Tubule

A tubule is a small tube-like structure found in many organisms. In biology, a tubule is typically an elongated, hollow conduit with a lumen and a surrounding wall, often lined by epithelium. Tubules can be simple or branched and may form networks. They serve to transport fluids, enable secretion or absorption, or separate functional compartments. The walls may include smooth muscle or connective tissue that provides support or contractile ability, and some tubules have specialized epithelial cells with microvilli or cilia to increase surface area.

In humans and other vertebrates, tubules appear in several organ systems. Renal tubules, forming part of the nephron, include the proximal tubule, loop of Henle, distal tubule, and collecting duct, and are central to filtrate processing through selective reabsorption and secretion. The seminiferous tubules in the testes are where sperm production occurs within a supportive environment. In teeth, dentinal tubules extend from the pulp toward the dentin surface and transmit fluids and nutrients, contributing to dentin’s properties.

Tubules are also a common histological motif in glandular and reproductive tissues, where they can be secretory units or conduits for the transport of substances. In cellular biology, the term can describe tube-shaped organelles or cytoskeletal elements that have a tubular geometry, though these structures may differ in composition and function from hollow bodily tubules.

Overall, tubules are defined by their tube-like shape, hollow lumen, and role as conduits that facilitate transport, secretion, absorption, or compartmental separation across diverse organisms and tissues.