ch01.4 - Homeostasis

ch01.4 - Homeostasis - Chapter 1: The Human Body: An...

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get rid of the nonuseful substances produced during digestion and metabolism. Several organ systems participate in excretion. For example, the digestive system rids the body of indigestible food residues in feces, and the urinary system disposes of nitrogen-containing metabolic wastes in urine. Reproduction Reproduction, the production of offspring, can occur on the cellular or organismal level. In cellu- lar reproduction, the original cell divides, produc- ing two identical daughter cells that may then be used for body growth or repair. Reproduction of the human organism, or making a whole new per- son, is the task of the organs of the reproductive system, which produce sperm and eggs. When a sperm unites with an egg, a fertilized egg forms, which then develops into a bouncing baby within the mother’s body. The function of the reproduc- tive system is exquisitely regulated by hormones of the endocrine system. Growth Growth is an increase in size, usually accom- plished by an increase in the number of cells. For growth to occur, cell-constructing activities must occur at a faster rate than cell-destroying ones. Survival Needs The goal of nearly all body systems is to maintain life. However, life is extraordinarily fragile and re- quires that several factors be available. These fac- tors, which we will call survival needs, include nu- trients (food), oxygen, water, and appropriate temperature and atmospheric pressure. Nutrients, taken in via the diet, contain the chemicals used for energy and cell building. Car- bohydrates are the major energy-providing fuel for body cells. Proteins and, to a lesser extent, fats are essential for building cell structures. Fats also cush- ion body organs and provide reserve fuel. Minerals and vitamins are required for the chemical reac- tions that go on in cells and for oxygen transport in the blood. All the nutrients in the world are useless unless oxygen is also available, because the chemical reactions that release energy from foods require oxygen. Approximately 20 percent of the air we breathe is oxygen. It is made available to the blood and body cells by the cooperative efforts of the respiratory and cardiovascular systems. Water accounts for 60 to 80 percent of body weight. It is the single most abundant chemical substance in the body and provides the ±uid base for body secretions and excretions. Water is ob- tained chie±y from ingested foods or liquids and is lost from the body by evaporation from the lungs and skin and in body excretions. For good health,
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This note was uploaded on 01/31/2011 for the course BIO 210 taught by Professor S during the Spring '10 term at University of Toronto.

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ch01.4 - Homeostasis - Chapter 1: The Human Body: An...

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