A trabecula (plural trabeculae, from Latin for "small beam") is a small, often microscopic, tissue element in the form of a small beam, strut or rod, generally having a mechanical function, and usually composed of dense collagenous tissue (such as the trabecula of the spleen). They can be composed of other materials; in the heart, for example, muscles such as trabeculae carneae and septomarginal trabecula form similar structures. The formation of trabeculae is known as trabeculation.
On histological section, trabeculae of a cancellous bone can look like septa, but in three dimensions they are topologically distinct, with trabeculae being roughly rod or pillar-shaped and septa being sheet-like.
When crossing fluid-filled spaces, trabeculae may have the function of resisting tension (as in the penis, see for example trabeculae of corpora cavernosa and trabeculae of corpus spongiosum) or providing a cell filter (as in the trabecular meshwork of the eye).
Multiple perforations in a septum may reduce it to a collection of trabeculae, as happens to the walls of some of the pulmonary alveoli in emphysema.
Diminutive form of Latin trabs, which means a beam or bar. In the 19th century, the neologism trabeculum (with an assumed plural of trabecula) became popular, but is less etymologically correct. Trabeculum persists in some countries as a synonym for the trabecular meshwork of the eye, but this can be considered poor usage on the grounds of both etymology and descriptive accuracy.
For the skull development component, see trabecular cartilage.