The Process of Thermogenesis
Thermogenesis is the process of heat production in organisms. It occurs mostly in warm-blooded animals, but a few species of thermogenic plants exist. One form of thermogenesis is called thermo-regulatory thermogenesis. This is involved with keeping the temperature of the human body regulated. The average body temperature is 98.7 degrees (F), which is quite a bit higher than the ambient (surrounding) temperature in most cases. There are two types of thermo-regulatory thermogenesis: shivering and non-shivering. Shivering helps the body create heat. D. U. Silverthorn (2004) states, “In shivering thermogenesis, the body uses shivering (rhythmic tremors caused by skeleton muscle contraction) to generate heat. Signals from the hypothalamic control center initiate these skeleton muscle tremors. Shivering generates five to six times as much heat as resting muscle. Shivering can be partially suppressed by voluntary control.” The skeletal muscles create the shivering. The heat results from friction between muscle elements (the same as during exertion), but no mechanical work is produced because opposing (antagonistic) muscle pairs are activated at the same time. Brain centers controlling muscle tone become more active (which in itself increases heat production); and when muscle tone has reached sufficient levels to alternatively stimulate stretch receptors in antagonistic muscles, involuntary shuddering contractions of the skeletal muscle begin. Shivering is very effective in increasing body temperature, because muscle activity produces large amounts of heat. (E. N. Marieb, 1992, p. 866) Non-shivering thermogenesis usually occurs in brown adipose tissue (brown fat) that is present in human infants and hibernating mammals. It is a process whereby substances such as free fatty acids (derived from triacylglycerols) remove purine (ADP, GDP and others) inhibition of thermogenin (uncoupling protein-1) which causes an influx of H+ into the matrix of the
References: Raff, H. & Strang, K.T. (2004) Vander Sherman, Luciano’s HUMAN PHYSIOLOGY: The Mechanisms of Body Function. New York: Mc-Graw-Hill. http://en.wikipedia.org/wiki/Thermogenesis Marieb, E.N. (1992) Human Anatomy and Physiology. California: The Benjamin/Cummings Publishing Company Inc. http://www.all-natural.com/thermo.html Silverthorn D.E. (2004) HUMAN PHYSIOLOGY: AN INTERGRATED APPROACH. California: Benjamin Cummings.