circulations

Circulations is a term used across disciplines to describe the movement or distribution of materials within a system. In everyday language it often refers to the flow of fluids, but in scientific and professional contexts it covers a range of patterned movements, from physiological transport to global climate flows and the lending of library materials.

In biology, circulations describe the cardiovascular and lymphatic systems that move blood and lymph through a body. The cardiovascular circulation typically splits into pulmonary circulation, which moves blood between the heart and the lungs for gas exchange, and systemic circulation, which supplies oxygen and nutrients to body tissues. The lymphatic system circulates lymph and plays a key role in immune function and fluid balance. Circulation also encompasses fetal circulation, where the placenta and specialized shunts route blood differently from postnatal patterns. Microcirculation refers to flow in the smallest vessels, including capillaries, where exchange with tissues occurs.

In environmental sciences, atmospheric and oceanic circulations describe large-scale movement of air and seawater. Atmospheric circulation models explain weather and climate through patterns such as Hadley, Ferrel, and polar cells, along with prevailing winds like trade winds and westerlies. Ocean circulation includes surface gyres driven by winds and deep thermohaline circulation driven by density differences, both contributing to climate regulation and nutrient transport.

Other uses include library circulation, the lending and borrowing of library materials, tracked by circulation statistics, and in physics and mathematics, circulation denotes the line integral of a vector field around a closed loop, related to concepts like curl and Stokes’ theorem.