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Chapter 27
Lecture Outline
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1
27.1
Introduction to
Nutrition
Learning
Objectives:
1.
Define both nutrition and
nutrients.
2.
Distinguish macronutrients
from micronutrients and
essential from nonessential
nutrients.
3.
Explain the meaning of
recommended daily
allowance (RDA).
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2
27.1 Introduction to Nutrition
• Nutrition—study of how living organisms obtain and utilize
nutrients needed to grow and sustain life
• Nutrients
–
–
–
–
–
–
Include most biomolecules, vitamins, and minerals
Required for synthesis of new molecules
Required for energy for maintenance, growth, and repair
Obtained through food
Water is considered a nutrient
Levels regulated during and following meals
3
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27.1 Introduction to Nutrition
• Categories of nutrients
– Macronutrients
o Must be consumed in relatively large quantities
o Needed in daily amounts
o All are organic molecules
– Carbohydrates, lipids, proteins
– Micronutrients
o Must be consumed in relatively small quantities
o Vitamins and minerals
– Essential
o Must be obtain and absorbed via digestive system from diet
– Nonessential
o Provided by biochemical processes of body
o Not required in diet
4
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27.1 Introduction to Nutrition
• Recommended daily allowance (RDA)
– Amount of each nutrient that must be obtained each day
– Established values for nutrients set by federal agencies
o Originally established by Food and Nutrition Board
o Reviewed and updated periodically
o Used for food planning, food labeling, education, etc.
o In the future your RDA could be based on your genetic makeup
5
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27.2
Macronutrients
Learning
Objectives:
1.
Identify the categories that are dietary
sources of carbohydrates, and give
examples of each category.
2.
Identify the types and dietary sources
of triglycerides, and describe their
function.
3.
Describe the sources and functions of
cholesterol.
4.
Describe why protein is required in
our diet and the general amount that is
needed.
5.
Explain the difference between a
complete protein and an incomplete
protein.
6.
Discuss nitrogen balance and include
the difference between a positive and
negative nitrogen balance.
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6
27.2 Macronutrients
• All macronutrients provide fuel for cellular
respiration to form ATP (i.e., they provide energy)
• This energy is measure in calories
̶
̶
Calorie = the amount of heat required to raise the
temperature of 1 g of water by 1ºC
Kilocalorie = 1000 calories, 1 Calorie
• Body weight is maintained when calories consumed
and calories expended are in balance
7
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27.2a Carbohydrates
• Carbohydrates
– Structurally classified as
o Monosaccharides
o Disaccharides
o Polysaccharides
– When describing dietary sources, classified as
o Sugars
o Starch
o Fiber
8
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27.2a Carbohydrates
• Sugars
̶
Include monosaccharides
̶
o Glucose
o Fructose
o Galactose
Include disaccharides
̶
o Sucrose (e.g., table sugar, syrup, fruits)
o Lactose (e.g., milk sugar)
o Maltose (e.g. found in cereals)
Other sugars
o Dextrose, brown sugar, honey, molasses, etc.
9
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27.2a Carbohydrates
• Starch
̶
Polysaccharide polymer of glucose molecules found in certain
foods
o E.g., tubers, grains, beans and peas
̶
Refined starches sometimes added as thickeners, stabilizers
o E.g., cornstarch
• Fiber
̶ Includes fibrous molecules of both plants and animals
̶ Cannot be chemically digested and absorbed by GI tract
̶ Sources
o Lentils, peas, beans, whole grains, oatmeal, berries, nuts
10
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11
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27.2a Carbohydrates
• Sugars and starch usually converted to glucose
̶
̶
Primary energy-supplying nutrient
Glucose not considered essential
o Can be synthesized from other monosaccharides by
gluconeogenesis
• Fiber serves different purpose
̶
Adds bulk
̶
o Stimulates peristalsis
o “Keeps you regular”
Lowers cholesterol
12
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27.2b Lipids
• Lipids include
̶
̶
Triglycerides
Phospholipids
Steroids
Eicosanoids
̶
̶
• Triglycerides—composed of glycerol and fatty acids
• Fatty acids organized into 3 categories—saturated,
unsaturated, polyunsaturated
̶
Depends on degree of saturation
13
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27.2b Lipids
• Saturated fatty acids
̶
̶
No double bond
Sources are solid at room temperature
Dietary sources
̶
o Fat in meat, milk, cheese, coconut oil, palm oil
• Unsaturated fatty acids
̶
̶
̶
One double bond
Sources are liquid at room temperature
Dietary sources
o Nuts, certain oils—canola oil, olive oil, sunflower oil
14
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27.2b Lipids
• Polyunsaturated fatty acids
̶
̶
̶
Two or more double bonds
Sources are liquid at room temperature
Dietary sources
o Certain oils—soybean oil, corn oil, safflower oil
15
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27.2b Lipids
• Cholesterol
̶
̶
̶
Required as component of plasma membrane
