NEET Exam  >  NEET Notes  >  Biology Class 12  >  Menstrual Cycle: Introduction, Duration & Phases

Menstrual Cycle: Introduction, Duration & Phases | Biology Class 12 - NEET PDF Download

Menarche

The beginning of menstruation or first menstruation is called menarche. The beginning menstruation varies. It usually occurs between 12 and 15 years.

Menstrual Cycle

Duration – 28 Days (Range - 22 to 32 days)

Menstrual Cycle: Introduction, Duration & Phases | Biology Class 12 - NEET

This is exhibited by the primate group of animals. In this cycle, the female body prepares itself for a possible pregnancy. If the pregnancy does not occur then the body aborts all preparation done and restarts the preparation for pregnancy again in a monthly cyclic manner.

Menstrual Cycle: Introduction, Duration & Phases | Biology Class 12 - NEETFlow Chart of Menstrual CycleThe menstrual cycle has three main phases:

  • Bleeding phase or menstruation phase.
  • Proliferative/preovulatory/follicular phase or oestrogenic phase.
  • Secretary/post-ovulatory/luteal phase or progesterone phase.
    Menstrual Cycle: Introduction, Duration & Phases | Biology Class 12 - NEET
    Schematic Diagram of Menstrual Cycle

Question for Menstrual Cycle: Introduction, Duration & Phases
Try yourself:
At what age does menarche typically occur?
View Solution

1. Bleeding Phase

The cycle starts with the bleeding phase in its first four to five days. During this bleeding, the part of the layer of the endometrium gets shed off. The total loss of blood per day is about 20 ml, so an average of 40 to 80 ml blood/cycle is lost. This blood can not clot.

2. Preovulatory/Proliferative Phase

  • After the first four of five days this phase begins. During this phase, due to the release of some GnRH, the Pituitary secretes some FSH to stimulate the ovarian follicle. The ovarian follicle now begins to develop.
    Menstrual Cycle: Introduction, Duration & Phases | Biology Class 12 - NEET
    Level of Hormones during Menstruation
  • Developing follicle now starts secreting an increasing amount of estrogen. The rising level of estrogen causes the endometrium to proliferate and thicken
  • It also causes an increase in the vascularity and granularity of the endometrium. The rising level of estrogen also activates the hypothalamus. 
  • Due to this, the hypothalamus releases more GnRH. This GnRH induces the pituitary to release more of FSH. The rising FSH levels now cause :
    (i) Further growth and development ovarian follicle to form Graafian follicle
    (ii) Even further release of estrogen from the theca interna of this developing follicle.
  • As the estrogen level goes on rising, by the end of 10 days the extreme levels of estrogen (which have by then caused maturation of Graafian follicle and growth of endometrium) now give positive feedback of high concentration of estrogen causing a rise in LH secretion but due to release of inhibin by graffian follicle, FHS falls secretome falls, therefore, the LH secretion from the pituitary goes on rising. 
  • This abrupt rise (on the 11th to 13th day) in LH concentration in blood is called an LH surge. This LH now causes the Graafian follicle to rupture after partial completion of II meiotic division in oocyte and thus the secondary oocyte released. The release of an egg (secondary oocyte) which occurs around 14 days is called ovulation.

3. Postovulatory/Secretory Phase

  • After ovulation, the ruptured Graafian follicle transforms into the corpus luteum. The granulosa and theca cells of the ruptured Graafian follicle (which is now called corpus luteum) are found only in mammals and contain yellow lutein or carotene pigment.
  • In case of absence of pregnancy, this corpus luteum will get degenerated after 14 days of its formation. The degenerated corpus luteum is called corpus Albicans (white body).
  • Stimulated by the rising levels of LH, the corpus luteum secretes the progesterone hormone.
  • The progesterone facilitates the preparation of the endometrium for receiving the embryo and its implantation. Progesterone inhibits the contractions of the uterus so that the pregnancy could be maintained. 
  • Progesterone also inhibits the development of the next new ovarian follicle. If pregnancy occurs then the corpus luteum persists and secretes progesterone. 
  • Progesterone is important to maintain the pregnancy and it is thus called the pregnancy hormone
  • By the fourth month of pregnancy, the placenta has developed completely. 
  • This placenta now takes over the job of further progesterone secretion. 
  • Ovary also secretes some amount of relaxin at the time of parturition
  • If pregnancy does not occur after ovulation, then as the progesterone level rise, its rising levels inhibit the release of GnRH from the hypothalamus. Due to this FSH, LH secretion by the pituitary falls and thereby progesterone secretion by the corpus luteum (which was due to the influence of LH) also now falls. 
  • As the progesterone level drops, the corpus luteum begins to degenerate and transform in corpus Albicans (which can not secrete progesterone). Due to the lack of progesterone.
    1) The overgrown endometrium now begins to break and separate from the inner uterine wall causing bleeding.
    2) The uterine contraction (which was till now inhibited due to the presence of progesterone) now starts.
  • Thus the separated endometrium along with blood is now being passed out via the vaginal route. 
  • This is again the beginning of the next menstrual or bleeding phase. 
  • The period between ovulation and the next menstrual bleeding (post-ovulatory period) is always constant (i.e. 14 days). 
  • However, the ovulation date may vary (causing a change in the pre-ovulatory period).
  • After ovulation, the ovum is viable only for two days, while sperms introduced into the vagina can survive for a maximum of four days. 
  • On the basis of the above data, the safe period method for family planning is calculated. 
  • Normally it is considered to be day 1 to day 8 and then from day 20 to day 28.

