Test: Oogenesis - NEET MCQ

• In human females, certain cells in the germinal epithelium divide by mitosis to produce a large number of oogonia (diploid).
• The oogonia multiply by mitotic divisions to form primary oocytes (diploid). Each primary oocyte undergoes two maturation divisions.
• In the first meiotic division, the primary oocyte divides into two very unequal haploid daughter cells- a large secondary oocyte and a small first polar body.
• In the second maturation division (mitotic), the first polar body may divide to form two second polar bodies and the secondary oocyte divides to form two unequal daughter cells, a large ootid, and a small polar body.
• The ootid grows into a haploid ovum. Thus, from one oogonium, one ovum and three polar bodies are formed.

• The first menstruation begins at puberty and is called menarche.
• Oogenesis continues till the time the ovarian follicles are receptive to hormones like FSH and oestrogen.
• And it stops around the age of 50 years known as menopause.

Zona pellucida is a thick, transparent, noncellular membrane that encloses a mammalian ovum.

Female egg structure:

The tertiary follicle grows in size and completes its first meiotic division. It is an unequal division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body.

The Corpus luteum produces progesterone and a small amount of estrogen.

The ovarian cycle and the formation of the Corpus Luteum:

The secondary oocyte forms a new membrane called zona pellucida surrounding it. The Graafian follicle ruptures to release the secondary oocyte(ovum) from the ovary by the process called ovulation.

These cells start division and enter into Diplotene of prophase-I of the meiotic division and get temporarily arrested at that stage, called primary oocytes.

• Oogonia are formed during fetal development.
• Soon they start undergoing meiosis but are arrested at Prophase I awaiting further cues of division.
• Oogonia at this stage are called primary oocytes.

In women luteinizing hormone stimulates the last stage of oogenesis, ovulation, development of corpus luteum. Ovulation is controlled by the increased level of LH in the blood.

Estrogen release from follicle is responsible for development of secondary sexual character.

Without pregnancy or fertilization corpus luteum get degenerated as level of LH decrease.

Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary; no more oogonia are formed and added after birth.

Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary.

Secondary spermatocytes & sec. Oocytes both are product of meiosis I and haploid.

• When a woman is born there are usually one million eggs in each ovary and one egg will be released, when she ovulates every month during her menstrual cycle, which is approximately 400-500 eggs over her lifetime.
• As a woman gets older the rest of the eggs disappear, break down or deteriorate and by the time she reaches menopause, there are no eggs left.

• During oogenesis, each primary oocyte gets surrounded by a layer of granulosa cells and then called the primary follicle.
• The primary follicles get surrounded by more layers of granulosa cells and a new theca and called secondary follicles.
• The secondary follicle soon transforms into a mature tertiary follicle or Graafian follicle, which is characterized by a fluid-filled cavity, called an antrum.

Zona pellucida is made up of glycoprotein.

Graffian follicle form before ovulation.

 Follicle-stimulating hormone (FSH) is responsible for the growth and maturation of ovarian follicles in the ovary. FSH stimulates the follicles to produce estrogen, which further aids in the development of the follicles and prepares the endometrium for potential pregnancy.

• The diploid oogonium goes through the first round of meiosis to form primary oocyte, which is arrested at Prophase I.
• Thus, the primary oocyte is also diploid.
• The division is completed after the formation of the secondary oocyte, which is haploid.
• The secondary oocyte undergoes another round of meiosis to form haploid ovum.

In all female between age of puberty till 50, all egg is released in form of secondary oocyte

The tertiary follicle further changes into the mature follicle or Graafian follicle The secondary oocyte forms a new membrane called zona pellucida surrounding it. The Graafian follicle now ruptures to release the secondary oocyte (ovum) from the ovary by the process called ovulation.

Explanation In case of non fertilization, corpus luteum Changes to corpus albicans and not produce progesterone.

The tertiary follicle further changes into the mature follicle or Graafian follicle. The secondary oocyte forms a new membrane called zona pellucida surrounding it.

Corpus luteum have endocrine role develp after ovulation.