The principles of feedback mechanisms

Question 1

What stages are involved in homeostatic control of any system?

Answer 1

1. Set point - Desired level system operates at
2. Receptor - detects changes from set point
3. Controller - coordinates information from various sources
4. Effector - brings about response to return system to set point
5. Feedback loop - Informs receptor of changes to system brought about by the effector

Question 2

Why is the feedback loop important?

Answer 2

If the information is not fed back to the receptor, the receptor will continue to stimulate the effector leading to an over-correction and causing a deviation in the opposite direction

Question 3

What are the two types of feedback?

Answer 3

Positive and negative feedback

Question 4

What is negative feedback?

Answer 4

A series of changes that result in a substance/system being restored to it’s normal level, important in homeostasis

Question 5

What is positive feedback?

Answer 5

Process which results in a substance that departs from its normal level becoming further from its norm. Occurs when the feedback causes the corrective measures to remain turned on.

Question 6

What is the advantage of having separate negative feedback mechanisms to control deviations away from normal?

Answer 6

Gives a greater degree of homeostatic control

Question 7

What does the menstrual cycle involve?

Answer 7

• A follicle developing in the ovary
• Ovulation
• Thickening of the uterus lining for a fertilised egg to be implanted
• Formation of a corpus luteum developing from the remains of a follicle

Question 8

What is a follicle?

Answer 8

An egg and the protective cells surrounding it

Question 9

What is ovulation?

Answer 9

An egg being released from the ovaries

Question 10

What happens if no fertilisation occurs?

Answer 10

The uterus lining breaks down and leaves the body via the vagina (menstruation) marks the end of one cycle ( 5 -7 day bleed i.e. period) and start of another one

Question 11

Which 4 hormones control the menstrual cycle?

Answer 11

FSH , LH , Oestrogen and Progesterone

Question 12

Which hormones are produced by the pituitary gland (brain) ?

Answer 12

FSH (follicle stimulating hormone) and LH (Luteinising hormone)

Question 13

Which hormones are produced by the ovaries?

Answer 13

Oestrogen and progesterone

Question 14

What is the role of FSH in the oestrous cycle?

Answer 14

Stimulates follicle development in the ovaries and stimulates the follicles in the ovaries to produce oestrogen

Question 15

What is the role of LH in the oestrous cycle?

Answer 15

Stimulates ovulation and stimulates ovary to produce progesterone from the corpus luteum

Question 16

What is the role of oestrogen in the oestrous cycle?

Answer 16

Re-develops uterus lining after menstruation and stimulates production of LH from pituitary gland

Question 17

What is the role of progesterone in the oestrous cycle?

Answer 17

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

Question 18

What happens in the first part of the menstrual cycle?

Answer 18

Loss of lining (period) marks day 1, lining passes through cervix and vagina over 4-5 days. From day 1 the pituitary gland releases FSH which stimulate follicles in the ovary to grow and mature. As the follicle grows, it slowly begins to release oestrogen. The low level of oestrogen causing lining to build up again and inhibits release of FSH and LH (negative feedback)

Question 19

What happens in the second part of the cycle?

Answer 19

As the follicle grows, more oestrogen is produced and by day 10 oestrogen reaches a critical point and there is now high levels, which promote release of FHS and LH (positive feedback). A surge in FSH and LH causes a follicle in the ovary to release it’s egg ( ovulation day 14)

Question 20

What happens in the third part of the cycle?

Answer 20

After ovulation LH stimulates follicle to develop into a corpus luteum, which secretes progesterone. Progesterone maintains the thick lining of uterus and inhibits release of FSH and LH (negative feedback). If the egg is not fertilised corpus luteum breaks down and no more progesterone is produced, causing the lining to break down, also FSH release is no longer inhibited and therefore resumes and the cycle repeats itself