13 Feedback mechanisms

Question 1

EQ

Hodgkin’s lymphoma (HL) is a type of cancer. It is usually treated using chemotherapy. In young female patients with HL, chemotherapy can reduce their ability to have children in later life. This is because some of the drugs used in chemotherapy destroy developing follicles in their ovaries.

Destruction of developing follicles during chemotherapy can lead to a much higher concentration of FSH in the young female patients’ bodies than normal. Use your knowledge of hormonal interactions to explain why (2)

Answer 1

1. No/less oestrogen produced (by
   follicles/ovaries);
2. No/less negative feedback (by oestrogen); (to inhibit fsh)
3. On pituitary (gland);

(fsh stimulates follicles)

Question 2

EQ

Some young female patients with HL are given an artificial hormone during chemotherapy. This artificial hormone reduces the release of FSH.

Suggest how the artificial hormone helps to prevent a reduction in their ability to have
children in later life. (3)

Answer 2

1. (Less FSH so) fewer/no follicles develop;
2. (So) fewer follicles (will be) destroyed (by
   chemotherapy);
3. (So) more follicles left for later in life/after
   treatment;
4. (So) more eggs;

Question 3

EQ

Figure 4 shows the structures of the artificial hormone and the hormone that normally causes the release of FSH. 4
Suggest how the artificial hormone reduces the release of FSH. (2)

Answer 3

1. Similar shape/structure/binding site to normal
   hormone;
2. So binds to (same) receptor and stops normal
   hormone binding;

Question 4

EQ

The concentration of LH in the blood is controlled by negative feedback. Use the curves for progesterone and LH to explain how. (3)

Answer 4

LH rises;
Increase in progesterone;
Progesterone inhibits LH;
(Then) LH falls;

Question 5

EQ

Explain how the change in progesterone concentration (increase) in March shows that ovulation
took place at the time indicated (just before). (2)

Answer 5

Corpus luteum;

Progesterone produced;

Question 6

EQ

Two pieces of information from the graph, other than the change in progesterone concentration, show that ovulation took place at the time indicated. Explain how. (4)

Answer 6

A lot of/ rise in oestrogen;
Associated with follicle growth/development/ LH surge;
OR
Fall in oestrogen;
Follicle breaks down;
Surge in LH (before ovulation);
(LH) stimulates ovulation/release of egg;
OR
Fall in LH (after ovulation);
Inhibited by progesterone;

Question 7

EQ

Give one piece of evidence from the graph that this pig was not pregnant at 25 days (1)

Answer 7

Fall in progesterone / progesterone same as at start /

progesterone low at 25 days;

Question 8

EQ

The relationship between oestrogen and LH is an example of positive feedback.
Explain how. (2)

Answer 8

Answer showing understanding of positive feedback i.e. more
produces more / differs further;
Answer showing understanding of positive feedback correctly
linked to oestrogen and LH i.e. more oestrogen produces
more LH;;

Question 9

EQ

Farmers sometimes give progesterone to sheep to prevent ovulation.
Explain how progesterone prevents ovulation. (2)

Answer 9

1. Progesterone has negative feedback effect / inhibits
   secretion of FSH/LH;
2. (FSH) stimulates follicle development / ( LH) stimulates
   ovulation;

Question 10

EQ

Explain how the graph supports the following statements.
Oestrogen causes the release of LH. (1)
The woman did not become pregnant during this cycle. (1)

Answer 10

1. LH increases/peaks after
oestrogen increases/peaks;
OR
2. Oestrogen increases/peaks
before LH increases/peaks; 

Progesterone falls / progesterone
returns to start / progesterone not
maintained;

Question 11

EQ

Implanon is a contraceptive device that is inserted under a woman’s skin and prevents
pregnancy for up to three years. It is a small rod that continuously releases
progesterone into her blood. This progesterone prevents fertilisation from taking place.
Explain how Implanon prevents fertilisation from taking place. (4)

Answer 11

1. FSH inhibited;
2. Follicle not stimulated /
   ripened / does not grow;
3. LH inhibited;
4. Ovulation prevented /
   egg/ovum not released;

Question 12

EQ

Suggest one advantage of using Implanon rather than an oral contraceptive. (1)

Answer 12

Will not forget to take Implanon /
may forget to take an oral
contraceptive / does not have to
be taken daily / not affected by
illness/vomiting;

Question 13

Define the menstrual cycle

On what day of the oestrous cycle does ovulation occur?

Answer 13

(in humans) the lining of the uterus is shed along with some blood between each cycle.

Day 14

Question 14

Why do only certain cells respond to hormones that control the oestrous cycle, despite it circulating in the blood plasma and reaching all parts of the body?

Answer 14

Certain receptors

Question 15

In pituitary gland:

FSH (2)
LH (2)

Answer 15

Stimulates follicle development.
Stimulates oestrogen production (from follicles)

Stimulates ovulation (follicle releasing an egg)  
Stimulates progesterone production (from corpus luteum)

Question 16

In ovaries:
Oestrogen (3)
Progesterone (3)

Answer 16

Causes repair of the uterus lining after menstruation.
Stimulates LH production
Inhibits FSH production (=negative feedback)

Maintains uterus lining ready for egg
Inhibits the production of FSH from the pituitary gland.
Inhibits LH production (=negative feedback)

Question 17

Corpus luteum
After ovulation? (2)
Egg not fertilised? (2)

Answer 17

Ovulation - follicle forms corpus luteum - produces progesterone

Egg not fertilised - corpus luteum degenerates - stops producing progesterone

Question 18

When effector has corrected any deviation and returned system to set point, what must happen?

Answer 18

this information must be fed back to receptor to avoid over-correction:

Question 19

Define negative feedback

Answer 19

corrective measures turned off, system returns to set point.

Question 20

Define positive feedback

Answer 20

corrective measures remain turned on, system deviates further from set point.

Question 21

Oestrogen only affects target cells. Explain why oestrogen does not affect other cells in the body. (1)

Answer 21

Other cells do not have the/oestrogen/ ERα receptors;