H4 Cartilage

Matrix rich in collagen type II, proteoglycan aggregates (e.g., chondroitin sulfates, keratan sulfate) and high water content (~75%). These attract Na+ and water, giving resilience. p.21,31,32

Mesenchymal cells condense, differentiate into chondroblasts which secrete matrix; cells become trapped and mature into chondrocytes, forming isogenous groups as they proliferate. [pages 33–37]

Locations include the nasal septum, larynx, tracheal rings, costal (rib) cartilages, articular surfaces, and as the embryonic skeleton/growth plates. p.11,12,14

Elastic cartilage resembles hyaline but contains abundant elastic fibers in the matrix giving a yellow color; chondrocytes lie in lacunae and it is usually covered by a perichondrium. [pages 16–17]

Contains collagen type II plus abundant elastic fibers (elastin) and proteoglycans—providing both strength and elasticity. p.17,29

Found in the external ear (auricle), external auditory canal, and parts of the larynx (e.g., epiglottis).

Fibrocartilage is dense, with abundant collagen type I (and some type II) fibers, a more eosinophilic (acidophilic) matrix, and lacks a perichondrium; chondrocytes often align between collagen bundles. [pages 20,29–30]

Rich in collagen type I (plus some type II) with relatively less proteoglycan than hyaline—resulting in a tough, fibrous matrix optimized for tensile strength. p.20,31

Located in intervertebral discs (annulus fibrosus), pubic symphysis, menisci, and at tendon/ligament attachments to bone (entheses). p.18,19

The perichondrium is a dense connective tissue layer (rich in collagen type I) that surrounds most cartilage, serving as a reservoir of progenitor (perichondrial fibroblast) cells for appositional growth and maintenance. It is absent in articular cartilage and fibrocartilage. [pages 24–25]

• Progenitor cells (perichondrial fibroblasts): give rise to chondroblasts.
• Chondroblasts: immature matrix‑secreting cells at the cartilage edge.
• Chondrocytes: mature cells trapped in lacunae that maintain the matrix (often in isogenic groups). p.21,22,26

Interstitial growth: mitotic division of chondrocytes within the matrix increases cartilage from inside. Appositional growth: peripheral perichondrial cells differentiate into chondroblasts adding new layers at the surface. Both contribute to cartilage enlargement. [pages 39–41]

Cartilage is avascular; nutrients and gases diffuse through the matrix from surrounding tissues. Chondrocytes rely mainly on anaerobic glycolysis for ATP.

Cartilage has limited regenerative capacity—defects often fill with fibrous tissue. Articular cartilage has especially poor healing. With ageing and osteoarthritis, there is loss of proteoglycans, matrix degradation, cell loss, and matrix mineralization making cartilage brittle. p.15,43

The collagen II + proteoglycan-rich, hydrated matrix provides compressive resilience and low-friction surfaces, making hyaline ideal for articular cartilage, growth plates, and structural support (e.g., trachea). p.12,14,31

Abundant elastic fibers in the matrix give flexibility and shape retention, so elastic cartilage supports structures that must bend and return to shape (e.g., auricle, epiglottis). [pages 16–17]

High content of collagen type I and an oriented fibrous matrix provide tensile strength and resistance to shear/compression, suited for load‑bearing and attachment sites like intervertebral discs and entheses. [pages 18–20]

The three types are hyaline cartilage, elastic cartilage, and fibrocartilage.

Hyaline cartilage is translucent, blue‑white, basophilic with a glassy matrix and contains collagen type II fibers; chondrocytes lie in lacunae often in isogenous groups. p.11,13