Think about… 4.1 Hormonal control of the menstrual cycle 4.2 Use of hormones Recall ‘Think...

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Think about…

4.1 Hormonal control of the menstrual cycle

4.2 Use of hormones

Recall ‘Think about…’

Summary concept map

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The performance of female athletes may be affected by their physiological conditions before or during menstruation.

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Some athletes may take drugs to prevent menstruation from occurring during sports games.

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The drugs contain hormones which are similar to those naturally produced in the female body.

What are the hormones involved?What are the hormones involved?

How do the drugs prevent menstruation?How do the drugs prevent menstruation?

Can menstruation be resumed later?Can menstruation be resumed later?

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Let’s revise the menstrual cycle first.

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The menstrual cycle

Cycle repeats until meno…

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The maturation and release of egg cells from the ovary are synchronized with changes in the uterus

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The Ovarian Cycle

• In the ovarian cycle– Hormones stimulate follicle growth, which results in

ovulation• Following ovulation

– The follicular tissue left behind transforms into the corpus luteum

Three phases: follicular --- ovulation --- lutealThree phases: follicular --- ovulation --- luteal

(1-14) (14) (14-28)(1-14) (14) (14-28)

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The Uterine Cycle

Three phases : Menstrual -- proliferative ------- secretoryMenstrual -- proliferative ------- secretory

(1-6) (6-14) (14-28)(1-6) (6-14) (14-28)

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Day 1 to 5 of the menstrual cycle


• uterine lining breaks down

• follicle begins to develop

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• uterine lining begins to thicken

• follicle becomes mature

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Day 14 of the menstrual cycle


• uterine lining becomes very thick

• ovulation occurs

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• uterine lining remains thick

• ovum is moved along the oviduct

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What are the hormones involved?


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• events synchronized by the interaction of four hormones:

follicle stimulating hormone (FSH)

pituitary gland

luteinising hormone (LH)

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oestrogen

follicleyellow body


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progesterone

yellow body


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How do the hormones interact?

• the hormones interact by feedback mechanisms

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pituitary gland

FSH

stimulation

ovary

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pituitary gland

follicle develops

ovary

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pituitary gland

Above a certain level, oestrogen stimulates FSH and LH secretion

ovary

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pituitary gland

LH

ovary

LH stimulates oestrogen secretion and oestrogen stimulates FSH and LH secretion ….

A positive feedback effect A positive feedback effect at around day 14 that raise LH to a peak level

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pituitary gland

ovulation

ovary

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pituitary gland

ovary

LH stimulates development of yellow body yellow body and hence progesterone secretion

yellow body

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pituitary gland

oestrogen and progesterone together inhibitinhibit LH and FSH

ovaryinhibition

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Let’s look at the menstrual cycle from day 5.

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Before ovulation

1 The pituitary gland secretes FSH.

2 FSH stimulates the development of follicles. As the follicle matures, it secretes more oestrogen.

to chart

3 Under the action of oestrogen, the uterine lining begins to thicken.

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4 Oestrogen level continues to rise and reaches a peak just before ovulation. A high level of oestrogen stimulates FSH and LH secretion. The peaks of FSH and LH occur just after the oestrogen peak.

5 A high level of LH causes ovulation to occur on day 14.

Before ovulation

to chart

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After ovulation

6 The remaining follicle cells form the yellow body. A high level of LH stimulates the yellow body to secrete oestrogen and progesterone. Oestrogen level rises again and progesterone level reaches a peak.

7 Under the action of oestrogen and progesterone, the uterine lining remains thick.

to chart

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After ovulation

8 High levels of oestrogen and progesterone together inhibit FSH and LH secretion. A low level of LH causes the yellow body to degenerate around day 24.

to chart

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After ovulation

9 The yellow body gradually stops secreting oestrogen and progesterone and the thickened uterine lining soon breaks down. Also, the inhibition of oestrogen and progesterone on FSH secretion is removed. The pituitary gland secretes more FSH again and the cycle repeats.

to chart

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levels of pituitary hormones in blood

events in ovary

levels of ovarian hormones in blood

thickness of uterine lining to text

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• Cyclic secretion of GnRH* from the hypothalamus– And of FSH and LH from the anterior pituitary

orchestrates the female reproductive cycle

FiveFive hormones involved in an elaborate scheme involving both positive and positive and negative feedbacknegative feedback

*Gonadotropin-releasing hormone

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Hormone Site of Secretion

Target Organ Function

Follicle Stimulating Hormone (FSH)

Pituitary gland Ovary

•stimulates the growth & development of the follicle •stimulates secretion of oestrogen •effect of LH in stimulating ovulation

Oestrogen Ovary Endometrium (lining of the uterus)

•stimulates repair of uterine lining •at high conc. inhibits FSH, however during 'pituitary hormone surge' it stimulates further FSH production •as conc. peaks stimulates release of LH

Lutenising Hormone (LH) Pituitary Ovary

•stimulates the final development of the follicle •stimulates ovulation •stimulates the development of the corpus luteum •stimulates production of progesterone

Progestrone Corpus luteum Uterus

•maintains uterine lining endometrium) •inhibits release of FSH •inhibits release of LH •fall in conc. results in menstruation •fall in conc. removes inhibition of FSH and a new cycle begins.

