Exercise generates heat. This occurs because the efficiency of converting the chemical energy in ATP into the mechanical energy of muscle contraction is between 20% and 25%. The other 75% to 80% of energy is lost as heat. In addition, the chemical reactions of aerobic and anaerobic metabolism also generate heat. For exercise to continue, the body must dissipate this heat.
There are a number of ways in which water helps to eliminate heat during exercise. The water in blood helps regulate body temperature by increasing or decreasing the amount of heat lost at the body surface.
When body temperature starts to rise, the blood vessels in the skin become wider, or dilate. This increases blood flow to the skin. When blood is close to the surface of the body, it can release some of the heat into the environment. This is why light skin reddens in hot weather or during strenuous activity. In a cold environment, the opposite occurs. The blood vessels in the skin constrict, reducing the flow of blood near the surface and conserving heat.
The most obvious way that water helps regulate body temperature is through sweating. When body temperature increases, the brain triggers the sweat glands in the skin to produce sweat, which is mostly water. Heat is lost as the sweat evaporates from the surface of the skin. This cools the body.
Water in the diet comes mostly from beverages (including water itself), but also from solid food. Low-fat milk is 90% water, apples are about 85% water, and meat is about 50% water. A small amount of water is generated inside the body through metabolism, but this is not significant in meeting the body’s water needs. Water is absorbed from the gastrointestinal tract by osmosis.
The volume of water and the concentration of nutrients consumed with the water influence the rate of absorption. Consuming a large volume of water increases its rate of absorption. Water consumed alone will easily move from the intestine into the blood, where the concentration of dissolved substances (solutes) is higher.
Absorption is slower when water is consumed with meals, because the digestion of nutrients from the meal increases the concentration of dissolved substances in the intestine. As the nutrients are absorbed and move into the blood, the concentration of dissolved substances in the intestine decreases. Water then moves by osmosis into the blood.
About 7 cups (1.7 liters) of water enter the GI tract each day from the diet. Another 29.5 cups (7 L) come from saliva and other gastrointestinal secretions. Most of this fluid is absorbed in the small intestine, and a smaller amount is absorbed in the colon.
Our website is not responsible for the information contained by this article. Articleinput.com is a free articles resource thus practically any visitor can submit an article. However if you notice any copyrighted material, please contact us and we will remove the article(s) in discussion right away.
Note: This article was sent to us by: Sabrina Reesle at 01122011
1. One of the problems with fluid and electrolyte balance is dehydration
All articles are property of their respective authors. Please read our Privacy Policy!
© 2009 ArticleInput.com.
Partners: Damenmode