Lacuna

A lacuna is a tiny chamber inside bone tissue where an osteocyte lives. It forms when a bone-building cell, called an osteoblast, gets surrounded by the new bone matrix it just created. Instead of dying, that trapped cell changes shape and becomes an osteocyte, settling permanently into its lacuna as a kind of living sensor built right into the bone structure.

From inside the lacuna, the osteocyte reaches out through tiny channels called canaliculi, extending long arm-like dendrites to connect with neighboring cells. This network of lacunae and canaliculi, known as the lacunar-canalicular system, lets fluid move through the bone when you put load on it. That fluid movement creates a signal the osteocyte can detect, which is thought to be the main way bone senses the forces placed on it.

Lacunae are small, but they are central to how bone works as a living, sensing tissue rather than just a rigid structure. Every lacuna houses one osteocyte, and together these countless tiny chambers and their connecting channels form the communication network that helps bone respond to the way you move and load it.