Lacuna (plural: lacunae or lacunas) is a small, cavity-like space within the extracellular matrix of connective tissues, most notably in bone and cartilage, that houses the resident cells of those tissues.
Etymology
From Latin lacūna ("ditch, gap, pool"), derived from lacus ("lake").
In Bone
In osseous tissue, a lacuna is a small oblong cavity situated between the lamellae (concentric layers of calcified matrix) of an osteon (Haversian system). Each lacuna contains a single osteocyte (a mature bone cell). The lacunae are interconnected by tiny canals called canaliculi, through which the dendritic processes of osteocytes extend, allowing for nutrient exchange, waste removal, and intercellular communication. This network is known as the lacuna-canalicular system.
- Diameter: approximately 15–20 μm.
- Location: at the borders of adjacent lamellae in compact bone; in a lattice-like arrangement within trabeculae in spongy (cancellous) bone.
- Function: protects the osteocyte from ossification and maintains cell viability.
In Cartilage
In cartilage, lacunae are cavities within the cartilaginous matrix that house chondrocytes. Unlike bone lacunae, a single cartilage lacuna may contain one, two, four, or up to eight chondrocytes (forming "cell clusters" or "isogenous groups") during cell division. The matrix immediately surrounding each lacuna is often arranged in concentric layers, forming the so-called capsule of the space.
- Function: encases chondrocytes and, because cartilage is avascular, helps provide essential nutrients for cell survival via diffusion through the extracellular matrix.
In Botany
In plant anatomy, "lacuna" also refers to the leaf gap — a gap in the vascular tissue of the stem through which a leaf trace (the connecting vascular bundle to a leaf) passes. This is a characteristic feature of angiosperms and some gymnosperms.
Clinical Significance
- Micropetrosis: the pathological mineralization (hypermineralization) of osteocyte lacunae and canaliculi, which occurs with aging and in conditions such as osteoporosis. Mineralized lacunae act as "plugs," disrupting the lacuna-canalicular network, impairing nutrient flow, reducing bone mechanosensitivity, and increasing bone fragility.
- Bisphosphonate therapy in osteoporosis patients has been associated with a reduced number of mineralized lacunae, suggesting potential utility of lacunar mineralization as an indicator of bone quality.
