Menstrual Cycle Flashcards
What hormone secreted by the hypothalamus controls the menstrual cycle?
What type of hormone is this?
Gonadotrophin releasing hormon, GnRH for short.
It is a peptide hormone.
In what way is GnRH released?
In a pulsatile fashion.
These pulses are necessary to stimulate pituitary release of LH and FSH.
What effect does low level oestrogen have on the amount of LH/FSH released by the anterior pituitary?
Low level oestrogen has an inhibitory effect (negative feedback) on LH.
What effect does high level oestrogen have on the amount of LH/FSH released by the anterior pituitary?
High level oestrogen has a stimulatory effect on LH/FSH release (positive feedback).
How do combine hormonal contraceptives inhibit ovulation?
CHC lead to a constant low level of oestrogen in the blood, leading to negative feedback on LH/FSH release, thereby inhibiting ovulation.
What effect does low level progesterone have on the release of LH/FSH?
Low level progesterone causes positive feedback, i.e. it stimulates the produciton of LH/FSH from the pituitary.
What effect does high level progesteron have on the amount of LH/FSH released by the anterior pituitary?
High level progesterone has a negative feedback effect on LH/FSH release, i.e. it inhibits their produciton
What are the three ovarian phases of the menstrual cycle?
- Follicular, where the follice(s) grow
- Ovulation, where the egg is released
- Luteal phase, where the corpus luteum forms from the remaining follicle
Why is the FSH peak smaller than the LH peak when oculation occurs?
This is due to the action of inhibin, produced by the Graafian Follicle, which specifically inhibits FSH production.
What are the two cell types found in the follicle (excluding oocyte)?
What receptors do they express, and which molecules do they produce?
Theca and Granulosa cells.
Theca cells express LH receptors. When stimulated, they produce androstenedione.
Granulosa cells express FSH receptors. When stimulated, they produce aromates, which converts androstenedione into oestradiol.
Describe the process that leads to the selection of the Graafian Follicle.
Several follicles start to mature independant of hormones. At some point they become hormone dependant - due to the increased production of oestradiol, however, there is negative feedback on the produciton of LH/FSH. Only the follicle with the mot LH and FSH receptors can continue growing - i.e. the Graafian Follicle.
What causes ovulation?
The LH surge due to the positive feedback of high oestradiol concentrations.
What do over-the-counter ovulation predictors measure?
They measure the LH surge.
Why should women who wish to conceive not take prostaglandin snythetase inhibitors?
It is thought that prostaglandins are involved in breakdown of the follicular wall to release the oocyte.
NSAIDs, who block prostaglandin synthesis, therefore might block ovulation.
How long do the phases of the menstrual cycle last?
The luteal phase lasts pretty much exactly 14 days.
The follicular phase is more variable, but also lasts around 14 days.
What causes menstruation?
Progesterone withdrawal (i.e. a drop in progesterone levels, as the corpus luteum has died).
The low concentration of progesterone also stimulates the production of FHS/LH and therfore the growth of more follicles.
What are the 3 endometrial phases of the menstural cycle?
- Menstruation (shedding of the layer)
- Proliferative (under oestrogen, the endometrium proliferates and becomes thicker)
- Secretory (spiral arteries form, endometrium prepares for implantation)
What is the endometrial thickness just before and just after menstruation?
Just after: 0.5mm
Just before: 3.5-5mm
How is amenorrhoea defined?
Amenorrhoea is defined as the absence of menstruation for more than 6 months in the absence of pregancy, lactation or the menopause in a women of fertile age.
Pirmary amenorrhoea is if a girls fails to menstruate by 16, secondary if she had periods that have now stopped.
How is oligomenorrhoea defined?
Oligomenorrhoea is defined as irregular periods at intervals of >35 day, with only 4-9 periods a year.
NICE just says: Oligomenorrhoea is defined as irregular periods at intervals of 35 days - 6 months.
What are the causes of (pathological) amenorrhoea?
Hypothalamic disorders: (hypothalamic hypogonadism)
- Excessive exercise/weight loss/stress
- Hypothalamic lesions
- Head injury
- Kallmann Syndrome (GnRH deficiency)
- Systemic disorders leading to infiltration of hypothalamo-pituitary region (e.g. Sarcoid)
- Drugs: progestogens, HRT, dopamine agonists
Pituitary disorders:
- Adenoma (e.g. prolactinoma)
- Pituitary necrosis (e.g. Sheehan’s)
- Iatrogenic (Surgery, radiotherapy)
- Congenital failure of pituitary development
Ovarian Causes:
- PCOS (anovulation)
- Premature ovarian failure
Endometrial disorders:
- Abesent uterus
- Outflow obstruction (imperforate hymen)
- Asherman Syndrome (scarring of the endometrial lining)
How would you investigate amenorrhoea/oligomenorrhoea?
Always put your Ix in perspective to the patient’s history!
Investigations to consider:
- Pregnancy test (if of reproductive age)
- LH (raised in PCOS)
- Testosterone (raised in PCOS)
- FSH (raised in primary ovarian failure)
- Prolactin (prolactinoma)
- TFT (both hyper- and hypothyroidism cause menstrual irregularities)
- Exclude Cushing’s and congenital adrenal hyperplasia
- USS (polycystic ovaries)
- MRI (if history consistent with prolactinoma)
- Hysteroscopy (is history suggestive of Asherman’s or obstruction)
- Karyotyping (if Kallmann’s or Turner’s suspected)
What are the physiological causes of amenorrhoea?
Physiological (non-pathological) causes of amenorrhoea include:
- (Primary) constitutional delay - common and often familial.
- (Secondary) pregnancy
- (Secondary) lactation
- (Secondary) menopause
