Heat-Release Designs In Mammals

Most people are aware that there is a risk of getting too cold during the winter time or in an accidental fall into very cold water. A good number of us realize that warmblooded creatures like us have a number of ways of keeping warm and reducing heat losses. Some forms of life have hair to insulate them from the cold. Others may have a layer of fat. Still others may lower their body temperatures in hibernation so that heat losses are less of a problem.

A much bigger problem for warmblooded creatures is how to avoid too much heat. Humans generate a huge amount of heat as our bodies process food and provide energy to sustain our bodily functions. The fact that our body temperature is around 98.6 F tells us that this process is active and liberates a great deal of heat even when we are not moving. Actively using a muscle produces massive amounts of extra heat that has to be removed from the body. Imagine the amount of heat that is generated when a large animal runs great distances or when a whale or porpoise swims actively through miles of ocean water.

Every animal is designed with a heat release system that insures its survival. Pregnancy produces an additional set of problems as the mother must release her heat and the heat generated by her baby. Expectant mothers know that their abdominal wall is unbelievably hot during this time.

Many cooling systems in mammals depend upon a unique property of water called the heat of vaporization. For water to change from the liquid state to the vapor state, 540 calories of heat must be removed for every gram of water that changes. That is why humans perspire. As the water evaporates from our bodies, it takes 245,160 calories of heat away from our bodies for every pound of water we lose. When a dog pants, it forces large amounts of air over its wet tongue evaporating large amounts of water, thus cooling the dog. Because water's heat of vaporization is so high, it is an ideal fluid to aid us in cooling our bodies.

Studies done on porpoises show a completely different method of cooling. In the porpoise, blood vessels are routed from the inside of the porpoises body to the tail and the dorsal fin where the vessels are brought into a network of special vessels that are close to the skin. This arrangement allows the porpoise to release large amounts of heat by conduction through the tail and the vertical fin. We are all aware of female porpoises having a special network of vessels that surround the uterus so that their babies can be kept cool during their development.

There are even some animals like the kangaroo that have special tissues that allow activity without using muscles to avoid the heat problem. Kangaroos have springlike tendons in their legs that allow 93% of the energy put into them to be used for the next jump. By not forcing muscles to do the jumping, a great deal of heat release is avoided.

Man has struggled in major ways when heat release problems threaten his machines. Finding a way for the shuttle to be cooled enough to re-enter the earth's atmosphere was a huge challenge. Even our automobiles are vulnerable to overheating problems if any malfunction occurs in their cooling systems. The incredible designs of each animal to release enough heat to assure its survival, but not so much heat as to freeze it, challenges the notion it could happen by chance. God's engineering is marvelously done and clearly seen in his living creatures.


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