Metabolism is a collection of chemical reactions that take place in the body’s cells.
Metabolism converts the fuel in the food we eat into the energy needed to power everything we do, from moving to thinking to growing.
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Specific proteins in the body control the chemical reactions of metabolism, and each chemical reaction is coordinated with other body functions.
In fact, thousands of metabolic reactions happen at the same time — all regulated by the body — to keep our cells healthy and working. Metabolism is a constant process that begins when we’re conceived and ends when we die. It is a vital process for all life forms — not just humans. If metabolism stops, living things die.
Here’s an example of how the process of metabolism works in humans — and it begins with plants:
First, a green plant takes in energy from sunlight. The plant uses this energy and a molecule called chlorophyll (which gives a plant its green color) to build sugars from water and carbon dioxide.
This process is called photosynthesis, and you probably learned about it in biology class.
When people and animals eat the plants (or if they’re carnivores, they eat animals that have already eaten the plants), they take in this energy (in the form of sugar), along with other vital cell-building chemicals. Then, the body breaks the sugar down so that the energy is released and can be distributed to, and used as fuel by, the body’s cells.
After the food is eaten, molecules in the digestive system called enzymes break proteins down into amino acids, fats into fatty acids, and carbohydrates into simple sugars like glucose. Sugar, amino acids, and fatty acids can be used as energy sources by the body when needed.
These compounds called ATP (or adenosine triphosphate) are absorbed into the blood, which carries them into the cells. In the cells, other enzymes act to speed up or regulate the chemical reactions involved with “metabolizing” the compounds. The energy from these compounds can be released for use by the body or stored in body tissues, especially the liver, muscles, and body fat.
Several of the hormones of the endocrine system are involved in controlling the rate and direction of metabolism. Thyroxine, a hormone produced and released by the thyroid gland, plays a key role in determining how fast or slow the chemical reactions of metabolism proceed in a person’s body.
Another gland, the pancreas secretes (gives off) hormones that help determine whether the body’s main metabolic activity at a particular time will be anabolic or catabolic.
Most of the time, your metabolism works well without you giving it any thought. But sometimes a person’s metabolism can cause major mayhem in the form of a metabolic disorder. In a broad sense, a metabolic disorder is any disease that is caused by an abnormal chemical reaction in the body’s cells.
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