Session 2 - Part II Flashcards by Chloe Crofts

What happens in the Preparatory phase of the Menstrual cycle?

Follicles grow in the ovary
Uterus prepares for sperm transport & implantation
Changes to facilitate sexual interactions
Also called Follicular/Proliferative phase

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What happens in the Ovulation phase of the Menstrual cycle?

Brief period of fertility (Around 36 hours)

Formation of the Corpus Luteum

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What happens in the Waiting phase of the Menstrual cycle?

Corpus Luteum in the ovary
Changes in preparation for pregnancy
Also called Luteal (Ovary) or Secretory (Uterus) phase

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What does species variation show us?

That ovulation can be very precisely linked to the environment

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What are Induced Ovulators?

There is no ovulation without copulation

eg cats & rabbits

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What are Induced Waiting phase?

Spontaneous ovulation

No Corpus Luteum formed without copulation

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What is unique about the Menstrual cycle in higher primates only?

They always ovulate and always have a waiting phase.

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How is the Menstrual cycle ended?

Shredding of part of the endometrium

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What hormones co-ordinate the Menstrual cycle?

Gonadotrophins (LH & FSH)
Gonadal steroids
Oestrogen
Progesterone

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What is the level of FSH on day 0 of the Menstrual cycle?

High

They then fall after the Preparatory phase

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When is the lowest level of FSH in the Menstrual cycle?

In the waiting phase

Peak for ovulation

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What is the level of LH on day 0 of the menstrual cycle?

Low

Increase for LH surge then drop again

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What are the actions of Gonadotrophins in the Follicular phase?

FSH binds to Granulosa cells
LH binds to Thecal cells in the Theca interna (Secretes Androgens which is then converted to Oestrogen then released)
Stimulates the development of the follicle

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What are the actions of Gonadotrophins in the Pre-ovulation phase?

LH surge stimulates ovulation

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What are the actions of Gonadotrophins in the Luteal phase?

LH maintains the Corpus Luteum

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How does LH cause ovulation?

At very high levels it breaks down collagen in the Theca externa. This causes it to burst and the ovum is released
Usually happens due to LH surge

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What are the actions of the Gonadal steroids in the Follicular phase?

Oestrogens stimulate -
Fimbrae in the fallopian tube to move the ovum
Endometrium to thicken
Vaginal changes
Changes in metabolism (And calcium metabolism)
A nutrient fluid produced to allow the sperm to fertilise the ovum
Cervical alkaline mucus, the sperm sticks to this

What are the actions of the Gonadal steroids in the Luteal phase?

Progesterone acts on the Oestrogen primed cells -
Endometrium thickens further (Myometrium thicker but with decreased motility)
Increased body temperature
Changes to mammary tissue
Change in electrolyte & fluid balance

What is the state of the ovum at the beginning of the Menstrual cycle?

The Corpus Luteum is absent

The follicles are only part developed

What is low at the beginning of the Menstrual cycle?

Steroids & Inhibin
Oestrogen & Progesterone
Due to no theca or follicle to secrete it

What is high at the beginning of the Menstrual cycle?

FSH & GnRH

Due to low levels of Inhibin

How does FSH effect follicular development?

It binds to Granulosa cells which causes follicular development to continue
A Theca interna develops which can then secrete oestrogen (stimulated by LH) Inhibin is also released which acts on the Anterior Pituitary gland to reduce FSH levels

How are more follicles prevented from developing during the mid follicular phase?

The oestrogen levels are rising (Positive feedback for LH)

Inhibin levels are rising (Selectively inhibits FSH)

How does positive feedback of Oestrogen change the follicle?

It causes the follicle to become more developed and it gets closer to ovulation.

How does Oestrogen indirectly cause ovulation?

It reaches a threshold value This causes a great increase in GnRH Huge increase in LH (LH surge) which breaks down Theca externa for ovum to be released

How is the LH surge effected by environmental factors?

They can effect the precise timing of when it occurs once oestrogen has reached its threshold value (creating a 'window of opportunity' for ovulation)

How can stress effect ovulation?

Delays it

How can copulation effect ovulation?

Ovulation occurs sooner if copulation occurs very soon after the increase in oestrogen levels

After ovulation, what is the role of the Corpus Luteum?

Forms spontaneously Secretes Progesterone & Oestrogen Maintains FSH suppression LH suppressed by Progesterone inhibiting the positive feedback loop

What occurs in the Luteal phase?

Corpus Luteum grows and secretes more steroids

How many days is it until the Corpus Luteum dies if there is not a pregnancy?

14 days exactly. | Secretes prostaglandins and therefore cuts off its own blood supply so it dies

If the woman is pregnant, what does the Corpus Luteum do?

It will continue to grow and secrete increasing amounts of steroids (Due to Human Chorionic Gonadotrophin from the developing placenta) and support the embryo

What does death of the Corpus Luteum cause?

Rapid fall in steroid levels (Progesterone more quickly than Oestrogen) Stimulates menses Relieves inhibition of FSH

What causes Menstrual bleeding in the Menstrual cycle?

The rapid decrease in Progesterone levels faster than Oestrogen causes Menstruation (Where necrotic tissue is cleared by blood)

Where does variation in the length of the cycle come from?

Variation in timing of ovulation. The waiting/luteal phase is always 14 days and the preparatory phase is fixed too

What is the pelvic clock?

The events of the ovarian cycle produce a timing signal

When, in the Menstrual cycle, is Oestrogen high?

Begins low on day 0, increases slowly until it peaks just before the LH surge. High for waiting phase then drops again

When, in the Menstrual cycle, is Progesterone high?

Begins low then increased when ovulation occurs | Peaks in the waiting phase (Higher than oestrogen) then drops lower than oestrogen resulting in menstration

What is the brain's involvement in the female reproductive cycle/menstrual cycle?

Stimulates the gonad, but then a follicle develops and it takes over the brain

How long does the Corpus Luteum support the embryo?

12-14 weeks then the placenta takes over

Why are weeks 10 - 12 a very vulnerable time?

The support of the embryo is changing from the Corpus Luteum to the Placenta. This can cause spontaneous miscarriage as the embryo is very delicate