Precursor hormone for steroid hormones, bile salts,
vitamin D
Comes from diet or metabolic pathway in liver
16
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27.2c Proteins
• Proteins
– Most structurally and functionally diverse molecules
– Needed in adequate quantities to replace worn out protein
structures
o Amount needed depends on age and sex
o More needed to fight an infection, following an injury, stressful
conditions, pregnancy
o Infants and children also need more for growth
– 8 amino acids are essential, other 12 can be synthesized in the
body
17
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27.2c Proteins
• Proteins (continued)
• Complete proteins
̶
̶
Contain all essential amino acids
Generally animal proteins
• Incomplete proteins
̶
̶
Do not contain all essential amino acids
Generally plant proteins
o Combinations of dishes containing plant proteins can provide all
essential amino acids
• No storage of excess, so must be supplied regularly
18
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27.2c Proteins
• Proteins (continued)
• Vegetarian—Does not eat meat, poultry, fish
– Lacto-ovo vegetarians
o Do not eat animal flesh, but eat milk, eggs, and cheese
– Vegans
o Do not eat any animal products
– Plant-based protein sources often individually incomplete
o Must obtain essential amino acids through complementary protein
sources
o Not necessarily eaten at the same meal, but regularly
19
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27.2c Proteins
• Nitrogen balance
– Proteins are a source of nitrogen
o Needed for synthesizing nitrogen-containing molecules
o E.g., DNA, RNA, porphyrin
– When equilibrium exists between dietary intake and loss
o Positive nitrogen balance, absorbing more nitrogen than excreted
– E.g., during growth, pregnancy, recovering from injury
o Negative nitrogen balance, more nitrogen excreted than absorbed
– E.g., during blood loss, malnutrition
– Can be fatal
20
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What did you
learn?
•
Which nutrient is a type of lipid
that is a component of all animalbased products and is a precursor
molecule for the formation of
steroid hormones, bile salts, and
fat-soluble vitamins?
•
What type of protein supplies all of
the essential amino acids?
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21
27.3
Micronutrients
Learning
Objectives:
1.
Distinguish between watersoluble and fat-soluble vitamins.
2.
List examples of how both
water-soluble and fat-soluble
vitamins function in the body.
3.
Describe the difference between
essential and nonessential
vitamins
4.
Define minerals, and list
examples of how minerals
absorbed in the small intestine
function in the body.
5.
Distinguish between major
minerals and trace minerals.
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22
27.3 Micronutrients
• Vitamins and minerals
–
–
–
–
–
Obtained primarily in foods, plants being a good source
Each type of food with a variety
No one food contains all we require
Variety is necessary in the diet to meet body’s needs
Can be obtained through supplements
23
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27.3a Vitamins
• Vitamins
–
–
–
–
Organic molecules required for normal metabolism
Present in only small amounts in food
Water-soluble or fat-soluble
Essential or nonessential
• Water-soluble vitamins
–
–
–
–
–
Dissolve in water
B vitamins and vitamin C
Easily absorbed into blood from digestive tract
Excess excreted in urine
Some coenzymes assist with normal enzyme function
24
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27.3a Vitamins
• Fat-soluble vitamins
̶
̶
̶
̶
̶
̶
Dissolve in fat
Vitamins A, D, E, and K
Absorbed from GI tract within micelles
Excess stored in fat
May become toxic if taken in excess
Functions
o Vitamin A, precursor of visual pigment retinal
o Vitamin D, forms calcitriol, increases calcium absorption from GI
tract
o Vitamin E, stabilizes and prevents damage to cell membranes
o Vitamin K, required for synthesis of blood clotting proteins
25
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27.3a Vitamins
• Essential and nonessential vitamins
– Essential vitamins
o Necessary from diet
o Deficiency if intake or absorption is impaired
o E.g., vitamin C, Vitamin A
– Nonessential vitamins
o Cofactors body produces and recycles as needed
o E.g., NADH, FADH2
See Table 27.2: Vitamins Required by Adults
26
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27.3b Minerals
• Minerals
– Inorganic ions obtained from diet
o Required in daily amounts
– Iron
o In hemoglobin, binds oxygen
o In mitochondria, in electron transport system binds electrons
– Calcium
o Required for formation and maintenance of skeleton and muscle
contraction, blood clotting, and exocytosis of neurotransmitters
27
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27.3b Minerals
• Minerals (continued)
– Sodium and potassium
o Maintain resting membrane potential in excitable cells
o Required to generate action potential
– Iodine
o Needed to produce thyroid hormone
– Zinc
o Roles in protein synthesis and wound healing
– All minerals are essential and must be obtained from the diet
28
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27.3b Minerals
• Minerals (continued)
– Major minerals
o >100 mg/day required
o E.g., calcium, chloride, potassium, phosphorus, magnesium, etc.
