The Menstrual Cycle Flashcards
What are the aims of the menstrual cycle?
Single oocyte selection Creation of haploid cells Regular, spontaneous ovulation Cyclical changes in the vagina, cervix and Fallopian tubes Uterus preparation Support of the fertilised egg
How long is a typical menstrual cycle?
28 days
When is the first day of the menstrual cycle?
First day of bleeding
What happens at (roughly) day 14 of the menstrual cycle?
Ovulation
What is the name of the first phase of the menstrual cycle?
Follicular phase
What is the name of the second phase of the menstrual cycle?
Luteal phase
What happens in the follicular phase of the menstrual cycle?
Growth of antral follicles up to ovulation
What is the follicular phase dominated by?
Oestradiol production from the follicles
What is the luteal phase dominated by?
Progesterone production from the corpus luteum
What happens in the luteal phase of the menstrual cycle?
Formation of the corpus luteum from the empty follicle
What are the feedback mechanisms that happen in the follicular phase?
Decrease in negative feedback, negative feedback reinstated, switch from negative to positive feedback and then negative feedback again
What induces the first decrease in negative feedback in the follicular phase?
Decrease in progesterone from the corpus luteum
What causes the reinstation of negative feedback in the follicular phase?
Oestradiol levels increase
What causes the switch from negative to positive feedback in the follicular phase?
As the dominant follicle grows it releases large amounts of oestradiol
What happens to the follicles when the FSH levels begin to rise at the start of the follicular phase?
Follicles are recruited into the menstrual cycle and produce oestrogen
What is the FSH threshold hypothesis?
One follicle from the group of antral follicles is at just the right stage to survive declining FSH and this becomes the dominant follicle which goes on to ovulate
How does the dominant follicle survive the fall in FSH?
Has LH receptors on it’s granulosa cells
What triggers the ovulation cascade?
The exponential rise in serum FSH
What happens in ovulation?
The egg is released, the corpus luteum is formed and produces progesterone
How does ovulation occur?
Blood flow to the follicle increases
An apex appears on the ovary wall
There is a local release of proteases and inflammatory mediators
Enzymatic breakdown of protein on the ovary wall
What happens 12-18 hours after the peak of LH?
The follicle wall is digested and ovulation occurs with the release of the cumulus-oocyte complex
What happens after the oocyte cumulus complex is extruded from the ovary?
Follicular fluid may pour into the pouch of Douglas
The egg is collected by fimbria of the Fallopian tube
Egg progresses down the uterine tube by peristalsis and action of cillia
What does the dominant follicle divide into?
First polar body and secondary oocyte
What is the difference between the secondary oocyte and first polar body?
The secondary oocyte has more cytoplasm
How many days does the secondary oocyte spend in the uterine tube?
2-3 days
What does the corpus luteum secrete?
Progesterone and oestradiol
What is the function of progesterone?
Supports the oocyte in its journey, maintains the corpus luteum, prepares the endometrium, controls cells in the Fallopian tubes and alters cervical secretions
How do you treat precocious puberty?
Constant GnRH
How much variation should a normal cycle show month to month?
4 days
Which of the luteal or follicular phases has a set time (and what is it)?
Luteal phase is always 14 days
What are the signs of ovulation?
Slight rise in basal body temperature, tender breasts, bloating, light spotting, changes in cervical mucus and pain on one side of the abdomen
What do ovulation prediction kits measure?
E3G
What is E3G?
A urinary metabolite of oestradiol
How long is the fertile period?
6 days
What affects the fertile period?
Lifespan of egg and sperm
What is the sperm survival dependant on?
The type and quality of mucus within the cervix and the quality of the sperm
