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Ovarian Cycle and Menstrual Cycle

Ovarian Cycle and Menstrual Cycle

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This lesson will describe the process of a females menstrual and ovarian cycle as well as identify hormones associated with either cycle.

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Tutorial

What's Covered

Welcome to this lesson today on the ovarian and menstrual cycle. Today you are going to be looking at:

  1. The Menstrual Cycle & Hormones
  2. The Ovarian Cycle
  3. Ovarian Cycle Hormones



1. The Menstrual Cycle & Hormones

The menstrual cycle is the cycle where oocytes are ovulated and the endometrium (uterine lining) of the uterus prepares to receive a fertilized egg and one menstrual cycle is equal to about 28 days. If the oocyte that is ovulated is not fertilized i.e. the woman does not become pregnant, the endometrium will break down and flow out through the vagina and the entire process will begin again. The process of the endometrium flowing out through the vagina is called menstruation.

Menarche is a woman's first menstruation, usually shortly after puberty, and menopause marks the end of a woman's fertility. A woman will menstruate through her life until menopause occurs, and then she is no longer able to conceive children and marks the end of her fertility. Menopause typically occurs around the age of 50.

Terms to Know

    • Menstrual Cycle
    • Monthly cycle in which an oocyte matures and is released from a woman's ovary.
    • Menstruation
    • The flow of the endometrium out the vagina if the oocyte was not fertilized during the menstrual cycle.
    • Menarche
    • A woman's first menstrual cycle.
    • Menopause
    • Marks the end of a woman's fertility in which a woman is no longer able to conceive.

Progesterone and estrogen are the hormones that prepare the endometrium for pregnancy and are very important in driving the menstrual cycle.

Terms to Know

    • Progesterone
    • A hormone released during the menstrual cycle that prepares the endometrium for implantation.
    • Estrogen
    • A female sex hormone that plays various roles in the female reproductive system, including preparing the endometrium for pregnancy.

2. The Ovarian Cycle

The ovarian cycle of the monthly reproductive cycle is where the primary oocyte will mature in the ovary and then be ovulated and all begins with something called the follicle. The follicle is the primary oocyte surrounded by a layer of protective cells that provide nourishment for the follicle. At this point meiosis I has been started but it is arrested or stopped. As the follicle or oocyte begins to mature and move through these phases before it is ovulated, it will complete meiosis I.

As the follicle matures, it will continue to go through meiosis I and complete it by the end of its maturation. The zona pellucida will begin forming around the maturing oocyte, which is this thick layer. Within the zona pellucida a buildup of estrogen-rich fluids accumulates in preparation for ovulation.

Terms to Know

    • Ovarian Cycle
    • The cycle in which an oocyte matures as the menstrual cycle advances.
    • Follicle
    • The primary oocyte surrounded by nourishing cells in the ovary.
    • Zona Pellucida
    • A protein that surrounds the follicle.

During ovulation the egg will be released from the ovary and the part being released is called the secondary oocyte with other material called a polar body. Now the primary oocyte has gone through and completed meiosis I, producing the secondary oocyte and a polar body.

If the ovulated egg is fertilized it will then begin meiosis II. If it does not become fertilized, it will not begin meiosis II making meiosis II dependent upon fertilization. The polar body is just this unnecessary material that will later disintegrate and is not needed. The polar body will disintegrate, the secondary oocyte moves towards the fallopian tubes where fertilization may occur.

Back in the ovary a structure called the corpus luteum forms from remnants of that ruptured follicle. This corpus luteum is going to secrete estrogen and progesterone, which help prepare the uterus for a fertilized egg. If the secondary oocyte not fertilized, this corpus luteum will start to break down causing progesterone and estrogen levels are going to drop.This will cause estrogen and progesterone levels to drop which in turn causes the arteries that supply the endometrium with blood to constrict. The constriction of these vessels causes the breakdown and shedding of the endometrium which is essentially the onset of menstruation.

Take a look at the image below for a better idea of where everything is located. 



Terms to Know

    • Secondary Oocyte
    • The oocyte formed after meiosis I has been completed in the ovary.
    • Ovulation
    • The process of expelling the secondary oocyte from the ovary to the oviduct.
    • Corpus Luteum
    • Formed from the remnants of the ruptured follicle which secretes hormones that prepare the endometrium for an embryo.



3. Ovarian Cycle Hormones

Follicle stimulating hormone, or FSH, is an important part of the cycle because it stimulates the growth and maturation of a primary follicle . GNRH, gonadotropic releasing hormone, plays a role in the production and the release follicle stimulating hormone. Follicle stimulating hormone will also increase the expression of luteinizing hormone, or LH, receptors; which is important for ovulation. Luteinizing hormone and follicle stimulating hormone have a permissive relationship with one another because follicle stimulating hormone increases the expression of luteinizing hormone receptors.

LH hormone, in addition to FSH, is released by the anterior lobe of your pituitary gland. FSH regulates the menstrual cycle and egg production. Lh also plays a crucial role in the menstrual cycle and can be detected in the urine. If you're taking a fertility test, for example, it's testing for LH. As the egg gets closer to ovulation, there's a surge in LH levels that can be detected by at-home fertility tests.


Terms to Know

    • FSH
    • Follicle Stimulating Hormone; a major hormone of the reproductive system which stimulates ovulation.
    • LH
    • Lutenizing hormone; A hormone released from the anterior pituitary gland and plays a large role in the reproductive system.

Summary

This lesson has been an overview on the processes that occur during the ovarian and menstrual cycles and the hormones significant to each cycle.

Keep up the learning and have a great day!

Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
  • Menstrual Cycle

    Monthly cycle in which an oocyte matures and is released from a woman's ovary.

  • Menstruation

    The flow of the endometrium out the vagina if the oocyte was not fertilized during the menstrual cycle.

  • Progesterone

    A hormone released during the menstrual cycle that prepares the endometrium for implantation.

  • Estrogen

    A female sex hormone that plays various roles in the female reproductive system, including preparing the endometrium for pregnancy.

  • Menarche

    A woman's first menstrual cycle.

  • Menopause

    Marks the end of a woman's fertility in which a woman is no longer able to conceive.

  • Ovarian Cycle

    The cycle in which an oocyte matures as the menstrual cycle advances.

  • Follicle

    The primary oocyte surrounded by nourishing cells in the ovary.

  • Zona Pellucida

    A protein layer that surrounds the follicle.

  • Secondary Oocyte

    The oocyte formed after meiosis I has been completed in the ovary.

  • Ovulation

    The process of expelling the secondary oocyte from the ovary to the oviduct.

  • Corpus Luteum

    Formed from the remnants of the ruptured follicle which secretes hormones that prepare the endometrium for an embryo.

  • FSH

    Follicle Stimulating Hormone; a major hormone of the reproductive system which stimulates ovulation.

  • LH

    Lutenizing hormone; A hormone released from the anterior pituitary gland and plays a large role in the reproductive system.