– Trace minerals
o <100 mg/day required
o E.g., chromium, copper, iodine, iron, zinc, etc.
– Stored to varying degrees within body
• Foods can be fortified
– Adding one or more essential nutrients
See Table 27.3: Minerals Required by Adults
29
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Clinical View: Iron Deficiency
• Iron required in hemoglobin and myoglobin
• Component of electron transport proteins
• Needed to synthesize
̶ Certain hormones, neurotransmitters, and amino acids
• Obtained from:
̶ Meat, poultry, fish, dark leafy vegetables, nuts, and whole
grains
• Most common nutritional deficiency
• Fatigue, weakness, pale skin, and sensitivity to cold
• Insufficient intake or iron loss
̶ E.g., excessive loss from bleeding
30
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What did you
learn?
•
Which vitamins are fat-soluble?
•
What is the difference between
major and trace minerals?
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31
27.4
Guidelines for
Adequate
Nutrition
1.
Describe MyPlate, which was
developed by the USDA to
help people eat healthy.
2.
Identify the items that are
included on a food label.
Learning
Objectives:
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32
27.4 Guidelines for Adequate Nutrition
• MyPlate
– United States
Department of
Agriculture (USDA)
recommendation
o Visual representation
of desired
proportions of food
Figure 27.1
33
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27.4 Guidelines for Adequate Nutrition
• Nutritional food labels
– Provide details on composition
of prepackaged items
o Serving size, calories, total fat,
cholesterol, sodium, etc.
o Helpful for meal planning
– To promote health in well
individuals
– For those with special dietary
needs
Figure 27.2
Martin Shields/Photo Researchers, Inc.
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34
What did you
learn?
•
What are the five categories of
food included in the USDA’s
MyPlate?
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35
27.5
Regulating
Blood Levels
of Nutrients
1.
Explain when the absorptive
state occurs and how nutrient
levels are regulated during
this time.
2.
Explain when the
postabsorptive state occurs,
and how nutrient levels are
regulated during this time.
Learning
Objectives:
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36
27.5a Absorptive State
• Absorptive state
– Time eating, digesting, and absorbing nutrients
– Lasts 4 hrs after a meal
– Concentrations of glucose, triglycerides, and amino acids
o Increase as absorbed from GI tract
– Blood glucose levels maintained within 70 to 110 mg/dL
37
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27.5a Absorptive State
• Insulin
– Major regulatory hormone released during absorptive state
– Released from pancreas in response to increased blood
glucose levels
– Stimulates liver and muscle cells
o Form glycogen from glucose
– Affects adipose tissue
o Increases uptake of triglycerides from blood
o Stimulates lipogenesis and inhibits lipolysis
– Stimulates most cells to increase amino acid uptake
o Causes accelerated protein synthesis
38
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Absorptive State
Figure 27.3
39
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27.5b Postabsorptive State
• Postabsorptive state
– Time between meals
o Body relying on stores of nutrients
o Body working to maintain homeostatic levels of nutrients
40
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27.5b Postabsorptive State
• Glucagon
– Major regulatory hormone released during postabsorptive
state
– Released in response to decreasing blood glucose levels
– Stimulates liver to increase breakdown of glycogen to glucose
– Stimulates gluconeogenesis from noncarbohydrate sources
– Causes adipose tissue to break down triglycerides
– No effect on amino acids or proteins in cells
41
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Postabsorptive State
Figure 27.4
42
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What did you
learn?
•
Contrast the role of insulin
and glucagon in stimulating
liver cells.
