Abandoned babies left on the steps of a church or a mosque are not unfamiliar news for many of us. We are not going to discuss the socio-cultural reasons and consequences of this outrageous act, but the amazing biological reality that these babies can survive cold while barely protected, if at all.
Some of the food we take in are used for our body heat. The amount of food reserved for heat is maximum in babies, which goes down as the child grows.
Food taken in in the form of carbohydrates, fat, and proteins are broken down to be captured by ATP (adenosine triphosphate) molecule. Energy is converted into ATP to be fueled to where it is needed. This conversion takes place in the mitochondrion, a membrane-bound organelle, during which almost 35% of energy is transformed to heat. The energy-protein synthesis in ATP are utilized for various functions like muscle contraction, transportation of some materials from external and inner organelle membranes, secretions from glands, forming the rest state potential for nerves, and conveying the signals across nerve fibers. During these functions another 38% of energy is released as heat. Thus a total of 73% of energy is converted to heat, while body functions consume only the remaining 27%, a great majority of which is also turned into heat through muscle movements and friction in tissues.
Other factors that increase body heat are shiver, heart pumping blood, friction in the veins, lungs expanding and contracting during breathing, tissue surfaces rubbing against each other, stomach and intestine activities. All of these contribute to maintaining the body heat at a certain level. Deeper tissues in our body are kept at ± 0,6 0C. Exercise and being nervous may contribute to increase in body heat, and obviously extreme cold outside would decrease it.
Metabolism is the combination of two kinds of chemical reactions: constructive metabolism and destructive metabolism. For example, the synthesis of proteins from amino acids is constructive metabolism, and the breakdown of proteins to amino acids and then to energy is destructive metabolism. When our metabolism increases, the body heat is also increased.
While under psychological conditions like pressure, excitement, and fear, metabolism increases, sympathetic nerves are triggered, and adrenaline and noradrenaline hormones from suprarenal gland are secreted into the blood. These will further increase the metabolism and body heat (chemical thermogenesis).
Another group of hormones that is effective on chemical thermogenesis is thyroid hormones (T3 and T4). When we feel cold, the secretion of TRH (Thyrotropin-releasing hormone) from hypothalamus is increased. This hormone is brought through blood veins to pituitary front lobe to start TSH (thyroid stimulant hormone) secretion. TSH has a role to increase the secretion of T3 and T4. These two hormones generate a rise in metabolism and thus body heat.
The brown fat tissue has a key role that relates metabolism increase to body heat. This issue is found in large amounts in the newborn babies, especially in their back on the upper half of the spine, and is functional for almost two years. What distinguishes this type of fat from white fat tissue are its unique qualities for the protection of the baby from hypothermia. In babies, the sympathetic system, adrenaline and noradrenaline hormones, and thyroid hormones (T3 and T4) increase the burning of food in mitochondria found in the brown fat tissue with oxygen. As opposed to other tissues, ATP is not produced as a result of this process in brown fat tissue. All the energy found in fat is transformed to heat.
Brown fat tissue is visible in some babies in between their shoulder blades. As the child grows, he or she can feel the changes in temperature and becomes strong enough to dress up, brown fat tissue disappears and is no longer visible. It is such a miracle that babies who are weak and in need of help are protected from cold and death with the wondrous capabilities given to the brown fat tissue.