F Physiology Basics

Question 1

What is the menstrual cycle?

Answer 1

• A regular monthly cycle
• Females can be sexually active at any time even if not ovulating
• If there is no conception then the endometrium is shed as a ‘period’

Question 2

Where does fertilisation normally occur?

Answer 2

Normally occurs in the fallopian tube.

Question 3

What are the steps leading up to fertilisation?

Answer 3

1. Oogonia undergoes mitotic division
2. This leads to 2 daughter cells being formed
3. One goes on to be the primary oocyte
4. Primary oocyte undergoes first meiotic division leading to:
5. Formation of two secondary oocytes
6. Secondary oocyte is joined with the sperm
7. Together these form the Zygote

[This process is started when there is a surge in Luetinizing hormone and takes 36 hrs for ovulation to occur]

Question 4

What is HPO?

Answer 4

Hypophalamic pituitary ovarian axis

These are the organs that are involved in controlling female reproduction.

Question 5

Please explain how ovulation and LH surge are connected.

Answer 5

• After the first 13 days of the cycle the levels of oestrogen and progesterone are low.
• The hypothalamus notices this and starts to produce FSH [Follicle stimulating hormone]
• Oestrogen spikes and this causes LH spike.
• The surge in LH causes the beginning of ovulation
• The most fertile time for a woman is after the beginning of the LH surge

Question 6

What does the hypothalamus release?

Answer 6

GnRH and this targets the anterior pituitary

Question 7

What does the pituitary release in response to the GnRH from hypo?

Answer 7

Releases FSH and LH.

Both target the ovaries.

Question 8

What effect does FSH have on the ovaries?

Answer 8

Stimulates (every month) a group of eggs to grow to release a single egg in that cycle.

Stimulate follicular recruitment and development.

Question 9

What effect does LH have on the ovaries?

Answer 9

Causes a mid cycle surge to make ovulation occur.

[Maintain the dominant follicle, induce follicular maturation and ovulation, stimulate corpus luteum function]

Question 10

What hormones do the follicles release at each stage within the reproductive cycle?

Answer 10

Follicle releases estrogen in follicular phase – after ovulation the follicle turns into corpus luteum and releases progesterone.

Question 11

Explain the feedback loops of the HPO axis.

Answer 11

The body sends neg feedback to pituitary and hypo to stop the cycle so to stop more than one egg being produced.

The postive feedback comes in as soon as one follicle is ready to release an egg there is an LH surge to help release the egg. Occurs 2 days mid cycle when egg needs to be released.

Question 12

What are the dual roles of oestrogen?

Answer 12

• Acts as negative feedback loop when it is in low conc.
• Acts as a positive feedback loop during days 12 to 14 and at high conc.

Question 13

What are the steps in the menstrual cycle?

Answer 13

Menstrual

• Shedding of the lining (period)
• Days 0-4

Proliferative

• The lining is proliferating to grow thick for implantation
• Days 4-14

[in between proliferative and secretory is ovulation]

Secretory

• Progesterone is released from corpus luteum – it dilates the blood vessels to prepare for pregnancy. Decidual changes.
• Endometrial blood vessels thicken up
• Days 14-26

Premenstrual

• Once day 26 is reached there is no pregnancy then all the hormones drop – signals stop of another cycle/menstrual bleed

Question 14

What are the steps in the ovarian cycle?

Answer 14

Follicular phase is before ovulation and luteal phase is after.

1. Primary follicle
2. Theca
3. Antrum
4. (after ovulation) Corpus luteum formation
5. Mature corpus luteum
6. Corpus albicans

Question 15

Role of oestrodial in ovulation?

Answer 15

(from granulosa cells)

Supports female secondary sexual characteristics and repro organs, neg feedback control of LH and GnRH, except in late follicular phase - positive control of LH surge, stimulates proliferative endometrium, negative control of FSH

Question 16

Role of progesterone in ovulation?

Answer 16

(from the corpus luteum)

Maintenance of the secretory endometrium, neg. feedback control of hypothalamic pituitary ovarian axis

Question 17

Explain the how ageing affects the numbers of immature follicles.

Answer 17

Fetal Development

• Germline stem cells proliferate, generating roughly 7 million oocytes

Birth

• Most oocytes degrade, so at birth roughly 2 million immature follicles remain

Puberty

• Subset of 4-10 immature follicles begin to mature with each menstrual cycle. One follicle ruptures, its oocyte is ovulated and can be fertilied

Menopause

• Too few immature follicles left to support monthly ovulation cycle

Question 18

What is the function of oestrogen?

Answer 18

Firstly: there are three types of oestrogens - oestrodiol, oestrone, oestriol.

It is the main female sexual hormone, which is responsible for the regulation and development of the female reproductive system, along with secondary sexual characteristics. Oestrogen is a hormone, which is secreted by the ovaries