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43
27.6
Functions of the
Liver
Learning
Objectives:
1.
Describe the anatomic
arrangement of liver lobules,
including the central vein,
hepatocytes, sinusoids, and
bile canaliculi.
2.
Explain the relationship of
dietary intake of cholesterol
and level of cholesterol
synthesis in the liver.
3.
Describe the transport of
lipids within the blood.
4.
Identify and briefly describe
the numerous roles of the
liver in metabolism.
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44
27.6a Anatomy of Liver Lobules
• Liver lobules
– Functional unit of liver
– Cords of hepatocytes radiating out from central vein
o Sinusoids located between cords of hepatocytes
o Contain oxygenated blood from hepatic artery
o Contains deoxygenated blood from hepatic portal vein
o Flows out via hepatic veins to inferior vena cava
– Bile canaliculi sandwiched between hepatocyte cords
o Drains into ducts until it enters small intestine
45
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The Liver and Cholesterol Synthesis
Figure 27.5a
46
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27.6b Cholesterol Synthesis
• Cholesterol synthesis
– Synthesized in liver
– Fatty acids transported in blood to enter hepatocytes
o Broken down into two-carbon units, acetyl CoA (beta oxidation)
o Molecules used to synthesize cholesterol
o Produces cholesterol at basal level, varies among individuals
o Synthesis decreased with higher cholesterol intake and vice versa
– Following its formation
o Released into blood in very-low-density lipoproteins, or
o Synthesized into bile salts as part of bile
˗ 90% of these reabsorbed while moving through ileum
47
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The Liver and Cholesterol Synthesis
Figure 27.5b
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48
What did you
learn?
•
With increased cholesterol
intake, what is the liver’s
response in its rate of
cholesterol synthesis?
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49
27.6c Transport of Lipids
• Lipoproteins
– Lipids with protein “wrap” to facilitate transport
– E.g., chylomicrons
o Absorbed lipids from the small intestine
– Other lipoproteins form in liver
o Classified by relative density
– Very-low-density lipoproteins (VLDL), contain the most lipid
– Low-density lipoproteins (LDL) with less lipid
– High-density lipoproteins (HDL) with least amount of lipid
50
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27.6c Transport of Lipids
• Transport from the liver to peripheral tissues
• VLDLs and LDLs involved
– Very-low-density lipoproteins (VLDLs)
o Various types of lipids with protein
o Assembled within liver and released into blood
o Circulate in blood, release triglycerides to peripheral tissues
– Primarily adipose tissue
o With release of triglycerides, becomes low-density lipoprotein
51
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27.6c Transport of Lipids
• Transport from the liver to peripheral tissues
(continued)
– Low-density lipoproteins (LDLs)
o Contain high amounts of cholesterol
o Deliver cholesterol to cells
o Bind to LDL receptors in plasma membrane of cell
o Engulfed by endocytosis
o Cholesterol incorporated into plasma membrane
o Used by certain tissues to produce steroid hormones
52
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27.6c Transport of Lipids
• Transport from peripheral tissues to the liver
– High-density lipoproteins (HDLs)
o Proteins formed in liver
o Released into blood without addition of lipid
o Circulate through blood and “fill” with lipids from peripheral tissue
o Make cholesterol available to steroid-producing tissue
o Lipids transported via HDLs to liver
o Excess cholesterol converted to bile salts within the liver
53
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Lipid Transport
Figure 27.6
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54
27.6d Integration of Liver Structure
and Function
• The liver is responsible for many metabolic processes
–
–
–
–
–
Carbohydrate metabolism
Protein metabolism
Lipid metabolism
Transport of lipids
Other functions
o E.g., storage and drug detoxification
55
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Carbohydrate Metabolism
Figure 27.7b
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56
Protein Metabolism
Figure 27.7c
57
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Lipid Metabolism
Figure 27.7d
58
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Lipid Transport
Figure 27.7e
59
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Figure 27.7f
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60
Clinical View: Blood Cholesterol Levels
• High levels of LDLs or total cholesterol and low
blood level of HDLs
̶ Risk factors for cardiovascular disease
̶ Above 200 mg/dL total cholesterol considered “high”
• LDLs considered “bad cholesterol”
̶ Excess cholesterol deposited on inner arterial walls
• HDLs considered “good cholesterol”
̶ Transport lipid from arterial wall to liver
61
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Clinical View: Blood Cholesterol Levels
(continued)
• Risk factors correlated with high cholesterol
̶ High saturated fat intake, cigarette smoking, caffeine intake,
and stress
• Statin drugs
̶ Developed to lower blood cholesterol
̶ Inhibitor for HMG-CoA, enzyme needed for cholesterol
synthesis
62
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What did you
learn?
