02 Reproduction in Lower and Higher Animals - part 04 - Female Reproductive System

02 Reproduction in Lower and Higher Animals - part 04 - Female Reproductive System

Female Reproductive System:

• The female reproductive system consist of the following parts -

1. A pair of ovaries 
2. A pair of oviducts 
3. Uterus 
4. Vagina 
5. External genitalia (vulva) 
6. A pair of vestibular glands 
7. A pair of mammary glands

1. Ovary :

• It is the primary female sex organ. 
• Its main function is production of egg or ovum and the female reproductive hormones. 
• It is solid, oval or almond shaped organ. 
• It is 3.0 cm in length, 1.5 cm in breadth and 1.0 cm thick. 
• It is located in the upper lateral part of the pelvis near the kidneys. 
• Each ovary is held in position by ligaments by attaching it to the uterus and the abdominal wall. 
• The largest of these is the broad ligament formed by a fold of peritoneum. It holds the ovary, oviduct and the uterus to the dorsal body wall. 
• The ovarian ligament attaches ovary to the uterus. 
• The ovary produces five hormones viz, -  
  

1. estrogen
2. progesteron
3. relaxin
4. activin and 
5. inhibin. 

Structure and development of the ovary :

• Each ovary is a compact structure differentiated into a central part called medulla and the outer part called cortex. 
• The cortex is covered externally by a layer of germinal epithelium. 
• The stroma or loose connective tissue of the medulla has blood vessels, lymph vessels, and nerve fibres. 
• The outer cortex is more compact and granular. 
• It shows large number of tiny masses of cells called ovarion follicles.
  
• These are collectively formed from the immature ova originating from cells of the dorsal endoderm of the yolk sac.
• The cells migrate to the gonadal ridge during embryonic development and divide mitotically. Now these cells are called oogonia. 
• As the oogonia continue to grow in size they are surrounded by a layer of granulosa cells and form the rudiments of the ovarian follicles. 
• The process of oogenesis starts much before the birth of the female baby and by the end of twelve weeks the ovary is fully formed.
•  It has more than two million primordial follicles in it.
  
• The cells of germinal epithelium give rise to groups of oogonia projecting into the cortex in the form of cords called egg tubes of Pfluger.
• Each cord at its end has a round mass of oogonial cells called egg nests, from which the primordial ovarian follicles develop. 
• Each primordial follicle has, at its center a large primary oocyte (2n) surrounded by a single layer of flat follicular cells. 
• The primary oocyte starts with its meiotic division but gets arrested it at meiosis I. 
• Of the two million primordial follicles embedded in the foetal ovary only about one million remain at birth and only about 40,000remain at the time of puberty.
• The large scale destruction of the primordial follicles during growth is called atresia. 
• The development of the primordial follicles into mature or Graafian follicles restarts with the onset of puberty.
•  During each menstrual cycle only one of the primordial follicle starts growing to form the Graafian follicle. 
• In each cycle, alternately one of the two ovaries produces theGraafian follicle. 
• The 1st menstrual cycle or menarche begins normally at about 13 years and Menopause i.e. stopping of the cycles happens at age 45 to 55 years. 
• The period in between menarche and menopause is the reproductive age of the female and is approximately 32 years. 
• In this time the female will be producing a maximum of about 416 eggs (32 ×13 = 416 eggs).

Ovarian histology of a mature female :

• In the histology of ovary, we have discussed the primary structure of ovary. 
• The following discussion includes the changes seen in a mature ovary, primarily in the cortex. 
• The different stages of development of the oocyte can be seen. 
• These changes in the ovary are cyclic, occuring during each menstrual cycle and it involves maturation of the primordial follicles into primary, secondary and Graafian follicles.
•  Each primary follicle has multilayered cuboidal follicular cells. 
• The stroma cells add theca over the follicle. It now changes into a secondary follicle. 
• There is growth of the oocyte and the granulosa cells increase in number. They start producing the hormone estrogen. 
• The secondary follicle grows into the Graafian follicle by addition of more follicular cells. 
• As this process of maturation of follicles takes place, they begin to move towards the surface of ovary. 
• The Graafian follicle presses against the thin wall of the ovary giving it a blistered appearance. 
• The egg is released from the Graafian follicle during ovulation and the remaining part of the follicle changes into a temporary endocrine gland called corpus luteum. 
• If fertilization does not take place the corpus luteum degenerates into a white scar called corpus albicans.

