BiologyChapter 6: Endocrine System of Man

6.4 Feedback Mechanism

Feedback Mechanism:

A feedback mechanism is a type of interaction in which a controlling mechanism is itself controlled by the product of reactions it is controlling. After receiving the signal, a change occurs to correct the deviation by depressing it with negative feedback or enhancing it with positive feedback.

Definition

Feedback Mechanism: It is a type of interaction in which a controlling mechanism is itself controlled by the product of reactions it is controlling.

Main Idea

A feedback mechanism is a type of interaction.
A controlling mechanism is controlled by the product of reactions it is controlling.
After receiving the signal, a change occurs to correct the deviation.
The deviation is either:
There are two types of feedback mechanisms:

Core Concept

Feedback mechanism = controlling mechanism controlled by its product
Negative feedback = reverses the direction of change; maintains homeostasis
Positive feedback = amplifies the change; rare in healthy individuals
Positive feedback example = childbirth (oxytocin)
Negative feedback example = blood glucose control (insulin and glucagon)

Detailed Explanation

Feedback Mechanism

It is a type of interaction in which a controlling mechanism is itself controlled by the product of reactions it is controlling.
After receiving the signal, a change occurs to correct the deviation by depressing it with negative feedback or enhancing it with positive feedback.

Positive Feedback

In positive feedback an end product speeds up its production.
These responses are not homeostatic and are rare in healthy individuals.
An example of positive feedback is childbirth.
The early contractions of labour begin to force the baby's head against the cervix to dilate (open).
Stretch-receptive neurons in the cervix respond to this extension by signalling the hypothalamus.
The hypothalamus responds by triggering the release of the hormone oxytocin that stimulates more and stronger uterine contractions.

Negative Feedback

In negative feedback end products results in the reversal of the direction of change and tends to maintain homeostasis.
In this system an endocrine gland is sensitive either to the concentration of a substance it regulates or to the concentration of a product from a process it controls.
For example, if blood glucose becomes too high, beta (β) cells in the islets of Langerhans respond by releasing insulin.
Insulin lowers blood glucose by making cell surface membranes more permeable to glucose.
It activates transport proteins in the membranes, allowing glucose to pass into the cells.
Insulin also activates enzymes inside the cells.
Some of these enzymes convert glucose to glycogen.
If the levels of blood glucose get too low, alpha (α) cells in the islets of Langerhans secrete glucagon.
This hormone fits into the receptor sites on the cell surface membranes, and activates the enzymes inside the cells that convert glycogen to glucose.
The glucose then passes out of the cells and into the blood, raising blood glucose levels.
In this way, negative feedback mechanism controls blood glucose.

Critical Thinking

Is the sensation of thirst associated with a negative or positive-feedback mechanism?

Comparison of Positive and Negative Feedback Mechanisms

Feature	Positive Feedback Mechanism	Negative Feedback Mechanism
Effect	Amplifies or increases the change, pushing the system further away from its set point	Counteracts the change, bringing the system back to its set point
Response	Leads to a rapid, escalating response until a specific endpoint is reached	Maintains stability and homeostasis within a system
Example	Uterine contractions during childbirth; blood clotting	Body temperature regulation; blood glucose control
Response to stimulus	The response reinforces the initial stimulus	The response opposes the initial stimulus
Overall function	To rapidly complete a process or reach a specific outcome	To maintain a stable internal environment

Intermediate Level

Feedback Mechanisms

Feature	Positive Feedback	Negative Feedback
Effect	Amplifies change	Reverses change
Response	Reinforces stimulus	Opposes stimulus
Function	Rapidly complete a process	Maintain stable internal environment
Example	Childbirth; blood clotting	Body temperature; blood glucose
Frequency	Rare	Common

Negative Feedback: Blood Glucose Control

Step	Event
1	Blood glucose becomes too high
2	Beta cells release insulin
3	Insulin lowers blood glucose
4	Blood glucose becomes too low
5	Alpha cells release glucagon
6	Glucagon raises blood glucose
7	Balance is maintained

Positive Feedback: Childbirth

Step	Event
1	Baby's head pushes against cervix
2	Nerve impulses from cervix transmitted to brain
3	Brain stimulates pituitary gland to secrete oxytocin
4	Oxytocin carried in bloodstream to uterus
5	Oxytocin stimulates uterine contractions and pushes baby towards cervix
6	Cycle repeats

