Human Female Reproductive System
The ovaries, uterine tubes, uterus, vagina, and external genitalia comprise the female reproductive system. The breasts, or mammary glands, are considered part of the female reproductive system due to their role in nourishing the offspring.
1. The ovaries
- In females, the ovaries are the primary sex organs.
- The ovaries are two paired structures in the upper pelvic cavity.
- Each ovary is about 2 to 4 cm long and shaped like an unshelled almond.
- The ovarian ligament (ovarian ligament) connects the ovary to the uterus.
- The mesovarium is a double-layered fold of the peritoneum that connects the uterine broad ligament, which is part of the parietal peritoneum, to the ovary.
- The ovaries, as we will see later, are in charge of producing female sex hormones and ova.
The ovary is made up of the following parts.
(i) The ovary is covered by a layer of cubical epithelium called the germinal epithelium. The germinal epithelium is covered by the visceral peritoneum.
(ii) Beneath the epithelium is the tunica albuginea- a layer of connective tissue and underlying it is the ovarian stroma.
(iii) The ovarian stroma cons a dense inner portion called the medulla. of a dense outer layer called the cortex and a less
(iv) No more oogonia are formed and added after birth.
- Oogonia (egg mother cells) divide by mitosis forming primary oocytes.
- Each primary oocyte then gets surrounded by a layer of granulosa cells called primary follicles.
- A large number of these follicles degenerate during the phase from birth to puberty.
- Therefore, at puberty, only 60,000-80,000* primary follicles are left in each ovary.
- The primary follicles are surrounded by more layers of granulosa cells and called secondary follicles.
- The secondary follicle soon changes into a tertiary follicle which is characterized by a fluid-filled cavity called follicular antrum (Gr. antrona cave).
- The tertiary follicle is further converted into a mature follicle or Graafian follicle.
(v) Interspersed throughout the cortex are many ovarian follicles (also called Grafian follicles) in different stages of development. The ovarian follicle comprises the following parts.
- A follicle consists of an oocyte covered by a homogenous membrane the zona pellucida.
- When the surrounding cells form a single layer they are called follicular cells. Later in development when they form several layers, they are referred to as granulosa cells.
- The surrounding cells nourish the developing oocyte and begin to secrete estrogens called membrana granulosa.
- The follicle has an eccentric follicular cavity or follicular antrum filled with a fluid, the follicular fluid or liquor folliculi.
- A solid mass of the follicular cells that surrounds the developing ovarian follicle is called the cumulus oophorus* formed by granulosa cells.
- It projects into the follicular cavity (= follicular antrum).
- Later, the granulosa cells lying in close vicinity of the oocyte and zona pellucida, become elongated to form the corona radiata.
- The membrana granulosa is surrounded by the theca interna (theca - cover) and theca externa.
- The total number of follicles in each ovary of a normal young adult woman is about 60,000 to 80,000.
- Many ovarian follicles (during the primary oocyte stage) undergo degeneration.
- This degenerative process of follicles is called follicular atresia and such follicles are known as atretic follicles.
- The release of secondary oocytes from the ovary is called ovulation.
- It occurs due to the rupturing of the ovarian follicle and the wall of the ovary.
- Generally, one secondary oocyte is released in each menstrual cycle (average duration 28 days) by alternate ovaries.
- Only about 450 secondary oocytes (ova) are produced by a human female over the entire span of her reproductive life which lasts about 40-50 years of age (in some cases 45-55 years).
- In addition to releasing an oocyte, the follicle also produces hormones.
- While the follicle is maturing, some of the follicular cells produce estrogens, mainly estradiol.
(vi) After ovulation many of the follicular cells remain in the collapsed follicle on the surface of the ovary.
- The antrum (cavity) of the collapsed follicle fills with a partially clotted fluid.
- The follicular cells enlarge and fill with a yellow pigment, lutein.
- Such a follicle is called a corpus luteum- literally, yellow body.
