. Mature follicles are known as Graafian follicles, which occupy a single cavity called antrum and contain a secondary oocyte ready for ovulation. The rupture of the Graafian follicle is called the corpus luteum, which is a temporary endocrine gland that secretes progesterone hormone for the maintenance of pregnancy. The corpus luteum loses its yellow colour and becomes inactive, transformed into a small cell mass called corpus albicans. Degenerated follicles are called atretic follicles.
Fig. : Diagrammatic sectional view of female pelvis showing reproductive system
The female child at birth possesses 80,000 follicles in the ovaries, but only about 400 of them mature and discharge their ova, while the rest undergo degeneration.
Click here for Male Reproductive System
SECONDARY SEX ORGANS/GLANDS
The female reproductive system includes various organs and structures responsible for the production and transportation of gametes, fertilization, and development of the fetus. The secondary sex organs and glands in females are the oviducts, uterus, vagina, and mammary glands.
The oviducts, also known as fallopian tubes, develop from the mullerian duct of the embryo. They convey the egg from the ovary to the uterus and provide the appropriate environment for fertilization. Each oviduct is differentiated into four parts – infundibulum (surrounded by finger-like projections called fimbriae), ampulla (place where fertilization of ovum takes place), isthmus, and uterine part. Fimbriae help in the collection of the ovum after ovulation. Tubectomy is a surgical procedure that involves cutting the oviduct and tying its two ends separately.
The uterus, also called the womb, is a pyriform, hollow muscular thick-walled but distensible median structure located above and behind the urinary bladder. It is meant for nourishing and development of the fetus. For this purpose, the uterus is capable of tremendous enlargement. The empty uterus is 7.5 cm long, 5 cm broad, and 2.5 cm thick. The surgical removal of the uterus is called hysterectomy.
The uterus has three layers – outer perimetrium, middle myometrium (thickest layer containing areolar connective tissue and smooth muscle fibers), and inner endometrium. During pregnancy, the endometrium forms the maternal section of the placenta. The uterus is the site of implantation of the pre-embryo and for the subsequent embryonic and fetal development.
The vagina is a tubular female copulatory organ and passageway for menstrual flow as well as the birth canal. It is about 10 cm in length. The vaginal wall is made of an internal mucosa, muscular layer, and an outer adventitia. Its mucous membrane is a non-keratinized stratified squamous epithelium. Glands are absent. However, cervical glands do pass on some mucus into it during ovulation. During reproductive life, the vagina contains certain bacteria (species of Lactobacillus and Lactoneustroc, also called Doderlein’s Bacillus) that bring about fermentation and produce acid, which inhibits the growth of other microorganisms. In virgins, the vaginal orifice is partially covered by an annular centrally perforated membrane called hymen.
Click here for Male Reproductive System
The female external genitalia include the mons pubis, labia majora, labia minora, hymen, and clitoris. The vulva (external female genitalia) is flanked by two pairs of fleshy folds of skin: the inner small, thin, moist labia minora and outer larger, hair-covered labia majora (homologous to the scrotal sac of males). All the labial folds have numerous sebaceous and sweat glands on both sides. A small erectile organ, the clitoris, lies at the anterior junction of the labia minora. It is homologous to the penis in the male but is very small and solid, having no passage through it. It consists of a short shaft with erectile tissue and ends in a rounded glans clitoridis. The latter is covered by a small hood of skin, the prepuce. Rubbing of the clitoris during intercourse produces a pleasurable sensation. This seems to be its only function. Urethra and vagina open by separate apertures, the upper urethral and lower vaginal orifices, into the vestibule. A fleshy elevation above the labia.
Click here for Male Reproductive System
HORMONAL CONTROL OF FEMALE REPRODUCTIVE SYSTEM
Ovaries are regulated by the hypothalamic-pituitary-ovarian axis. The hypothalamus secretes gonadotropin-releasing hormone (GnRH) which stimulates the anterior pituitary to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH and LH then regulate the development and maturation of follicles in the ovary, ovulation, and the subsequent formation and function of the corpus luteum. Estrogen is secreted by the developing follicles and the corpus luteum. It promotes the growth, maintenance, and functioning of secondary sex organs such as the uterus and vagina, and also contributes to the development of secondary sexual characteristics such as breast development and distribution of body fat. Progesterone is primarily secreted by the corpus luteum and later by the placenta during pregnancy. It prepares the endometrium for implantation of a fertilized egg, helps to maintain pregnancy by suppressing uterine contractions and the immune response to the developing embryo, and also prepares the breasts for milk production. At the end of pregnancy, the placenta secretes relaxin which softens and relaxes the pelvic ligaments and cervix in preparation for childbirth.
Click here for Gametogenesis (Part-3)
(Click here for pregnancy & Embryonic Development(Part-4)