The Ovarian and Menstrual Cycles

Question 1

What are the 3 stages of the ovarian cycle?

Answer 1

Follicular, ovulatory and luteal phases

Question 2

Describe the follicular phase of the ovarian cycle

Answer 2

5-12 primordial follicles are stimulated to grow and develop –> one will for Graafian follicle –> releases the oocyte at ovulation

Question 3

Describe the ovulatory phase of the ovarian cycle

Answer 3

Graafian follicle bulges from ovary wall and ovulation occurs when the wall rupture and expels the oocyte into the peritoneal cavity

Question 4

Describe the luteal phase of the ovarian cycle

Answer 4

Granulosa cells of the Graafian follicle divide to form the corpus luteum which secretes hormones to maintain the endometrium to allow a fertilised oocyte to implant and grow

Question 5

When does the LH surge occur?

Answer 5

Just prior to ovulation

Question 6

What are the 3 stages of the menstrual cycle

Answer 6

Menstrual, proliferative and secretory phases

Question 7

Describe the menstrual phase

Answer 7

When there is withdrawal of steroid support (oestrogen and oestrogen) –> endometrium collapses and is shed with blood from the ruptured arteries and the detached endometrial tissue and blood pass out of the vagina

Question 8

Describe the proliferative phase

Answer 8

Oestrogen from the Graafian follicle stimulates the thickening of the endometrium –> glands and spiral arteries form –> oestrogen stimulates synthesis of progesterone receptors on endometrial cells

Question 9

Describe the secretory phase

Answer 9

Progesterone from corpus luteum acts on endometrium to stimulate gland enlargement to increase mucus and glycogen secretion in preparation for implantation of a fertilised oocyte. If fertilisation doesn’t occur, the corpus luteum degenerates, progesterone levels fall, endometrium degenerates and the cycle restarts

Question 10

Describe what happens instead of the menstrual phase if fertilisation occurs

Answer 10

The blastocytst implants into the endometrium –> developing placenta secretes hCG (syncytiotrophoblasts)–> corpus luteum doesn’t degenerate –> progesterone levels don’t fall and this maintains the endometrium

Question 11

What is the role of FSH and where is it produced?

Answer 11

Responsible for the maturation and growth of the follicles in the ovary; produced in the anterior pituitary gland

Question 12

What is the role of LH and where is it produced?

Answer 12

Causes release of mature oocyte into the fallopian tube; produced by the anterior pituitary gland

Question 13

What is the role of oestrogen and where is it produced?

Answer 13

Stimulates the growth of the endometrial lining and prepares the endometrium to be as nourishing to a possible fertilised egg; produced by follicles/immature eggs

Question 14

What is the role of progesterone and where is it produced?

Answer 14

Helps endometrium prepare for implantation by increasing vascularity and secretions of the tissue and halts oestrogen secretion to prevent overgrowth of the endometrial cells; produced in the corpus luteum

Question 15

What is the role of hCG and where is it produced?

Answer 15

Produced when a women is pregnant; by syncytiotrophoblast in the placenta

Question 16

Outline the hormones involved in the follicular phase

Answer 16

GnRH (hypothalamus) –> LH and FSH (anterior pituitary) –> stimulates maturation and growth of follicles –> Graafian follicle secretes oestrogen –> oestrogen inhibits further LH and FSH via negative feedback (large amounts of oestrogen cause positive feedback) –> oestrogen stimulates growth of endometrium

Question 17

Outline the hormones involved in the ovulatory phase

Answer 17

Oestrogen levels in high enough quantities –> positive feedback of FSH and LH –> LH and FSH surge –> stimulates meiosis I completion in primary oocyte –> secondary oocyte –> meiosis II in secondary oocyte –> surge in LH involved in facilitating ovulation

Question 18

Outline the hormones involved in the luteal phase

Answer 18

Granulosa cells of the ruptured follicle go on to form the corpus luteum –> oestrogens and progesterone, where the progesterone works to prepare the endometrium for implantation

Question 19

Describe the normal process of ovulation

Answer 19

Release of secondary oocyte from a Graafian follicle into the oviduct, uses intrafollicular pressure (due to proteoglycan presence) as well as the LH surge

Question 20

What is the function of spiral arteries in the menstrual phase?

Answer 20

These arteries contract in order to reduce bleeding from the shedding of the endometrium

Question 21

What is the normal age range for menarche?

Answer 21

Usually 12-15 but can be as early as 8 and be normal

Question 22

Why are there fluctuating oestrogen levels at the start of puberty?

Answer 22

Due to follicular development failing to reach ovulation and as a result, the endometrium is affected and undergoes cycles of proliferation and regression which eventually lead to the first period

Question 23

When is ovulation established in puberty?

Answer 23

When the oestrogen feedback mechanism is fully established, generally 6-9 months after the first period