Thermoregulation is the process of maintaining a relatively constant core body temperature to maintain optimum enzyme activity.

Ectotherms are animals that use their surroundings to regulate their body temperature.

Their core body temperature is heavily dependent on their environment.

Examples of ectotherms include invertebrate animals, fish, amphibians, and reptiles.

Endotherms are animals that rely on their metabolic processes to control their body temperature.

They usually maintain a very stable core body temperature regardless of the temperature of the environment.

Examples of endotherms include mammals and birds.

Peripheral temperature receptors are located in the skin and they detect changes in the surface temperature.

Temperature receptors in the hypothalamus in the brain control responses that maintain the core body temperature.

1. Vasodilation - arterioles near the surface of the skin dilate and more blood moves through capillary networks close to the skin's surface, increasing heat loss
2. Sweating - water in sweat evaporates from the skin using heat from the blood below the surface of the skin
3. Lower hair, fur, or feathers - erector pili muscles in the skin relax causing hair, fur, or feathers to flatten

1. Vasoconstriction - arterioles near the surface of the skin constrict, so less blood moves through capillary networks close to the skin's surface, reducing heat loss
2. Decreased sweating - less heat lost by evaporation
3. Raising body hair, fur, or feathers - erector pili muscles in skin contract, pulling hair, fur, or feathers up and trapping a layer of insulating air
4. Shivering - rapid, involuntary contraction and relaxation of muscles, which involves exothermic reactions that generate metabolic heat

The two control centres involved in thermoregulation are the heat loss centre and the heat gain centre.

When blood temperature increases, impulses are sent to the heat loss centre in the hypothalamus, which sends impulses to the effector organs to increase heat loss and return the body temperature to the optimum point.

When blood temperature decreases, impulses are sent to the heat gain centre in the hypothalamus, which sends impulses to effector organs to reduce heat loss and return the body temperature to the optimum point.

1. Sweat glands
2. Arterioles
3. Pili erector muscles
4. Voluntary skeletal muscles during shivering