A guide to our reproductive system

Alisha Arora
10 min readJan 9, 2021

We all know that time of the month, where we have to go through our period.

The time of the month where there is a lot of ice cream, tears and cramps involved!

Yep! Your period.

I took some time to do a little test and see if women knew why they get their period.

Alarmingly out of 20 of my closest girl friends, only 3 knew why and how our menstruation cycle works.

This being said, it’s time we start understanding our reproductive system.

A Menstrual Cycle lasts 28 days (from the age of early adolescence to menopause) and is a set of two cycles that happen simultaneously.

The two processes go through a women’s body for about 30 ish years.

  1. Uterine Cycle: responsible for the thickening and shedding of the endometrial layer (otherwise known as the period)
  2. Ovarian Cycle: responsible for the changes in the ovary (release of an egg into the uterus)

While two cycles are going on in the 28 days there are also two phases (each is around 14 days)

  • Follicular phase: first day of a period to day 14 when the ovaries release an egg.
  • Luteal phase: all the events that lead up to a period (days 14–28)

It’s important to note that unless a girl is pregnant (temporarily disables menstruation), women will always be in this cycle from around 13 years old to 50 years old.

We have all heard of the dreadful menopause. Oddly enough women go through three main (not one) major transition points.

  1. Menarche
  2. Pregnancy
  3. Menopause

But, first. Let’s understand the reproduction system

This is our reproductive system! Isn’t it exciting?

Now let’s go over the 9 most important parts to have a base knowledge.

  • Uterus: Centre of reproduction! The uterus is also the only organ that can grow another organ (a human!!)
  • Vagina: The vagina is the connector of the uterus to the outside world. It has 3 main uses; a pathway for birth, periods and sexual intercourse.
  • Ovary: Organ that stores eggs and produces ovum, where it goes down the fallopian tube into the uterus, where it may become fertilized by a sperm.
  • Cervix: Connects the uterus and the vagina.
  • Endometrium: Outer lining layer made up of glandular cells that produce cervical mucus. The endometrium thickens and sheds, which creates “periods.”
  • Fallopian Tube: Tubes that stretch from the uterus to the ovaries and are used for transferring fertilized eggs.
  • Myometrium: Muscle below endometrium surrounding the uterus
  • Uterine Fundus: Connects fallopian tubes to the uterus.
  • Fimbriae: Finger-like projections that capture the egg, and send it down the fallopian tubes.

Now that we have a good understanding of the reproductive system, let’s dive right into the changes it has to go through.

Uterine Cycle

The uterine cycle also more commonly known as the menstrual cycle is all about the shedding of the blood and it deals with the Endometrium.

So let’s dive a bit deeper into the Endometrium.

The endometrium consists of two layers

  • Basal Layer: Innermost layer that consists of basal cells, these cells continually divide, and new cells constantly push older ones up toward the surface of the skin, where they are eventually shed. The thickness of the layer never changes.
  • Functional Layer: is a dynamic layer consists of permanent stromal tissue and deep ends of the uterine glands. This layer changes its thickness depending on hormonal layers.

High estrogen and progesterone levels stimulate increased endometrial thickness.

High estrogen and progesterone levels stimulate increased endometrial thickness.

Menstrual cycles last from the first day you get your period to 25–36 days later. Only 10 to 15% of women have cycles that are exactly 28 days.

  1. During the first day to typically another 5 days when the endometrium sheds (period). It does so to regrow a new functional layer for the incoming ovum.
  2. The endometrium regrows in preparation for fertilization leading up to ovulation (when hormones trigger an ovary to release an egg in the menstrual cycle).
  3. If pregnancy does not occur then, the cycle starts again with shedding the endometrium and creating a new layer.

The role of the endometrium

While the role of the endometrium is to get our period. Think about why we get our period?

To get pregnant!

Therefore the role of the endometrium is to make the uterus as “comfy” as possible to prepare for pregnancy.

How does it do this?

Just before ovulation when a fallopian tube releases an egg, the endometrium goes through a couple of changes also known as the process of vascularization.

Vascularization is when uterine glands become longer and cells tiny tiny blood vessels proliferate for the endometrial lining to become thicker and enriched with blood so that it’s ready to receive a fertilized egg while also supporting a placenta (the organ that develops during pregnancy to supply a fetus with essentials such as oxygen and nutrition).

So what about if birth control is being taken?

Birth control is formed of two man-made forms of the hormones estrogen and progestin.

Both of these hormones are preventing an ovary from just releasing an egg. This works because the levels of the natural hormones the body makes are being changed.

For example; Progestins make the mucus around a woman’s cervix thick and sticky, which helps prevent sperm from entering the uterus.

Now obviously if an egg isn’t fertilized then the endometrium goes back to shedding, and we go back to cramps and donuts for breakfast (don’t tell me that’s just me).


  • The endometrium plays a key role in reproduction and either shed or thickens depending on the time of the month.

So what’s the ovarian cycle all about?

Ovarian Cycle

The ovarian cycle is directly associated with the uterine cycle as they are both working towards creating a 👶🏻

Ovarian as you can guess has to do with ovaries.

Ovaries are kind of like the kingdom for female reproductive cells which are also known as eggs and ovum.

Now, these cells are called gametes.

