Bone and cartilage are types of connective tissues in the body. A bone is hard tissue that forms the skeletal structure of the body. Cartilage, by comparison, is not as hard and rigid as bone, and is present in areas of the body like the ear, nose, and joints. In the joints of the body, cartilage covers the ends of the bones and acts as a shock absorber to prevent bones from rubbing against each other.
Differences in Physical Structure
The structure of bones is a combination of living and dead cells embedded in a matrix. The outer hard layer of the bone is referred to as compact bone and has few spaces. The internal part of bone also called spongy tissue is porous and harbors the bone marrow and blood vessels. Other tissue found in bone includes endosteum, periosteum, and nerves. Bone matrix has organic (mineral) components and inorganic components such as collagen. Bone formation is the result of hardening of this matrix.
Cartilage essentially consists of chondrocyte cells which produce an extracellular matrix consisting of collagen fibres, proteoglycan, and elastin fibres. Different types of cartilage contain these components in different proportions. Cartilage, unlike bones, does not contain blood vessels.
Cellular Structure of Bones vs. Cartilages
Bone or osseous tissue is made up of osteoblasts, the progenitor cells that give rise to osteocytes, which are mature bone cells; and osteoclasts, large cells that breakdown bone tissue for growth, repair, and remodelling. Another type of bone lining cells is present to regulate the movement of calcium and phosphate in and out of the bone.
Cartilage comprises of chondrocytes, produced by precursor cells known as chondroblasts. Chondroblast produces a dense matrix comprised of collagen and elastin fibres, in which mature chondrocyte cells are embedded.
Cartilage vs. Bone Diseases
Common bone disorders include osteoporosis, wherein the mineral density of bones is reduced, thus increasing the likelihood of fracture; osteosarcoma, a cancerous condition of the bone; osteomyelitis, which is an infection of the bone marrow; and osteogenesis imperfecta, which is a genetic disorder.
Diseases of the cartilage include osteoarthritis, a condition in which the cartilage is thinned out, resulting in friction between bones; achondroplasia, which leads to dwarfism; costochondritis, which is inflammation of the cartilage in the ribs, resulting in chest pain; and chondrodystrophies, which are a group of diseases caused by the disturbance of cartilage growth and subsequent ossification (hardening) of cartilage.
Types of Bones and Cartilages
Bones are classified into long, short, flat, irregular, sesamoid, and sutural types. Most bones of the limb are long bones characterized by a long shaft and curved structure; examples include the femur, tibia, fibula, humerus, ulna, and radius. Short bones are the same in length and width and are present in the ankle and wrist. Flat bones are thin and curved and found in the skull and sternum. Irregular bones are found in the spine and hip region. Sesamoid bones are developed in the tendons and most commonly found in kneecaps, the palms of the hands, and the soles of the feet. Sutural bones are very small and located in the sutures between the cranial bones; they vary in different persons.
Types of cartilage include hyaline cartilage, fibrocartilage, and elastic cartilage. Hyaline cartilage is the most abundant of the three types. It is found mainly in the bronchial tubes, larynx, nose, and trachea, in the end of long bones, and in the embryonic skeleton. It serves to provide structure and smooth movement. Fibrocartilage is a tough form of cartilage found at the site of fractures, intervertebral discs, and joints, such as those found in the knee and hip. Fibrocartilage provides rigidity and structure to the attached structures. Elastic cartilage is more elastic and is present in the external ear, auditory tubes, and epiglottis.
Differences in Function
Bones perform a variety of functions in vertebrates, often protecting the body against mechanical damage. For example, the skull protects the brain, and the rib cage protects the internal organs, and so on. Bones assist in the movement of the body, as skeletal muscles are attached to the bones. They provide a framework and shape for the body and store minerals like calcium and phosphorous. They also store red bone marrow, which produces erythrocytes (red blood cells) and leucocytes (white blood cells), and yellow bone marrow, which also contains adipose cells that reserve energy.
The main functions of cartilage tissue include reducing friction at the joints, supporting tracheal and bronchial tubes, acting as shock absorbers between vertebrae, and maintaining the shape and flexibility of the ear, nose, etc.