1. Nutrition, Metabolism, and Body Temperature Regulation
Chapter 25
Nutrition, Metabolism, and Body Temperature Regulation
Part A

2. Nutrition
Nutrient – a substance that promotes normal growth, maintenance, and repair
Major nutrients – carbohydrates, lipids, and proteins
Other nutrients – vitamins and minerals (and technically speaking, water)
Grains, fruits, vegetables, meats and fish, and milk products

3. Nutrition
Figure 25.1

4. Carbohydrates
Complex carbohydrates (starches) are found in bread, cereal, flour, pasta, nuts, and potatoes
Simple carbohydrates (sugars) are found in soft drinks, candy, fruit, and ice cream
Glucose is the molecule ultimately used by body cells to make ATP
Neurons and RBCs rely almost entirely upon glucose to supply their energy needs
Excess glucose is converted to glycogen or fat and stored

5. Carbohydrates
The minimum amount of carbohydrates needed to maintain adequate blood glucose levels is 100 grams per day
Starchy foods and milk have nutrients such as vitamins and minerals in addition to complex carbohydrates
Refined carbohydrate foods (candy and soft drinks) provide energy sources only and are referred to as “empty calories”

6. Lipids
The most abundant dietary lipids, triglycerides, are found in both animal and plant foods
Essential fatty acids – linoleic and linolenic acid, found in most vegetables, must be ingested
Dietary fats:
Help the body to absorb vitamins
Are a major energy fuel of hepatocytes and skeletal muscle
Are a component of myelin sheaths and all cell membranes

7. Lipids Fatty deposits in adipose tissue provide:
A protective cushion around body organs
An insulating layer beneath the skin
An easy-to-store concentrated source of energy
Prostaglandins function in:
Smooth muscle contraction
Control of blood pressure
Inflammation
Cholesterol stabilizes membranes and is a precursor of bile salts and steroid hormones

8. Lipids: Dietary Requirements
Higher for infants and children than for adults
The American Heart Association suggests that:
Fats should represent less than 30% of one’s total caloric intake
Saturated fats should be limited to 10% or less of one’s total fat intake
Daily cholesterol intake should not exceed 200 mg

9. Proteins
Complete proteins that meet all the body’s amino acid needs are found in eggs, milk, milk products, meat, and fish
Incomplete proteins are found in legumes, nuts, seeds, grains, and vegetables
Proteins supply:
Essential amino acids, the building blocks for nonessential amino acids
Nitrogen for nonprotein nitrogen-containing substances
Daily intake should be approximately 0.8g/kg of body weight

10. Proteins: Synthesis and Hydrolysis
All-or-none rule
All amino acids needed must be present at the same time for protein synthesis to occur
Adequacy of caloric intake
Protein will be used as fuel if there is insufficient carbohydrate or fat available

11. Proteins: Synthesis and Hydrolysis
Nitrogen balance
The rate of protein synthesis equals the rate of breakdown and loss
Positive – synthesis exceeds breakdown (normal in children and tissue repair)
Negative – breakdown exceeds synthesis (e.g., stress, burns, infection, or injury)
Hormonal control
Anabolic hormones accelerate protein synthesis

12. Vitamins Organic compounds needed for growth and good health
They are crucial in helping the body use nutrients and often function as coenzymes
Only vitamins D, K, and B are synthesized in the body; all others must be ingested
Water-soluble vitamins (B-complex and C) are absorbed in the gastrointestinal tract
B12 additionally requires gastric intrinsic factor to be absorbed

13. Vitamins
Fat-soluble vitamins (A, D, E, and K) bind to ingested lipids and are absorbed with their digestion products
Vitamins A, C, and E also act in an antioxidant cascade

14. Minerals Seven minerals are required in moderate amounts
Calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium
Dozens are required in trace amounts
Minerals work with nutrients to ensure proper body functioning
Calcium, phosphorus, and magnesium salts harden bone

15. Minerals
Sodium and chloride help maintain normal osmolarity, water balance, and are essential in nerve and muscle function
Uptake and excretion must be balanced to prevent toxic overload

16. Metabolism
Metabolism – all chemical reactions necessary to maintain life
Cellular respiration – food fuels are broken down within cells and some of the energy is captured to produce ATP
Anabolic reactions – synthesis of larger molecules from smaller ones
Catabolic reactions – hydrolysis of complex structures into simpler ones

17. Metabolism
Enzymes shift the high-energy phosphate groups of ATP to other molecules
These phosphorylated molecules are activated to perform cellular functions

18. Stages of Metabolism
Energy-containing nutrients are processed in three major stages
Digestion – breakdown of food; nutrients are transported to tissues
Anabolism and formation of catabolic intermediates where nutrients are:
Built into lipids, proteins, and glycogen
Broken down by catabolic pathways to pyruvic acid and acetyl CoA
Oxidative breakdown – nutrients are catabolized to carbon dioxide, water, and ATP

19. Stages of Metabolism
Figure 25.3

20. Oxidation-Reduction Reaction
Oxidation occurs via the gain of oxygen or the loss of hydrogen
Whenever one substance is oxidized, another substance is reduced
Oxidized substances lose energy
Reduced substances gain energy
Coenzymes act as hydrogen (or electron) acceptors
Two important coenzymes are nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD)

21. Mechanisms of ATP Synthesis: Substrate-Level Phosphorylation
High-energy phosphate groups are transferred directly from phosphorylated substrates to ADP
ATP is synthesized via substrate level phosphorylation in glycolysis and the Krebs cycle
Figure 25.4a

22. Mechanisms of ATP Synthesis: Oxidative Phosphorylation
Uses the chemiosmotic process whereby the movement of substances across a membrane is coupled to chemical reactions
Is carried out by the electron transport proteins in the cristae of the mitochondria
Nutrient energy is used to pump hydrogen ions into the intermembrane space
A steep diffusion gradient across the membrane results
When hydrogen ions flow back across the membrane through ATP synthase, energy is captured and attaches phosphate groups to ADP (to make ATP)

23. Mechanisms of ATP Synthesis: Oxidative Phosphorylation
Figure 25.4b

24. Carbohydrate Metabolism
Since all carbohydrates are transformed into glucose, it is essentially glucose metabolism
Oxidation of glucose is shown by the overall reaction:
C6H12O6 + 6O2  6H2O + 6CO2 + 36ATP + heat
Occurs in three pathways
Glycolysis
Krebs cycle
The electron transport chain and oxidative phosphorylation

25. Carbohydrate Metabolism
Figure 25.5

26. Glycolysis A three-phase pathway in which: Pyruvic acid:
Glucose is oxidized into pyruvic acid
NAD+ is reduced to NADH + H+
ATP is synthesized by substrate-level phosphorylation
Pyruvic acid:
Moves on to the Krebs cycle in an aerobic pathway
Is reduced to lactic acid in an anaerobic environment

27. Glycolysis
Figure 25.6

28. Glycolysis: Phase 1 and 2 Sugar activation Sugar cleavage
Two ATP molecules activate glucose into fructose-1,6-diphosphate
Sugar cleavage
Fructose-1,6-diphosphate is cleaved into two 3-carbon isomers
Dihydroxyacetone phosphate
Glyceraldehyde 3-phosphate

29. Glycolysis: Phase 3 Oxidation and ATP formation
The 3-carbon sugars are oxidized (reducing NAD+)
Inorganic phosphate groups (Pi) are attached to each oxidized fragment
The terminal phosphates are cleaved and captured by ADP to form four ATP molecules
The final products are:
Two pyruvic acid molecules
Two reduced NAD+ (NADH + H+) molecules
A net gain of two ATP molecules