The human skeleton is composed of cartilage and bones. There are in all 206 bones. It is divided into two functional parts:
- Axial Skeleton
- Appendicular skeleton
The axial skeleton consists of bones of the head, neck and vertebral column and rib cage, which is in all 80 bones. The axial skeleton supports and protects organs in the dorsal (posterior) and ventral (anterior) body cavities. It provides surface area for muscle attachment.
The appendicular skeleton on the other hand, consists of the bones of the upper and lower limb, including the pectoral (shoulder) and pelvic girdles. It provides movement and are 126 bones in all.
Cartilage is a form of connective tissue. It is semi rigid yet flexible. It forms parts of the body where more flexibility is required. For example the joints between bones, where the costal cartilage attaches the rib to the sternum, the ear, the nose, the elbow, the knee, the ankle, and the intervertebral discs.
The amount of cartilage in the human body varies with age. A young person has more cartilage than an elderly person. Cartilages are composed of cells called chondrocytes that produces extracellular matrix called collagen. Cartilage does not have any blood vessels.
Bones make up most of the skeleton. They are living tissue and are the hard form of connective tissue. Bones provide:
- Support for the body
- Protection for vital structures
- Mechanical of basic movement
- Mineral storage
- Blood production
The bone is covered by a fibrous connective tissue called the periosteum. There are two types of bones:
- Compact bone
- Spongy bone
Compact bones are the hard densely packed hard outer layer of bone. It surrounds spongy bone. Spongy bone is found in the inside of bone and at the end of long bones. It’s the weak part of bone and it’s where bone marrow is found. A compact bone provides strength for weight bearing.
Bones are classified into four types according to their shape.
- Long bones
- Short bones
- Flat bones
- Irregular bones
- Sesamoid bones
Long bones are tubular. These includes are the bones of the humerus, femur and tibia. Short bones are cubelike and are found only in the ankle and wrist. Flat bones are plate-like and serves protective functions. They are bones of the skull, ribs and scapulae. Irregular bones as the name suggests, varies in shape. They can be long, short or flat. They are found in the bones of the face. Sesamoid bones are round and they develop in certain tendons and are found where tendons cross the ends of long bones. They include the knee cap or patella. Sesamoid bones protect the tendon from excessive wear.
Parts of a Long Bone
- Epiphyseal plate (of cartilage)
- Medullary Cavity
- Compact and spongy bone
- Bone marrow