Question

11. (short answer) What is the significance of negative feedback? Positive feedback? Which is the more common regulatory tool?

Answer 1

Positive feedback is a process in which the end products of an action cause more of that action to occur in a feedback loop. This amplifies the original action. It is contrasted with negative feedback, which is when the end results of an action inhibit that action from continuing to occur.

Negative feedback mechanisms control a process; it can turn it off, whereas positive feedback accelerates the process, allowing the cell no control over it

Example of negative feedback.

• Thermoregulation (if body temperature changes, mechanisms are induced to restore normal levels)
• Blood sugar regulation (insulin lowers blood glucose when levels are high ; glucagon raises blood glucose when levels are low)
• Osmoregulation (ADH is secreted to retain water when dehydrated and its release is inhibited when the body is hydrated)

Examples of positive feedbck loop

• Childbirth – stretching of uterine walls cause contractions that further stretch the walls (this continues until birthing occurs)
• Lactation – the child feeding stimulates milk production which causes further feeding (continues until baby stops feeding)
• Ovulation – the dominant follicle releases oestrogen which stimulates LH and FSH release to promote further follicular growth
• Blood clotting – platelets release clotting factors which cause more platelets to aggregate at the site of injury.

More regulatory tool will be -ve feedback.

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