Bones are those individual organs that are elements of the skeletal system. 4-7. TYPES

The individual bones of the skeleton can be categorized into three major groups according to their general shapes:

c. Irregular.



A "typical" long bone, as the name implies, has more length than width. (See Figure 4-1.)

Figure 4-1. "Typical" long bone section.

a. Shaft (Diaphysis). In effect, the long bone has a shaft, with proximal and distal ends. The shaft tends to be cylindrical in form.

(1) It has a cortex (outer portion) of dense bony tissue called compact bone tissue. The cortex is usually thickest at the middle of the shaft.

(2) The inside of the shaft is usually hollow, except that it is filled with yellow marrow (in adults, but red marrow in small children and infants).

b. Ends (Epiphyses). At the ends of the long bone, the cortex is much thinner. Each end is filled with a lattice-or sponge-like network of bony tissue, called cancellous bony tissue. The strands of bone forming this lattice are called trabeculae. The trabeculae are aligned with the lines of applied forces, particularly tension and compression. The spaces within the cancellous bony tissue are filled with red marrow.

c. Some Special Parts. The skeletal muscles pull and create tensions at their attachments to the bone. These tensions will often cause the bone to react and form spines, tubercles, ridges, and the like.

d. Articular Cartilages. The surface of each end of the bone is covered by an articular cartilage. This cartilage is located where the bone contacts another bone at a joint. The cartilage is made up of hyaline-type cartilage tissue. The articular cartilage makes the movement between the bones smoother.

e. Periosteum. The periosteum surrounds the bone, except where the articular cartilages are located. The periosteum is an envelope of the bone and consists mainly of dense FCT. In fact, the periosteum may be considered the outermost portion of the bone.

(1) However, the periosteum has a special layer of cells immediately adjacent to the surface of the bone. Since this layer is able to produce bone material, it is called the osteogenic layer of the periosteum.

(2) When a long bone is fractured or a portion of the bone is lost without losing the periosteum, the fracture is healed by the combined action of the osteogenic layer of the periosteum and the osteoblasts of the bone itself.

f. NAVL. Associated with the periosteum are the "service tissues." These are the NAVL (nerves, arteries, veins, and lymphatics), which nourish and stimulate the living tissues of the bone and periosteum.

(1) Neurovascular bundle. Branches from the main NAVL of the body go as a unit to the bone. This unit, the neurovascular bundle, consists of NAVL within a common fibrous connective sheath.

(2) Branches of neurovascular bundle. Portions of these NAVL spread out through the periosteum as periosteal branches over the outer surfaces of the bone. Other branches penetrate through the cortex of the bone to spread out through the medullary (or marrow) cavity. The holes through the cortex are known as the nutrient canals. The branches are known as the nutrient branches.

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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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