Animals: Homeostasis - BIOL 101 General Biology I

Homeostasis

  • For cells to function efficiently and interact properly, internal body conditions must be relatively constant.

Components of A Feedback System

  • Negative feedback: The end result of a process feeds back to limit the process.

Negative Feedback Example: Room Temperature

  • Stimulus: Room temperature changes from the set point.
  • Sensor: Thermometer in wall unit detects the change in temperature.
  • Integrating Center:
    • Set Point = 70°F
    • Thermostat compares temperature with set point.
  • Effector & Response (If Below Set Point):
    • Furnace turns on.
    • Room warms; temperature increases toward the set point.
  • Effector & Response (If Above Set Point):
    • AC turns on.
    • Room cools; temperature decreases toward the set point.

Mammals and Birds: Endothermic

  • Maintain a relatively constant body temperature independent of the environmental temperature.
  • Humans: 37°C or 98.6°F.
  • Changes in body temperature are detected by the hypothalamus in the brain.

Antagonistic Effectors and Body Temperature Control

  • If hypothalamus detects high temperature:
    • Promotes heat dissipation via sweating and dilation of blood vessels in skin.
  • If the hypothalamus detects low temperature:
    • Promotes heat conservation via shivering and constriction of blood vessels in skin.

Negative Feedback Example: Body Temperature

  • Stimulus: Body temperature deviates from the set point.
  • Sensor: Neurons in the hypothalamus detect the change in temperature.
  • Integrating Center:
    • Set Point = 37°C
    • Neurons in hypothalamus compare input from sensory neurons with set point.
  • Effector & Response (If Below Set Point):
    • Blood vessels to skin contract.
    • Muscles contract, shiver.
    • Body temperature rises.
  • Effector & Response (If Above Set Point):
    • Blood vessels to skin dilate.
    • Glands release sweat.
    • Body temperature drops.

Positive Feedback

  • Enhances a change (not common).
  • These do not help to maintain homeostasis.
  • Examples:
    • Blood clotting.
    • Contraction of the uterus during childbirth.

Example Question

  • If a mammal suffered damage to the temperature sensor in its brain, what would be the result?
  • Correct Answer:
    • D. The integrating center would not receive inputs to compare to the set point. Body temperature could rise or fall to dangerous levels.

Group Activity - Homeostasis

  • Blood pressure changes = Stimulus
  • Baroreceptors detect change in BP = Receptors
  • Medulla = Integrating center
  • Increase blood pressure = Response
  • Decrease blood pressure = Response
  • Decrease heart rate/blood vessels dilate = Effector
  • Increase heart rate/blood vessels constrict = Effector
  • This is Negative feedback.