Feedback Mechanisms

Question 1

Negative feedback causes…

Answer 1

Corrective measures brought about by effectors to be turned off, system is returned to normal level

Question 2

Positive feedback causes…

Answer 2

The corrective measures to remain turned on, system deviates further from norm

Question 3

What are the 4 main hormones involved in the menstrual cycle

Answer 3

LH
FSH
Oestrogen
Progesterone

Question 4

What happens during days 1-5 of menstrual cycle?

Answer 4

The uterus lining is shed, along with blood

Question 5

What does FSH cause?

Answer 5

• growth and maturation of follicle that contains egg

- stimulates oestrogen

Question 6

What does oestrogen do?

Answer 6

• causes uterus lining to build up

- inhibits release of FSH and LH from pituitary gland

Question 7

When oestrogen reaches a critical level (day 10), what happens?

Answer 7

Stimulates pituitary gland to release more FSH and LH

Question 8

What does LH do?

Answer 8

• causes ovulation (day 14)

- stimulates empty follicle to develop into corpus luteum which secretes progesterone

Question 9

What does progesterone do?

Answer 9

• maintains thick lining of uterus in readiness of egg

- inhibits production of FSH and LH

Question 10

What happens if the egg is not fertilised?

Answer 10

• the corpus luteum degenerates, so less progesterone is released
• uterus lining breaks down (menstruation)
• this means production of FSH and LH is no longer inhibited, therefore cycle repeats

Question 11

What is an example of positive feedback in menstrual cycle?

Answer 11

• when oestrogen reaches critical level, it causes further secretion of FSH and LH

Question 12

What is an example of negative feedback in menstrual cycle?

Answer 12

• progesterone inhibits further release of FSH and LH

- oestrogen inhibits FSH and LH