- The lutein cells secrete a small amount of estradiol hormone and a significant amount of progesterone hormone.
- The Corpus luteum also secretes the relaxin hormone.
(vii) Degenerated part of the corpus luteum is called corpus Albicans, literally meaning white body. In fact, it is a white scar-like area.
Functions of Ovaries. Production of ova and secretion of female sex hormones.
Two Fallopian tubes (oviducts), uterus and vagina constitute the female accessory ducts.
2. Fallopian tubes consist of the following parts:
(i) The infundibulum is a dilated trumpet-like portion opening into the peritoneal cavity. The end of the tube has finger-like projections called fimbriae which help in the collection of the ovum after ovulation.
(ii) The ampulla is the widest and longest part of the Fallopian tube.
(iii) The isthmus is the short, narrow thick-walled portion that follows the ampulla.
(iv) The uterine part passes through the uterine wall and communicates with the uterine cavity.
Functions of Fallopian Tubes. The Fallopian tube conveys the ovum from the ovary to the uterus. It is done by peristalsis. Fertilization of the ovum generally takes place in the upper portion of the Fallopian tube (ampulla).
3. Uterus (Metra or Hystera or Womb)
- The uterus is a hollow muscular and inverted pear-shaped structure. It lies in the pelvic cavity between the urinary bladder and the rectum.
- It comprises three parts:
(i) The fundus is the upper dome-shaped part of the uterus above the openings of the uterine parts of the Fallopian tubes.
(ii) Cornua (sing Cornu). They are the upper corners where the oviducts enter the uterus.
(iii) The body (corpus) is the main part that is narrowest inferiorly where it continues with the cervix.
(iv) The cervix is the part that joins the anterior wall of the vagina and opens into it. The cavity of the cervix is called the cervical canal. The cervix communicates above with the body of the uterus by an aperture called internal os and with the vagina below by an opening, the external os.
Lateral View of Female Reproductive System
- The uterine walls are made up of three layers of tissue.
(i)The perimetrium is the peritoneum's thin outer covering.
(ii)The myometrium is a thick layer of smooth muscle fibres in the middle of the uterus that contracts strongly during childbirth.
(iii)The endometrium is the uterine cavity's inner glandular layer. During the menstrual cycle, the endometrium undergoes cyclical changes.
Differences between Endometrium and Myometrium
Functions of Uterus. After puberty, the uterus goes through the menstrual cycle. If the fertilization has taken place, the embryo gets attached to the uterine wall where it is nourished and protected. At the end of the gestation period, labour begins and concludes when the child is born.
- The vagina is a tube, about 10 cm long, that extends from the cervix to the outside of the body.
- It is easily stretched.
- The opening of the vagina, called the vaginal orifice (vaginal opening), is partially covered by a membrane called the hymen.
Functions of Vagina. It provides a passageway for the menstrual flow, serves as the receptacle for sperm during intercourse, and forms part of the birth canal during labour.
The hymen is often torn during the first coitus (intercourse). However, it can also be broken by a sudden fall or jolt, active participation in some sports like horseback riding, bicycling, etc. In some women, the hymen remains even after coitus. In fact, the presence or absence of a hymen is NOT a reliable indicator of virginity.
5. External Genitalia (Vulva): Vulva means external genitalia of the female. It includes mons veneris, labia majora, labia minora, clitoris, hymen, vestibule & related perineum.
(i)Mons veneris (mons pubis):- It is a cushion of fatty tissue or of subcutaneous connective tissue, lying in front of the pubis & is covered by pubic hairs in the adult female.
(ii) Labia majora:- Vulva is bounded on each side by the elevation and fleshy folds of skin & subcutaneous tissue. Its inner surface is hairless. The outer surface is covered by the sebaceous gland, Sweat gland & hair follicles. It is homologous with the scrotum in the male.
