Female Reproductive System
Human Female Reproductive System:-
The female reproductive system consists of a uterus, a pair of ovaries, a pair of fallopian tubes (oviducts), a vagina and the external genitalia. Because of their role in nourishing the offspring, the breasts or mammary glands are considered part of the female reproductive system.
- The uterus consists of:
(i) Body (corpus) with bulging upper surface, the fundus, and
(ii) Neck called cervix.
- The uterine cavity is small, triangular in shape with three openings:
(i) two for fallopian tubes at its upper outer angles,and
(ii) one directed downwards (internal os) which opens into the cervical canal and leads via external os into the vagina.
- (i) The prepubertal uterus is a small organ weighing 10-15 gms.
(ii) The post-pubertal uterus is pear shaped, grows under the influence of oestrogen, measures 7.5 cm x 5 cm x 2.5 cm (3" x 2" x 1") and weighs 30-60 gms.
(iii) During late pregnancy the uterus enlarges considerably through stretching by the growing foetus and by hormonal action; the final weight being 800-1000 gms.
- The body of the uterus consists of '3' coats: (i) Innermost coat is of mucous membrane called Endometrium.
(ii) Middle thick coat is of smooth muscle called Myometrium, which gives strength to uterus.
(a) thickest in the fundus which contracts forcefully, and
(b) thinnest in the cervix which dilates during delivery.
(iii) Outermost coat is a serous coat of parietal peritoneum which covers only upper 3/4th of the uterus.
i)It plays an important role in reproduction.
(a) It undergoes characteristic changes during the Menstrual Cycle i.e. recurrent monthly discharge of blood from female genital tract.
(b) It helps in implantation of fertilized ovum and supplying the nutrients essential for its growth and development.
(ii) Two kinds of arterial vessels pass through the myometrium to enter the endometrium, spiral and basal arteries:
- Spiral arteries are tortuous arteries and end in capillaries which supply the middle and superficial portion of the endometrium (Stratum Functionale).
- (b) Basal (straight) arteries which run only for a short distance and supply the basal portion of the endometrium (Stratum Basale).
(iii) The secretions from the progestational endometrium (endometrium influenced by ogesterone) are rich in:
(a) Glucose - which provides energy and nourishes the blastocyst for a few days before implantation takes place in the hormonally prepared endometrium.
(b) Enzymes and proteins which stimulate RNA and protein synthesis in the blastocyst.
- The Cervix
- It is much less muscular compared to the rest of the uterus, and contains more connective tissue. Its mucosa, called Endocervix contains columnar mucus secreting epithehum with some ciliated cells. Endocervix is not shed at the time of menstruation.
- (ii) Cervical secretion normally contains approximately 92% water, NaCl and glycoprotein(sialomucin type). Its composition and character changes in response to hormonal influences
(iii) Functions(a) Allows entry of spermatozoa (sperms) from the vagina into the uterus and to store viable sperms for 1-2 days.
(b) Allows escape of menstrual wreckage.
(c) Permits passage of the foetus at term.
(d) Prevents entry of infectious microorganisms.
- The Fallopian Tubes (Oviducts)
Each Fallopian tube consists of the following parts.
(i) The uterine part lies within the wall of the uterus between the fundus and the body.
(ii) The isthmus is the straight narrow part just lateral to the wall of the uterus.
(iii) The ampulla is the widest part of the tube and is long.
(iv) The infundibulum is a dilated trumpet-like portion opening into the peritoneal cavity.The end of the tube has finger-like projections called fimbriae.
(iv) Each fallopian tube length is approx. 10 cm (4").
(v) It consists of same three coats as that in the uterus.
The functions of the Fallopian tube are to convey the ovum from the ovary to the uterus. It is done by the peristalsis. Fertilization of the ovum generally takes place in the upper portion of the Fallopian tube (ampulla).
- Ovaries are primary sex organs in human female.
- There are two ovaries, one on each side, behind and below the fallopian tubes of upper pelvic cavity.
- Total weight of the adult ovaries is 10-20 gm, which decreases with increasing age.
- Each ovary, shaped like an unshelled almond, is about 3.5 cm long, 2 cm wide, and 1 cm thick.
- The ovarian ligament (ligment of ovary) attaches the ovary to the uterus.
- Each ovary is also supported by the mesovarium, a membrane that attaches the ovary to the broad ligament.
- ovaries are responsible for producing female sex hormones and ova.
