ch01.3 - Maintaining Life

ch01.3 - Maintaining Life - Chapter 1 The Human Body An...

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Respiratory System The job of the respiratory system is to keep the body constantly supplied with oxygen and to remove carbon dioxide. The respiratory system consists of the nasal passages, pharynx, larynx, tra- chea, bronchi, and lungs. Within the lungs are tiny air sacs. It is through the thin walls of these air sacs that gas exchanges are made to and from the blood. Digestive System The digestive system is basically a tube running through the body from mouth to anus. The or- gans of the digestive system include the oral cav- ity (mouth), esophagus, stomach, small and large intestines, and rectum. Their role is to break down food and deliver the products to the blood for dispersal to the body cells. The undigested food that remains in the tract leaves the body through the anus as feces. The breakdown activi- ties that begin in the mouth are completed in the small intestine. From that point on, the major function of the digestive system is to reclaim wa- ter. The liver is considered to be a digestive organ because the bile it produces helps to break down fats. The pancreas, which delivers digestive en- zymes to the small intestine, also is functionally a digestive organ. Urinary System The body produces wastes as by-products of its normal functions, and these wastes must be dis- posed of. One type of waste contains nitrogen (ex- amples are urea and uric acid), which results from the breakdown of proteins and nucleic acids by the body cells. The urinary system removes the nitrogen-containing wastes from the blood and ±ushes them from the body in urine. This system, often called the excretory system, is composed of the kidneys, ureters, bladder, and urethra. Other important functions of this system include main- taining the body’s water and salt (electrolyte) bal- ance and regulating the acid-base balance of the blood. Reproductive System The reproductive system exists primarily to produce offspring. Sperm are produced by the testes of the male. Other male reproductive system structures are the scrotum, penis, accessory glands, and the duct system, which carries sperm to the outside of the body. The ovary of the female pro- duces the eggs, or ova; the female duct system consists of the uterine tubes, uterus, and vagina. The uterus provides the site for the development of the fetus (immature infant) once fertilization has occurred. Maintaining Life Necessary Life Functions Now that we have introduced the structural lev- els composing the human body, the question that naturally follows is: What does this highly organized human body do? Like all complex ani- mals, human beings maintain their boundaries, move, respond to environmental changes, take in and digest nutrients, carry out metabolism, dispose of wastes, reproduce themselves, and grow. We will discuss each of these necessary life functions briefly here and in more detail in later chapters. Organ systems do not work in isolation; in-
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ch01.3 - Maintaining Life - Chapter 1 The Human Body An...

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