A vitamin that your cells and tissues use for many essential functions, vitamin A is found in ready-to-use form in animal-based foods, but your body can also convert beta-carotene from plant-derived foods into vitamin A when needed.

Acid reflux occurs when stomach acid moves upwards into the esophageal tract, leading to a burning sensation and feeling of irritation. Cayenne pepper, with its spicy taste, can trigger acid reflux.

Pain in the right lower quadrant -- the lower right area of the abdomen -- can arise from a variety of causes. These underlying causes range in severity from minor to potentially life-threatening, possibly requiring emergency surgery.

The cell is the basic unit of life. Organisms can consist of one cell, known as unicellular organisms, or many cells. There are two basic classifications of cells: prokaryotes, which mostly consist of bacteria, and eukaryotes, which are more advanced.

The prostate gland is part of the male reproductive system. It surrounds a portion of the urethra and makes some components of semen. As a man ages, the prostate sometimes enlarges in a condition called benign prostatic hyperplasia, or BPH, a noncancerous condition.

The American Council for Drug Education reports marijuana, also known as THC for its active ingredient of delta-9-tetrahydrocannabinol, as the most commonly used illegal drug.

While most people take iron safely, excessive amounts of iron can be toxic. Symptoms may range from fatigue to life-threatening shock. The signs and symptoms of acute iron toxicity are different than those of chronic toxicity.

Bone scans and magnetic resonance imaging, or MRI, are tools used to determine the presence of certain diseases in bones. Both imaging tests are commonly used in the diagnosis of infections and cancer in the bones.

Although your body needs only small amounts of iodine, its role in your body is anything but small. Iodine is critical for the production of your thyroid hormone, which has many important roles.

An ecosystem is a living system that includes the sun as an energy source, soil, rocks, water, air, plant life and living beings. We humans are only one part of any ecosystem, but many people believe that we have a disproportionate effect. Our actions tend to affect not just our surroundings, but the world at large.

The most common contagious diseases are categorized as bacterial, viral, fungal and protozoan. Bacteria are tiny organisms that are pathogenic (cause infectious diseases) or beneficial (aid in digestion).

Just as you eat to nourish the rest of your body, you must also nourish your brain. Protein, fat, carbohydrate, vitamins and minerals provide nutrients that keep your brain functioning, prevent deficiencies and promote the activities of substances known as neurotransmitters -- the chemical messengers in the brain.