The Menstrual Cycle

Question 1

How long does the menstrual cycle last and how does each phase last

Answer 1

21-35 days

Luteal phase is 14 +/- 2 days

Follicular phase varies in length

Question 2

What happens if there is continuous production of GnRH

Answer 2

GnRH become desensitised if exposed to continuous presence of GnRH

This results in infertility as the cycle shuts down and LH and FSH production stops

Question 3

How is the HPO axis controlled

Answer 3

HPO axis is controlled by positive and negative feedback of gonadal hormones

Question 4

Describe the start of the menstrual cycle

Answer 4

FSH causes growth and development of the follicles

Low steroid and inhibin levels means little inhibition at pituitary and hypothalamus -> FSH and LH levels can rise

FSH binds to granulosa cells and causes them to multiply

Theca interna appears allowing follicle to secrete oestrogen and inhibin

Inhibin inhibits FSH release

Question 5

Describe what happens during the mid-follicular phase

Answer 5

Oestrogen levels rise to a concentration where they exert positive feedback at the hypothalamus and pituitary resulting in LH levels rising - LH surge

Ovulation occurs due to the LH surge

Question 6

What forms the corpus luteum and what does it produce

Answer 6

Granulosa and theca interna form the corpus luteum

Corpus luteum secretes oestrogen and progesterone

Progesterone inhibits release of LH

Question 7

Describe the luteal phase

Answer 7

Corpus luteum produces progesterone, oestrogen and inhibin

Progesterone prevents another LH surge by inhibing hypothalamus and pituitary to prevent oestrogen production

Question 8

How does the endometrium respond to hormones produced by the ovary

Answer 8

Endometrium responds to oestrogen by proliferating

Endometrium responds to oestrogen and progesterone by secreting - becomes glandular

Question 9

What are the tissue layers of the uterus

Answer 9

Myometrium - muscular wall

Endometrium - epithelial lining:

• Functional layer - responds to hormone. Is shed is pregnancy does not occur
• Basal layer - provides source from which a new functional layer is developed

Question 10

How does the uterus change over the menstrual cycle

Answer 10

Early proliferative - glands are sparse and straight

Later proliferative - functional layer has doubled. Glands are coiled and can respond to progesterone

Early secretory - coiled glands are very pronounced

Late secretory - glands adopt saw-tooth appearance

After late secretory, functional layer is shed

Question 11

What happens to the corpus luteum if pregnancy occurs and what happens to it if pregnancy does not occur

Answer 11

If fertilisation occurs, syncytiotrophoblast produces hCG which exerts a luteinising effect and supports the corpus luteum. At end of 1st trimester, placenta is capable of producing enough steroid hormones to control HPO -> corpus luteum regresses

If fertilisation does not occur, corpus luteum regresses and cycle restarts

Question 12

Describe the functions of oestrogen during the follicular phase

Answer 12

Oestrogen causes mildly anabolic changes to metabolism, it depresses appetite and maintains bone structure

There is increased growth and motility of the myometrium

Endometrium thickens and becomes glandular

Thin, alkaline cervical mucosa is secreted that is conducive to sperm

There is growth and motility of fallopian cilia

There is secretion and muscular contraction in fallopian tube

There is increased mitotic activity in the vaginal epithelium

Question 13

Describe the functions of progesterone during the luteal phase

Answer 13

Progesterone stimulates mildly catabolic changes in metabolism

Body temperature is raised

There are changes in salt and water secretion - net Na and water retention

Endometrium thickens further, increases secretion and develops spiral arteries

Myometrium thickens to reduce myometrial motility and ensures the foetus is not expelled

There is reduced fallopian tube motility, secretion and cilia activity

There is thickening and acidification of cervical mucosa which inhibits sperm transport

Question 14

Name some chromosomal anomalies that cause menstrual disorders

Answer 14

MRKH syndrome - vagina and uterus are underdeveloped or are absent. Normal external genitalia

Turner’s syndrome

Androgen insensitivity sydrome

Congenital adrenal hyperplasia

Question 15

Name some non-chromosomal causes of menstrual disorders

Answer 15

Disorders to the HPO axis

Structural or anatomical abnormalities

Bleeding diathesis

Drugs

Thyroid disease

Chronic illness

Question 16

Name some structural causes of menstrual disorders

Answer 16

Agenesis/hypoplasia of the genital tract

Imperforate hymen

Leiomyoma

Asherman’s syndrome - adhesions within uterus causes it to stick to itself

Cervical stenosis

Question 17

What is amenorrhea

Answer 17

Absence of menstruation

Primary - failure to establish menstruation by 16yrs

Secondary - cessation of normal menstruation. Must be >6mths otherwise it might just be oligomenorrhea

Question 18

What is oligomenorrhea

Answer 18

Infrequent menstruation

>35 days between menstrual cycles

Question 19

What is menorrhagia and what is it more commonly known by

Answer 19

Complaint of excessive menstrual loss over consecutive cycles or >80mls per menstruation

Commonly known as heavy menstrual bleeding (HMB)

Question 20

What can cause heavy menstrual bleeding

Answer 20

Uterine fibroids - location determines severity of bleeding. Fibroids can increase SA for bleeding to occur from

Uterine polyps - increase SA for bleeding

Endometrial cancer

Bleeding diathesis

Copper IUD

Drugs

Question 21

What is dysmenorrhoea

Answer 21

Pain during menses, assocaited with uterine cycle

Primary - idopathic

Secondary - can be due to endomestriosis or obstructed menses

Question 22

What is intermenstrual bleeding

Answer 22

Bleeding in between menstrual cycles

Question 23

What is dysfunctional uterine bleeding

Answer 23

Heavy, irregular menstrual bleeding that occurs secondary to anovulation

Question 24

What is endomestriosis

Answer 24

Ectopic deposists of endometrium outside the uterus

They respond to GnRH -> grow, causing pain and discomfort

Bleed during menstruation