Structure of Graafian follicle :

• Graafian follicle is a mature ovarian follicle. 
• An eccentric secondary oocyte is surrounded by a non-cellular layer of zona pellucida secreted by the vitelline membrane of oocyte. 
• The outermost protective and fibrous covering is called theca externa. 
• Inner to it is cellular theca interna. It produces the hormone estrogen. Inner to the theca interna, the follicular cells form the membrana granulosa. 
• From the membrana granulosa the cells differentiate into discus proligerus and the corona radiata cells. 
• Cumulus oophorus is the term used for the oocyte and surrounding granulosa cells . 
• A fluid filled cavity called antrum lies between the oocyte and the membrana granulosa. It is filled with a fluid called liquor folliculi.

2. Oviduct / Fallopian tube / Uterine tube:

• These are a pair of muscular ducts lying horizontally over the peritoneal cavity. 
• The proximal part of the tube lies close to the ovary, and distally it opens into the uterus. Each tube is 10 to 12 cm in length. 
• It is internally lined by ciliated epithelium. 
• It can be divided into three regions :

1. Infundibulum 
2. Ampulla 
3. Isthmus / Cornua

a. Infundibulum :

• The proximal funnel like part with an opening called ostim surrounded by many finger like processes called fimbriae (of these at least one is long and connected to the ovary). 
• The cilia and the movement of fimbrae help in driving the ovulated egg to the ostium. 

b. Ampulla :

• It is the middle, long and straight part of the oviduct. 
• Fertilization of the ovum takes place in this region. 

c. Isthmus / Cornua :

• The distal narrow part of the duct opening into the uterus.

3. Uterus :

• It is commonly also called the womb. 
• It is a hollow, muscular, pear shaped organ, located above and behind the urinary bladder. 
• It is about 7.5 cm long, 5 cm broad and 2.5 cm thick. 
• The uterus can be divided into three regions :

1. Fundus 
2. Body
3. Cervix 

 a. Fundus :

• It is the upper dome shaped part.
•  Normally implantation of the embryo occurs in the fundus. 

b. Body :

• It is the broad part of the uterus which gradually tapers downwards. 

c. Cervix :

• It is the narrow nec about 2.5 cm in length. 
• It extends into the vagina.
•  Its passage has two openings : an internal os towards the body, and an external os towards the vagina. 
• Internally the uterine wall can be distinguished into three layers :

1. perimetrium
2. myometrium
3. endometrium 

• Outermost perimetrium
• middle thick muscular myometrium, made up of thick layer of smooth muscles. Vigorous contractions of these muscles cause labour during the parturition (child birth). 
• The innermost layer called endometrium or mucosal membraneis made up of stratified epithelium. 
• The thickness of this layer regularly undergoes changes in during the menstrual cycle. 
• It is richly supplied with blood vessels and uterine glands. These provide nourishment to the developing foetus.

Uterus cancer:

• Most of the uterine cancers begin in the layer of cells that form the lining of endometrium of uterus. 

Symptoms :

• Abnormal bleeding between periods
• vaginal bleeding after menopause
• an abnormal watery
• blood-tinged discharge from vagina
• pelvic pain. 

Detection :

• It is diagnosed with Pap smear test, biopsy, Ultrasound. 

Treatment :

• Chemotherapy
• radiation
• surgical removal of uterus (hysterectomy).

4. Vagina :

• It is a tubular, female copulatory organ, 7 to 9 cm in length. 
• It lies between the cervix and the vestibule. 
• The vaginal wall has - 

1. an inner mucosal lining
2. the middle muscular layer and 
3. an outer adventitia layer. 

• The mucosal epithelium is stratified and non-keratinised and stores glycogen. 
• There are no glands but the cervical secretion of mucus is recieved in the vagina. 
• The opening of the vagina into the vestibule is called vaginal orifice. 
• This opening is covered partially by a fold of mucus membrane called hymen. 
• The vagina acts as a passage for menstrual flow as well as birth canal during parturition. 

