Phases of Menstrual cycle and Fertilization.

Importance of fertilization.

(a) It acts as a stimulant for the egg to finish maturing.

(b) Through recurrent mitotic division, it stimulates the ovum to grow into a new person.

(c) Fertilization restores the zygote’s diploid number of chromosomes (46 in man) by adding the haploid set of chromosomes from the male.

(d) It increases the metabolic activity of the egg.

(e) It mixes the personalities of two parents while introducing new elements. As a result, contribute to evolution.

(f) Sperm sex chromosomes are either X or Y, which aids in sex determination.

(g) Fertilization membrane, produced after sperm entry, prevents new sperm from entering.

(h) The axis of division is set by the copulation path.

Cycle of Menstruation

(1) Humans, apes, and old world monkeys all have menstrual periods.

(2) Menstruation is the bleeding of adult females’ uteruses at one lunar month intervals.

(3) Menarche is the start of menstruation or the first (1st) period.

(4) The start of menstruation differs from person to person. It usually happens between the ages of 12 and 15.

(5) The Menstrual Cycle is the sequence of events that occurs from one menstruation to the next.

(6) In human females, menstruation occurs every 28/29 days on average.

(7) During the midst of each menstrual cycle, one ovum is discharged (ovulation).

(8) Certain hormones, some of which are released by the pituitary gland, regulate it.

(9) releasing factors produced in the hypothalamus stimulate the pituitary gland.

(10) The pituitary gland’s hormones have an effect on the ovaries. The ovaries’ hormones have an effect on the uterus’s walls.

Menstrual Cycle Phases

The menstrual cycle is being grouped into four phases:

(1st Phase ) The Menstrual Cycle:

(i) Menstruation occurs on days 3-5 of a 28-day menstrual cycle.

(ii) LH production from the pituitary gland’s anterior lobe is diminished.

(iii) The corpus luteum degenerates when this hormone is absence, resulting in a reduction in progestrone synthesis.

(iv) Oestrogen production is also lowered during this time.

(v) The uterine endometrium breaks down, and menstruation begins.

The menstrual flow is made up of cells from the endometrium, blood, and unfertilised ovum.

(2nd Phase ) Follicular Phase:

(i) In a 28-day cycle, this phase normally comprises cycle days 6-13 or 14.

(ii) The anterior lobe of the pituitary gland secretes follicle stimulating hormone (FSH), which stimulates the ovarian follicle to secrete oestrogens.

(iii) Oestrogen causes the endometrium of the uterine wall to proliferate.

(iv) Rapid cell proliferation thickens the endometrium, which is accompanied by an increase in uterine glands and blood vessels.

(3rd Phase ) Ovulatory Phase: 

(i) In the middle of the cycle, both Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH) reach their highest levels (about 14th day).

(ii) The amount of oestrogen in the blood increases.

(iii) There is a great secretion of Luteinizing hormone (LH) which causes graffian follicle rupturing and, as a result, leads to ovum discharge.

(iv) Luteinizing hormone does, in fact, cause ovulation.

Luteal Phase (4th Phase ):

(I) Cycle days 15 to 28 are included.

(ii) Progestrone is secreted by the corpus luteum.

(iii) The endometrium thickens .

(iv) The uterine glands begin to secrete.

Menstrual Cycle Hormonal Control

(i) Follicle-stimulating hormone (FSH) increases the production of oestrogens by ovarian follicles.

(ii) Luteinizing hormone (LH) promotes progestrone secretion in the corpus luteum.

(iii) The increased synthesis of oestrogens causes the menstrual phase.

(iv) Luteinizing hormone (LH) is responsible for ovulation.

(v) The increased production of oestrogens causes the proliferative phase.

(vi) The secretory phase is brought on by a rise in progestrone production.