Fluid regulation is essential to homeostasis. If water or electrolyte levels rise or fall beyond normal limits, many bodily functions fail to proceed at their normal rates. Maintaining normal pH levels is also important for normal body functioning because small changes in pH can produce major changes in metabolism.
Water is a constituent of all living things. It is often referred to as the universal biological solvent. Only liquid ammonia is able to dissolve more substances than water.
The importance of water as a biological solvent is due to its polar asymmetry (H+- OH-) and its high affinity for other water molecules. As a polar molecule, water is highly interactive with other polar molecules and acts to compete with them for hydrogen bonding, thus weakening their electrostatic forces. This allows a greater number of polar molecules to coexist and undergo reactions; in a non-polar solvent, these polar molecules would form strong bonds with one another and thus be unavailable for further reaction.
The affinity of water molecules for each other is very high. When non-polar molecules are placed in water, the polar water molecules are attracted to other water molecules.
This action tends to leave the non-polar molecules clustered together. This clustering property is important in structuring macromolecules, binding enzymes to their substrates, and in membrane formation.
Water acts to minimize temperature changes throughout the body because of its high specific heat.
A considerable amount of energy is needed to break the hydrogen bonds between water molecules in order to make the water molecules move faster (that is, increase the temperature of water). Therefore, water can absorb much heat without rapidly changing it's own temperature.
The adult human body consists of about 60% water by weight, depending upon age and the amount of body fat. The water content of the tissues of the body varies. Adipose tissue (fat) has the lowest percent of water; the skeleton has the second lowest water content. Skeletal muscle, skin, and the blood are among the tissues that have the highest content of water in the body.
Infants have a higher percent of water than adults do as much as 77%. The total water content of the body decreases most dramatically during the first 10 years and continues to decline through old age, at which time it may be only 45% of the total body weight. Men tend to have higher percentages of water (about 65%) than women (about 55%) mainly because of their increased muscle mass and lower amount of subcutaneous fat. Fat has less water content than any other body tissue. This also accounts for a lower than normal water percentage in obese people.
Functions of water within the body:
Water in the body is in a constant state of motion. Shifting between the three major fluid compartments of the body and in addition is continuously lost from and taken into the person.
In a normal, healthy human being WATER INPUT = WATER OUTPUT.
Maintaining this ratio is of prime importance in maintaining health.
Approximately 90% of the body's water intake comes via the gastro-intestinal tract. The remaining 10% is called metabolic water and is produced as the result of various chemical reactions in the cells of the body's tissues.
The normal healthy adult loses water via:
Gastro-intestinal tract (feces) 6%
Lungs (water vapor) 13%
Skin (diffusion & sweat) 19%
Kidneys (urine) 62%
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