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Paterson 13_11 Biology - The Menstrual Cycle

Menstruation, Ovulation, Hormonal Feedback Loop
by

Emily Paterson

on 18 August 2013

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Transcript of Paterson 13_11 Biology - The Menstrual Cycle

The Menstrual Cycle
Year 11 Biology
USC

Emily Paterson
May 2013

Overview
Ovary
Fallopian tube
Cervix
Uterus
Endometrium
Vagina
The Female Reproductive System
The Menstrual Cycle
Ovulation
The process of
ovulation
and
menstruation
in women and other female primates
Definition
The release of an ovum from the ovary (usually midway in the menstrual cycle)
Menstruation
The periodic discharge of blood and cell debris from the uterus, occurring approximately monthly from puberty to menopause in nonpregnant women
Also referred to as:
Menses (from Latin mensis = month)
A period
Menstrual bleeding
Catamenia
Menstrual Cycles Vary Between Females
Average cycle:
28 days
Note: menstrual cycles can be different between individuals e.g. some women menstruate 2-3 times a month, whereas others will menstruate 2-3 times a year!
Ovulation & Menstruation
Regulated by
hormones
that participate in a
feedback loop
The Menstrual Cycle Process
Chemicals that communicate messages between the
brain
,
ovaries
, and the
uterus
via the
blood
The Menstrual Cycle is Regulated by a Feedback Loop of Hormones
Brain
Ovaries
Uterus
Hormones
Pituitary Gland
Oestrogen
Progesterone
FSH
LH
The Menstrual Cycle Consists of 4 Phases
1. Menstruation (days 1-5)

2. Follicular Phase (days 6-14)

3. Ovulation (days 12-15)

4. Luteal Phase (15-28)
FSH + LH
Oestrogen
Progesterone
Oestrogen


FSH & LH stimulate ovarian follicles to
mature

One follicle dominates, matures and
begins to secrete oestrogen

High levels of oestrogen tell the brain to
secrete more FSH & LH
3. Ovulation
Days 12-15

Oestrogen levels peak and trigger LH to rise

Peak causes oestrogen levels to fall dramatically

Oestrogen levels continue to fall

LH peak weakens wall of follicle, thus releasing the egg

Ovulation begins on day 14 and lasts 48 hours
4. The Luteal Phase
Days 15-28

As the egg travels into the fallopian tubes, the follicle continues to grow and is know as the corpus luteum

The corpus luteum secretes progesterone and oestrogen

Progesterone signals endometrial lining to thicken for implantation of a fertilised egg

The corpus luteum needs the hormones secreted by a fertilised egg to keep uterus thick to support implantation

If it does not receive those hormones, progesterone levels will fall and menstruation begins
Days 1-5

Elimination of the thickened
uterine lining, mucous and egg

Generally a sign a woman has
not become pregnant
Fertile Window
Most likely to get pregnant:

5 days before to 1-2 days after ovulation
Summary of Menstrual Cycle
Occurs in 4 phases
Menstruation
Follicular phase
Ovulation
Luteal Phase
Is a complex process controlled by feedback mechanism of levels of 4 hormones
Sex glands (gonads) - progesterone, oestrogen
pituitary gland - LH & FSH
Hormonal Contraception
The Pill

Contains synthetic oestrogen and progesterone

Most popular method of contraception

99% effective if used properly

Works in 2 ways:
affects development of egg - stops ovulation taking place - does not allow LH to rise
alters lining of uterus - does not allow implantation to occur
Hormones Control the Menstrual Cycle
Follicle Stimulating Hormone (FSH)



Luteinising Hormone (LH)



Oestrogen



Progesterone
Released from the brain
Stimulates development of ovum from oocyte
Released from the brain
Triggers ovulation of an ovum
Released from the ovary
Thickens endometrium
Released from the ovary
Thickens endometrium
Prepares the uterus for pregnancy ("
p
regnancy hormone")
Summary of the Menstrual Cycle
This will be in the test
Supplementary Material
The Menstrual Cycle Feedback Loop
Ovulation
Menstruation
Maturation of follicle
containing oocyte
FSH + LH
Release of ovum
from ruptured follicle
Formation of
corpus luteum
"yellow body"
Degradation of
corpus luteum
(scar)
oestrogen
FSH+LH
progesterone
oestrogen
FSH + LH
LH
1. The Menstrual Phase
2. The Follicular Phase
Days 5-14
Oestrogen
Progesterone
Oestrogen
Secretion of oestrogen & progesterone
from the ovary cause the endometrium to
thicken


Progesterone continues to promote thickening
of the endometrium



If the egg is unfertilised, the endometrium is
sloughed off and excreted
Follicular
Luteal
Phase
Full transcript