Structure of overies | Follicular Development | Ovulation | Biology | NEET

FEMALE REPRODUCTIVE SYSTEM

The female reproductive system consists of a pair of ovaries, a pair of Fallopian tubes or oviducts, uterus, vagina, external genitalia or vulva. A pair of mammary glands or breasts are also considered as part of reproductive system due to their role in child care.

Ovaries

Ovaries are the primary sex organs in human female . They are paired structures located in the upper pelvic cavity

Each ovary is held in place within peritoneal cavity by several ligaments.

Structure of ovaries

Anatomically , it is differentiated into following parts - germinal epithelia , the outermost layer of the ovary which forms oogonia in the fetus ; is made up of squamous or alboidal epithellum , tunica albuginea , sheath of dense connective tissue that lies below germinal epithelium and ovarian stroma , differentiated into dense outer cortex and less dense inner medulla .

At birth the ovaries contain an estimated total of 2 to 4 million oogonia ( egg mother cells ) . No more oogonia are formed and added after birth.

Foilicular development

During feial life , all the oogonia develop into primary oocytes , which then begin a first meiotic division by replicating their DNA They do not complete the division in the fetus .

Accordingly , all the eggs present at birth are primary oocytes which contain 46 chromosomes each with two sister chromatids . The cells are said to be in a state of meiotic arrest

This stare continues until puberty and the onset of renewed activity in the ovaries .

The dormant primary oocyte surrounded by follicular cells in the ovary of a newborn female is called primordial follicle .

At puberty , oogenesis is resumed and primordial follicle enlarges to form primary follicle .

in the primary follicle , development proceeds , the follicular cells keep dividing to form several layers around the primary copte and at this stage these cells are known as the granulosa cells .

The primary cocyte secetes an acellular glycoprotein layer around itself called the zona pellucida .

As the granulosa cells keep on dividing a small cavity appears between these cells called the antrum which is filled with a fluid, liquor folliculi , secreted by the granulosa cells . At this stage the follicle is known as secondary follicle.

Around the granulosa cells , connective tissue of ovanan stroma get differentiated into two layers a vascular theca interna and a fibrous theca externa .

The Innermost layer of granulosa cells around the zona pellucida consists of columnar cells and is known as the corona radiata .

Ovulation

The fully formed mature dominant follicle with a large antrum is called Graafian follice. It has a primary oocyte , which is still in meiotic arrest . Just before ovulation this primary oocyte completes its first melotic division to form a haploid secondary oocyte and a polar body .

This secondary oocyte is released in the peritoneal cavity during ovulation from where it is picked up by the fimbria of the oviduct.

The ovulated secondary oocyte is carried into the Fallopian tube where fertilisation occurs .

Manish Mevada

M.Sc, M.Phil, B.Ed