Menstrual Cycle: Part 2

The Menstrual Cycle Part 2: Hormones and what happens during the cycle 

A summary of the important hormones related to the menstrual cycle, including estrogen, progesterone, luteinising hormone and follicle stimulating hormone. Also learn about what your hormones do throughout your body during different stages of the cycle.


Estrogen

Estrogen is produced in the ovaries, adrenal glands and fat tissues and circulates through the bloodstream. It moves through the body and binds to receptors on cells in the breasts and uterus. Estrogen controls the growth of the uterine lining during the first part of the menstrual cycle, which is the pre-ovulatory phase.

As the follicle develops in the ovary it produces estrogen, which causes the uterine lining to thicken

  • if fertilisation doesn’t occurs, estrogen levels drop quickly and the uterine lining breaks down

  • if fertilisation does occur, estrogen levels continue increase to prevent ovulation from occurring

Progesterone

Progesterone is produced in the ovaries, placenta and adrenal glands. It helps prepare the body for conception and pregnancy, and also encourages growth of milk producing glands if required. Progesterone is crucial in the second half of the menstrual cycle, following the release of the egg (ovulation).

It causes the endometrium to secrete certain proteins during the second part of the cycle to help prepare the uterus for an implanted egg

  • if fertilisation does not occur, progesterone will drop quickly and the endometrium will break down

  • if fertilisation does occur, progesterone is made in the placenta and is kept at high levels throughout the pregnancy to prevent ovulation from occurring

Luteinising hormone

Luteinising hormone (LH) is produced and released in the anterior pituitary gland and is crucial in regulating the ovaries. In weeks 1-2 of the cycle, LH is required to stimulate ovarian follicles in the ovary to produce estrogen. At approximately Day 14 there is a surge in LH which causes the follicle to tear and release an egg (ovulation). In weeks 3-4 of the cycle, the remnants of the follicle form the corpus luteum and LH stimulates the corpus luteum to produce progesterone to support pregnancy if it is required.

Follicle stimulating hormone

Follicle stimulating hormone (FSH) is produced and released in the anterior pituitary gland, it is essential in the development of a women’s body during puberty and also development of the ovaries. FSH increases estrogen production, which is controlled by the hypothalamic-pituitary-gonadal axis. Towards the end of the menstrual cycle, hormone levels fall which is sensed by the nerve cells in the hypothalamus this sets off a cascade, which produces more FSH and LH. An increase in FSH stimulates follicle growth in the ovary

Day 1-5

  • The amount of estrogen and progesterone drop, this drop in hormones allows the endometrium to begin to shed and menstruation occurs

  • The drop in estrogen and progesterone sets off a cascade and the pituitary begins to create more FSH and LH to stimulate the growth of the new follicle

Day 7

  • By day 7, the endometrium has already rebuilt to roughly 2mm thick

  • One of the follicles in the ovaries outgrows the others and begins to produce a high amount of estrogen

Day 7-12

  • The high levels of estrogen stimulates

  • the uterine lining to proliferate

  • the glands in the cervix to produce mucous

Day 12-13

  • The continual high levels of estrogen act on the anterior pituitary gland, which stimulates LH production

  • The surge in LH stimulates the production of lytic enzymes and prostaglandins in the dominant follicle

Day 14

  • The dominant egg is released when the enzymes create a break in the follicle wall and the prostaglandins stimulate the movement of the egg through the fallopian tube

Day 15-25

  • The corpus luteum is formed from the empty follicle and produces progesterone and estrogen which

  • stimulates the endometrium to secrete nutrients

  • inhibits the pituitary gland from producing more FSH and LH

Day 25-28

  • The corpus luteum dies and the level of progesterone and estrogen to drop which causes

  • the start of the period flow as the endometrium begins to break down

  • the pituitary gland to once again start the production of FSH and LH to ripen up the next group of follicles

I hope this blog gives you some insight into what your hormones do throughout your menstrual cycle! Part 3 of this blog series will delve into some common menstrual related issues, so keep your eyes peeled!


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Maya, x