The largest organ of the body is the skin . The skin protects the body from organisms that cause disease, the physical environment, and water loss. The skeletal system supports and protects the body. The muscular system includes muscles that are and are not under our voluntary control. The circulatory system transports chemical messages of the endocrine system, nutrients of the digestive system, gases of the respiratory system, wastes of the excretory system, and heat.
Homeostasis depends on the control and regulation of the organs and organ systems.
If cells cool to below 0 o C, ice crystals can form in them and damage their structures If cells warm to above 45 o C, proteins will denature and lose their functional properties Most cellular functions are limited to the range of 0-45 o C, the thermal limits of life. In the day when the air is warm, a lizard shuttles between sun and shade. In the day when the air is hot, a lizard avoids the sun and stays in the shade. At night when the air is cold, a lizard goes into its ground burrow. Endotherms also use behavior to regulate body temperature Besides doing what lizards do, endotherms also build nests, huddle, and select clothing.