The skeleton is the bony structure of the body responsible for movement. The human skeleton is the internal framework of the body. It is composed of around 270 bones at birth – this total decreases to around 206 bones by adulthood after some bones get fused together.The bone mass in the skeleton reaches maximum density around age 21. The human skeleton can be divided into the axial skeleton and the appendicular skeleton. The axial skeleton is formed by the vertebral column, the rib cage, the skull and other associated bones. The appendicular skeleton, which is attached to the axial skeleton, is formed by the shoulder girdle, the pelvic girdle and the bones of the upper and lower limbs.
**The axial skeleton**
The axial skeleton is the part of the skeleton that consists of the bones of the head and trunk of a vertebrate. In the human skeleton, it consists of 80 bones and is composed of six parts; the skull bones, the ossicles of the middle ear, the hyoid bone, the rib cage, sternum and the vertebral column. The axial skeleton together with the appendicular skeleton form the complete skeleton. Another definition of axial skeleton is the bones including the vertebrae, sacrum, coccyx, ribs, and sternum
Diagram of the axial skeleton
The appendicular skeleton
The appendicular skeleton is the portion of the skeleton of vertebrates consisting of 126 bones that support the appendages. Appendages appeared as fins in early fish, and subsequently evolved into the limbs of tetrapods. The appendicular skeleton includes the skeletal elements within the limbs, as well as supporting pectoral and pelvic girdles in the case of tetrapods (these are lacking in fish).The word appendicular is the adjective of the noun appendage, which itself means a part that is joined to something larger.
diagram of the Appendicular skeleton
Function of the human skeleton
SUPPORT.
MOVEMENT .
PROTECTION
PRODUCTION OF BLOOD CELLS
STORAGE OF MINERALS
ENDOCRINE REGULATION
SUPPORT
The skeleton provides the framework which supports the body and maintains its shape. The pelvis, associated ligaments and muscles provide a floor for the pelvic structures. Without the rib cages, costal cartilages, and intercostal muscles, the lungs would collapse.
MOVEMENT
The joints between bones allow movement, some allowing a wider range of movement than others, e.g. the ball and socket joint allows a greater range of movement than the pivot joint at the neck. Movement is powered by skeletal muscles, which are attached to the skeleton at various sites on bones. Muscles, bones, and joints provide the principal mechanics for movement, all coordinated by the nervous system.
It is believed that the reduction of human bone density in prehistoric times reduced the agility and dexterity of human movement.
PROTECTION
The skeleton helps to protect our many vital internal organs from being damaged.
The skull protects the brain
The vertebrae protect the spinal cord.
The rib cage, spine, and sternum protect the lungs, heart and major blood vessels.
BLOOD CELL PRODUCTION
The skeleton is the site of haematopoiesis, the development of blood cells that takes place in the bone marrow. In children, haematopoiesis occurs primarily in the marrow of the long bones such as the femur and tibia. In adults, it occurs mainly in the pelvis, cranium, vertebrae, and sternum.
STORAGE
The bone matrix can store calcium and is involved in calcium metabolism, and bone marrow can store iron in ferritin and is involved in iron metabolism. However, bones are not entirely made of calcium, but a mixture of chondroitin sulfate and hydroxyapatite, the latter making up 70% of a bone. Hydroxyapatite is in turn composed of 39.8% of calcium, 41.4% of oxygen, 18.5% of phosphorus, and 0.2% of hydrogen by mass. Chondroitin sulfate is a sugar made up primarily of oxygen and carbon.
ENDOCRINE REGULATION
Bone cells release a hormone called osteocalcin, which contributes to the regulation of blood sugar (glucose) and fat deposition. Osteocalcin increases both the insulin secretion and sensitivity, in addition to boosting the number of insulin-producing cells and reducing stores of fat.