Architecture of a Long Bone

^ The diaphysis (shaft), composed of compact bone, is hollow and is usually lined by a thin band of spongy bone.

^ An epiphysis, the knob at either end of the diaphysis, is composed of a thin rim of compact bone. The spongy bone in its interior houses red marrow.

^ Metaphysis. Flared region between diaphysis and epiphysis.

^ Epiphyseal plate. Hyaline cartilage separating epiphysis and metaph-ysis in growing bones. Growth in bone length occurs as hyaline cartilage in the epiphyseal plate goes through various stages of regression, providing a framework on which bone is deposited. When the hyaline cartilage in the epiphyseal plate is exhausted, growth stops. The epiphysis and metaphysis fuse in the adult, leaving an epiphyseal line as a remnant of the epiphyseal plate.

^ Marrow

• Red marrow, found in all bones of the fetus, is restricted to spongy bone areas of selected bones in the adult and contains hematopoi-etic tissue that forms blood cells.

• Yellow marrow, found in the shafts of long bones in the adult, consists mainly of adipose connective tissue that retains the potential to become red marrow under hemorrhagic stress.

^ Articular cartilage is composed of hyaline cartilage and covers articular surfaces of bone. This cartilage does not possess a perichondrium; the glassy, smooth cartilage provides a good articulating surface.

Longitudinal Section Long Bone
figure 5.1. Longitudinal section of an adult long bone.

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