Introduction
- for support;
- for protection of soft tissues;
- for mineral storage;
- for blood formation.
There are 206 bones in the human body.
The skeleton is divided into two sections:
- axial skeleton, which consists of the skull, vertebrae, sacrum, ribs, and sternum. The axial skeletal system protects the brain, spinal cord, sensory organs, and soft tissue of chest cavity and supports the body weight over the legs.
- appendicular skeleton, which consists of the limbs and supporting bones. The appendicular skeletal system provides internal support and positioning of arms and legs. It also supports and moves the axial skeleton.
Types of Bone Tissue:
- Compact bone is comprised of osteon or haversian system, a term describing the very precise arrangements of osteocytes, matrix, and blood vessels of bone. Halversian was named for Clopton Havers, a 17th century English anatomist who wrote a book on bone structure. The arrangement involves cylinders of bone matrix with osteocytes in concentric rings around central haversian canals (blood vessels). The osteocytes (bone cells) are in contact with the blood vessels and with each other through microscopic channels (canaliculi) in the matrix. The matrix of bone contains calcium salts (calcium carbonate – CaCO3, and calcium phosphate -- Ca3(PO4)2, and collagen.
- Spongy bone is named for its appearance. Osteocytes, blood vessels, and matrix are present, but not arranged in haversian systems. The cavities often contain red bone marrow, which produces RBCs, platelets, and five types of WBCs.
Classification of Bones:
- Long bones are the bones of the arms, legs, hands, and feet. The shaft is called the diaphysis (hollow, but made of compact bone to form a canal within the shaft known as the marrow canal). The ends are called epiphyses (made of spongy bone covered with a thin layer of compact bone, as are the short, flat, and irregular bones). The marrow canal, or medullary cavity, contains yellow bone marrow, which is mostly adipose tissue which gradually replaces the red bone marrow during aging.
- Short bones are the bones of the wrists and ankles.
- Flat bones are the bones of the ribs, shoulder blades, hips, and cranium.
- Irregular bones are those of the vertebrae and face.
This page was updated in November 2005.
