PHYSIOLOGY OF MENSTRUATION

Question 1

What are the 2 layers of the endometrium?

Answer 1

Functional layer - superficial, thickens in response to oestrogen, shed during menstruation, spiral arterioles
Basal layer - thin, feeds overlying functional layer, contains straight arterioles, doesnt shed in menstruation

Question 2

What is adrenarche?

Answer 2

“The awakening of the adrenal gland”
Growing of pubic hair, body odour, skin oiliness, libido, mild acne

Question 3

What is thelarche? age?

Answer 3

Onset of breast development
9-10
(Usually the first sign of puberty in girls)

Question 4

What is menarche?

Answer 4

Onset of first menstrual period

Question 5

Average age of menarche?

Answer 5

11-15 - average is 12

Question 6

Link between body weight and menarche?

Answer 6

The body’s fat content must account for 17% of the body’s weight before menarche can occur and, from the age of 18, must be at least 22% for the maintenance of regular cycles

Age of menarche is getting lower because of childhood obesity

Question 7

How many oogonia do women have? At what age do the levels decline at an accelerated rate, making it harder to get pregnant?

Answer 7

Women are born with an absolute number of oogonia
At birth, 200,000 - 2 million primary oocytes remain in each ovary. Of these about 40,000 are still present at puberty. 400 will matures and ovulate during reproductive lifetime.

Levels decline most prominent from 37-39 years old - much harder to get pregnant from then on

Question 8

What is oogenesis?

Answer 8

the process of formation of female gametes

Question 9

Where do primordial germ cells originate?

Answer 9

In the yolk sac of the embryo

Question 10

Outline the mitosis 1 in oogenesis?

Answer 10

During foetal life the primordial germ cells from the yolk sac move to colonise the cortex of the primordial gonad.
Replication by mitosis peaks at 7 million by about 20 weeks
After this cell death occurs to leave about 2 million.

Question 11

Outline meiosis 1 in oogenesis?

Answer 11

In each foetal ovary oogonia enter meiosis 1 and are arrested at prophase 1. These are now known as primary oocytes
These oocytes form primary follicles
Over time atresia occurs leaving about 40,000 eggs by puberty

Question 12

How many primary oocytes begin to mature each month once puberty begins?

Answer 12

15-20

Question 13

What happens in the pre-antral stage of oogenesis?

Answer 13

The primary oocyte within the primordial follicle grows dramatically and follicular cells grow and proliferate to form granulosa cells
Granulosa cells secrete glycoproteins which form the zona pellucida around the primary oocytes
Surrounding connective tissue cells differentiate to become theca cells

Question 14

What happens in the antral stage of oogenesis?

Answer 14

Fluid-filled spaces form between the granulosa cells and these eventually combine to form the antrum (fluid filled central space). This is now a secondary follicle
Each monthly cycle, 1 of these secondary follicle becomes the Graafian follicle and develops further

Question 15

Outline how the Graafian follicle releases the ovum?

Answer 15

The LH surge causes increased collagenase activity which weakens the wall of the follicle. There are also muscular contractions of the ovarian wall, resulting in the ovum being released from the ovary.
The ovum is then taken up into the fallopian tube by fimbriae

Question 16

What happens to the ovum if fertilisation does not occur?

Answer 16

The oocyte will degenerate 24 hours after ovulation to create the corpus luteum
This causes a drop in the levels of progesterone and oestrogen resulting in endometrial shedding

Question 17

What happens the the ovum if fertilisation does occur?

Answer 17

It will complete meiosis II to form a mature oocyte and the second polar body

Question 18

When does meiosis II complete in oogenesis?

Answer 18

After fertilisation

Question 19

When does meiosis I complete in oogenesis?

Answer 19

After puberty in every monthly cycle

Question 20

Average length of menstrual cycle?

Answer 20

28
23-35 days

Question 21

What day of the menstrual cycle is ovulation?

Answer 21

14 days before the start of the next period/cycle

Question 22

What is the follicular phase? Which phases of the endometrium does this align with?

Answer 22

The first 14 days (roughly as this length is not fixed and dependant on cycle length) - the weeks leading up to ovulation
Corresponds to the menstrual and proliferative phases of the endometrium

Question 23

What is the luteal phase? Which phases of the endometrium does this align with?

