Menstrual cycle Flashcards
How long is the menstrual cycle?
Around 28 days
Name the gonadotropins.
FSH - follicle stimulating hormone
LH - luteinising hormone
What are oestrogen & progesterone made of?
Cholesterol
Name the phases of the menstrual cycle. How long is each?
Follicular & Luteal
Both about 14 days long
What is GnRH?
Gonadotropin releasing hormone
Where is GnRH released?
Hypothalamus
What does GnRH do?
Stimulates release of FSH from anterior pituitary gland
What happens when FSH levels rise?
A few follicles are stimulated, they compete for maturity as they develop. One wins
What does the ‘winning’ follicle do?
Secretes oestrogen
The oocyte begins to develop
What causes LH to be released?
When levels of oestrogen get high enough a positive feedback loop occurs
What effect does LH have?
It causes the follicle membrane to get thinner, rupture and thus release the oocyte (ovulation)
Describe what happens to the oocyte and where it goes after released from the follicle.
Matures into an ootid and then a mature ovum
Goes into peritoneal space, then to fallopian tube via fimbriae
What day does ovulation occur?
Day 14
What happens to the ruptured follicle?
FSH and LH cause it to become a corpus luteum
What does the corpus luteum do?
Releases progesterone
What does progesterone do?
Causes levels of FSH and LH to fall and therefore the corpus luteum to break down and progesterone release stops
What hormone is released if the egg is fertilised?
hCG - human chorionic gonadotropin
What effect does hCG have?
Maintains the corpus luteum, so progesterone continues to be released.
This prevents menstruation.
What organ takes on the role of the corpus luteum if pregnancy occurs?
Placenta
What is the follicular phase?
From hypothalamus releasing GnRH to release of oocyte and ovum’s journey to fallopian tube
What is the luteal phase?
From the formation of the corpus luteum to its breakdown (if pregnancy does not occur)
Describe hormone levels at start of menstrual cycle.
FSH - increasing
LH - low
Oestrogen - low
Progesterone - low
Describe hormone levels during ovulation.
FSH - med/high
LH - high
Oestrogen - high
Progesterone - high
Describe hormone levels just after ovulation.
FSH - med/low
LH - low
Oestrogen - high
Progesterone - increasing
Describe hormone levels at start of menstruation.
FSH - low
LH - low
Oestrogen - decreasing
Progesterone - decreasing
Name the stages in follicular development.
Primordial follicle ↓ Primary follicle ↓ Secondary follicle ↓ Graafian follicle ↓ OVULATION ↓ Corpus luteum ↓ Corpus albicans