5. External genitalia :

• The external genital organs of female include parts external to the vagina and are collectively called `vulva' (covering or wrapping), or pudendum. 
• They include the following parts : 

1. Vestibule 
2. Labia minora
3. Clitoris 
4. Labia majora
5. Mons pubis

a. Vestibule -

• It is a median vertical depression of vulva enclosing the urethral and vaginal opening. 

b. Labia minora -

• These are another pair of thin folds inner to the labia majora with which they merge posteriorly to form the fore chette 
• while towards anterior end they converge into a hood-like covering around the clitoris.

c. Clitoris -

•  A small conical and sensitive projection lying at the antirior end of labia minora.
•  It has a pair of erectile tissue - The corpora cavernosa and ishomologous to the penis. 

d. Labia majora -

• These are a pair a fleshy folds of skin forming the boundary of vulva. 
• They are homologous to the scrotum. 
• They surround and protect the other parts of external genitalia and enclose the urethral and vaginal openings in the vestibule. 

e. Mons pubis -

• It is a fleshy elevation above the labia majora. 
• The Mons pubis and outer part of labia majora show pubic hair. 

6. Accessary glands / Vestibular glands / Bartholin's glands :

• It is a pair of glands homologous to the Bulbourethral or Cowper's glands of the male. 
• They open into the vestibule and release a lubricating fluid. 

Mammary glands :

• Accessory organs of female reproductive system for production and release of milk after parturition.
•  Development of the mammary gland occurs at puberty under theinfluence of estrogen and progesteron. 
• Lactotropic hormone (LTH) or prolactin helps in development of lactiferous tubules during pregnancy.
• The mammary glands are a pair of rounded structures present in the subcutaneous tissue of the anterior thorax in the pectoral region (from 2nd to 6th rib). 
• These are modified sweat glands. 
• Each mammary gland contains fatty connective tissue and numerous lactiferous ducts. 
• The glandular tissue of each breast is divided into 15-20 irregularly shaped mammary lobes, each with alveolar glands and lactiferous duct. 
• Alveolar glands secrete milk which is stored in the lumen of alveoli. 
• The alveoli open into mammary tubules. 
• The tubules of each lobe join to form a mammary duct. 
• Many mammary ducts join to form a wider mammary ampulla, which is connected to lactiferous duct. 
• These converge towards the nipple located near the tip of the breast. It is surrounded by a dark brown coloured and circular area of the skin called areola.

Do you know ?
Breast cancer :
Symptoms:

• First symptom of breast cancer is a lump in breast or underarm. 
• Lump is painless. 
• Swelling of all or part of breast. 
• Skin irritation, Breast or nipple pain, nipple retraction
• Redness, scaliness or thickening of nipple or breast skin, discharge, etc. 

Detection :

• Mammogram (x-ray)
• ultrasound
• MRI, Biopsy
• Blood test. 

Treatment:

• Radiation therapy
• chemotherapy lumpectomy
• Mammoplasty

Do you know ?
Weaning :

• Mother's milk is replaced gradually by solid food after some time. This process is called weaning.

Puberty / Sexual maturity in Males :

• Puberty is the age at which the reproductive system becomes functional, sex organs begin to produce gametes and sex hormones. 
• In males the onset of puberty occurs at age 12-15 years. 
• Under the influence of testosterone, the secondary sexual characters appear. Thereafter it remains functional throughout the life.

Puberty / Sexual maturity in Females :

• The reproductive system becomes functional at puberty. 
• It is characterised by onset of menstrual cycle also called menarche, which usually occurs at age 10 -14 years. 
• However, unlike in the males, the mature females show cyclic changes in their reproductive system- the menstrual cycles. 
• These cycles continue only upto menopause. This normally happens at age 45-50 years. 
• The period from menarche to menopause is thus the reproductive age of the female. 
• The female is unable to bear children (by natural method) after menopause. 
• Menarche, menstrual cycles and menopause are controlled by gonadotropic hormones.