A guide to our reproductive system

  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)
  • 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)
  1. Menarche
  2. Pregnancy
  3. Menopause

But, first. Let’s understand the reproduction system

  • 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.

Uterine Cycle

  • 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.
  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

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

Ovarian Cycle


  • 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 Hormonal System: How it all comes together!

Follicular Phase

  • 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

  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)

Hormonal Influence

  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

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

Luteal Phase

  • 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.

The complete cycle

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Alisha Arora

Alisha Arora

15 yo futurist, change maker and innovator at The Knowledge Society.