Cartilage

Cartilage is a semi-rigid connective tissue that provides support and cushioning in various parts of the body. It consists of chondrocytes embedded in a dense extracellular matrix rich in collagen and proteoglycans, with a high water content. Cartilage is avascular and aneural, receiving nutrients by diffusion from surrounding tissues. There are three main types: hyaline cartilage, elastic cartilage, and fibrocartilage. Hyaline cartilage covers joint surfaces and forms structures such as the nasal septum and tracheal rings; elastic cartilage gives shape and flexibility to the ear and epiglottis; fibrocartilage provides tough, load-bearing support in intervertebral discs and the pubic symphysis.

Chondrocytes reside in lacunae and synthesize the extracellular matrix, which is rich in collagen type II, aggrecan, and other proteoglycans. The matrix is highly hydrated, enabling resilience under compression. Growth of cartilage occurs by interstitial growth (cell division within the matrix) and appositional growth (new matrix produced at the surface by a perichondrium). Most cartilage is surrounded by a perichondrium, a layer of dense connective tissue that supplies nutrients and progenitor cells, except for articular cartilage, which lacks a true perichondrium.

Functionally, cartilage provides smooth surfaces for joint movement, distributes loads, and maintains integrity of soft tissues. Its limited blood supply means repair and regeneration are slow, so damage can persist and contribute to conditions such as osteoarthritis. Treatments for damaged cartilage range from microfracture and autologous chondrocyte implantation to tissue-engineered cartilage and scaffolds, aiming to restore function and reduce pain. Cartilage remains a focus of study for understanding development, aging, and regenerative medicine.