Summary
Gaseous signaling molecules are gaseous molecules that are either synthesized internally (endogenously) in the organism, tissue or cell or are received by the organism, tissue or cell from outside (say, from the atmosphere or hydrosphere, as in the case of oxygen) and that are used to transmit chemical signals which induce certain physiological or biochemical changes in the organism, tissue or cell. The term is applied to, for example, oxygen, carbon dioxide, sulfur dioxide, nitrous oxide, hydrogen cyanide, ammonia, methane, hydrogen, ethylene, etc. Select gaseous signaling molecules behave as neurotransmitters and are called gasotransmitters. These include nitric oxide, carbon monoxide, and hydrogen sulfide. Historically, the study of gases and physiological effects was categorized under factitious airs. The biological roles of each of the gaseous signaling molecules are outlined below. Gasotransmitter Gasotransmitters are a class of neurotransmitters. Only three gases are accepted to be classified as gasotransmitters including nitric oxide, carbon monoxide, and hydrogen sulfide. Carbon dioxide, CO2, is one of the mediators of local autoregulation of blood supply. If its levels are high, the capillaries expand to allow a greater blood flow to that tissue. Bicarbonate, HCO3−, ions are crucial for regulating blood pH. A person's breathing rate influences the level of CO2 in their blood. Breathing that is too slow or shallow causes respiratory acidosis, while breathing that is too rapid leads to hyperventilation, which can cause respiratory alkalosis. Although the body requires oxygen for metabolism, low oxygen levels normally do not stimulate breathing. Rather, breathing is stimulated by higher carbon dioxide levels. The respiratory centers try to maintain an arterial CO2 pressure of 40 mm Hg. With intentional hyperventilation, the CO2 content of arterial blood may be lowered to 10–20 mm Hg (the oxygen content of the blood is little affected), and the respiratory drive is diminished.
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