Injury and Repair

Despite their strength, bones will crack or even break if they are subjected to extreme loads, sudden impacts, or stresses from unusual directions. The crack or break is referred to as a fracture. If circulation is maintained and the periosteum survives, healing will occur even if the damage to the bone is severe.

figure 45-5

The cross section in (a) shows the internal structure of compact bone. A micrograph of a Haversian canal (380x) surrounded by lamellae in compact bone is shown in (b).

figure 45-5

The cross section in (a) shows the internal structure of compact bone. A micrograph of a Haversian canal (380x) surrounded by lamellae in compact bone is shown in (b).

Bones of Lead

Millions of Americans have been exposed to lead in the environment. Following exposure to lead, the kidneys excrete most of the metal. But 7 to 10 percent of the remaining lead in the body is stored in bone and can stay there for a lifetime. The rapid bone uptake of lead acts as a detoxifying mechanism. But lead may not be permanently locked in bone. As people age, bone degeneration may occur, releasing lead into the bloodstream. Even very small concentrations of lead in the bloodstream can cause damage to kidneys, and high blood pressure.

The United States has outlawed the addition of lead to gasoline, water pipes, and paint. As a result, people who are now under age 25 may not accumulate as much lead in their bones as people from earlier generations.

Cartilage cells

New bone

Cartilage cells

New blood vessels

New bone

Epiphyseal plate figure 45-6

The epiphyseal plate, found at the ends of immature long bones, such as the fibula shown above, is the site of bone elongation. This region is rich with cartilage cells, which divide, enlarge, and push older cells toward the middle of the bone shaft. As older cells move back, they are replaced by new bone cells, forming new regions of bone. A long bone (a) will grow in length, circumference, and density in this manner, as shown in (b).

LONG-BONE GROWTH (b)

Epiphyseal plate

New blood vessels

LONG-BONE GROWTH (b)

figure 45-6

The epiphyseal plate, found at the ends of immature long bones, such as the fibula shown above, is the site of bone elongation. This region is rich with cartilage cells, which divide, enlarge, and push older cells toward the middle of the bone shaft. As older cells move back, they are replaced by new bone cells, forming new regions of bone. A long bone (a) will grow in length, circumference, and density in this manner, as shown in (b).

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www.scilinks.org Topic: Bones and Joints Keyword: HM60187

www.scilinks.org Topic: Bones and Joints Keyword: HM60187

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