Parts of Ovary:-
(i) The ovary is covered by a layer of cubical epithelium called the germinal epithelium. The germinal epithelium is covered by visceral peritoneum.
(ii) Beneath the epithelium is the tunica albuginea— a layer of connective tissue and underlying it is the stroma.
(iii) The stroma consists of a dense outer layer called the cortex and a less dense inner portion called the medulla.
(iv) Interspersed throughout the cortex are many ovarian follicles (also called Graafian follicles) in different stages of development. The ovarian follicle comprises the following parts.
- Primary functions:
(a) to produce and discharge Ova (eggs); and
(b) to secrete female hormones called ovarian hormones (oestrogen and progesterone mainly).
(a) Production and Discharge of Ova:-
Process of formation of ova is called Oogenesis.
(i) Ova are formed from approx. the 10th week of foetal life from Oogonia which multiply freely by mitosis and by 5th month of the intrauterine life the two ovaries contain 6-7 million germ cells.
(ii) Formation of oogonia ceases by the 7th month and at term all the oogonia have become Primary Oocytes. There are approx. 2 million 'oocytes' at birth, falling to 300,000 at 7 years. Completion of the first meiotic division does not occur until ovulation at puberty when, after extrusion of the First Polar Body, Secondary Oocytes are formed. The second meiotic division begins immediately, but this division stops at metaphase and is completed only when a sperm penetrates the oocyte.
(iii) During the course of maturation the primary oocyte first becomes surrounded by a basal lamina to form a Primordial Follicle.
(iv) The spindle shaped cells inside the basal lamina become cuboidal forming Primary Follicle
(v) Later, these cuboidal cells multiply to Granulosa Cells, around which stromal cells outside the basal lamina differentiate to form the Theca. The "Theca" is vascularized but granulosa cells receive no blood supply.
(vi) The 'oocyte' is immediately surrounded by Zona Pellucida through which protoplasmic processes pass from the granulosa cells to make contact with the cell membrane of the oocyte and may provide nutrients and maternal proteins.
(vii) The zona pellucida is surrounded by follicular cells called membrana granulosa. The cells are called granulosa cells.
(viii) The membrana granulosa is surrounded by the theca interna (theca= cover) and theca externa.
(ix) The follicle has an eccentric follicular cavity or follicular antrum filled with a fluid, the liquor folliculi.
(x) The oocyte adheres to the wall of the follicle through a pedicel, the cumulus oophorus formed by granulosa cells and thus, remains suspended in the liquor folliculi.
(xi) Later, the granulosa cells lying in close vicinity of the oocyte and zona pellucida, become elongated to form the corona radiate.
(xii) After the 7th month of intrauterine life some of the primary follicles show accumulation of fluid rich in oestrogen, which comes from the granulosa cells and thus form Graafian Follicles (also called secondary follicles).
(xiii) The total number of follicles in two ovaries of a normal young adult woman is about four lakhs.
(xiv) Many ovarian follicles (during primary oocyte stage) undergo degeneration. This degenerative process of follicles is called follicular atresia and such follicles are known as atretic follicles.
(xv)The release of secondary oocyte from the ovary is called ovulation. It occurs due to the rupturing of ovarian follicle and the wall of the ovary.
(xvi) 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).
(xvii) In addition to releasing an oocyte, the follicle also produces hormones. While the follicle is maturing, some of the follicular cells produce oestrogens, mainly estradiol.
(xviii) After ovulation many of the follicular cells enlarge and fill with a yellow pigment, lutein. a follicle is called a corpus luteum( yellow body).
(xix) The luteal cells secrete small amounts of estradiol hormone and significant amounts of the progesterone hormone.
(xx) Corpus luteum also secretes relaxin hormone.
(xxi) Degenerated part of the corpus luteum is called corpus albicans(white body).
(i) The vagina is a tube, about 10 cm long, that extends from the cervix to the outside of the body.
(ii) 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.
(iii) The opening of the vagina, called the vaginal orifice (vaginal opening), is partially covered by a membrane called the hymen.
- External genitalia (Vulva).
The external genitalia are collectively called the vulva that consists of different structures like.
- Mons pubis. It is the anterior most portion of the external genitalia which is a fatty area covered with skin and pubic hair.
- (b) Posterior to the mons pubis is the clitoris which corresponds to the penis of the male. It contains erectile tissue.
- Clitoris differs from male penis as it is very much reduced in size and does not have any passage (it is solid structure, however, male penis has urethra).
