Kiertokulku

Kiertokulku is a Finnish term used to describe a recurring loop in which a substance, energy or information moves through a system in a repeating cycle. The word combines kierto (cycle, rotation) and kulku (passage, movement). In Finnish scientific and technical writing kiertokulku is used as a general descriptor for transport and recycling processes that operate in cycles, rather than naming a single anatomical or physical structure.

In biology and physiology kiertokulku can refer to circulatory processes in a broad sense. The cardiovascular system exemplifies a kiertokulku where blood is pumped by the heart through arteries and veins in a continuous loop. Plants also rely on cyclic transport of water, nutrients and assimilates through tissues such as xylem and phloem. Metabolic pathways can be described as kiertokulku when substrates and products are repeatedly regenerated through cycles, such as various biochemical cycles in cells.

In ecology and environmental science kiertokulku is used to discuss nutrient and energy cycles, including carbon and nitrogen cycles, which involve uptake, transformation, and recycling of elements within ecosystems.

In engineering and technology the term appears in descriptions of closed-loop systems, such as coolant circuits, heating and cooling loops, or other engineering processes where a fluid or medium circulates in a controlled loop.

In economics or systems theory kiertokulku can be used metaphorically to describe circular flows of goods, services, or capital, though the more specialized Finnish terms such as kiertotalous are common in policy and industry discussions.