3.6.4.1 Principles of homeostasis and negative feedback

• Hormones are slower, long-lasting, and widespread.
• How is body temperature detected and controlled?

  • Thermoreceptors in the skin and hypothalamus detect changes in temperature.
  • The hypothalamus sends signals to effectors (sweat glands, muscles) to regulate heat production or loss.
• What happens during vasodilation?

  • Blood vessels near the skin surface widen, increasing blood flow and heat loss to cool the body.
• What happens during vasoconstriction?

  • Blood vessels near the skin surface narrow, reducing blood flow and conserving heat to warm the body.
• Sweat evaporates from the skin's surface, removing heat and cooling the body.
• Shivering involves rapid muscle contractions that generate heat through increased respiration.
• The hypothalamus acts as the body’s thermostat, detecting temperature changes and coordinating responses.
• Hair erection traps an insulating layer of air close to the skin to conserve heat in cold conditions.
• Negative feedback is a regulatory mechanism where a change in a condition triggers a response that counteracts the initial change, restoring balance.
• Homeostasis is maintaining a constant internal environment within a narrow range, despite changes in external or internal conditions.

  • Homeostasis ensures optimal conditions for enzyme action and cell function.
• Examples of variables regulated by homeostasis:

  • Body temperature.
  • Blood glucose concentration.
  • Water potential.
• Why is Homeostasis Important?

  • Enzyme activity: Enzymes are sensitive to changes in pH and temperature. Homeostasis maintains conditions that allow enzymes to function efficiently.
  • Cell water balance: Maintains stable water potential, preventing osmotic damage to cells.
  • Glucose levels: Ensures sufficient glucose is available for respiration but prevents damage caused by high or low blood sugar.
• A homeostatic system uses a feedback mechanism involving:

  1. Receptors: Detect changes in the internal or external environment (stimulus).
  2. Control centre: Processes the information from the receptor and sends appropriate signals.
  3. Effectors: Bring about a response to restore the internal environment to its set point.
• How does Negative Feedback Work?

  1. Stimulus: A change is detected.
  2. Receptor: Detects the change and sends a signal to the control centre.
  3. Control centre: Compares the current level to the set point and sends a corrective signal.
  4. Effector: Carries out the response.
  5. Response: The system returns to its set point, and the signal is reduced or stopped.
• Positive feedback amplifies a change rather than reversing it.
• Temperature Regulation (Thermoregulation)

  • Increase in body temperature:
  • Detected by thermoreceptors in the skin and hypothalamus.
  • Effectors: Sweat glands secrete sweat, and vasodilation of blood vessels occurs.
  • Decrease in body temperature:
  • Detected by thermoreceptors.
  • Effectors: Muscles shiver, vasoconstriction reduces heat loss.
• A negative feedback mechanism is involved in body temperature regulation.