Feedback Mechanisms

Question 1

Negative Feedback

Answer 1

Occurs when the feedback causes the corrective measures to be turned off.

Question 2

Positive Feedback

Answer 2

Occurs when the feedback causes the corrective measures to remain turned on. Causes the system to deviate even more from original value. e.g. action potential

Question 3

Where is positive feedback more common?

Answer 3

When there’s a breakdown of control systems. e.g. typhoid fever -> hyperthermia

Question 4

Follicle-stimulating hormone (FSH)

Answer 4

Stimulates the development of follicles in the ovary, which contains eggs, and stimulates the follicles in the ovaries to produce oestrogen

Question 5

Luteinising hormone (LH)

Answer 5

Causes ovulation to occur, and stimulates the ovary to produce progesterone form the corpus luteum

Question 6

Oestrogen

Answer 6

Causes rebuilding of the uterus lining after menstruation and stimulates the pituitary gland to produce LH

Question 7

Progesterone

Answer 7

Maintains the lining of the uterus in readiness to receive the fertilised egg and inhibits the prod, of FSH from the pituitary gland.

Question 8

Which 2 hormones are released from the pituitary gland?

Answer 8

FSH and LH

Question 9

Which 2 hormones are produced from the ovaries?

Answer 9

Oestrogen and progesterone

Question 10

Outline the first 5 days of the menstrual cycle

Answer 10

1. Begins when the uterus lining is shed, along with some blood (1-5)
2. From day 1, pituitary gland releases FSH into the blood which stimulates follicles in the ovary to grow and mature. Each follicle contains an egg
3. The growing follicles secrete small amounts of oestrogen into the blood. This low level of oestrogen causes the uterus lining to build up again and also inhibits the release of FSH and LH from pituitary gland (negative feedback)

Question 11

Outline days 10-14 of the menstrual cycle

Answer 11

1. As the follicles grow, more oestrogen is produced. The level of oestrogen increases until day 10.
2. A critical point is reached which stimulates the pituitary gland to release more FSH and LH (positive feedback)
3. There is a surge in FSH and LH production.
4. This surge in LH causes one of the follicles in the ovary to release its egg. Ovulation Day 14

Question 12

Outline Days 14-21

Answer 12

1. After ovulation LH stimulates the empty follicle to develop into a structure called the corpus luteum, which secretes progesterone
2. Progesterone maintains the thick lining of the uterus and inhibits the release of FSH and LH by the pituitary gland (negative feedback)
3. If the egg isn’t fertilised, the corpus luteum degenerates and so no longer produces progesterone
4. With less progesterone, the lining of the uterus is no longer maintained and so breaks down. Less progesterone means that FSH release is no longer inhibited
5. FSH release therefore resumes and the cycle repeats itself