- There are present urethral orifice (urethral opening) and vaginal orifice (vaginal opening) in the midline of the vulva.
- Labia majora. These are two large thick folds of skin which form the boundary of vulva. They are partly covered by pubic hair and contain large number of sebaceous (oil) glands. The labia majora are considered homologous to the scrotum of the male.
- Labia minora. These are two smaller folds of skin which lie between the labia majora. Posteriorly the labia minora are fused together to form the fourchette. They also contain numerous sebaceous glands. The area between the labia minora is called the vestibule.
- Perineum is the area which extends from the fourchette to the anus. The clinical perineum is the area between the vaginal orifice (opening) and the anus.
Vestibular glands are of two types.
- Paraurethral glands or glands of Skene:- The lesser vestibular glands (= Paraurethral glands or glands of Skene) are numerous minute glands that are present around the urethral orifice (opening). These glands are homologous to the male prostate and secrete mucus.
- Bartholin's glands :- The greater vestibular glands (= Bartholin's glands) are paired glands, situated one on each side of the vaginal orifice (opening). These glands are homologous to the bulbourethral (Cowper's) glands of male and secrete viscid fluid that supplements lubrication during sexual intercourse.
Important notes by AKB sir:-
- After birth no new oocytes are formed. On the other hand, in the male, spermatogenesis begins at puberty and new sperms are continually being formed thereafter, to gradually cease in old age.
- Only 300-400 follicles proceed to 'ovulation' during the years of female fertile life from menarche to menopause.
All oestrogen are steroid hormones with cholesterol as the main precursor.
The physiological active natural oestrogens are:
- 17 β-oestradiol (most potent);
- oestrone, intermediate precursor of (1), and
- oestriol (least potent).
- Theca interna cells of the graafian follicles. These cells have many LH receptors.
- Granulosa cells of the graafian follicles
- Adrenal cortex - in small amounts.
- Testis - in small amounts
- 97% circulates in blood bound to plasma
- 60% to albumin
- (ii) 37% bound-firmly to gonadal steroid binding globulin - GBG.
Total (free + bound) plasma oestradiol level is 50-300 pg/mL.
- 3% circulates in blood in free form.
- In females:
(i) 35-500 µgm/day in different stages of menstrual cycle. There are two peaks of secretion: 1st just before ovulation (200-500 µgm/day), and 2nd during mid luteal phase (250 µgm/day).
(ii) 15-45 mg during pregnancy.
(iii) After menopause, decreases to low levels.
- 2. In males: 50 µgm/day.
Circulating oestrogens are conjugated in the liver to form water soluble sulphates and glucuronides which are then excreted.
(i) 65% excreted in urine, 80% of which is excreted as oestrone and oestriol; and remaining 20% as
(ii) 10% excreted in faeces.
The fate of remaining 25% is not known.
Mechanism of Action
It is specifically and rapidly taken up by target organs, such as uterus, vagina, anterior hypothalamus and anterior pituitary, in which there is a specific binding protein in the cell cytoplasm or in lysosomes. The bound product rapidly enters the nucleus and via DNA and RNA initiates changes which enhance cell replication and/or protein synthesis .
- It is a C21 steroid.
- Corpus luteum and the placenta (major source).
- (ii)Testes and adrenal cortex (in small amounts).
- It is non-hormone i.e. it has no action of its own.
- Plasma level
- in men - 0.3 mg/mL
- (ii) in women - 0.9 mg/mL during follicular phase of menstrual cycle which increases by 20 folds during the luteal phase.
- Transport: 98% circulates in blood bund to plasma proteins; 80% is bound to albumin and 18% is bound to GBG; and approx. 2% circulates in blood in free form.
- It has a short half life and is converted in the liver to pregnediol, which is conjugated to glucuronic acid and excreted in the urine.
- Mechanism of Action: It acts by an action on DNA to initiate synthesis of new mRNA.
- It is a polypeptide with MW 8000.
- Corpus luteum (mainly); its concentration increases in tissues and blood during
- (ii) Also produced by the uterus and the placenta.
- (iii) In the prostate gland in males.
(i) Facilitates delivery by:
(a) Relaxation of the symphysis pubis and other pelvic joints.
(b) Inhibition of uterine contractility, and
(c) softening and dilatation of the cervix.
(ii) In males, it is found in semen, where it helps to maintain sperm motility and aid in sperm penetration of the ovum.