Menstrual Cycle Flashcards
When does the menstrual cycle begin and end?
It begins at menarche and ends at menopause
What are the 4 purposes of the menstrual cycle?
- generate oocyte
- facilitate fertilisation
- optimise endometrium for implantation
- protect the developing embryo
How is the menstrual cycle divided into 2 phases?
Follicular phase runs from day 1 - 14
Luteal phase runs from day 14 to 28
How is the menstrual cycle divided into 3 phases?
Menstrual phase runs from day 1 - 5
Proliferative phase runs from day 5 - 14
Secretory phase runs from day 14 - 28
What happens during the menstrual phase?
Menstruation
This is when the uterine lining is shed
Levels of oestrogen and progesterone are low
What happens during the proliferative phase?
The endometrium thickens
What happens during the secretory phase?
The uterine lining produces chemicals that will:
- support an early pregnancy
- prepare the lining to break down if pregnancy does not occur
What happens during the follicular phase?
This is the time between the start of the menstrual cycle and ovulation
Oestrogen levels are high
What happens during the luteal phase?
This is the time between ovulation and the start of menstruation
Progesterone levels peak and then drop
What is the name of the axis involved in endocrine control of the menstrual cycle?
Hypothalamo-pituitary-ovarian axis
What is involved in endocrine control through the hypothalamo-pituitary-ovarian axis?
- hypothalamus secretes GnRH
- GnRH stimulates the anterior pituitary gland to release FSH and LH
- FSH and LH travel to the ovary
What is the example of negative feedback in the hypothalamo-pituitary-ovarian axis?
The ovary produces oestrogens
The oestrogens feedback on the hypothalamus and anterior pituitary
This prevents release of GnRH and FSH/LH
What is the structure of GnRH?
It is a decapeptide
What is GnRH secreted by and how often?
It is secreted by mid basal hypothalamic neurones
It is secreted in hourly pulses
How is GnRH transported to the anterior pituitary gland?
It is transported via the hypophyseal portal blood system
What 6 factors will affect secretion of GnRH?
- bereavement
- anxiety
- time zone
- day/night duty
- exercise
- weight loss/gain
Where are FSH and LH secreted from?
Basophils in the anterior pituitary gland
FSH and LH are glycoproteins
What is the role of FSH?
What hormone does it lead to the production of?
It stimulates follicular activity
It promotes estradiol production from granulosa cells
What is the role of LH?
What hormone does it lead to the production of?
It triggers release of egg from dominant follicle
It promotes development of the corpus luteum and production of progesterone
How is GnRH, LH and FSH production inhibited?
It is inhibited by rising E2 levels
This is negative feedback
What happens near midcycle relating to the levels of GnRH, LH and FSH?
Levels of E2 lead to a surge in LH release
This triggers ovulation
This is positive feedback
What are the follicles that are present in the ovary at birth?
How many are there?
Primordial follicles
There are 2,000,000 in the foetus at 6 months
What happens to the numbers of follicles as age increases?
At birth - 750,000
At puberty - 400,000
Around 450 follicles develop and produce an egg - the rest degenerate
How are new follicles produced?
No new follicles are produced
What are the stages of follicular development leading up to ovulation?
- primordial follicle
- preantral follicle (primary)
- antral follicle (secondary)
- preovulatory follicle
OVULATION
What is the first stage in follicular development?
Between the primordial follicle and the preantral follicle, there is proliferation of granulosa cells
What is significant about the development of the antral follicle?
The antrum develops in the granulosa cells
This is a fluid-filled space which develops around the oocyte
What are the layers of the follicle?
- oocyte is in the centre
- zona pellucida
- granulosa cells
(antrum within this layer) - theca
What is the purpose of gap junctions and cytoplasmic processes between the oocyte and granulosa cells?
They allow for communication and passage of low molecular weight materials (nutrients)
What develops after proliferation of thecal cells?
Theca interna and theca externa
What is the difference between the theca interna and the theca externa?
The theca interna is glandular and highly vascularised
The theca externa is a fibrous capsule
Why is interaction between follicular cell types critical?
Androgens are secreted by theca interna cells
These are converted to estradiol 17-B in granulosa cells
What are the stages leading up to ovulation?
- high levels of E2 (estradiol) from almost mature follicle stimulate release of more GnRH and LH
- GnRH promotes release of FSH and more LH
- LH surge brings about ovulation
What is meant by corpus hemorrhagicum?
This is a ruptured follicle
The follicle ruptures during ovulation when a secondary oocyte is released
What is the name of the almost mature follicle?
Graafian follicle
What happens to the empty Graafian follicle post-ovulation?
The granulosa cells undergo luteinisation
This leads to production of the corpus luteum after 12 days
What happens to the corpus luteum if pregnancy occurs?
It secretes progesterone and oestradiol 17B
What happens to the corpus luteum if there is no fertilisation?
The corpus luteum degenerates/fibroses
It becomes the corpus albicans
What is the endometrium?
The lining of the uterus
What happens to the endometrium during the proliferative phase?
The endometrium thickens
This is driven by estradiol - E2
There is an increase in stromal cells, glands and blood vessels
How thick is the endometrium by ovulation?
By ovulation, the endometrium is 2-3 mm thick
What is the dominant hormone during the secretory phase?
Progesterone
What happens to the endometrium during the secretory phase?
- increased secretion
- increase in lipids and glycogen
- increased blood supply
How thick is the endometrium by the end of the secretory phase?
4-6 mm thick
How does the endometrium supply the optimal conditions for implantation of the fertilised egg?
It is stable, vascular and nutrient-rich
What is the first stage in menstruation?
Vasodilation due to vasospasm of blood vessels
This is brought about by PGF2a
What is the result of vasospasm of blood vessels?
The necrotic outer layers of the endometrium separate from the uterus
What happens once the outer layers of the endometrium have separated from the uterus?
The separated tissue and blood initiate uterine contractions
This works to expel the contents
What is produced from columnar glands in the cervix?
Mucus
What is the mucus from the columnar glands like mid-cycle?
Why?
It is stringy and runny - spinnbarkeit
This facilitates sperm access at ovulation
What is the mucus from the columnar glands like in the luteal phase?
Why?
It is tenacious and inelastic
This protects the developing embryo by preventing microbial ingress
It forms a mucus ‘plug’
What is contained in the combined oral contraceptive?
Estradiol and progestagen
Progestagen is synthetic progesterone
How does the combined oral contraceptive work?
It inhibits GnRH, FSH, LH through negative feedback
This prevents ovulation
It leads to a thin endometrium and tenacious mucus
How is an egg collected for in vitro fertilisation?
Superovulation involves daily injections of FSH