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

1. Feedback mechanism is a type of interaction.
2. A controlling mechanism is controlled by its product.
3. After receiving the signal, a change occurs to correct the deviation.
4. Deviation is depressed with negative feedback.
5. Deviation is enhanced with positive feedback.
6. Positive feedback amplifies the change.
7. Positive feedback is rare in healthy individuals.
8. Example of positive feedback: childbirth.
9. Oxytocin stimulates uterine contractions.
10. Negative feedback reverses the change.
11. Negative feedback maintains homeostasis.
12. Example of negative feedback: blood glucose control.
13. Insulin lowers blood glucose.
14. Glucagon raises blood glucose.
15. Beta cells secrete insulin.
16. Alpha cells secrete glucagon.
17. Insulin converts glucose to glycogen.
18. Glucagon converts glycogen to glucose.
19. Negative feedback is common.
20. Positive feedback is rare.

Remember

- Feedback mechanism = controlling mechanism controlled by its product
- Positive feedback = amplifies the change; rare in healthy individuals
- Positive feedback example = childbirth (oxytocin)
- Negative feedback = reverses the change; maintains homeostasis
- Negative feedback example = blood glucose control (insulin and glucagon)
- Insulin = lowers blood glucose
- Glucagon = raises blood glucose
- Beta cells = secrete insulin
- Alpha cells = secrete glucagon

Common Mistakes

1. Confusing positive and negative feedback — Positive = amplifies; negative = reverses.
2. Thinking positive feedback is common — Positive feedback is rare in healthy individuals.
3. Mixing up the examples — Childbirth = positive; blood glucose = negative.
4. Forgetting the role of oxytocin — Stimulates uterine contractions.
5. Confusing insulin and glucagon — Insulin lowers blood glucose; glucagon raises it.
6. Mixing up the cells — Beta cells = insulin; alpha cells = glucagon.
7. Thinking negative feedback amplifies — Negative feedback reverses.
8. Believing positive feedback is homeostatic — Positive feedback is not homeostatic.
9. Mixing up the disorders — Diabetes mellitus = disruption of negative feedback.
10. Forgetting the role of the hypothalamus — It triggers oxytocin release.

Quick Revision

It is a type of interaction in which a controlling mechanism is itself controlled by the product of reactions it is controlling. After receiving the signal, a change occurs to correct the deviation by depressing it with negative feedback or enhancing it with positive feedback. In positive feedback an end product speeds up its production. These responses are not homeostatic and are rare in healthy individuals. An example of positive feedback is childbirth. The early contractions of labour begin to force the baby's head against the cervix to dilate (open). Stretch-receptive neurons in the cervix respond to this extension by signalling the hypothalamus, which response by triggering the release of the hormone oxytocin that stimulates more and stronger uterine contractions. In negative feedback end products results in the reversal of the direction of change and tends to maintain homeostasis. In this system an endocrine gland is sensitive either to the concentration of a substance it regulates or to the concentration of a product from a process it controls. For example if blood glucose becomes too high, beta (β) cells in the islets of Langerhans respond by releasing insulin. Insulin lowers blood glucose by making cell surface membranes more permeable to glucose. It activates transport proteins in the membranes, allowing glucose to pass into the cells. Insulin also activates enzymes inside the cells. Some of these enzymes convert glucose to glycogen. If the levels of blood glucose get too low, alpha (α) cells in the islets of Langerhans secrete glucagon. This hormone fits into the receptor sites on the cell surface membranes, and activates the enzymes inside the cells that convert glycogen to glucose. The glucose then passes out of the cells and into the blood, raising blood glucose levels. In this way, negative feedback mechanism controls blood glucose.

60-Second Revision

Feedback mechanism = controlling mechanism controlled by its product
Positive feedback = amplifies the change; rare in healthy individuals
Positive feedback example = childbirth (oxytocin)
Negative feedback = reverses the change; maintains homeostasis
Negative feedback example = blood glucose control (insulin and glucagon)
Insulin = lowers blood glucose
Glucagon = raises blood glucose
Beta cells = secrete insulin
Alpha cells = secrete glucagon
Warning: Positive feedback is rare in healthy individuals; negative feedback is common

CHAPTER COMPLETED

Chapter Completed:
6. Endocrine System of Man

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7. Support and Movement

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7.1 HUMAN SKELETON

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