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Feedback control of human menstrual cycle

Atresia of corpus luteum -- degeneration and resorption of corpus luteum in ovary

Estradiol -- Oestrogen

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Hormonal feedback control of menstrual cycle

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• The reproductive cycle of the human female

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• The reproductive cycle of the human female

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If fertilization occurs …

placenta

human chorionic gonadotrophin (HCG)• acts like LH

secretes

• prevents degeneration of yellow body

secretes oestrogen and progesterone uterine lining remains thick for embryo

development

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What is the significance of hormonal control of the

menstrual cycle?

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i) Ensure one ovum is released at a time

• after ovulation, high levels of oestrogen and progesterone together inhibit FSH and LH secretion

prevents maturation of another follicle

Higher survival chance!

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Avoid wasting of energy!

i) Ensure one ovum is released at a time

• after ovulation, high levels of oestrogen and progesterone together inhibit FSH and LH secretion

prevents maturation of another follicle

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ii) Prepare for implantation• oestrogen and progesterone stimulate

the thickening of the uterine lining

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iii) Prepare for the next possible pregnancy

• if no fertilization occurs, levels of oestrogen and progesterone fall which causes menstruation to occur and the pituitary gland secretes more FSH again

• the menstrual cycle repeats

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1 Hormonal control of menstrual cycle:


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a After ovulation, levels of oestrogen and progesterone together inhibit FSH and LH secretion.

2 Significance of hormonal control of the menstrual cycle:

high


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a This prevents the maturation of another follicle and ensures only one ovum is released in each cycle. This would result in higher survival chance of the foetus.



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b Oestrogen and progesterone stimulate the thickening of the uterine lining to prepare for the


implantation


of the embryo.

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c If no fertilization occurs, levels of oestrogen and progesterone fall which causes to occur. The pituitary gland begins to secrete more again.


menstruation


FSH

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c The menstrual cycle repeats to prepare for the next possible pregnancy.



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4.2 Use of hormones• used as contraceptives or in the

treatments of infertility

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How are hormones used to prevent pregnancy?• contraceptive pills contain synthetic

progesterone or a combination of synthetic oestrogen and progesterone

high levels inhibit FSH and LH secretion

follicle development and ovulation do not occur

4.2 Use of hormones

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4.2 Use of hormones

for 21 days

contraceptive pills

for 28 days

hormone-free

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4.2 Use of hormones

contraceptive patches and injections

to be replaced weekly

to be taken every 3 months

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How the injection works (ref)• The contraceptive injection works in the same way as the implant. It steadily releases

the synthetic hormone progestogen into your bloodstream. • The continuous release of progestogen:• stops a woman releasing an egg every month (ovulation) • thickens the mucus from the cervix (neck of the womb), making it difficult for sperm to

pass through to the womb and reach an unfertilised egg • makes the lining of the womb thinner so that it is unable to support a fertilised egg

Disrupted periods• Periods irregular and may be very heavy, or shorter and lighter, or stop altogether.

This may settle down after the first year, but may continue as long as the injected progestogen remains in your body.

• It can take a while for your periods and natural fertility to return after you stop using the injection. It takes around eight to 12 weeks for injected progestogen to leave the body, but you may have to wait longer for your periods to return to normal if you are trying to get pregnant.

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• morning-after pills contain a high dose of synthetic progesterone or a combination of synthetic oestrogen and progesterone

4.2 Use of hormones

prevent pregnancy after sexual intercourse

prevent ovulation and implantation

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They are not for regular use and must be

prescribed by doctors.

4.2 Use of hormones

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How are hormones used to treat infertility?• causes of

infertility:

4.2 Use of hormones

- does not produce enough sperm

- sperm have low motility

- sperm have structural defects

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How are hormones used to treat infertility?• causes of

infertility:

4.2 Use of hormones

- fails to release ova from the ovaries

- oviducts are blocked

- uterine environment does not allow implantation

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• fertility drugs contain:

4.2 Use of hormones

stimulates follicle development

- FSH

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4.2 Use of hormones

stimulates ovulation

- LH


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4.2 Use of hormones

stimulates the thickening of the uterine lining to prepare for implantation of the embryo

- synthetic oestrogen and progesterone


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are present in1 Synthetic andoestrogen

4.2 Use of hormones

contraceptives. They inhibit and secretion by the pituitary

progesteroneFSH

LHgland. This prevents follicle development and ovulation, so that no ova are released into the oviducts for fertilization.

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2a FSH, LH, , synthetic oestrogen and progesterone are present in fertility drugs.

HCG

4.2 Use of hormones

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2b FSH promotes development. LH and HCG stimulate . Synthetic oestrogen and progesterone stimulate the thickening of the uterine lining to prepare for

follicle

4.2 Use of hormones

ovulation

implantation .

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What are the hormones present inthe drugs?1The drugs contain synthetic oestrogen and progesterone.

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How do the drugs preventmenstruation?2High levels of oestrogen and progesterone in blood maintain the thickness of the uterine lining to prevent menstruation.

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How can menstruation be resumed?3Menstruation will resume after the female has stopped taking the drugs.

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is controlled by interaction of

Menstrual cycle

ovarian hormones

pituitary hormones

can be used as

contraceptives treatment of fertility

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include

follicle development

pituitary hormones

luteinising hormone (LH)

follicle stimulating hormone (FSH)

stimulates stimulatesovulation

yellow body formation

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ovarian hormonesinclude

progesteroneoestrogen

low levels cause

menstruationuterine lining

stimulate thickening of

implantationto prepare for

Think about… 4.1 Hormonal control of the menstrual cycle 4.2 Use of hormones Recall ‘Think...

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