What is a canaliculus? Mention its function

A canaliculus is a microscopic channel that connects small spaces within tissues, enabling transport of fluids, solutes, or signals. Two clinically important types:

• Bone (osteocytic) canaliculi: Tiny tunnels radiating from lacunae that house osteocytes. Canaliculi interconnect osteocytes with each other and with blood supply in Haversian/Volkmann canals. Through gap junctions at canalicular tips, osteocytes exchange nutrients, remove waste, and transmit mechanosensory signals regulating bone remodeling (osteoblast/osteoclast activity). This network keeps deep bone cells alive despite mineralization acting as a diffusion barrier.
• Hepatic (bile) canaliculi: Narrow grooves formed between adjacent hepatocytes sealed by tight junctions. They collect bile secreted by hepatocytes and channel it toward canals of Hering, then bile ducts, ultimately reaching the gallbladder or intestine. Functionally, they are the first conduits in bile flow, crucial for fat emulsification (via bile salts), excretion of bilirubin, cholesterol, and xenobiotics.

Thus, a canaliculus is a fine conduit for cellular communication or fluid transport, essential for bone viability and for liver bile drainage, depending on the organ context.