(iii)Labia minora:- They are two thin folds of skin present just within the labia majora. The lower portion of the minora fuses across the midline & form a fold of skin called a fourchette.
(iv)Clitoris:- It is a tiny finger-like structure that lies at the upper junction of the two labia minora above the urethral opening. It is made up of two erectile bodies (corpora cavernosa). The skin which covers the glans of the clitoris is called a prepuce. At the terminal part of the vagina, the urethra opens separately, so they form a common chamber called the vaginal vestibule or urinogenital sinus. The vulva has the following openings:-
(a) Urethral opening – Lies on the anterior end
(b) Vaginal orifice – Lies on the posterior end.
It is incompletely closed by a septum of mucous membrane called the hymen, but it may not be a true sign of virginity.
(c) Opening of Bartholin's ducts: These are opening of one pair of bartholin's/greater vestibular glands situated on the lateral side of the vagina. They secrete alkaline fluid during sexual excitement.
(v) Perineum. It is the area that extends from the fourchette to the anus.
- The mammary glands are paired structures (breasts) that contain glandular tissue and a variable amount of fat.
- The glandular tissue of each breast is divided into 15-20 mammary lobes containing clusters of cells called alveoli.
- The cells of alveoli secrete milk, which is stored in the cavities (lumens) 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 ampulla which is connected to the lactiferous duct through which milk is sucked out.
- Mammary glands produce a nutritive fluid, milk for the nourishment of young ones.
- Milk protects the young ones from various infections up to some months after birth.
- The mammary glands of the female undergo differentiation during pregnancy and start producing milk towards the end of pregnancy by the process called lactation.
- This helps the mother in feeding the newborn.
- Breast-feeding during the initial period of infant growth is recommended by doctors for bringing up a healthy baby.
Human milk consists of water and organic and inorganic substances. Its main constituents are fat (fat droplets), casein (milk protein), lactose (milk sugar), mineral salts (sodium, calcium, potassium, phosphorous, etc.) and vitamins. Milk is poor in iron content. Vitamin C is present in very small quantities in milk. The process of milk secretion is regulated by the nervous system. It is also influenced by the psychic state of the mother. The process of milk production is also influenced by hormones of the pituitary gland (already mentioned), the ovaries and other endocrine glands. A nursing woman secretes 1 to 2 litres of milk per day. Inhibitory Peptide. Milk contains an inhibitory peptide. If the mammary glands are not fully emptied the peptide accumulates and inhibits milk production.
Functions of Female Reproductive System
1. Germinal epithelial cells of the ovary produce ova (oogenesis).
2. Fertilization takes place in the Fallopian tube (ovíduct).
3. After puberty the uterus goes through the menstrual cycle.
4. Implantation and prenatal growth take place in the uterus.
5. The vagina receives the seminal fluid during copulation.
6. Parturition (the process of the birth of a child) is also an important function of the female reproductive system.
7. Mammary glands of the female secrete milk after parturition.
Female Reproductive System Hormonal Control
- The hypothalamus secretes GnRH, which stimulates the anterior lobe of the pituitary gland to secrete luteinizing hormone (LH) and FSH.
- FSH promotes the growth of ovarian follicles as well as the development of egg/oocytes within the follicle to complete meiosis I and form secondary oocytes.
- FSH also promotes the production of estrogens.
- The corpus luteum is stimulated by LH to secrete progesterone.
- Rising progesterone levels inhibit GnRH release, which in turn inhibits the production of FSH, LH, and progesterone.
The onset of Puberty in the Human Females
- Females reach puberty around the age of thirteen.
- The pituitary gland starts producing follicle-stimulating hormones around this time (FSH).
- FSH stimulates the development of the ovaries, which results in the production of the hormone estrogen.
- This hormone is in charge of the development of female secondary sex characteristics such as voice change and the development of external genitalia, breasts, body hair, pubic hair, and feminine shape.
- This shape is characterized by a widening of the pelvis and fat deposits in the thighs, buttocks, and face.