19 Chapter 19: Skeletal System
Bones make good fossils. While the soft tissue of a once living organism will decay and fall away over time, bone tissue will, under the right conditions, undergo a process of mineralization, effectively turning the bone to stone. A well-preserved fossil skeleton can give us a good sense of the size and shape of an organism, just as your skeleton helps to define your size and shape. Unlike a fossil skeleton, however, your skeleton is a structure of living tissue that grows, repairs, and renews itself. The bones within it are dynamic and complex organs that serve a number of important functions, including some necessary to maintain homeostasis.
Learning Objectives
After studying this chapter you should be able to:
- List and describe the functions of bones.
- Describe the difference between compact bone and spongy bone.
- Identify the major bones of the axial and appendicular skeletons as listed in the table below.
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Axial Skeleton Bone (s) Body region Skull Head Mandible Lower jaw Ribs Thoracic cage (chest) Sternum Chest Vertebral column Back Appendicular Skeleton Scapula Shoulder Clavicle Collarbone Humerus Upper arm Radius Forearm Ulna Forearm Carpals Wrist Metacarpals Hand Phalanges Fingers and thumb Pelvis Hip Femur Thigh Patella Knee cap Tibia Lower leg Fibula Lower leg Tarsals Ankle Metatarsals Foot Phalanges Toes
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- Define joints, ligaments, cartilage, and tendons, and understand how they work together to connect bones to each other and muscles to bones.
19.1 Functions of the Skeletal System
Bone, or osseous tissue, is a hard, dense connective tissue that forms most of the adult skeleton, the support structure of the body. In the areas of the skeleton where bones move (for example, the ribcage and joints), cartilage, a semi-rigid form of connective tissue, provides flexibility and smooth surfaces for movement. The skeletal system is the body system composed of bones, cartilage, and ligaments and performs the following critical functions for the human body:
- supports the body
- facilitates movement
- protects internal organs
- produces blood cells
- stores and releases minerals and fat
Support, Movement, and Protection
The most apparent functions of the skeletal system are the gross functions—those visible by observation. Simply by looking at a person, you can see how the bones support, facilitate movement, and protect the human body.
Just as the steel beams of a building provide a scaffold to support its weight, the bones and cartilage of your skeletal system compose the scaffold that supports the rest of your body. Without the skeletal system, you would be a limp mass of organs, muscle, and skin.
Bones also facilitate movement by serving as points of attachment for your muscles. While some bones only serve as a support for the muscles, others also transmit the forces produced when your muscles contract. From a mechanical point of view, bones act as levers and joints serve as fulcrums (Figure 19.2). Unless