Structure of a Long Bone

A typical long bone (Fig. 19-5) has a shaft or diaphysis composed of compact bone tissue. Within the shaft is a medullary cavity containing the yellow form of bone marrow, which is high in fat. The irregular epiph-ysis at either end is made of a less dense, spongy bone tissue containing the blood-forming red bone marrow. A thin layer of cartilage covers the epiphysis and protects the bone surface. Between the diaphysis and the epiphysis at each end of the bone, in a region called the metaphysis, is the growth region or epiphyseal plate. When the bone stops growing in length, this area becomes fully calcified but remains visible as the epiphyseal line. The thin layer of fibrous tissue that covers the outside of the bone, the periosteum, nourishes and protects the bone and also generates new bone cells for growth and repair.

Long bones are found in the arms, legs, hands, and feet. Other types of bones are described as flat (i.e., cranial bones), short (i.e., wrist and ankle bones), or irregular (i.e., facial bones and vertebrae).

Iliac crest Sacrum

Iliac crest Sacrum

The Human Body Health And Disease
FIGURE 19-4. The pelvis. (Reprinted with permission from Cohen BJ, Wood DL. Memmler's The Human Body in Health and Disease. 9th Ed. Philadelphia: Lippincott Williams & Wilkins, 2000.)

Cartilage

Proximal epiphysis

Diaphysis -

Distal epiphysis

Cartilage

Diaphysis -

Structure Long Bone

Artery

Growth lines

Spongy bone (containing red marrow)

Endosteum Compact bone

Medullary cavity

Yellow marrow Periosteum

Artery

FIGURE 19-5. Structure of a long bone. (Reprinted with permission from Cohen BJ, Wood DL. Memmler's The Human Body in Health and Disease. 9th Ed. Philadelphia: Lippincott Williams & Wilkins, 2000.)

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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