Grade 12 Human Reproduction Part 4 Menstrual Cycle

Question 1

What two cycles does the menstruation cycle consist of?

Answer 1

1. Uterine cycle
2. Ovarian cycle

Question 2

When does the uterine and ovarian cycle occur?

Answer 2

From puberty till menopause

Question 3

The ovarian cycle consists of 3 stages, namely:

Answer 3

1. Development of the Graafian follicle (day 1 - 14)
2. Ovulation (day 14)
3. Formation of the corpus luteum (from day 15 on)

Question 4

Phase 1 - the Follicular phase is the first part of the ovarian cycle. What happens during this phase?

Answer 4

• The primary follicles mature and get ready to release an egg cell.
• Under the influence of FSH (follicle stimulating hormone), from the pituitaty gland, a primary follicle develops into a fluid-filled Graafian follicle.
• During this process the primary oocyte in the follicle undergoes meiosis and develops into haploid egg cell (ovum)
• Usually only one egg cell is formed.

Question 5

Explain Phase 2 - the Ovulation phase

Answer 5

• The Graafian follicle contains the **egg cell (ovum) **
• As the follicle matures and enlarges it moves to the surface of the ovary
• Approximately mid-cycle, a second homone luteinizing hormone (LH) is also released from the pituitary gland
• Causes the Graafian follicle to **rupture releasing an egg cell **in an event called ovulation
• Approximately day 14 of cycle

Question 6

Explain Phase 3 - The Formation of the Corpus Luteum

Answer 6

• After ovulation the remains of the Graafian follicle, under the influence of:
• FSH and LH
• changes into a glandular tissue called the corpus luteum (yellow body)
• This structure produces large amounts of progesterone as well as oestrogen
• If pregnancy does not occur, the corpus luteum will begin to disintegrate and disappear 10 - 14 days after ovulation
• If preganancy does occur - it remains as it is needed to sustain healthy pregnancy

Question 7

What happens to the corpus luteum if pregnancy doesnt occur and if it does occur?

Answer 7

**Pregnancy doesnt occur? **
If pregnancy does not occur, the corpus luteum will begin to disintegrate and disappear 10 - 14 days after ovulation

Pregnancy does occur?
If preganancy does occur - it remains as it is needed to sustain healthy pregnancy

Question 8

What makes human ovulation unique?

Answer 8

heHuman females can be sexually active at any time in their cycle, even when they are not about to ovulate.
Other mammal females are only sexually active in the oestrus phase of their cycle - when “in heat”

Question 9

Study the Ovarian Cycle on page 100 of your textbook and PAGE 2.33 of Answer Series.

Question 10

Define the Uterine Cycle:

Answer 10

• A series of changes in the endometrium and is regulated by hormones.
• 2 Phases: Changes in Endometrium & Menstruation

Question 11

Discuss Phase 1 in the Uterine Cycle: **Changes in the endometrium **

Answer 11

• Hormone, oestrogen, secreted from the maturing follicles starts the repair of the endometrium
• Day 6 - 14 of menstrual cycle.
• Later under the influence of two hormones (oestrogena and progesterone) from the corpus luteum, the endometrium thickens
• becoming more glandular (secretes mucus and nutrients) and
• becomes more vascular (has blood vessels)
• It is now suitable for** IMPLANTATION** of a fertilised egg (BLASTOCYST)

Question 12

Discuss Phase 2 of the Uterine Cycle: Menstruation

Answer 12

1. High levels of oestrogen and progesterone exert a negative feedback on the pituitary - inhibiting the release of homones FSH and LHA as result = corpus luteum degenerates and progesterone secretion is reduced and then stops
2. With no hormones to maintain the endometrium, the lining breaks down and is shed = process called menstruation
3. The detached tissue and blood pass out throught the vagina as menstrual flow for 3 - 7 days.

Question 13

Explain the** simple negative feedback process** that control the secretion of pituitary hormones (FSH and LH) and ovarian hormones (oestrogen and progesterone):

Answer 13

• The signalling mechanism is the increased concentration of each hormone in the blood.
• An increased level of one will negatively affect or stop the release of another.

Question 14

**How does the simple negative feedback process work? Draw the cycle as you study this section!

Answer 14

1. Under influence of FSH - a primary follicle develops into a Graafian follicle and causes ovaries to produce oestrogen
2. Oestrogen stimulates pituitary gland to** produce LH**
3. LH causes the Graafian follicle to form the corpus luteum, which secretes progesterone
4. Increased progesterone and oestrogen concentrations activate a negative feedback mechanism, which stops the pituitary glands secreting FSH and LH
5. As there is no FSH a Graafian follicle will not develop and no oestrogen, and later progesterone, will be released by the ovary.
6. Beacause low levels of oestrogen and progesterone the secretion of FSH, and later LH, from the pituitary gland no longer is suppressed and - whole cycle starts again.

Question 15

What is menopause?

Answer 15

• Age 46 - 54 on average
• Ovaries stop producing oestrogen and progesterone
• Thus - ovaries stop releasing eggs and
• menstruation no longer occurs
• Woman has reached menopause

Question 16

Name some changes in a woman during menopause:

Answer 16

Hot flushes, mood changes

Question 17

What does post-menopausal conditions include?

Answer 17

• Atrophy (degeneration of reproductive organs)
• Bone mass loss
• Increasing risk of cardiac disease

Question 18

What can be used to help women cope with menopause?

Answer 18

• HRT (hormone replacement therapy)
• Low-dose oestrogen-progesterone perparations

Question 19

What is the difference between copulation and fertilisation?

Answer 19

Copulation: Sexual intercourse / coitus - transfer of sperm into vagina of the female when male organ, penis, is inserted and sperm are deposited near the cervix
Fertilisation: fusion of sperm nucleus with egg nucleus to form a diploid cell known as zygote