About 8.1 million people in the United States use marijuana, also called cannabis, on a daily or almost daily basis, reports the 2013 National Survey on Drug Use and Health. Like tobacco, marijuana smoke contains high concentrations of many chemicals, and some of them are known cancer-causing substances.

Although you doubtless appreciate the role your muscular system plays in your daily activities, you may be unaware of the different types of muscle tissue in your body and the special role each plays in keeping you functioning to your best advantage.

Enzymes are specialized proteins your body uses to carry out a wide variety of chemical reactions. Without enzymes, these reactions would not occur fast enough to sustain human life.

As soon as food enters your mouth, it starts the process of digestion. Food needs to be broken down into smaller nutrients so that the body can store or utilize it. Your body produces specialized enzymes that work on digesting the different types of foods you consume.

There are many different roles that nucleic acids, which include DNA and RNA, play in the human body and in other living organisms. Scientists continue to identify new and different functions of nucleic acids on a regular basis.

Blood clots that form to halt bleeding after an injury can be life-saving. But clots that form spontaneously within a blood vessel -- in the calf or elsewhere in the body -- could be a sign of trouble. The calves are the most common site of spontaneous blood clots.

If you have a knee injury, staying in shape without making the knee worse is a major concern. Cardiovascular exercise is important for general health and also aids in healing injuries by providing freshly oxygenated blood cells to the area.

Alkaline phosphatase -- commonly abbreviated as ALP -- is a protein found in all cells of the body. The highest concentrations of ALP are located in cells of the liver, bones and bile ducts. ALP in the blood is primarily derived from excess ALP that is released from these cells.

At some point during your pregnancy, your obstetrician will hand over a small bottle of a sugary flavored drink and ask you to down it just before you come to your next appointment. Within about 60 minutes of taking the drink, you'll have a blood sample taken.

Cortisol is the primary hormone released by the body during times of stress. Although cortisol does have necessary functions in the body, such as regulating energy and dictating energy sources, elevated levels, particularity over extended periods of time, can have several negative side effects.

Humans have survived on this planet for thousands of years because of our ability to adapt. Physiological adaptations start to occur almost immediately when beginning a new exercise program.

Scoliosis is a condition that can be diagnosed at any time of life, but is most common in teenagers. It is characterized by curvature of the spine, which can cause one hip to be pushed forward or one shoulder to sit higher than the other.