Ovulation Physiology

Question 1

Define oligomenorrhea, primary amenorrhea & secondary amenorrhea

Answer 1

Oligomenorrhea - cycles >42 days (<8 periods/yr)
Primary amenorrhea - Never had a period
Secondary amenorrhea - Absent period but previously had one

Question 2

Describe the HPO axis

Answer 2

Hypothalamus releases GnRH
Pituitary releases LH & FSH
Ovaries release progesterone & oestrogen

Question 3

FSH Function

Answer 3

• stimulates follicular development
• thickens endometrium

Question 4

LH Function

Answer 4

• Peak levels stimulate ovulation
• Stimulates corpus luteum development
• thickens endometrium

Question 5

Describe the pattern of GnRH release & the effects of low frequency vs high frequency pulses

Answer 5

GnRH is synthesised by neurons in the hypothalamus in a pulsatile release.

• Low frequency pulse - stimulates FSH release
• High frequency pulse - stimulates LH release

Question 6

Surge of which hormone triggers ovulation

Answer 6

LH

Question 7

Peak of which hormone follows ovulation

Answer 7

Progesterone

Question 8

Oestrogen function

Answer 8

• Fertile cervical mucus (thinner & sticky)
• Thickens endometrium

Question 9

Progesterone function

Answer 9

• Infertile cervical mucus (thicker & dry)
• Thickens endometrium
• Thermogenic effect on basal body temp
• Supports pregnancy.
• Relaxes smooth muscle

Question 10

Describe the positive and negative feedback involved in the HPO axis

Answer 10

• Progesterone negatively feedbacks on the anterior pituitary gland
• Oestrogen positively feedbacks on the hypothalamus & anterior pituitary gland during follicular phase
• Oestrogen negatively feedbacks on the hypothalamus & anterior pituitary gland during luteal phase

Question 11

Summarise hormone production (where & when)

Answer 11

Oestrogen
- From follicles & adrenal cortex (& placenta = pregnancy)
- Peaks in follicular phase just before ovulation & slowly rises with a lower peak midway through luteal phase

Progesterone
- From corpus luteum & adrenal cortex (& placenta = pregnancy)
- Luteal phase

Luteinising hormone (LH):
- From anterior pituitary gland
- Peaks in follicular phase just before ovulation

Follicle-stimulating hormone (FSH):
- From anterior pituitary gland
- Peaks in follicular phase just before ovulation

Question 12

How long is a regular period cycle and how do you identify day 1

Answer 12

Regular period - 28-35 days
Day 1 - First day of bleeding
Regular bleeding duration ~5 days

Question 13

Name the two phases of a period cycle and state which is constant and which is variable

Answer 13

Follicular phase
- before ovulation
- variable

Luteal phase
- after ovulation
- constant 14 days

Question 14

Summarise the phases of the menstrual cycle & the hormones involved:
- early follicular phase
- mid-follicular phase
- ovulation
- luteal phase

Answer 14

• Early follicular phase: FSH levels are high, while LH levels are low. FSH stimulates the maturation of ovarian follicles.
• Mid-follicular phase: LH levels rise due to positive feedback from estrogen levels.
• Ovulation: FSH and LH levels peak, causing ovulation.
• Luteal phase: Corpus luteum forms, progesterone levels rise & peak

Question 15

Which day of the cycle does body temperature increase and which point in the day should it be measured

Answer 15

Just after ovulation in response to progesterone production from the corpus luteum.

Basal body temperature should be measured in the morning just before moving and eating and after at least six hours of sleep

Question 16

What hormone is detected by an ovulation predictor kit and what does a positive result mean

Answer 16

Detects LH surge,
This occurs ~24-36 hours before ovulation