Phases of Menstrual CyclePhases of Menstrual Cycle

Question for Menstrual Cycle: Introduction, Duration & Phases
Try yourself:
During which phase of the menstrual cycle does the release of an egg (secondary oocyte) occur?
View Solution

Description of Different Phases of Menstrual Cycle

Menstrual Cycle: Introduction, Duration & Phases | Biology Class 12 - NEET

Menopause

It is a medical term that refers to the cessation of menstruation. It is the period in a woman's life when ovulation and menstruation cease. Period. It occurs between the ages of 45 and 55. Some women experience irregular menstrual cycles for months or years before menopause. Others simply discontinue menstruation abruptly.

Symptoms. The uterus and vagina gradually deteriorate (decreased work). During menopause, women may experience temporary depression, hot flashes, and other physiological and psychological issues. The majority of these symptoms can be alleviated by taking hormones prescribed by a doctor. However, due to some negative side effects, hormone replacement therapy is not recommended.

The document Menstrual Cycle: Introduction, Duration & Phases | Biology Class 12 - NEET is a part of the NEET Course Biology Class 12.
All you need of NEET at this link: NEET
158 videos|393 docs|239 tests

Up next

FAQs on Menstrual Cycle: Introduction, Duration & Phases - Biology Class 12 - NEET

1. What is menarche?
Ans. Menarche refers to the first occurrence of menstruation in a woman's life. It marks the onset of puberty and the ability to become pregnant.
2. What is the duration of the menstrual cycle?
Ans. The duration of the menstrual cycle varies from woman to woman, but on average, it lasts about 28 days. However, cycles can range anywhere from 21 to 35 days.
3. What are the phases of the menstrual cycle?
Ans. The menstrual cycle consists of four phases - the menstrual phase, the follicular phase, the ovulatory phase, and the luteal phase. The menstrual phase is when menstruation occurs, the follicular phase is when the egg develops, the ovulatory phase is when the egg is released, and the luteal phase is when the uterus prepares for pregnancy.
4. What are the common symptoms experienced during the menstrual cycle?
Ans. Common symptoms experienced during the menstrual cycle include bloating, breast tenderness, mood swings, fatigue, and cramps. These symptoms can vary in intensity and duration from woman to woman.
5. What is menopause?
Ans. Menopause refers to the natural cessation of menstruation in a woman's life. It usually occurs between the ages of 45 and 55 and marks the end of the reproductive years. During menopause, hormone levels change, leading to various physical and emotional changes in a woman's body.
158 videos|393 docs|239 tests
Download as PDF

Up next

Explore Courses for NEET exam

How to Prepare for NEET

Read our guide to prepare for NEET which is created by Toppers & the best Teachers
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Download the FREE EduRev App
Track your progress, build streaks, highlight & save important lessons and more!
Related Searches

mock tests for examination

,

video lectures

,

Duration & Phases | Biology Class 12 - NEET

,

shortcuts and tricks

,

Summary

,

pdf

,

Previous Year Questions with Solutions

,

practice quizzes

,

Menstrual Cycle: Introduction

,

Duration & Phases | Biology Class 12 - NEET

,

ppt

,

Free

,

Menstrual Cycle: Introduction

,

Important questions

,

Semester Notes

,

Sample Paper

,

Exam

,

MCQs

,

Extra Questions

,

Viva Questions

,

Duration & Phases | Biology Class 12 - NEET

,

past year papers

,

Menstrual Cycle: Introduction

,

Objective type Questions

,

study material

;