1. Nutrition and Metabolism
Chapter 17
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2. Learning Objectives Lesson 17.1: Nutrition and Metabolism
Explain metabolism, and define and contrast catabolism and anabolism.
Describe the metabolic roles of carbohydrates, fats, proteins, vitamins, and minerals.
Define basal metabolic rate and list some factors that affect it.
Discuss the physiological mechanisms that regulate body temperature.
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Definitions
Nutrition
Food, vitamins, and minerals that are ingested and assimilated into the body (Figure 17-1)
Metabolism
Process of using food molecules as energy sources and as building blocks for our own molecules
Catabolism
Breaks food molecules down, releasing their stored energy; oxygen used in catabolism
Anabolism
Builds food molecules into complex substances
Proper nutrition requires a balance of three basic food types: carbohydrates, fats, and proteins, plus essential vitamins and minerals.
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Food Guide
Figure 17-1: Canada, the United States, and many other countries provide online, individualized food guides that help people determine proper amounts and a healthy balance of nutrients.
is hosted by the United States Department of Agriculture (USDA).
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5. Metabolic Function of the Liver
Secretes bile, which breaks down large fat globules
Helps maintain normal blood glucose level
Helps metabolize carbohydrates, fats, and proteins
Synthesizes several kinds of protein compounds
Removes toxins from the blood
Hepatic portal vein delivers blood directly from the gastrointestinal tract to the liver.
Liver cells carry on the first steps of protein and fat metabolism. These proteins, when released into blood, are called plasma proteins.
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Macronutrients
Dietary sources of nutrients
Macronutrients: Carbohydrates, fats, and proteins
Micronutrients: Vitamins and minerals
Carbohydrate metabolism
Carbohydrates are preferred energy food of the body
Three series of chemical reactions in glucose metabolism (Figure 17-2)
Glycolysis
Changes glucose to pyruvic acid
Anaerobic (uses no oxygen)
Occurs in cytoplasm
Glycolysis occurs in cytoplasm and yields small amount of energy, generating two adenosine triphosphate (ATP) molecules.
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7. Macronutrients (Cont.)
Carbohydrate metabolism
Three series of chemical reactions in glucose metabolism
Citric acid (Krebs) cycle
Changes pyruvic acid to carbon dioxide
Aerobic (requires oxygen)
Occurs in mitochondria
Electron transfer system (ETS)
Transfers energy from high-energy electrons (from citric acid cycle) to ATP molecules
Located in mitochondria
Citric acid occurs in mitochondria and yields large amount of energy (mostly as high energy electrons).
Electron transfer system is located in mitochondria and transfers energy.
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Metabolism of Glucose
Figure 17-2 shows the metabolism of glucose.
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9. Macronutrients (Cont.)
Carbohydrate metabolism
The mitochondrial part of the pathway (citric acid cycle and electron transport system) is aerobic (requires oxygen) and generates up to 36 ATP molecules per original glucose molecule
Carbohydrates are primarily catabolized for energy
Adenosine triphosphate (ATP)
Molecule in which energy obtained from breakdown of foods is stored
Serves as a direct source of energy for cellular work (Figure 17-3)
ATP is made up of an adenosine group and three phosphate groups.
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10. Macronutrients (Cont.)
Carbohydrate metabolism
Storage of glucose
Glucose that is not needed immediately for making ATP is stored as glycogen (a long chain of glucose subunits) in the liver and muscle cells
Glycogenesis
Anabolic process of joining glucose molecules together in a chain to form glycogen (to store glucose for later use)
Glycogenolysis
Catabolic process of breaking apart glycogen chains, releasing individual glucose molecules for use in making ATP
Glycogenesis is carried on chiefly by liver and muscle cells.
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11. Adenosine Triphosphate (ATP)
Figure 17-3, A, shows the structure of ATP. B shows the ATP energy cycle.
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12. Macronutrients (Cont.)
Carbohydrate metabolism
Blood glucose (imprecisely, blood sugar)
Normally stays between about 80 and 110 mg per 100 mL of blood during fasting
Insulin accelerates the movement of glucose out of the blood into cells, therefore decreases blood glucose and increases glucose catabolism
Fat metabolism
Catabolized to yield energy and anabolized to form adipose tissue (Figure 17-4)
Protein metabolism
Primarily anabolized and secondarily catabolized
Fats not needed for catabolism are anabolized to form triglycerides and stored in adipose tissue.
Only about half of the required 20 types of amino acids can be made by the body; the remaining must be supplied in diet.
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13. Catabolism of Nutrients
Figure 17-4: Fats, carbohydrates, and proteins can be converted to products that enter the citric acid cycle to yield energy.
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Micronutrients
Vitamins
Organic molecules that are needed in small amounts for normal metabolism (Table 17-3)
Minerals
Inorganic molecules found naturally in the earth, required by the body for normal function (Table 17-4)
Most vitamins cannot be made in the body, so we must eat them in our food.
Without essential minerals, the brain, heart, and respiratory tract would cease to function.
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Major Vitamins
Table 17-3 shows the major vitamins, their dietary sources, their functions, and the consequences of deficiency.
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Major Minerals
Table 17-4 shows major minerals, their dietary sources, their functions, and symptoms of deficiency.
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17. Regulating Food Intake
Hypothalamic centers
Appetite center: Promotes feeling of hunger
Satiety center: Promotes feeling that we are satisfied or “full”
Our body’s regulation of food intake is complex with many factors including:
Hormones
Neurotransmitters
Emotions
Environmental cues
Food sensations
Habits
Mechanisms for regulating food intake are still not clearly understood.
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Metabolic Rates
Basal metabolic rate (BMR)
Rate of metabolism when a person is resting but awake, is not digesting food, and is comfortably warm
Total metabolic rate (TMR)
Total amount of energy (expressed in calories) used by the body per day (Figure 17-5)
When the number of your calories in your food intake equals your TMR, your weight remains the same.
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19. Basal and Total Metabolic Rates
Figure 17-5 shows the factors that determine the basal and total metabolic rates.
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Body Temperature
Hypothalamus
Regulates the homeostasis of body temperature (thermoregulation) through a variety of processes
Skin
Can cool the body by losing heat from the blood through four processes: radiation, conduction, convection, and evaporation (Figure 17-6)
More than 60% of our energy released from nutrient molecules during catabolism is converted to heat rather than being transferred to ATP.
When the body is overheated, blood flow to the skin increases.
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21. Mechanisms of Heat Loss
Figure 17-6 shows the four mechanisms of heat loss.
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Questions?
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