Thermoregulation

Rucete ✏ Biology In a Nutshell

1. Types of Organisms by Body Temperature

a) Ectotherms (Poikilotherms)

• Organisms whose body temperature varies with the environment
• Rely on external sources of heat
• Examples: reptiles, amphibians, fish

b) Endotherms (Homeotherms)

• Organisms that maintain constant body temperature internally
• Generate heat through metabolic activities
• Examples: mammals, birds

2. Mechanisms of Thermoregulation

a) Cooling by Evaporation

• Sweating or panting releases heat as water evaporates from the body surface

b) Warming by Metabolism

• Muscle contractions and other metabolic processes generate heat
• Example: shivering in humans

c) Adjusting Surface Area

• Vasodilation: Blood vessels near the skin widen, increasing heat loss
• Vasoconstriction: Blood vessels narrow, conserving heat

d) Countercurrent Exchange

• Heat from warm blood in arteries is transferred to cool blood in veins
• Reduces heat loss and helps maintain core body temperature
• Common in limbs of birds and marine mammals