Menstrual Cycle

When we talk about biology, the subject is endless and limitless. If you start observing things around, you will find biology in each and everything - a tree, birds, little ants moving around, and so on.

When you break the word biology, you get ‘bio’, which means life and ‘logy’ means study. So biology is nothing but the study of life around you. In this particular article, we will study one such important concept of biology that is the Menstrual Cycle. 

Table of content - 

• An introduction

• Structure of reproductive organ

• Phases of Menstrual cycle 

1. Menstrual Phase

2. Follicular Phase

3. Ovulatory Phase

4. Luteal Phase 

• Hormonal control of menstrual Cycle 

• Key points from the Chapter

• Frequently Asked Questions

Introduction

Scientifically, a man’s reproductive age starts from puberty till death. This means a man can reproduce throughout his life, starting from puberty. Contrary to this, a woman’s reproductive age is much shorter. They can only reproduce for a period between puberty and menopause. The phase-in between when a woman is in her reproductive stage of life is also called the menstrual age. A menstrual cycle is the process of ovulation or egg production and menstruation in women. It is a natural change that regularly occurs in a female reproductive system, which also is the basis of pregnancy.

During this phase, a woman’s body goes through a variety of changes. The menstrual cycle ensures the production of oocytes and prepares the uterus for pregnancy. When an ovum is not fertilized in the absence of the sperm, the lining of the uterus sheds and leads to a haemorrhage called menstruation. The menstrual age starts from the age of 10 to 15 when a girl attains puberty and this beginning is known as menarche. The cessation of menstruation is called menopause which usually takes place at the age of 50.

The menstrual cycle begins with the first day of bleeding and the cycle repeats itself every 28 to 33 days, depending on the individual menstrual cycle. Let’s quickly understand a female reproductive organ in short first before moving on to the menstrual cycle.

A Female Reproductive System Consists of the Following-

• A pair of ovaries- It releases the ovum or the egg.

• A uterus or womb- It’s where a fertilized egg gets implanted and fetal development occurs.

• A pair of Fallopian Tubes- These tubes connect the ovaries to the uterus.

• A girl is born with a pre-decided number of ovaries that she will produce in her reproductive stage. During puberty, various hormones trigger the production and release of eggs.

Phases of Menstruation Cycle

Each cycle of menstruation occurs in four different phases-

1.  Menstrual Phase

It’s the phase when the uterus lining or the endometrial lining is shed off from the body. It’s marked as the day1 of periods which normally lasts for 3 to 7 days. The endometrial fluid is composed of the blood, cells from the lining of the uterus (endometrial cells), and mucus.

2.  Follicular Phase

Followed by hormonal stimulation, the ovary produces around 5 to 20 follicles (tiny nodules or cysts), which bead on the surface. Each follicle consists of an immature egg. Out of these, only one follicle matures into an egg. Finally, a mature egg follicle releases an egg from one of the two ovaries. The follicular growth also stimulates the lining of the uterus to thicken in preparation for a possible pregnancy.

3.  Ovulatory Phase

This is also known as the Mid-cycle phase. It is marked by the release of a mature egg from the surface of the ovary. Day 13-17 is mostly the period of ovulation. Various hormones trigger ovulation and simultaneously release the egg into the fallopian tubes. The egg swiftly moves through the fallopian tubes towards the uterus. If fertilization occurs within 24 hours, the egg turns into an embryo. If not, it dies and disintegrates.

4.  Luteal Phase

The ruptured follicle that had stayed behind on the surface of the ovary during the ovulatory phase starts to develop into a structure called the corpus luteum. This layer releases hormones to thicken the uterine lining for any possible implantation of a fertilized egg. Corpus luteum is maintained if pregnancy is established. If pregnancy doesn’t occur, it disintegrates. This usually occurs at 22-28 days. Another set of hormonal changes causes the uterine lining to fall away, thus causing menstruation. The next cycle starts with this.

(Image will be uploaded soon)

Hormonal Control of Menstrual Cycle

Hormones are chemical messengers in the body, directing the body what to do and when. They are produced and released by endocrine organs. The menstrual cycle is also a process controlled by hormones in the female body. Some exclusive female hormones are released to bring about every cycle of menstruation. Varying levels of hormones- Estrogen, Progesterone, Luteinizing Hormone (LH), and Follicle Stimulating Hormone (FSH) different direct phases of the menstrual cycle.

• FSH

It is released by the pituitary gland on signalling from the hypothalamus. It stimulates the ovary to produce egg follicles.

• LH

Rising levels of LH which are also prompted by the hypothalamus and released by the pituitary gland trigger ovulation and lead to the release of the egg in fallopian tubes.

• Estrogen

It is the hormone that prompts the growth of the uterine lining or the endometrial lining.

• Progesterone

The corpus luteum releases some amounts of progesterone to maintain the thick lining of the uterus for a possible healthy pregnancy.

Thus, various female hormones do their part in keeping the menstrual cycle regular and making the ovaries release one egg every month for fertilization.

Menstruation is a biofeedback system. Each structure and gland involved are affected by the activity of others. And malfunctioning of any leads to an onset of menstrual problems and diseases. Various female hormones regulate the menstrual cycle along with leading to some other chemical and physical changes in the female body.

Key points from the chapter - 

• A woman's reproductive cycle is shorter than a man’s cycle as women have a specific time frame from puberty to menopause. 

• The natural and biological process of the menstrual cycle helps in the formation of eggs in a woman's body. This is basic for pregnancy. 

• When the eggs are not fertilized with sperms, the menstruation cycle continues to take place every 24 - 28 days. 

• The menstrual cycle is divided into four phases, and these phases have different roles to play. 

• Hormones are nothing but chemical messenger in the body and give it directions. 

• The process of menstruation is natural and social stigmas should not be attached to the process.

• Both genders need to be educated about the female’s reproductive health.