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ReproductionDraw and label diagrams of the adultmale and female reproductive systems

Outline the role of hormones in themenstrual cycle

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Production of Eggs (Oogenesis) 

• Egg development - Cyclical process of28 days. Takes place in the ovaries. It iscontrolled by hormones from the

hypothalamus and the pituitary gland. • At birth, each ovary in a female has

hundreds of thousands of eggs, but

they are immature and remain dormantuntil her first menstrual cycle, whichoccurs during puberty (sexual maturity).

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• Every 28 days or so, from puberty untilmenopause, between one and three eggs,are released from the ovaries. This isknown as ovulation.

• The eggs are then move down thefallopian tubes towards the Uterus for

possible fertilisation and implantation.

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The menstrual cycleThe function of the menstrual cycle is to provide a favourable environmentfor a fetus to grow. If fertilization does not occur, the uterus lining is shedin menstruation.

The menstrual cycle is controlled by thefollowing hormones:

Gonadotropin releasing hormone (GnRH) progesterone oestrogen follicle stimulating hormone (FSH) luteinizing hormone (LH)

The secretion of these hormones is controlled by interacting positive andnegative feedback loops.

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3 stages to menstruation

• Follicular 0-14 days

• Ovulation 14

•

Luteal 14-28 days

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Hormones from the brain

• Hypothalamus releases GnRH

• The pituitary gland is the target of the

GnRH• The pituitary gland releases FSH and

LH into the blood stream.

•

The target tissues for FSH and LH arethe ovaries.

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Hypothalamus

Anterior lobe ofpituitary gland

ovaries

GnRH

FSHLH

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Effects of FSH on ovaries

• Stimulate the maturation of an ovarianfollicle

• Increase production of oestrogen by theovaries

• Oestrogen stimulates the secretion of LH• A spike in the amount of FSH and LH leads

to ovulation (release of the oocyte from

the ovarian follicle)• The inner lining of the follicle and theoocyte are released and enter the fallopiantubes.

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How do hormones control the cycle?

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Ovulation

• The outer ring of the follicle cellsremain in the ovary

• These follicle cells produceprogesterone

• The follicle cells form a glandularstructure – the corpus luteum

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Progesterone•

The corpus luteum producesprogesterone for 10-12 days afterovulation

• Progesterone maintains the thickened,highly vascular endometrium (providingthe conditions for an embryo to implant)

• Progesterone acts on the hypothalamus

and prevents the production of GnRH• FSH and LH not produced, another

follicle cannot be formed

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Hypothalamus

Anterior lobe ofpituitary gland

ovaries

GnRH

FSHLH

Endometrium of uterus

Progesterone(after ovulation)

oestrogen

negativefeedback

negativefeedback

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No pregnancy

• Corpus luteum breaks down

• Progesterone and oestrogen levelsdecline

• Endometrium is no longer maintained

• Menstruation begins

•

GnRH secreted by hypothalamus• Cycle begins again

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How do hormones control the cycle?

Wh h h

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Which hormone?

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What hormone is released by the hypothalamus?

What two hormones are stimulated by the by thishormone?

What organ do these two hormones act on?

What hormone is released?

What is the effect of the LH spike?

What secretes progesterone?

What two hormones cause the build up of the uterinelining?