If you want to take away one thing from this article remember gametes.

These reproductive cells are produced through a certain cell division called meiosis. Where girls have “egg” cells, and guys have sperm “cells”.

Because we are humans, our gametes cells only have 23 chromosomes while a normal cell should have 46 (23 from your mom, and 23 from your dad).

Then when two gametes meet (sperm + egg) the result will be a full set of chromosomes which is most of the time going to develop a zygote (an early form of a BABY!!)

The ovary releases an egg to be accompanied by sperm to fertilize it!


Embryos (the early stage of development of a multicellular organism) can either be euploid or aneuploid.

Aneuploid embryos carry an abnormal number of chromosomes which means that they are at a lower risk of implantation in the uterine lining, are at a higher risk for miscarriage and likely to develop chromosomal disorders like down syndrome. While euploid embryos, which contain the correct number of chromosomes, and are most likely to lead to a living birth.

For a recap

  • Once in a normal 28-day cycle, an ovary releases an egg down the fallopian tube (also known as ovulation). If the egg is accompanied by a sperm, then you are pregnant!

The thickening or shedding of the endometrium and the changes of the ovaries create the menstrual cycle. Now let’s understand how these 2 cycles work together, with HORMONES!

The Hormonal System: How it all comes together!

Sister: She’s so moody today.

Mom: It’s the hormones, leave her alone.

Yes, that is mostly what we hear when we are on our period and our “hormones” are doing something crazy.

But what is going on?

Well, hormones are chemical messengers that initiate the change in our cycles.

Our bodies control hormonal changes via the pituitary and hypothalamus. (In the brain).

Our bodies control hormonal changes via the pituitary and hypothalamus. (In the brain).

The menstrual cycle has two distinct phases (follicular, luteal). So let’s take a look at how hormones affect these specific phases.

Follicular Phase

During the follicular phase from day 1–14, 2 cycles are going on

  • The Ovarian cycle is maturing the ovum, preparing it for ovulation on day 14.
  • The Uterine cycle is adjusting the endometrium, in preparation for that egg (if it is to get fertilized).

Ovum Maturation

The maturation of the ovum is in other words the survival of the fittest.

During the follicular phase there are 4 stages a ovum goes through:

  1. Primordial follicles (eggs stay frozen since birth)
  2. Primary follicles
  3. Secondary follicles
  4. Tertiary follicle
  5. Mature graafian follicles (follicles are ready to ovulate)

At the beginning of the cycle, there are over a thousand follicles that start maturing. However, after a few days when hormonal resources start to run low, follicles start dying. From there, our bodies try to determine the most dominant follicle, and that follicle then gets completely matured.

Hormonal Influence

Two main hormones influence this part of the cycle.

Follicle Stimulating Hormones (FSH) instructs the maturation of follicles by telling secondary follicles to start developing.

Luteinizing hormones (LH) instructs ovulation as it helps release the ova near the time for ovulation

Steps to ovulation

  1. FSH stimulates the maturation of the ova and is enough to get a couple of thousand cells running.
  2. The bi-product of FSH being released is estrogen is also released.
  3. When follicles start to die it’s because the estrogen stops the increase of FSH and LH, which boosts competition for follicles to find the dominant follicle.
  4. When estrogen increases in the blood, FSH spikes causing ovulation.
  5. LH also increases causing the ovum to release from fallopian tubes

Endometrium thickens

2/3 of the menstrual cycle takes place in the follicular phase.

Menstrual Phase

Shedding of the endometrium (period)

Proliferative Phase

Estrogen levels dramatically start to increase which stimulates the growth of a new functional endometrium layer.

This impacts cervical mucus.

  • Mucus in the cervical region becomes thin, for the sperm to “slip” into the uterus.

For a recap

  • Ovum matures, and the most dominant ovum prepares to be released to fallopian tubes
  • Old endometrium lining sheds in the first 5 days
  • Growing a new functional layer and making cervical mucus

Once the body preps for ovulation (the follicular phase), it’s time to move on to the luteal phase.

Luteal Phase

During the Luteal Phase, the cycles are up to:

  • Ovulatory: turning old follicle into a corpus luteum (cells that form that are responsible for the production of the hormone progesterone during early pregnancy)
  • Uterine cycle: thickening the endometrium and producing a thick, cervical fluid.

ts important to understand that the ovum is only a small part of the follicle structure. When it ovulates, it exits the follicle, but there is still stuff that remains that we can plenty of remains to play around with.

The remaining bits of the follicle turns into a structure called the corpus luteum, and it starts to produce hormones.

Kind of think of the corpus luteum as a hormone making machine as it produces some estrogen, a lot of progesterone, and inhibit.

It produces these hormones as Estrogen and progesterone prepare the endometrium for implantation (when a fertilized egg attaches to the uterine wall). This begins the development of an embryo.

The complete cycle

This is it! Why do we menstruate, and get pregnant? Thank our reproductive system.

Here’s a good diagram to check out:

Female health tends to be a topic many are uncomfortable talking about. Menstruation and reproduction are difficult and painful for women, trust me, I get cramps all the time.

This being said I like to look at understanding Female Health as an opportunity! An opportunity to change the current way in which we live of assuming that paralyzing half a woman’s body during birth is beneficial.

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