<P> Cartilage does not contain blood vessels (it is avascular) or nerves (it is aneural). Nutrition is supplied to the chondrocytes by diffusion . The compression of the articular cartilage or flexion of the elastic cartilage generates fluid flow, which assists diffusion of nutrients to the chondrocytes . Compared to other connective tissues, cartilage has a very slow turnover of its extracellular matrix and does not repair . </P> <P> In embryogenesis, the skeletal system is derived from the mesoderm germ layer . Chondrification (also known as chondrogenesis) is the process by which cartilage is formed from condensed mesenchyme tissue, which differentiates into chondroblasts and begins secreting the molecules (aggrecan and collagen type II) that form the extracellular matrix . </P> <P> Following the initial chondrification that occurs during embryogenesis, cartilage growth consists mostly of the maturing of immature cartilage to a more mature state . The division of cells within cartilage occurs very slowly, and thus growth in cartilage is usually not based on an increase in size or mass of the cartilage itself . </P> <P> The articular cartilage function is dependent on the molecular composition of the extracellular matrix (ECM). The ECM consists mainly of proteoglycan and collagens . The main proteoglycan in cartilage is aggrecan, which, as its name suggests, forms large aggregates with hyaluronan . These aggregates are negatively charged and hold water in the tissue . The collagen, mostly collagen type II, constrains the proteoglycans . The ECM responds to tensile and compressive forces that are experienced by the cartilage . Cartilage growth thus refers to the matrix deposition, but can also refer to both the growth and remodeling of the extracellular matrix . Due to the great stress on the patellofemoral joint during resisted knee extension, the articular cartilage of the patella is among the thickest in the human body . </P>

Where is cartilege located in the human body