The Menstrual Cycle

The Menstrual Cycle Releasing of one egg

(ovulation) every month from the ovaries

4 steps: Preparing the egg Releasing egg Preparing the

endometrium Shedding endometrium

if egg is not fertilized Takes about 28 days

There are four principal hormones involved in the control ofthe human menstrual cycle

FSH – Follicle Stimulating Hormone – secreted into the blood from the pituitary glandLH – Luteinising Hormone – secreted into the blood from the pituitary gland

OESTROGEN – secreted by the developing follicles (ball of cells around ova) in the ovaryPROGESTERONE – secreted by the yellow body (corpus luteum) in the ovary

Hormonal Control of the Menstrual Cycle

Pre-Ovulation Hormones

Post-Ovulation Hormones

Hormones of thePituitary Gland

Anterior lobe of the pituitary gland

Hypothalamus

FSH – Follicle Stimulating Hormone

LH – Luteinising Hormone

Follicle Stimulating Hormone = FSH

Causes follicles (ball of cells that help develop ova) to develop in the ovary.

Stimulates follicular cells of the ovary to secrete oestrogen & small amounts of progesterone.

Luteinising Hormone = LH

Causes ovulation Causes a follicle

after ovulation to develop into a Yellow body (corpus luteum) which produces oestrogen and progesterone.

1 5 14 28

oocyte

prim aryfollicle

corpusluteum

m enses follicular phase luteal or secretory phase

OVARY

UTERUS(thickness ofendom etrium )

Tim e (days)

m enstruation

1 2 3 4 5 6 7 8 9 10 11 12 13 14 1516 17 18 19 20 21 22 23 25 26 27 28

Concentration ofFSH and LH

in blood

Concentration ofoestrogens and

progesteronein blood

new cycle

developingfollicles

ovulation

OESTROGENSPR OGESTERONE &

SOM E OESTROGENS

FSH

LH

oestrogens

28 Day Cycle:

1-5:•

Menstruation; endometrium is shed

• FSH increases

6-12: • Follicles

develop and oestrogen increases

12-14: • Oestrogen at

peak; LH and FSH spike

14:• Ovulation

1 5 14 28

oocyte

prim aryfollicle

corpusluteum

m enses follicular phase luteal or secretory phase

OVARY

UTERUS(thickness ofendom etrium )

Tim e (days)

m enstruation

1 2 3 4 5 6 7 8 9 10 11 12 13 14 1516 17 18 19 20 21 22 23 25 26 27 28

Concentration ofFSH and LH

in blood

Concentration ofoestrogens and

progesteronein blood

new cycle

developingfollicles

ovulation

OESTROGENSPR OGESTERONE &

SOM E OESTROGENS

FSH

LH

oestrogens progesterone

28 Day Cycle:

14-25: LH causes follicle to change to yellow body (corpus luteum) which raises progesterone levels

• Endometrium thickens and FSH inhibited

1 5 14 28

oocyte

prim aryfollicle

corpusluteum

m enses follicular phase luteal or secretory phase

OVARY

UTERUS(thickness ofendom etrium )

Tim e (days)

m enstruation

1 2 3 4 5 6 7 8 9 10 11 12 13 14 1516 17 18 19 20 21 22 23 25 26 27 28

Concentration ofFSH and LH

in blood

Concentration ofoestrogens and

progesteronein blood

new cycle

developingfollicles

ovulation

OESTROGENSPR OGESTERONE &

SOM E OESTROGENS

FSH

LH

oestrogens progesterone

28 Day Cycle:

No feritilization25-28: High progesterone levels inhibit LH (negative feedback)• Yellow body

(corpus luteum) degrades so progesterone drops

• FSH increases and endometrium is lost (menstruation)

Endometrial Changes The events occurring in the ovary during the menstrual

cycle are accompanied by changes in the endometrial lining of the uterus

Endometrium isbeing shed

duringmenstruation

Oestrogen secretedby the

developing follicles repairs

the endometrium

Progesteronethickens the endometrium

Progesterone stimulates

glands in the endometrium to increase in size

Spiral arteries

1 5 14 28

oocyte

prim aryfollicle

corpusluteum

m enses follicular phase luteal or secretory phase

OVARY

UTERUS(thickness ofendom etrium )

Tim e (days)

m enstruation

1 2 3 4 5 6 7 8 9 10 11 12 13 14 1516 17 18 19 20 21 22 23 25 26 27 28

Concentration ofFSH and LH

in blood

Concentration ofoestrogens and

progesteronein blood

new cycle

developingfollicles

ovulation

OESTROGENSPR OGESTERONE &

SOM E OESTROGENS

FSH

LH

oestrogens progesterone

28 Day Cycle:

Fertilization

• Endometrium stays due to progesterone from yellow body

• Placenta forms and keeps oestrogen levels high

• LH is inhibited so ovulation does not start again

1 5 14 28

oo cyte

prim aryfoll icle

corpu sluteum

m enses foll icular p hase luteal or secreto ry phase

O VA RY

UTE RU S(th ickn ess of

en dom etrium )

Time (d ays)

men struation

1 2 3 4 5 6 7 8 9 10 11 12 13 14 1516 17 18 19 20 21 22 23 25 26 27 28

Co ncentration ofFSH an d L H

in b lood

C on centrat ion ofo estrogens an d

prog estero nein b lood

new cyc le

deve lo pin gfo llic les

o vu latio n

Implantation