The Human Biology chapter provides an overview of the physiology of humans, from the skin inward. In addition
to the skin, the skeletal, muscular, nervous, endocrine, circulatory, respiratory, digestive, excretory, immune, and
reproductive systems are described.
How is the human body similar to a well-tuned machine?
Many people have compared the human body to a machine. Think about some common machines, such as drills and
washing machines. Each machine consists of many parts, and each part does a specific job, yet all the parts work
together to perform an overall function. The human body is like a machine in all these ways. In fact, it may be the
most fantastic machine on Earth.