16.2 - Feedback Mechanisms

Question 1

What are the key stages of homeostatic control?

Answer 1

Optimum point: The desired level (norm) at which the system operates.
Receptor: Detects any deviation (stimulus) from the norm.
Coordinator: Integrates information from various sources.
Effector: Brings corrective measures to return to the norm.
Feedback mechanism: Ensures the effector’s actions are appropriate and prevents over-correction.

Question 2

Why is feedback important in homeostatic systems?

Answer 2

• Feedback ensures that once the effector corrects the deviation and returns the system to the optimum point, the receptor is informed.
• Without feedback, the receptor would continue to stimulate the effector, leading to over-correction and a deviation in the opposite direction.

Question 3

What are the two types of feedback mechanisms?

Answer 3

• Negative feedback: The corrective measures are turned off, returning the system to its optimum level and preventing overshoot.
• Positive feedback: The corrective measures remain turned on, causing the system to deviate further from the norm

Question 4

Describe negative feedback using fall in blood glucose as an example.

Answer 4

Fall in blood glucose:
1) Detected by α cells in the pancreas (islets of langerhans).
2) α cells secrete glucagon.
3) Glucagon stimulates liver cells (effectors) to convert glycogen to glucose, increasing blood glucose concentration.
4) Raised glucose reduces α cell stimulation, decreasing glucagon secretion (negative feedback).

Question 5

Describe negative feedback using rise in blood glucose as an example.

Answer 5

Rise in blood glucose:
1) Detected by β cells in the pancreas (Islets of langerhans).
2) β cells secrete insulin.
3) Insulin increases glucose uptake by cells and converts glucose to glycogen and fat.
4) Reduced glucose lowers β cell stimulation, decreasing insulin secretion (negative feedback)

Question 6

What is the advantage of having separate negative feedback mechanisms for blood glucose regulation?

Answer 6

• It provides greater homeostatic control by allowing specific corrective actions for deviations in either direction.
• For example, glucagon raises blood sugar while insulin lowers it, ensuring rapid correction to the optimum glucose level.

Question 7

What is positive feedback, and give an example?

Answer 7

• Positive feedback occurs when the feedback causes the corrective measures to stay turned on, leading to further deviation from the norm.
• Example in neurons: A small sodium ion influx increases neuronal permeability to sodium, causing more sodium ions to enter. This amplifies the signal and leads to rapid action potential generation

Question 8

When does positive feedback commonly occur?

Answer 8

• During breakdowns of control systems, such as in certain diseases.
  Example:
• In typhoid fever, temperature regulation breaks down, causing hyperthermia.
• In hypothermia, the body’s temperature regulation fails, leading to further drops in temperature

Question 9

Explain negative feedback in temperature control.

Answer 9

1) Increase in blood temperature:
- Thermoreceptors in the hypothalamus detect the change.
- Hypothalamus stimulates the heat loss center.
- Effector responses: Vasodilation, sweating, and lowering of body hairs reduce blood temperature.

2) Return to normal temperature:
- Cooler blood passes through the hypothalamus.
- Thermoreceptors send fewer impulses to the heat loss center.
- Effector responses (e.g., vasodilation) stop, preventing hypothermia.

Question 10

Why is feedback essential in negative feedback systems like temperature control?

Answer 10

• Feedback prevents continuous activation of effectors, which could lead to over-correction and hypothermia.
• Cooler blood signals the hypothalamus to stop stimulating the effectors, maintaining a stable normal temperature