The human body is composed of organs, muscles, bones, and fat. Muscle and fat tissues take up more or less space depending upon the body composition of the person in question. The 11 major organ systems and the skeletal system make up the remainder of the body.
Bones
According to Gillian Houghton in her book, "Bones: the Skeletal System," the adult human body has 206 bones, while an infant is born with around 270. Some bones fuse together during development. The skull starts out in 22 pieces, including the mandible, and joins together with sutures. Bones exist to protect organs, support the body, and provide movement. Bones also produce red and white blood cells within the marrow, and store all minerals essential for life. Bones are made up of periosteum, compact bone, cancellous bone, and bone marrow. Houghton estimates that bones make up roughly 15 percent of the average adult's total body mass.
Fat
Adipose tissue, commonly called fat, is loose connective tissue which stores energy, cushions the body, provides buoyancy, and insulates the organs. Fat is found within bones, in breast tissue, around the organs, and under the skin. According to the American College of Sports Medicine, athletes who are extremely lean have between 6 and 11 percent body fat, while the average person has between 15 and 25 percent body fat. Obese or overly fat persons have body fat over 25 percent.
Muscle
Muscles are the contractive tissue of humans, responsible for motion. Muscles may work either voluntarily, such as skeletal muscles, or involuntarily, like the heart. There are three types of muscle in the human body: skeletal, smooth, and cardiac. According to Elaine and Hoehn, in their book "Human Anatomy and Physiology," the average male adult is made up of approximately 42 percent skeletal muscle while females are made up of approximately 36 percent of skeletal muscle. Smooth muscles are found within the intestines, lungs, bladder, urethra, uterus (in women), stomach, blood vessels, and the esophagus, and are not controlled by conscious thought.
Body Composition
Human body composition may be determined by a number of different tests. Hydrostatic weighing uses water displacement to estimate the amount of lean tissue versus adipose tissue. Another fairly accurate test is dual-emission X-ray absorptiometry, called DXA, which uses two x-ray beams of different energy levels. Soft-tissue absorption is subtracted and bone density can be determined by the amount of beam absorption into bone. The DXA test may also be used to determine body composition fairly accurately. Less accurate tests used to determine body composition are the Body Mass Index, bioelectrical impedance analysis, and caliper testing.
References
- "Bones: the Skeletal System"; Gillian Houghton, 2007
- American College of Sports Medicine Resources for the Personal Trainer, 2007
- "Sports Medicine Essentials: Core Concepts in Athletic Training and Fitness"; Jim Clover; 2001
- "Human Anatomy & Physiology"; Marieb, Elaine; Katja Hoehn, 2007
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