Cellular respiration is defined as the set of all metabolic processes in your body that use oxygen to convert nutrients such as sugars and fats into a molecule called ATP. ATP is known as a "molecular currency" that transfers energy to the organs. One of its largest tasks, for example, is to provide energy for muscle contractions. Every time you exercise, the production of ATP greatly increases to compensate for the energy demands. The metabolism has numerous regulatory mechanisms such as creatine kinase and thyroid hormones to control the rate of energy production.
Creatine is a type of organic acid that increases the formation of ATP. Much of the creatine in your body originates directly from the consumption of red meat, poultry and fish, but the cells can also synthesize creatine from several amino acids that are also found in meat. Creatine is popular as a supplement among bodybuilders and competitive athletes because it increases muscle mass and enhances physical performance during high-intensity, short duration exercise.
The liver and kidneys produce and process most of the creatine in your body. It's then transported through the blood and taken up by the tissue in which energy demand is particularly high. Approximately 95 percent of it is concentrated in the skeletal muscles, and the presence of creatine is strongly correlated with muscle damage accumulated from exercise. Creatine, acting as a kinase, increases ATP production in the muscles. A kinase is a special type of enzyme that modifies another molecule. Creatine kinase quickly acts to regenerate ATP whenever energy demand increases. During injury, creatine kinase leaks out of the muscle tissue and into the blood. For this reason it may also indicate major problems with the heart.
The thyroid gland is an organ in the front of the neck that produces two hormones called T3 and T4, both of which regulate and control your body's metabolism and the physiological processes that are associated with the metabolism. For example, they increase heart rate and blood flow to the organs, stimulate carbohydrate metabolism and enhance the mobilization and metabolism of fat. Thyroid hormones do not control creatine kinase directly, but they do regulate the metabolic activity of which creatine is a major part.
Thyroid dysfunctions are often correlated with muscular disorders and the amount of creatine kinase in the blood to such a degree that creatine kinase tests are valuable in screening for the existence of hypothyroidism, a condition characterized by a depression in the production of thyroid hormones. A 2007 study published in the "Journal of Medical Education and Research" found that there is a strong relationship between decreased levels of T3 in the blood and elevated levels of creatine kinase. The mechanism behind this relationship is currently unknown, but it may have something to do with the problems of muscle functionality that is associated with thyroid disorders increasing kinase levels.