They remove bone structure by releasing lysosomal enzymes and acids that dissolve the bony matrix. Osteoclasts are large bone cells with up to 50 nuclei. Osteoblasts become trapped in these secretions and differentiate into less active osteocytes. Osteoblasts synthesize and secrete the organic part and inorganic part of the extracellular matrix of bone tissue, and collagen fibers. Osteoblasts are bone cells that are responsible for bone formation.
Trabeculae in spongy bone are arranged such that one side of the bone bears tension and the other withstands compression.īone consists of four types of cells: osteoblasts, osteoclasts, osteocytes, and osteoprogenitor cells. The neck of the femur must be strong enough to transfer the downward force of the body weight horizontally to the vertical shaft of the femur (Figure 19.20).
The weight of the body pushes it down near the joint, but the vertical diaphysis of the femur pushes it up at the other end. The neck of the femur is horizontal like the toothpick in the wall. The toothpick will break off right at the wall. The force on the picture is straight down to the floor, but the force on the toothpick is both the picture wire pulling down and the bottom of the hole in the wall pushing up. In this case, the function of the toothpick is to transmit the downward pressure of the picture to the wall. Now drill a hole and stick the toothpick into the wall to hang up the picture. You could hold up one side of the picture with a toothpick if the toothpick was perpendicular to the floor and the picture. Imagine laying a heavy framed picture flat on the floor.
The epiphyses of bones, such as the neck of the femur, are subject to stress from many directions. Spongy bone is prominent in areas of bones that are not heavily stressed or where stresses arrive from many directions. Spongy bone reduces the density of bone and allows the ends of long bones to compress as the result of stresses applied to the bone. The red bone marrow of the femur and the interior of other large bones, such as the ileum, forms blood cells. Blood vessels within this tissue deliver nutrients to osteocytes and remove waste. Red bone marrow is found between the trabuculae. Instead, it consists of trabeculae, which are lamellae that are arranged as rods or plates. Spongy bone tissue does not contain osteons that constitute compact bone tissue. Whereas compact bone tissue forms the outer layer of all bones, spongy bone or cancellous bone forms the inner layer of all bones.
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