Cells are the simplest units of life. In some organisms, cells function as the complete living creature--bacteria, for instance, consist of only a single cell. In other organisms, many cells working together comprise the organism.

Almost everyone has problems with occasional constipation, and approximately 63 million people in North America have persistent constipation problems, according to an April 2004 "American Journal of Gastroenterology" article.

Cells in the human body require many compounds to survive. The main substances found in every cell are a combination of lipids, carbohydrates, nucleic acids and proteins.

More than 2,000 years ago, the Greek doctor Hippocrates began categorizing diseases in a scientific way. This practice continues into modern times. The World Health Organization's current disease classification system can be summarized in 10 broad areas.

The intestines are highly specialized organs responsible for the digestion of food and the absorption of its nutrients. Despite following a balanced and nutritious diet, you might still fall short of your nutrient needs if you can't absorb nutrients properly.

If you find yourself hustling to the washroom soon after drinking a cup of coffee, you aren't experiencing an abnormal reaction to your choice of beverage. Although caffeinated coffee affects everyone differently, it commonly results in an urge to have a bowel movement.

According to Minnesota State University's Emuseum, one of the most important ways the skeletal system works with other systems is via protection. Of particular importance is the skeletal system's ability to protect the central nervous system, which is made up of the spinal cord and the brain.

The immune system is responsible for protecting the body against invasion by diseases and other pathogens including viruses, bacteria and parasites. The immune system is also involved in the normal healing response to trauma as a protection against infection.

According to the U.S. Centers for Disease Control and Prevention (CDC), 5 to 20 percent of Americans contract the influenza (flu) virus each year. Flu produces a spectrum of disease, ranging from mild, self-limited respiratory disease to life-threatening pneumonia.

Creatinine comes from your body's everyday use of your muscles -- and also from eating meat. As blood flows through the kidneys, creatinine is excreted out into your urine along with other waste products.

New discoveries about how the body's systems function and work together continue to emerge almost daily. However, a very basic and fundamental understanding of the body's integrated working parts and organ systems has been in place for centuries.

Blood sugar, or glucose, serves as the fuel your body uses to generate energy. The level of glucose in your blood remains fairly stable, slightly rising after eating and declining a small amount between meals or after exercising. Blood glucose can be measured in many ways.