Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 40.2 Feedback Control Maintains the Internal Environment in Many Animals
Animals regulate their internal environment through feedback control systems that help maintain homeostasis—a stable internal state despite external fluctuations. This ability is key to survival in changing environments.
Homeostasis and Set Points
- Homeostasis maintains internal stability (e.g., temperature, pH, glucose).
- Each variable has a set point. Stimuli cause responses when values deviate.
- Response system:
- Sensor: detects change.
- Control center: compares to set point.
- Effector: carries out corrective actions.
Negative Feedback: The Primary Mechanism
- Negative feedback dampens the original stimulus.
- Example: Mammalian temperature regulation:
- Heat → sweating, vasodilation
- Cold → shivering, vasoconstriction
- Helps maintain stability and prevents overcorrection.
Positive Feedback: Less Common, More Amplifying
- Positive feedback reinforces the stimulus.
- Example: Oxytocin in childbirth enhances uterine contractions.
- Used to drive processes to completion.
Thermoregulation in Animals
- Classified by:
- Heat source:
- Endotherms: generate heat metabolically (e.g., birds, mammals)
- Ectotherms: rely on external heat (e.g., reptiles, amphibians)
- Temperature stability:
- Homeotherms: stable internal temperature
- Poikilotherms: variable internal temperature
- Heat source:
Endothermy vs. Ectothermy:
- Endotherms: high energy cost, active across environments
- Ectotherms: energy-efficient, activity limited by environment
Balancing Heat Gain and Loss
- Methods used:
- Insulation: fur, feathers, fat
- Circulatory adaptations:
- Vasodilation: heat loss
- Vasoconstriction: heat retention
- Countercurrent exchange: conserves heat (e.g., marine mammals)
- Evaporative cooling: sweating, panting
- Behavioral responses: basking, burrowing
- Thermogenesis: shivering, metabolic heat
- Brown fat: non-shivering heat in infants and some mammals
Acclimatization and Set Point Adjustment
- Acclimatization: physiological changes for seasonal adjustment
- Thicker fur in winter
- Enzyme shifts, fluidity, antifreeze proteins
- Set points can shift:
- Circadian rhythms
- Developmental stages
- Stress conditions (e.g., fever)
In a Nutshell
Animals maintain internal balance through feedback mechanisms. Negative feedback stabilizes variables like temperature and pH, while positive feedback pushes processes to completion. Thermoregulation strategies—from behavioral changes to metabolic adaptations—enable survival in diverse environments.