The cells of the human body require a constant supply of oxygen to produce the energy necessary to accomplish their life-sustaining functions. Oxygen derived from the air is delivered via the bloodstream to the body organs and tissues.

While you might be tempted to grab a sweetened beverage or sugary snack for energy, several hours later you may feel worse. Simple sugars cause spikes in blood sugar, resulting in feeling lightheaded or weak.

Preservatives are chemicals used to keep food fresh. Although there are a number of different types of food preservatives, antimicrobials, antioxidants, and products that slow the natural ripening process are some of the most common.

When your potassium and magnesium levels are too high or too low, complications can arise. Supplements may be appropriate if you are deficient in either mineral. Deficiencies should be closely monitored and corrected under the care of a health care professional.

Before your body can use the food you eat for fuel, as well as for cell and tissue growth, the food has to go through the process of digestion. The digestive process begins in the mouth and continues in the stomach, where certain enzymes begin to break down foods into their basic components so cells can use them.

Dehydration occurs when your body doesn't have as much fluid as it needs. You lose fluid through breathing, sweating, urinating, bowel movements and, when you're sick, through vomiting or diarrhea.

Calcium and phosphorus are essential minerals found in the bone, blood and soft tissue of the body and have a role in numerous body functions. Phosphorus levels can affect calcium levels in the body, and vice versa.

As part of a urinalysis test, urine may be examined under a microscope to check for the presence of crystals. Urine contains many chemicals, some of which can form solid particles, or crystals, under certain conditions.

Humans--and all other living organisms--need nucleic acids. The nucleic acids, which include deoxyribonucleic acid, or DNA, and ribonucleic acid, or RNA, encode genetic information and allow humans and other organisms to follow their genetic instructions.

Your immune system forms a barrier against infectious disease. Lymphocytes, a class of white blood cells, play a key role in recognizing and fighting harmful pathogens.