BonePart3

Summary

The lecture reviews the structural organization of bone, including compact and spongy bone, bone-shape categories, the anatomy of long bones, and the coverings that help bone grow and remodel.

Compact and spongy bone

• Compact (dense) bone forms the sturdy outer structure and is especially prominent along the shaft of long bones.
• Spongy bone consists of thin ridges or plates called trabeculae. It is also referred to as trabecular or spicular bone.
• The spaces between trabeculae contain red bone marrow, where blood cells are produced.
• In the flat bones of the skull, compact bone forms outer and inner plates, with spongy bone between them. This middle layer is called the diploë.
• Red marrow is found in spongy bone, including at the ends of long bones and in many flat bones, such as the ribs, sternum, scapula, cranial bones, clavicle, and coxal bone.
• In children, the shaft of a long bone contains red marrow. As a person matures, much of this marrow is replaced by yellow marrow, which stores fat.

Bone-shape categories

• Long bones are longer than they are wide. Examples include the femur, humerus, radius, ulna, tibia, fibula, metacarpals, metatarsals, and phalanges.
• Flat bones have a flattened shape and commonly have spongy bone between two plates of compact bone. Examples include the sternum and cranial bones.
• Short bones are wider than they are long. Examples include the carpals and tarsals.
• Irregular bones do not fit the other categories. Vertebrae are an example.

Long-bone regions and growth

• The diaphysis is the shaft of a long bone. It surrounds the medullary cavity, which contains red marrow in children and is commonly filled with yellow marrow in adults.
• The proximal and distal ends of long bones contain spongy bone.
• The epiphyseal plate, commonly called the growth plate, is made of hyaline cartilage in juveniles and enables bones to lengthen.
• As a person matures, the plate ossifies and becomes an epiphyseal line. Once this happens, lengthwise bone growth ends.

Bone coverings and remodeling

• The periosteum covers the outer surface of bone and has two layers:
  • The superficial layer is dense irregular connective tissue that supports the attachment of ligaments and tendons.
  • The deeper layer contains osteoprogenitor cells that contribute to new bone formation.
• The endosteum lines the medullary cavity and other internal bone surfaces. It contains osteoprogenitor cells involved in bone formation and remodeling.
• The lecture concludes by introducing the next topic: osteogenesis, or the formation, rebuilding, and remodeling of bone.

Speaker

Larry Young — lecturer and presenter.