Answer 23

The 2 weeks following ovulation - this length is fixed
This corresponds to the secretory phase of the endometrium

Question 24

Outline how levels of GnRH change as we reach puberty?

Answer 24

Before puberty the hypothalamus produces low-frequency pulses of GnRH at night
As we reach puberty, the hypothalamus begins to increase its frequency of pulses of GnRH to every 90 minutes.

Question 25

Outline the what happens int eh follicular phase

Answer 25

Day 1-5: menstrual phase - shedding of functional endometrium due to decreased oestrogen and progesterone levels. FSH released from pituitary gland, stimulating growth of several ovarian follicles
Day 6-10: FSH stimulates development and maturation of follicles in ovaries. The first follicle to become fully mature/develops the most FSH receptors begins to produce large amounts of oestrogen which inhibits the growth of other competing follicles. Rising oestrogen levels cause endometrium to thicken, cervical mucus to thin and inhibition of LH production (in preparation for potential fertilised egg implantation)
Day 12 - as oestrogen levels rise, they eventually surpass a threshold level and conversely stimulate LH production causing a surge. The high amounts of LH cause the membrane of the Graafian follicle to become thinner and within 48 hours the follicle ruptures releasing a secondary oocyte. This quickly matures into an optic and then a mature ovum and its released into the peritoneal space and taken into the fallopian tube by fimbriae

Question 26

How do the follicles create and secrete oestrogen?

Answer 26

During the follicular phase of the menstrual cycle, theca cells develop receptors for LH which they cn bind to cause secretion of androstenedione
Granulosa cells develop FSH receptors which they bind to produce aromatase. Aromatase converts androstenedione into estradiol which is a member of the oestrogen family

Question 27

Outline the stages in the luteal phase?

Answer 27

Once ovulation has occurred, LH and FSH stimulate the Graafian follicle to develop into the corpus luteum
This begins to produce progesterone
Increased progesterone levels causes the endometrium to be receptive to implantation of the blastocyst, negative feedback to decrease LH and FSH and an increase int he woman’s basal body temperature
The luteinized granulosa cells also release inhibin which also inhibits the pituitary gland from making FSH
As levels of FSH and LH falls, the corpus luteum degenerates
This results in a loss of progesterone production which triggers menstruation

Question 28

Outline the proliferative phase of the uterine cycle?

Answer 28

High oestrogen levels stimulates thickening of the functional layer of the endometrium, growth of secretory glands and emergence of spiral arteries - basically it stimulates repair and growth after recent menstruation

Question 29

Outline the secretory phase of the uterine cycle?

Answer 29

Day 14-28 Once ovulation has occurred…
Corpus luteum produces progesterone which results in the secretion by endometrial glands and coiling of spiral arteries

Question 30

Outline the menstrual phase of the uterine cycle?

Answer 30

At the end of the luteal phase, if no implantation occurs, the corpus luteum degenerates
This results in decreased progesterone production
This causes the spiral arteries in the functional endometrium to contract, and the loss of blood supply causes the functional endometrium to become ischaemic and necrotic
As a result the functional endometrium is shed and exits through the vagina as menstruation

Question 31

What does FSH stimulate once it binds to ovaries?

Answer 31

Follicle development and maturation
Binds to receptors on granulosa cells and uses aromatose to convert androstenedione to estradiol

Question 32

When is a woman considered fertile?

Answer 32

5 days running up to ovulation, the day of ovulation and 1 day after
(Usually day 9-16)

Question 33

How long can sperm survive in the uterus?

Answer 33

Up to 5 dayd

Question 34

When the corpus luteum involutes after 14 days, what does it become?

Answer 34

Corpus albicans

Question 35

What can be produced for “luteotrophic rescue” of the corpus luteum to maintain the endometrium?

Answer 35

HCG

Question 36

Where are LH and FSH produced?

Answer 36

Anterior pituitary

Question 37

What is the primary source of progesterone at the start of preganncy?

Answer 37

The corpus luteum (from the 8th week its the placenta as the corpus luteum breaks down)

Question 38

In a normal 28 day menstrual cycle, when would you expect the LH surge to occur?

Answer 38

On day 12 - as 24-48 hours after ovulation usually occurs due to rupture of the Graafian follicle