The Shapes of Bones

Bones are classified into four groups according to their shapes and corresponding functions (fig. 7.1):

1. Long bones are conspicuously longer than wide. Like crowbars, they serve as rigid levers that are

1 skelet = dried up

Table 7.1

Functions of the Skeletal System

Function

Examples or Explanation

Support

Bones of the legs, pelvis, and vertebral column hold up the body; the mandible supports the teeth; nearly all bones provide support for muscles; many other soft organs are directly or indirectly supported by nearby bones.

Protection

Bones enclose and protect the brain, spinal cord, lungs, heart, pelvic viscera, and bone marrow.

Movement

Skeletal muscles would serve little purpose if not for the rigid attachment and leverage provided by bones. Leg and arm movements are the most obvious examples of skeletomuscular movement; a less obvious one is that ventilation of the lungs depends on movement of the ribs by skeletal muscles.

Blood formation

Red bone marrow is the major producer of blood cells, including most cells of the immune system.

Electrolyte balance

The skeleton is the body's main mineral reservoir. It stores calcium and phosphate and releases them according to the body's physiological needs.

Acid-base balance

Bone buffers the blood against excessive pH changes by absorbing or releasing alkaline salts.

Detoxification

Bone tissue removes heavy metals and other foreign elements from the blood and thus reduces their effects on nervous and other tissues. It can later release these more slowly for excretion.

Saladin: Anatomy & I 7. Bone Tissue I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 7 Bone Tissue 219

Ulna

1 jf

Radius

Femur il

Long

Talus

Capitate (carpal) bone s

Sternum

Sphenoid bone ft

Short

Flat

Irregular

Figure 7.1 Classification of Bones by Shape.

acted upon by the skeletal muscles to produce body movements. Long bones include the humerus of the arm, the radius and ulna of the forearm, the metacarpals and phalanges of the hand, the femur of the thigh, the tibia and fibula of the leg, and the metatarsals and phalanges of the feet.

  1. Short bones are more nearly equal in length and width. They include the carpal (wrist) and tarsal (ankle) bones. They have limited motion and merely glide across one another, enabling the ankles and wrists to bend in multiple directions.
  2. Flat bones enclose and protect soft organs and provide broad surfaces for muscle attachment. They include most cranial bones and the ribs, sternum (breastbone), scapula (shoulder blade), and os coxae (hipbone).
  3. Irregular bones have elaborate shapes that do not fit into any of the preceding categories. They include the vertebrae and some of the skull bones, such as the sphenoid and ethmoid.

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