12.2.1 The Structure of Bone

Question 1

The Structure of Bone

Answer 1

• The long bones consist of a shaft called a diaphysis and ends called epiphyses.
• Bones can be classified by shape.
• Bones develop within embryonic cartilage from a center of ossification.
• Bones consist of compact and spongy bone.
• In the shaft of the long bone, compact bone surrounds the medullary cavity, which contains bone marrow and is lined with the endosteum.
• The outside of the bone is covered by the periosteum, a tough membrane that extends over joints and thickens to produce ligaments.
• Bones grow in length during childhood from a layer of cartilage called the epiphysal plate.

Question 2

note

Answer 2

• The long bone consists of a shaft called a diaphysis and two ends called epiphyses.
• Bones can be classified by their shape. The long bones, such as the humerus, are longer than they are wide. Short bones, such as the carpels, are about equal in length and width. Flat bones, such as the skull bones and shoulder blades, are thin and flattened. Irregular bones, such as the vertebrae, have different and complicated shapes. The sesamoid bones, such as the patella, are shaped like a sesame seed and grow within a tendon.
• Before the age of 8 weeks, the skeleton of the embryo is composed of hyaline cartilage and fibrous membranes. At this age, a process called endochondral ossification takes place. In the middle of the “bone,” centers of ossification form. Osteoblasts begin to deposit fibers of collagen, mucopolysaccharides that bind the collagen together and phosphorus and calcium salts that harden the bone. The cartilage begins to die as the bone is formed.
• The osteoblasts mature into osteocytes within the units of mature bone called the Haversian system, or osteon.

Question 3

note 2

Answer 3

• A bone’s structure reflects its mechanical and biological functions. A bone contains both spongy bone and compact bone.
• Spongy bone consists of an open network of plates called trabeculae. The plates act as struts, providing strength at low weight. Spongy bone is found in the interior of a bone.
• Compact bone occurs on the outside of the bone especially in the shaft. Compact bone appears solid and is heavier. The hollow column created by compact bone is a very strong structure.
• In the shaft of the bone is the hollow medullary cavity. This cavity and the spaces in spongy bone are lined with the endosteum. Endosteum is a cellular tissue layer active in bone growth, repair, and remodeling.
• Marrow is a loose connective tissue found in the medullary cavity and spongy bone of some bones. Yellow marrow contains fat cells. Red marrow contains stem cells and the blood cells they make in the process called hemopoesis.
• The bone is covered in a connective tissue called the
  periosteum. The periosteum grows into the bone tissue to make a strong and intimate connection. It also grows into tendons to form a strong connection for muscle attachment. The periosteum thickens and extends to form ligaments that connect one bone to another and enclose joints.
• Bones must grow in length during childhood. This is
  accomplished through addition of bone tissue at the epiphysal plate, a cartilaginous region between the epiphysis and diaphysis.
• Within these locations chondrocytes continuously divide and produce more chondrocytes toward the diaphysis, increasing the bone’s length. The farthest of these begin to die and are replaced by osteoblasts that form bone.
• In this way the long bones increase in length.