Menstrual and Ovarian Cycle Physiology Flashcards
What is menarche?
The onset of the menstrual cycle.
What happens to the ovaries and uterus during the menstrual cycle?
Ovaries - produce a follicle and release it into the Fallopian tube.
Uterus - prepares the endometrium for fertilisation, if there’s none then the lining is shed.
How long is the menstrual cycle?
28 days is most common.
Regular periods between 21 - 40 days is normal.
What are the phases of the menstrual cycle?
Follicular phase (1st 2 weeks) Luteal phase (last 2 weeks)
Which hormones stimulate follicle development?
FSH and LH (from anterior pituitary).
Which hormone causes endometrial thickening?
Oestrogen
Which hormone causes ovulation?
LH - theres an LH surge during the middle of the cycle.
What does the follicle become when it has released the oocyte?
The corpus luteum
What does the corpus luteum secrete?
Progesterone.
What affect does progesterone have on the endometrium?
It prepares the endometrium for fertilisation AFTER ovulation.
What controls the menstrual cycle?
The hypothalamus - GnRH - anterior pituitary - LH, FSH
What do LH and FSH do in the menstrual cycle?
FSH - stimulation of the follicle to develop
LH - causes the follicle to release the oocyte
Where does LH bind to?
LH receptors on Theca cells in the ovaries.
What does theca cells secrete?
Androstenedione (pro-hormone which can become progesterone or oestrogen)
What does FSH bind to?
FSH receptors on granulosa cells in the ovary.
What do granulosa cells secrete?
They turn the androstenedione into estradiol/progesterone
What happens in the follicular phase (in the ovaries)?
FSH makes the follicles grow
FSH causes an increase in oestrogen - this is negative feedback and inhibits FSH/LH release
There is therefore only enough FSH to continue stimulating one follicle (dominant follicle)
The ovaries continue to secrete oestrogen and once it reaches a threshold it causes positive feedback - there is a surge of FSH/LH
the follicle then ruptures and releases a secondary oocyte - ovulation.
What happens during the luteal phase (in the ovaries)?
The LH is still high and it turns the follicle into the corpus luteum
The follicle that ruptured becomes the corpus luteum - it secretes lots of progesterone
Progesterone has a negative feedback on the hypothalamus - this inhibits FSH/LH and oestrogen
If fertilisation happens the corpus luteum continues to secrete progesterone until the placenta forms
If fertilisation doesn’t occur the corpus luteum secretes progesterone for 10 days then stops - it becomes the corpus albicans.
When does oestrogen behave in a positive feedback loop?
Only during the days of ovulation (usually days 12-14)
What is the most common site of fertilisation?
Ampulla of the Fallopian tube.
What happens during the follicular phase (to the uterus)?
The endometrium thickens under the influence of oestrogen to prepare for fertilisation.
What happens during the luteal phase (to the uterus)?
Spiral arteries form
If theres no fertilisation - they collapse and the superficial layer of the endometrium dies and is shed.
When does ovulation occur?
Usually day 14 (of a 28 day cycle)
Usually always 14 days before the first day of menstruation, regardless of the cycle length.
When does the FSH/LH surge happen?
Usually 1-2 days before ovulation.
When is fertilisation highest?
Day 11-15 of a 28 day cycle.
Why do the spiral arteries collapse?
Because the corpus luteum becomes the corpus albicans and doesn’t secrete progesterone.
The spiral arteries collapse when progesterone is at its lowest.
What phase can change in length?
The follicular phase is more likely to change
The luteal phase is almost always 14 days before menstruation
What is another name for the follicular phase?
The menstrual phase
What is another name for the luteal phase?
The secretory phase.
What is the precursor for oestrogen and progesterone?
Cholesterol.
What effects does oestrogen have on the body?
Secondary sex characteristics - growth of breasts, widening hips, fat distributed to bum and hips
Maturation of Fallopian tubes, uterus, cervix and vagina
Protects cardiovascular system
Protects bone density
What produces oestrogen and progesterone during pregnancy?
The placenta
What happens in menopause?
Theres no functional follicular cells left.
Theca cells and granulosa cells don’t produce oestrogen and progesterone.
The lack of oestrogen is what gives the menopausal symptoms.
What happens in menopause?
Theres no functional follicular cells left.
Theca cells and granulosa cells don’t produce oestrogen and progesterone.
The lack of oestrogen is what gives the menopausal symptoms.
