The adults human skeleton consists of 206 bones. There are more bones present at birth but they gradually fuse together as the body matures. The skeleton is divided into two parts.
The axial skeleton includes the bones of the skull, face and spine along with the ribs and breastbone.
The appendicular skeleton includes the bones of the arms, hands, legs, feet and pelvis as well as the clavicles and shoulder blades. The skeleton serves several vital functions.
The skeleton gives the body its shape, which changes with growth. It determines height, the size of the hands and feet, it keepsbody shape stable and enables essential functions such as breathing – a stable rib cage and spine enable the lungs to fully inflate fully.
The skeleton gives support to the body and keeps the internal organs in their correct places. The strong bones of the spine, pelvis and legs allow people to stand upright, supporting the weight of the entire body. The skull holds the brain, the chest cavity houses the heart and lungs, and the abdominal cavity maintains the organs of the digestive, urinary and internal reproductive systems.
Bones are held together by ligaments. Tendons attach the muscles to the bones of the skeleton. The muscular and skeletal systems work together to enable the body to move and remain stable. When muscles contract, they pull on bones of the skeleton to produce movement or hold the bones still in one position.
The shape of the bones and the way that they fit together at the joints allows for different types of movement. For example, the leg bones come together at the knee to form a hinge joint that enables the knee to bend back and forth. The joining portions of the bones of the hip and shoulder have a much different shape and form ball-and-socket joints that allow movement in multiple directions.
The skeleton protects the internal organs from damage by surrounding them with bone. Bone is living tissue that is hard and strong, yet slightly flexible to resist breaking. The strength of bone comes from its mineral content, which is primarily calcium.
Examples of the protective bones of the skeleton include the skull, spinal column and rib cage, which protect the brain, spinal cord, and heart and lungs.
5. Blood Cell Production
Larger bones contain bone marrow Marrow is responsible for production of all of the body’s red blood cells and many of its white blood cells. Red blood cells are produced at an average rate of approximately 200 million per day. These cells carry oxygen to the body tissues.
The marrow is found mainly in the breastbone, hips, ribs, skull, spinal bones and at the end of long bones of the arms and legs. Several types of white blood cells, which protect the body from infections, are also produced in red bone marrow.