Session 2 - Part II Flashcards
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
What happens in the Ovulation phase of the Menstrual cycle?
Brief period of fertility (Around 36 hours)
Formation of the Corpus Luteum
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
What does species variation show us?
That ovulation can be very precisely linked to the environment
What are Induced Ovulators?
There is no ovulation without copulation
eg cats & rabbits
What are Induced Waiting phase?
Spontaneous ovulation
No Corpus Luteum formed without copulation
What is unique about the Menstrual cycle in higher primates only?
They always ovulate and always have a waiting phase.
How is the Menstrual cycle ended?
Shredding of part of the endometrium
What hormones co-ordinate the Menstrual cycle?
Gonadotrophins (LH & FSH)
Gonadal steroids
Oestrogen
Progesterone
What is the level of FSH on day 0 of the Menstrual cycle?
High
They then fall after the Preparatory phase
When is the lowest level of FSH in the Menstrual cycle?
In the waiting phase
Peak for ovulation
What is the level of LH on day 0 of the menstrual cycle?
Low
Increase for LH surge then drop again
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
What are the actions of Gonadotrophins in the Pre-ovulation phase?
LH surge stimulates ovulation
What are the actions of Gonadotrophins in the Luteal phase?
LH maintains the Corpus Luteum
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
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
