Cell signaling of adjacent cells. In cardiac muscle, gap junctions between adjacent cells allows for action potential propagation from the cardiac pacemaker region of the heart to spread and coordinately cause contraction of the heart. The notch signaling mechanism is an example of juxtacrine signaling (also known as contact-dependent signaling) in which two adjacent cells must make physical contact in order to communicate. This requirement for direct contact allows for very precise control of cell differentiation during embryonic development. In the worm "Caenorhabditis elegans", two cells of the developing gonad each have an equal chance of terminally differentiating or becoming a uterine
Cardiac output cycle that delivers oxygen, nutrients and chemicals to the body's cells and removes cellular waste. Because it pumps out whatever blood comes back into it from the venous system, the quantity of blood returning to the heart effectively determines the quantity of blood the heart pumps out – its cardiac output, "Q". Cardiac output is classically defined alongside stroke volume (SV) and the heart rate (HR) as: In standardizing what CO values are considered to be within normal range independent of the size of the subject's body, the accepted convention is to further index equation () using Body surface area