The Menstrual Cycle Flashcards
What kind of secretion of GnRH does there have to be?
→ pulsatile
What does the antral follicle produce and what does this do?
→ Estrogen
→ Progesterone
→ feedsback to hypothalamus and pituitary
What is the first day of the menstrual cycle?
→ The first day that bleeding occurs
What is the length of an ideal menstrual cycle?
→ 28 days
What is the follicular phase?
→ Growth of follicles until ovulation
What is the main hormone in the follicular phase?
→ Estrogen
What happens to the follicle after ovulation?
→ It becomes the corpus luteum
What does the corpus luteum produce?
→ Progesterone
What kind of feedback does progesterone have?
→ negative
Describe the hypothalamic/ovarian axis
1) Progesterone produced from the corpus luteum exerts negative feedback on the hypothalamus
2) If there is no pregnancy the CL dies and progesterone levels drop - no negative feedback
3) FSH levels rise again - intercycle rise in FSH
4) the early antral follicles respond to FSH and grow again
5) the follicles are producing estrogen
6) This exerts a negative feedback and FSH drops
7) the antral follicles start to die except the dominant one
8) the dominant follicle grows exponentially and produces a lot of estrogen
9) Estrogen levels are sustained for 48 hours over 300pmol
10) there is positive feedback which results in a big increase in LH but not FSH because the dominant follicle produces inhibin which inhibits FSH
11) complettion of Meiosis I and entry into meiosis II
12) LH produces proteases which ‘cut’ the oocyte out and cause it to be ovulated
13) It also triggers luteinization
14) CL produces progesterone
Why is the intercycle rise and fall in FSH important?
→ It allows the selection of a single follicle
What is the rise in FSH for?
→ Selection of antral follicles
What is the drop in FSH for?
→ The dominant follicle survives and the others die off
What type of growth occurs consistently?
→ Pre antral growth
What kind of follicles need FSH to grow?
→ follicles that have an antrum
What is the FSH threshold hypothesis?
→ One follicle from the group of antral follicles is at the right stage at the right time
→ It has the most number of FSH receptors
→ It becomes the dominant follicle which goes on to ovulate
Describe how the dominant follicle survives the fall in FSH?
→ The gene which produces the LH receptor is switched on
→ Follicle responds to LH
→ increases FSH receptors so it is responsive to falling levels of FSH
→ increases the number of granulosa cells
What receptors do theca cells have?
→ LH receptors
What do theca cells produce?
→ androgen
→ progesterons
What is the pathway to make estrogen?
Acetate
↓
Cholesterol
↓
Pregneneolone
↓
progesterone
↓
testosterone/androstenedione
↓
EstrogensWhat are the three things that can affect the hypothalamic axis?
→ Stress
→ hyperinsulinemia
→ Adipocytes
Why are estrogen levels raised at the end of the follicular phase?
→ The dominant follicle produces a lot of estrogen
What does the raised estrogen level (produced by the dominant follicle) cause?
→ Estrogen feedback switches from - to +
→ Massive release of LH from the pituitary
→ triggers ovulation
Describe ovulation
→ Blood flow to the follicle increases
→ Increase in vascular permeability which increases intra-follicular pressure
→ stigma on the ovary wall
→ local release of proteases
→ A hole appears in the ovary wall and ovulation occurs
What happens to the egg after ovulation?
→ Collected by the fimbria
→ progresses down the tube by peristalsis and action of cilia
What is the advantage of remaining in meiosis I ?
→ Permits the oocyte to retain all of the DNA and remain as large as possible
What happens to the chromosomes when the egg becomes a secondary oocyte?
→ 1/2 the chromosomes are put in a small package in the egg called the 1st polar body
If pregnancy occurs what is the CL supported by?
→ LH
→ HcG
What are the functions of progesterone?
→ Alters secretions in cervix
→ Prepares endometrium
What is the lifespan of the CL?
→ 14 days
