Cartilage and bone are both stiff connective tissues which form an essential structural component of the body of animal organisms, including human beings. However, they are also quite different in both composition and function. Bones are extremely hard, dense tissue which provide a supportive frame for the body (i.e. the skeleton), as well as serving as production and storage centres for cells and minerals, whereas cartilage is a more flexible tissue found in more specific locations of the body, essentially midway between dense, rigid bone matter and flexible, pliable muscle tissue.
- Cartilage -
Cartilage can be found in the human body both around joints as well as in certain hard but not inflexible areas of the body, like the nose and the ear. Joints with cartilage include the rib cage, the elbow, and, in the legs, the knees and ankles. Cartilage is hard, but not so rigid as bone matter. Instead, it is somewhat flexible, albeit less so than the much less dense muscle tissue. Thus cartilage can play a structural function in certain areas, like the nose, but cannot perform this function to the same extent as dense bones do.
Cartilage is made up of a special type of cell called the chondrocyte, as well as two materials produced by the chondrocytes, collagen fibres and elastin fibres. There are different types of cartilage, characterized by the differing ratios of fibres contained within them.
In addition, cartilage is the only connective tissue in the human body which is not exposed to the blood circulation via its own network of arteries or veins. Instead, blood and nutrients diffuse through the cartilage to the extent that they are pushed through the material by movement and pumping action. This makes cartilage the slowest tissue to grow and, when damaged, the slowest to repair itself.
- Bone -
Bones can be found throughout the human body as basic structural components providing form to the body and protecting internal organs (for example, the rib cage). The human body contains 206 bones, and more in infants and very young children. (These bones later fuse together to form single units as the infant matures.) In addition to its structural and protective functions, the body's bones are also essential production centres for red blood cells (which supply oxygen to the rest of the body) and white blood cells (which are the front line of the body's immune system). Cell production takes place in the core of the bones, in a material known as the bone marrow. Minerals, fats, and hormones can also be stored within the bone to an extent.
Bones are produced from a type of tissue known as osseous tissue, and, unlike the collagen fibre which makes up cartilage, bones are primarily made up of calcium compounds. Both bones and teeth (which are a type of bone, but exposed to the outside world) rely on this calcium to form extremely dense, hard structures less prone to breakage. However, calcium is only one defining element of the bones; indeed, they also contain sufficient collagen to add a small degree of flexibility. As with steel, bones could not rely solely on a rigid material or else they would become dangerously brittle and excessively prone to snapping under sudden stress.