Sources of energy can be stored in the body

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Although the cells of the body use energy continuously, most animals do not eat continuously. Therefore, animals must store fuel molecules that can be released as needed between meals.

Carbohydrates are stored in liver and muscle cells as glyco-gen, but the total glycogen store represents only about a day's basal energy requirements (1,500-2,000 Cal). Fat is the most important form of stored energy in the bodies of animals. Not only does fat have more energy per gram than glycogen, but it can be stored with little associated water, making it more compact. Migrating birds store energy as fat to fuel their long flights; if they had to store the same amount of energy as glycogen, they would be too heavy to fly! Proteins are not used as energy storage compounds, although body protein can be metabolized as an energy source of last resort.

If an animal takes in too little food to meet its energy requirements, it is undernourished, and must make up the shortfall by metabolizing some of the molecules of its own body. This consumption of self begins with the energy storage compounds glycogen and fat. Protein loss is minimized

Our major energy reserve is fat; a person of average body weight can survive 4 or 5 weeks without food.

Our major energy reserve is fat; a person of average body weight can survive 4 or 5 weeks without food.

Steps Starvation

,345 Weeks of starvation

Carbohydrate reserves are depleted by only a single day without food intake.

,345 Weeks of starvation

Carbohydrate reserves are depleted by only a single day without food intake.

When body fat has been exhausted, protein is lost at an accelerating rate, with serious consequences.

When body fat has been exhausted, protein is lost at an accelerating rate, with serious consequences.

1857 Animal Fat

50.3 The Course of Starvation (a) In a person subjected to undernutrition, the energy reserves of the body are eventually depleted. (b) The swollen (due to edema) abdomen, face, hands, and feet of this young Somalian girl, as well as her spindly limbs, are symptoms of kwashiorkor. This syndrome results from the body breaking down blood proteins and muscle tissue to obtain needed amino acids.

for as long as possible, but eventually a starving animal begins to break down its own proteins for fuel (Figure 50.3a). The syndrome that results is called kwashiorkor (Figure 50.3b). Blood proteins are among the first to be used, resulting in loss of fluid to the intercellular spaces (edema; see Chapter 49). Additional consequences of protein deficiency are breakdown of the immune system and degeneration of the liver. Muscles waste away, and eventually even brain protein is lost, leading to mental retardation. If starvation continues, the breakdown of body proteins eventually leads to death.

Undernourishment is rampant among people in nonindustrialized and war-torn nations, and a billion people—one-sixth of the world's population—are chronically undernourished. Ironically, one cause of life-threatening undernourishment in Western nations is a self-imposed starvation syndrome called anorexia nervosa that results from a psychological aversion to real or imagined body fat.

When an animal consistently takes in more food than it needs to meet its energy requirements, it is overnourished. The excess nutrients are stored as increased body mass. First, glycogen reserves build up; then additional dietary carbohydrates, fats, and proteins are converted to body fat. In some species, such as hibernators, seasonal overnutrition is an important adaptation for surviving periods when food is not available. In humans, however, overnutrition can be a serious health hazard, increasing the risk of high blood pressure, heart attack, diabetes, and other disorders.

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Responses

  • Oronzo
    Does the plasma membrane store energy?
    7 years ago
  • Goytiom
    Can plasma be restored in the body?
    5 years ago
  • fethawi
    Why store glycojen is known as file reserve in our body?
    2 years ago

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