Menstrual cycle

Question 1

How long is the menstrual cycle?

Answer 1

• 21-35 days (average 28 days)

Question 2

Compare the lengths of the luteal and follicular phases

Answer 2

• Follicular phase variable in length
• Luteal phase is always 14 phases

Question 3

What are the feedback mechanisms of the menstrual cycle?

Answer 3

• GnRH causes release of LH and FSH
• FSH stimulates maturation of ovarian follicles
• LH stimulates steroid release, ovulation, and progesterone release by corpus luteum
• Oestrogen and inhibin exert negative feedback in FSH and LH release
• Oestrogen in high levels stimulates LH surge (positive feedback)
• This causes ovulation

Question 4

What are the phases of the ovarian cycle?

Answer 4

• Follicular phase (days 1-14)
• Ovulation on day 14
• Luteal phase (days 15-28)

Question 5

What are the phases of the uterine cycle?

Answer 5

• Menstrual phase
• Proliferative phase
• Secretory phase

Question 6

How do the phases of the ovarian and uterine cycles line up?

Answer 6

• Follicular phase lines up with menstrual phase and proliferative phase
• Then ovulation occurs
• luteal phase lines up with secretory phase

Question 7

Describe GnRH release in females

Answer 7

• Normally released in a pulsatile
• Persistent release would lead to desensitisation of its receptors on gonadotrophs
• FSH and LH production would cease as would gonadal steroid production

Question 8

What is the purpose of the ovarian cycle?

Answer 8

• Preparation of gamete for release

Question 9

Outline the early follicular phase of the ovarian cycle

Answer 9

• Days 0-5
• No ovarian hormone production
• Granulosa cells secrete activin
• FSH levels increase - stimulates follicle growth
• Theca interna appears - androgens produced so oestrogen levels increase
• Enhanced aromatase function
• Inhibin produced by dominant follicle granulosa cells

Question 10

What is the function of activin?

Answer 10

• Increase FSH production
• Increase FSH receptors on granulosa cells
• Reduce production of androgens by theca cells

Question 11

What is the function of aromatase?

Answer 11

• Follicle capable of enhanced oestrogen production

Question 12

Outline the late follicular phase of the ovarian cycle

Answer 12

• Days 5-14
• Dominant follicle (Graafian Follicle) granulosa cells produce oestrogen and inhibin

Question 13

What is the function of oestrogen in the ovarian cycle?

Answer 13

• Increases FSH receptors on follicle
• Initially exerts negative feedback to reduce FSH production
• Increases LH receptors on granulosa cells - prep for ovulation

Question 14

What is the function of inhibin in the ovarian cycle?

Answer 14

• Decreases FSH production so no other follicles can develop
• Helps LH to increase androgen production by theca cells

Question 15

Outline the ovulatory phase of the ovarian cycle

Answer 15

• Oestrogen continues to rise
• Exerts positive feedback on hypothalamus and anterior pituitary
• LH production surges
• Ovulation occurs
• FSH levels do not rise due to inhibin presence
• Granulosa cells start secreting progesterone

Question 16

Describe the state of the oocyte at ovulation

Answer 16

• Meiosis I completed
• Meiosis II begins but not yet completed
• Mature oocyte travels through capsule of ovary into fallopian tube

Question 17

Outline the luteal phase of the ovarian cycle

Answer 17

• LH stimulates remaining follicle to develop into corpus luteum
• Corpus luteum secretes oestrogen and progesterone in large quantities
• Inhibin also secreted
• Prepares endometrium for implantation
• Oestrogen and progesterone exert negative feedback on LH
• FSH levels remain low

Question 18

How long does the corpus luteum stay until it degenerates?

Answer 18

• 14 days +/- 2
• If fertilisation occurs hCG production maintains corpus luteum
• Otherwise it degenerates to form corpus albicans

Question 19

What are the effects of oestrogen on the endometrium?

Answer 19

• Drives proliferative phase of uterine cycle
• When oestrogen and progesterone are both present, they drive secretory phase of uterine cycle

Question 20

What are the different layers of the endometrium?

Answer 20

• Endometrium is epithelium and stroma
• Functional layer is responsive to hormones and is shed during menstruation
• Basal layer develops into a new functional layer
• Myometrium
• Perimetrium

Question 21

Outline how the endometrium changes as it passes through the uterine cycle

Answer 21

• Early proliferative - sparse glands, straight
• Late proliferative - thicker functional layer, coiled glands
• Secretory - endometrial thickness at maximum, very coiled glands, coiled arteries

Question 22

What happens at the end of the menstrual cycle if fertilisation does not occur?

Answer 22

• Corpus luteum becomes corpus albicans
• Dramatic fall in oestrogen, progesterone and inhibin
• Loss of negative feedback so FSH begins rising slowly
• Decrease in progesterone triggers menstruation
• New cycle starts

Question 23

What happens at the end of the menstrual cycle if fertilisation occurs?

Answer 23

• Syncytiotrophoblast produces hCG
• Extends lifespan of corpus luteum before placenta forms

Question 24

What is the action of oestrogen during the menstrual cycle?

Answer 24

• Key in follicular phase
• Thickening of endometrium
• Fallopian tube function
• Growth and motility of myometrium
• Thin alkaline cervical mucus
• Vaginal changes
• Changes in skin, hair, metabolism

Question 25

What is the action of progesterone during the menstrual cycle?

Answer 25

• Key in luteal phase
• Further thickening of endometrium in secretory phase
• Thickening of myometrium and reduction of motility
• Thick acidic cervical mucus
• Development of breast tissue
• Increased body temperature
• Metabolic/electrolyte changes

Question 26

What can cause disruptions to the menstrual cycle?

Answer 26

• Pregnancy, lactation
• Emotional stress
• Body weight
• Infertility