Discuss the physiology of the HPO axis and normal menstrual cycle

Question 1

What happens during the secretory phase of the uterine cycle if fertilisation has not occurred?

Answer 1

1. corpus luteum hormones decline
2. spiral arteries spasm
3. endometrium degenerates
4. menstruation follows in approx. 24 hours

Question 2

What is the uterine cycle and what is its purpose?

Answer 2

1. the uterine cycle consists of changes occurring in the uterus
2. to prepare the endometrium for possible implantation by the fertilised embryo

Question 3

What is the duration of the uterine cycle and what does it correspond with?

Answer 3

1. 28 days approx.
2. the ovarian cycle

Question 4

Describe the process of ovulation

Answer 4

1. the follicle ruptures and the 2º oocyte is expelled into the abdominal cavity
2. the oocyte enters the fimbriated end of the fallopian tube

Question 5

When does the proliferative phase of the uterine cycle start?

Answer 5

• when bleeding ceases
• corresponding with follicular phase of ovarian cycle

Question 6

What does the follicular phase end with?

Answer 6

ovulation

Question 7

How are FSH and LH released?

Answer 7

In a cycle by the anterior pituitary

Question 8

Why is there a mid-cycle surge in LH?

Answer 8

• FSH and LH are produced in response to stimulation of the pituitary by oestrogen reaching a critical point.
• It is to stimulate ovulation and the formation of corpus luteum

Question 9

True or false? Changes in the duration of the ovarian cycle can be due to either the follicular or luteal phase

Answer 9

False - the duration of the luteal phase remains unchanged

Question 10

What 3 phases make up the uterine cycle?

Answer 10

1. proliferative
2. secretory
3. menstrual

Question 11

Which phase occupies days 15-28 of the ovarian cycle?

Answer 11

The luteal phase

Question 12

What happens in the luteal phase?

Answer 12

1. the ruptured (from ovulation) follicle caves in and fills with a blood clot
2. granulosa and theca cells increase and form the corpus luteum

Question 13

How long does the menstrual phase of the uterine cycle last?

Answer 13

3-6 days

Question 14

When does the secretory phase of the uterine cycle occur?

Answer 14

• in correspondence with the luteal phase of the ovarian cycle
• 14 days duration

Question 15

What is the corpus luteum?

Answer 15

• essential in preparing for fertilisation and for maintaining pregnancy
• secretes progesteronee and oestrogen
• degenerates after 12-14 days if fertilisation does not occur

Question 16

How do FSH and LH control the release of oestrogen and progesterone?

Answer 16

1. FSH + LH stimulate initial follicular development and oocyte maturation
2. small amounts of oestrogen produced by the follicle inhibits FSH+LH by negative feedback
3. oestrogen levels reach critical point
4. this causes oestrogen to stop inhibiting and start stimulating the anterior pituitary to release FSH and LH (+ve FB)
5. following ovulation, the corpus luteum secrets oestrogen and progesterone to inhibit FSH/LH
6. if pregnancy does not occur, the fall in LH causes the corpus luteum to degenerate and reduce levels of O+P
7. this removed the inhibition and enables the pituitary to secrete FSH and LH again, starting a new cycle

Question 17

What happens in the follicular phase of the ovarian cycle?

Answer 17

1. primordial follicles become 1º follicles
2. 1º follicles mature into 2º follicles
3. the zona pellucida and theca folliculi are formed
4. cells of the theca produce oestrogen during the maturation process
5. mature graffian follicles are ready to release a 2º oocyte at ovulation

Question 18

Which hormones control the ovarian cycle?

Answer 18

FSH and LH

Question 19

What happens during the menstrual phase of the uterine cycle?

Answer 19

1. spiral arteries dilate and bleed into the necrotic stratum functionalis
2. clotting of the menstrual blood flow is prevented in the uterus by release of fibrinolysins
3. the uterus contracts in response to prostaglandins to expel the blood

Question 20

What is the HPO axis and what is its role?

Answer 20

• Hypothalamic pituitary ovarian axis
• the system controlling female reproduction

Question 21

Describe the features of the secretory phase of the uterine cycle that prepares for an embryo

Answer 21

1. progesterone causes the glands in the endometrium to secrete glycogen (to nourish the embryo at implantation)
2. cervical mucus changes to a thick plug (blocking the cervical canal and protecting embryo)

Question 22

Describe the proliferative phase of the uterine cycle

Answer 22

1. following menstruation, only the basal layer of the endometrium remains (stratum basalis)
2. the release of oestrogen results in cell proliferation and regeneration of the stratum functionalis
3. phase ends with the maturation of the graffian follicle and ovulation at approx. day 14

Question 23

Which phase occupies days 1-14 of the ovarian cycle?

Answer 23

the follicular phase, including ovulation

Question 24

What is the duration of the ovarian cycle?

Answer 24

approximately 28 days