Chapter 25, part 1

1. Chapter 25, part 1 Metabolism and Energetics

2. Learning Objectives • Understand the functions of metabolic and anabolic dynamics • Summarize the characteristics of the absorptive and postabsorptive metabolic states • Explain what constitutes a balanced diet and why such a diet is important • Define metabolic rate and discuss the factors involved in determining an individual’s BMR

3. SECTION 25-1An Overview of Metabolism

4. Metabolism • Metabolism is all the chemical reactions that occur in an organism • Cellular metabolism • Cells break down excess carbohydrates first, then lipids • Cells conserve amino acids • 40% of the energy released in catabolism is captured in ATP • Rest is released as heat

5. Figure 25.1 An Introduction to Cellular Metabolism Figure 25.1

6. Anabolism • Performance of structural maintenance and repairs • Support of growth • Production of secretions • Building of nutrient reserves

7. Figure 25.2 Metabolic Turnover and Cellular ATP Production Figure 25.2

8. Cells and Mitochondria • cells provide small organic molecules for their mitochondria • Mitochondria produce ATP used to perform cellular functions

9. Homeostasis • No one cell of the human body can perform all necessary homeostatic functions • Metabolic activities must be coordinated

10. Body has five metabolic components • Liver • The focal point for metabolic regulation and control • Adipose tissue • Stores lipids primarily as triglycerides • Skeletal muscle • Substantial glycogen reserves

11. Body has five metabolic components • Neural tissue • Must be supplied with a reliable supply of glucose • Other peripheral tissues • Able to metabolize substrates under endocrine control

12. The absorptive state • The period following a meal • Nutrients enter the blood as intestinal absorption proceeds • Liver closely regulates glucose content of blood • Lipemia commonly marks the absorptive state • Adipocytes remove fatty acids and glycerol from bloodstream • Glucose molecule are catabolized and amino acids are used to build proteins

13. Figure 25.15 The Absorptive State Figure 25.15

14. The Postabsorptive state • From the end of the absorptive state to the next meal • Body relies on reserves for energy • Liver cells break down glycogen, releasing glucose into blood • Liver cells synthesize glucose • Lipolysis increases and fatty acids released into blood stream • Fatty acids undergo beta oxidation and enter TCA

15. The Postabsorptive state • Amino acids either converted to pyruvate or acetyl-CoA • Skeletal muscles metabolize ketone bodies and fatty acids • Skeletal muscle glycogen reserves broken down to lactic acid • Neural tissue continues to be supplied with glucose

16. Figure 25.16 Metabolic Reserves Figure 25.16a

17. Figure 25.17 The Postabsorptive State Figure 25.17

18. SECTION 25-7Diet and Nutrition

19. Diet and Nutrition • Nutrition • Absorption of nutrients from food • Balanced diet • Contains all the ingredients necessary to maintain homeostasis • Prevents malnutrition

20. Food • Food groups and food pyramids • Used as guides to avoid malnutrition

21. Food Groups • Six basic food groups of a balance diet arranged in a food pyramid • Milk, yogurt and cheese • Meat, poultry, fish, dry beans, eggs, and nuts • Vegetables • Fruits • Bread, cereal, rice and pasta • Base of pyramid • Fats, oils and sweets • Top of pyramid

22. Figure 25.18 The Food Pyramid and Dietary Recommendations Figure 25.18

23. Nitrogen balance • N compounds contain nitrogen • Amino acids, purines, pyrimidines, creatine, porphyrins • Body does not maintain large nitrogen reserves • Dietary nitrogen is essential • Nitrogen balance is an equalization of absorbed and excreted nitrogen

24. Minerals • Act as co-factors in enzymatic reactions • Contribute to osmotic concentrations of body fluids • Play a role in transmembrane potentials, action potentials • Aid in release of neurotransmitters and muscle contraction • Assist in skeletal construction and maintenance • Important in gas transport and buffer systems • Aid in fluid absorption and waste removal

25. Vitamins • Are needed in very small amounts for a variety of vital body activities • Fat soluble • Vitamins A, D, E, K • Taken in excess can lead to hypervitaminosis • Water soluble • Not stored in the body • Lack of adequate dietary intake = avitaminosis

26. SECTION 25-8Bioenergetics

27. Bioenergetics • The study of acquisition and use of energy by organisms • Energy content of food expressed in Calories per gram (C/g)

28. Food and energy • Catabolism of lipids yields 9.46 C/g • Catabolism of proteins and carbohydrates yields ~4.7 C/g

29. Metabolic rate • Total of all anabolic and catabolic processes underway • Basal metabolic rate (BMR) is the rate of energy used by a person at rest

30. Thermoregulation • Homeostatic regulation of body temperature • Heat exchange with the environment involves four processes: • Radiation • Conduction • Convection • Evaporation

31. Figure 25.19 Routes of Heat Gain and Loss Figure 25.19

32. Regulation of heat gain and loss • Preoptic area of hypothalamus acts as thermostat • Heat-loss center • Heat-gain center • Mechanisms for increasing heat loss include: • Peripheral vasodilation • Increase perspiration • Increase respiration • Behavioral modifications

33. Mechanisms promoting heat gain • Decreased blood flow to the dermis • Countercurrent heat exchange • Shivering thermogenesis and nonshivering thermogenesis • Differs by individuals due to acclimatization

34. Figure 25.20 Countercurrent Heat Exchange Figure 25.20

35. Thermoregulation • Problems in infants • Lose heat quickly due to their small size • Do not shiver • Use brown fat to accelerate lipolysis - energy escapes as heat • Variations in adults • Use subcutaneous fat as an insulator • Different hypothalamic thermostatic settings

36. Pyrexia is elevated body temperature • Fever is body temperature greater than 37.2oC • Can result from a variety of situations including: • Heat exhaustion or heat stroke • Congestive heart failure • Impaired sweat gland activity • Resetting of the hypothalamic thermostat by circulating pyrogens

37. You should now be familiar with: • Why cells need to synthesis new organic components • The characteristics of the absorptive and postabsorptive metabolic states • What constitutes a balanced diet and why such a diet is important • Metabolic rate and the factors involved in determining an individual’s BMR