|MadSci Network: Biochemistry|
Well, before I start to answer your question directly - think of conductance. For, example we know that some metals conduct electricity better than other metals. In the same way some materials are better conductors of heat energy than others.
Think of a styrofoam cup, when you pour hot water into the cup you do not feel as much heat (comming from the water) through the styrofoam cup as you would a glass cup. This is because styrofoam cups have a poor ability to conduct heat. Which is a good thing, as you do not want to burn yourself while drinking coffee!
So, in this case fat is like the styrofoam cup - it doesn't conduct heat energy as well as muscle would. Having this poor ability to conduct heat, fat tissue drastically reduces the amount of heat energy leaving the body out towards its environment.
Muscle tissue tends to have many more blood vessles associated with it than fat tissue. In many cases, skeletal muscle lies beneath the skin. This means that more blood vessles are exposed nearer the surface of the skin of the animal. All of these blood vessles that are located so close to the surface of the skin will cause heat energy to escape the body and out to the environment faster. This is why when you get hot in the summer your blood vessles stand out more - they are trying to lose heat so the body can cool down. As you can see this would be bad in a cold climate. So, the further away from the surface of the skin you can keep most of your blood vessles the better (this is a generalization). In other words we would wear thick winter clothes to increase insulation - and hopefully what we are wearing in these cold climates doesn't conduct heat energy to well.
Having more fat will help increase the barrier between the body and the environment. There will be less surface area exposed to the environment with fattier tissue. This is because there will be less branching blood vessles in fat tissue than in muscle tissue. That means less surface area equals less contact with outside environment. Muscle tissue, again, is loaded and surrounded with blood vessles - hence more surface area will lead to faster heat loss with the outside environment.
Also, fat itself has less of a surface area than musscle. Fat help restict blood flow to the surface of the skin. However in humans additional fat may not help as much on the extremities (arms & legs) as it would the trunk of the body. Mainly because human physiology is not set up for cold climates such as polar bears.
Withers PC (1992) Comparative animal physiology. Saunders College Pub.,
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