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Figure

(a) The femur of the thigh is a long bone, (b) a tarsal bone of the ankle is a short bone, (c) a parietal bone of the skull is a flat bone, (d) a vertebra of the backbone is an irregular bone, and (e) the patella of the knee is a sesamoid bone.

Articular cartilage- mS¡$

Spongy bone

Space occupied by red marrow

Endosteum Compact bone Medullary cavity

Yellow marrow

Periosteum

Epiphyseal plates

Space occupied by red marrow

— Proximal epiphysis

— Distal epiphysis

Femur

Figure 7.2

Major parts of a long bone.

— Proximal epiphysis

Diaphysis

— Distal epiphysis

Femur

Figure 7.2

Major parts of a long bone.

bone) with thin layers of compact bone on their surfaces (fig. 7.3b). Spongy bone consists of many branching bony plates called trabeculae (trah-bek'u-le). Irregular connecting spaces between these plates help reduce the bone's weight. The bony plates are most highly developed in the regions of the epiphyses that are subjected to compressive forces. Both compact and spongy bone are strong and resist bending.

A bone usually has both compact and spongy bone tissues. Short, flat, and irregular bones typically consist of a mass of spongy bone that is either covered by a layer of compact bone or sandwiched between plates of compact bone (fig. 7.3c).

Compact bone in the diaphysis of a long bone forms a semirigid tube with a hollow chamber called the medullary cavity (med'u-lar"e kav'I te) that is continuous with the spaces of the spongy bone. A thin membrane containing bone-forming cells, called endosteum (en-dos'te-um), lines these areas, and a specialized type of soft connective tissue called marrow (mar'o) fills them.

Compact bone

Yellow marrow in medullary cavity

Compact bone

Yellow marrow in medullary cavity

Remnant of epiphyseal disk

Spongy bone

Compact bone

Remnant of epiphyseal disk

Spongy bone

Compact bone

Spongy bone

Compact bone

Figure 7.3

Spongy bone

Compact bone

Figure 7.3

(a) In a femur, the wall of the diaphysis consists of compact bone.

(b) The epiphyses of the femur contain spongy bone enclosed by a thin layer of compact bone. (c) This skull bone contains a layer of spongy bone sandwiched between plates of compact bone.

Marrow exists in two forms, red marrow and yellow marrow, described later in the chapter (see also fig. 7.2).

Essentials of Human Physiology

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