Test: Gametogenesis & Menstrual Cycle (November 3) - NEET MCQ

During embryonic development the primordial germ cells migrate to the testis where they become spermatogonia. At puberty the spermatogonia proliferate rapidly by mitosis. Some undergo growth phase to become primary spermatocytes that further undergo through meiotic division I to become secondary spermatocytes. After completion of meiotic division II the secondary spermatocytes produce spermatids which differentiate to form spermatozoa.

The axial filament in the tail of human sperm has 9+2 microtubular arrangement like that of flagella and cilia.

Oogenesis is the process of formation of functional haploid ova from the diploid germinal cells in the ovary. Oogenesis begins during embryonic development but is completed only at puberty of the secondary oocyte with the sperm.

In human males, the primordial germ cells divide mitotically and produce spermatogonia. Some of the spermatogonia grow into large primary spermatocytes. Each primary spermatocyte undergoes first maturation division which is a reductional (meiotic) one. Thus, the primary spermatocyte divides into two haploid daughter cells called secondary spermatocytes. Each secondary spermatocyte now undergoes second maturation division which is a mitotic one. Thus, each secondary spermatocyte gives rise to two spermatids that undergo transformation to form two sperms. Overall, two secondary spermatocytes give rise to four sperms.

The middle piece of sperm contains mitochondria coiled around the axial filament. They provide energy for the movement of the sperm.

If fertilisation does not occur, the secondary oocyte undergoes autolysis and progesterone (secreted by persistent corpus luteum) inhibits the release of LH from pituitary. Reduction of LH level causes regression of corpus luteum by autolysis and thus fall in the progesterone level in the blood. Due to deficiency of progesterone, uterine lining sloughs off causing bleeding. This whole phase is called bleeding phase.

Menstrual flow occurs due to shedding of the endometrium, which is the inner lining of the uterus.

Estrogen secreted from ovarian follicles under the influence of FSH, causes proliferation of the endometrium of the uterine wall.

Follicular atresia means degeneration of follicles. Thus, if all follicles get degenerated at the age of 45-50 years, there will be no ovulation and hence no menstruation which leads to menopause.