|a histidine-derived amine compound that is released mainly by damaged mast cells in allergic reactions, causing dilation and permeability of blood vessels and lowering blood pressure|
|a pulsation of the heart, including one complete systole and diastole|
involuntary in·vol·un·tar·y (ĭn-vŏl'ən-těr'ē)
Not subject to control of the volition.
Acting or done without or against one's will.
|involuntary (ĭn-vŏl'ən-těr'ē) Pronunciation Key
Not under conscious control. Most of the biological processes in animals that are vital to life, such as contraction of the heart, blood flow, breathing, and digestion, are involuntary and controlled by the autonomic nervous system.