Survival Needs
The goal of nearly all body systems is to maintain life. However, life is
extraordinarily fragile and requires that several factors be available. These
factors, which we will call survival needs, include nutrients (food), oxygen,
water, and appropriate temperature and atmospheric pressure.
Nutrients, which the body takes in through food, contain the chemicals used
for energy and cell building. Carbohydrates are the major energy-providing fuel
for body cells. Proteins and, to a lesser extent, fats are essential for building cell
structures. Fats also cushion body organs and provide reserve fuel. Minerals
and vitamins are required for the chemical reactions 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,
human cells can survive for only a few minutes without it. 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 fluid base for body
secretions and excretions. We obtain water chiefly from ingested foods or
liquids, and we lose it by evaporation from the lungs and skin and in body
excretions.
If chemical reactions are to continue at life-sustaining levels, normal body
temperature must be maintained. As body temperature drops below 37°C
The goal of nearly all body systems is to maintain life. However, life is
extraordinarily fragile and requires that several factors be available. These
factors, which we will call survival needs, include nutrients (food), oxygen,
water, and appropriate temperature and atmospheric pressure.
Nutrients, which the body takes in through food, contain the chemicals used
for energy and cell building. Carbohydrates are the major energy-providing fuel
for body cells. Proteins and, to a lesser extent, fats are essential for building cell
structures. Fats also cushion body organs and provide reserve fuel. Minerals
and vitamins are required for the chemical reactions 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,
human cells can survive for only a few minutes without it. 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 fluid base for body
secretions and excretions. We obtain water chiefly from ingested foods or
liquids, and we lose it by evaporation from the lungs and skin and in body
excretions.
If chemical reactions are to continue at life-sustaining levels, normal body
temperature must be maintained. As body temperature drops below 37°C
