NEET Biology Notes Animal Reproduction day and Reproductive Health Female Reproduction
The female reproductive system consists of a pair of ovaries along with a pair of oviducts, uterus, cervix, vagina and the external genitalia located in pelvic region.
- Ovary and its Anatomy
These are two in number, 3 cm long 2 cm wide and 1 cm thick, almond-shaped female gonads. The ovary remains attached to the abdominal wall by a ligament called mesovarium. 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.
- Cortex is covered by tunica albuginea (dense connective tissue layer), which imparts the whitish colour to the ovary.
- Surface of the ovary is covered by germinal epithelium, which is formed of simple squamous or cuboidal epithelial cells.
- The fluid of the antrum is called liquor folliculi.
- Maturing oocyte connects to wall of follicle through cumulus oophorus, which is formed by granulosa cells and remains suspended in the liquor folliculi. The oocyte of mammal is enclosed in a perforated membrane called zona pellucida. Next to zona pellucida, cells of inner margin of discus proliferous (cumulus) present a characteristic radial arrangement and is termed as corona radiata.
- Follicle itself have three layers, i.e. outer theca externa, middle theca interna and inner membranous granulosa.
- Generally, only one ovum is liberated in each menstrual cycle by alternate ovaries. Average duration of menstrual cycle is 28 days.
- A woman produces about 450 ova in her entire reproductive life span. Reproductive life of a girl begins from menarche (first menstrual flow about 10-16 years age) and ends by menopause (about 40-50 years of age).
- If fertilisation takes place, corpus luteum persists and enlarges by influence of Luteinizing Hormone (LH).
- If fertilisation does not occur then corpus luteum will degenerate and endometrium will separate from uterus.
- Oviduct or Fallopian Tube
Fertilisation in mammal occurs in Fallopian tube (10-12 cm) (i.e. upper portibn or ampulla). The embryo develops up to blastocyst stage in Fallopian tube. Fallopian tube conveys ovum from the ovary to the uterus through peristalsis. Fallopian tube consists of uterine part, isthmus, ampulla and infundibulum. At the junction of isthmus and ampulla fertilisation occurs. The wall of the oviduct is composed of three layers; a mucosa at the luminal surface, followed by a muscularis and a serosa, composed of visceral peritoneum.
- Uterus (Womb)
Uterus consists of body or corpus, a narrow uterine cavity and a lower cylindrical structure, the cervix. The attachment of developing foetus (trophoblast) with the wall of the uterus is known as implantation#.. Implantation takes place after 7 days of fertilisation (7-10 days in human). The outermost invest of the uterus, is either the serosa (connective tisspe or mesothelium) or the adventitia (connective tissue only).
There are no glands in vagina. The wall of vagina consists of mucosa, a muscular layer and an adventitia. The vagina opens to the exterior by an aperture called vaginal orifice (vaginal opening).
- External Genitals
External genitals are as follows :
- Vestibular Gland (Bartholin’s Gland)
Occurs in female mammals and helps in vestibular lubrication. Bartholin’s gland of female corresponds to bulbourethral gland (Cowper’s gland) of the male.The hymen is a thin mucous membrane that stretches across the opening of the vagina. The hymen is normally ruptured during female’s first copulation. It may be broken during sports event or riding. Vestibule opens to outside through vulva or urinogenital opening guarded by two labia majora (in rabbit). The scrotal sacs of a male mammals are homologous to labia majora of female.
- Mammary Glands
The mammary glands are modified sweat glands. Production of milk in mammary glands is stimulated by the hormone prolactin, which is secreted by anterior part of pituitary gland, while the ejection of milk into the ducts of mammary glands is stimulated by the hormone oxytocin, which is secreted by posterior part of pituitary gland.
The reproductive cycle in female primates (e.g. monkeys, apes and humans) is called menstrual cycle. In human females menstruation is repeated at an average interval of about 28/29 days and the cycle of events starting from one menstruation till the next one is called menstrual cycle.
The first menstruation begins at puberty is called menarche. One ovum is released during the middle of each menstrual cycle. The cycle starts with the menstrual phase and the menstrual flow lasts for 3-5 days. Lack of menstruation may be indicative of pregnancy. However, it may also be caused by stress, poor health, hormonal imbalance, etc. The LH level decreases causing regression of corpus luteum.
The next phase is proliferative phase, in which primary follicles in the ovary grow to become fully mature Graafian follicle. Simultaneously the endometrium of uterus regenerates through proliferation. In the ovulatory phase, both LH and FSH hormone levels attain maximum level during mid cycle called LH surge. This induces rupture of Graafian follicle and thereby the release of ovum (ovulation).
The ovulatory phase is followed by luteal phase in which the remaining parts of the Graafian follicle transform as the corpus luteum. The corpus luteum secretes large amounts of progesterone, which is needed for the maintenance of endometrium, which is required for implantation of fertilised ovum and other events of pregnancy. In the absence of fertilisation, the corpus luteum degenerates. This causes disintegration of endometrium leading to a new cycle of menstruation. Menstrual cycle ceases around 50 years of. age, i.e. menopause.
It is the production of gametes (i.e. both male and female gametes). The production of male gametes or sperms is called spermatogenesis and the production of female gamete or egg is called oogenesis. Spermatogenesis occurs in testes and oogenesis in ovaries. Both spermatogenesis and oogenesis involve meiotic division (reduction division), which halves the number of chromosomes from diploid condition (i.e. the presence of two sets of chromosomes) to haploid condition (i.e. the presence of single set of chromosomes).
Oogenesis in initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each foetal ovary, no more oogonia are formed and added after birth. Spermatogenesis is a continuous process of sperm production in seminiferous tubules of the testes. Both spermatogenesis and oogenesis start with cells in the outer layer of the gonad known as the germinal epithelium. Spermatogenesis and oogenesis involve three stages :
- Multiplication Stage
The stage in which involves repeated mitotic divisions producing many spermatogonia and oogonia.
- Growth Stage
The stage in which spermatogonia and oogonia undergo a period of growth in preparation for the first meiotic division and cell division.
- Maturation Stage
The stage in which first and second meiotic division occur followed by the formation of mature haploid gametes. Cells formed by gametogenesis show variation due to independent assortment of chromosomes and crossing over.
- Multiplication Stage
Structure of Sperm
- Sperm is a microscopic structure composed of head, neck, middle piece and a tail.
- The sperm head contains an elongated haploid nucleus, the anterior portion of which is covered by a cap-like structure acrosome.
- The uppermost pole of an egg that is the site of maturation division is called animal pole. The lower pole of the ovum that is opposite to the animal pole is called vegetal pole.
- The cytoplasm of ovum is called ooplasm. The egg is covered by three kinds of membranes.
- The sperms in the female’s genital tract are made capable of fertilising the egg by secretions of the female genital tract. These secretions alter or remove certain molecules from semen. This process is known as capacitation.