•
Which of these molecular
structures (VLDLs, LDLs, or
HDLs) is responsible for
transporting cholesterol from
peripheral tissues to the liver?
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63
27.7
Central Role
of Cellular
Respiration
1.
Describe where the following
nutrient molecules enter the
metabolic pathway of cellular
respiration: glucose, the
breakdown products of
triglycerides, and amino
acids.
2.
Explain deamination of
proteins.
3.
Describe the physiologic
advantages of the ability to
interconvert nutrient
biomolecules.
Learning
Objectives:
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64
27.7a ATP Generation
• Four stages of cellular respiration
1. Glycolysis
̶ Anaerobic metabolic pathway in cytoplasm
̶ Glucose oxidized to 2 pyruvate molecules
̶ 2 ATP formed, 2 NADH formed from NAD+
̶ Pyruvate converted to lactate if insufficient O2 available
2. Intermediate stage
̶ This and following steps, aerobic and within the
mitochondria
̶ Pyruvate converted to acetyl CoA
̶ CO2 formed and NADH produced
65
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27.7a ATP Generation
• Four stages of cellular respiration (continued)
3. Citric acid cycle
̶ Acetyl CoA forms citric acid
̶ CO2, ATP, FADH2, and NADH produced in cycle
“turn”
4. Electron transport system
̶ Transfer of hydrogen and electron from NADH and
FADH2
̶ ATP formed through oxidative phosphorylation
66
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27.7a ATP Generation
• Glycerol and fatty acids
– Building blocks of triglycerides
– Glycerol enters pathway of glycolysis
o Converted to glucose within the liver
– Carbons of fatty acids removed to form acetyl CoA
o Beta oxidation
o Molecules enter citric acid cycle
67
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27.7a ATP Generation
• Amino acids
– May be used to generate ATP
– Amine group of amino acids removed by deamination
o Occurs within liver hepatocytes
o Amine group converted to urea
o Eliminated through kidney in urine
– Remainder enters metabolic pathway at different steps
o Depends on specific amino acid
o May enter glycolysis, intermediate stage, or citric acid cycle
68
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Cellular
Respiration:
Generation of
ATP Molecules
and
Interconversion
of Nutrient
Molecules
Figure 27.8
69
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27.7b Interconversion of Nutrient Biomolecules
and Their Building Blocks
• Nutrient interconversion
– Changing of one nutrient biomolecule into another
– Due to biochemical pathways associated with cellular
respiration
o E.g., glucose broken down to acetyl CoA
˗ Then synthesized into triglycerides and stored
˗ Instead of entering citric acid cycle
o E.g., protein and fat consumed in low-carbohydrate diet
˗ Reversal of biochemical pathways of cellular respiration
˗ Converted to glucose
70
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What did you
learn?
•
Where in the biochemical pathway
of cellular respiration does glycerol
enter? Fatty acids?
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71
27.8
Energy and
Heat
1.
Define metabolic rate.
2.
Explain how both basal
metabolic rate and total
metabolic rate are measured,
and the variables that
influence each.
3.
Define core body
temperature, and explain why
it must be maintained.
4.
Explain the neural and
hormonal controls of
temperature regulation.
Learning
Objectives:
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72
27.8a Metabolic Rate
• Metabolic rate
̶ Measure of energy used in a given period of time
̶ Basal metabolic rate and total metabolic rate
• Basal metabolic rate (BMR)
̶ Amount of energy used at rest
̶ Individual not eaten for 12 hours, relaxed, temperature
about 20°C
̶ Measured by calorimeter or respirometer
73
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27.8a Metabolic Rate
• Basal metabolic rate (BMR) (continued)
– Calorimeter
o Person placed in water-filled chamber
o Heat released from body alters temperature of water
o Change in temperature measured
– Respirometer
o Instrument measures oxygen consumption
o Indirect measure BMR
– Oxygen used to produce ATP
– ATP utilized to produce heat
74
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27.8a Metabolic Rate
• Basal metabolic rate (BMR) (continued)
– Varies due to age, lean body mass, sex, and levels of
hormones in the blood
– Decreases with age—3% each decade beginning ~30
– Greater lean body mass = higher BMR
– Thyroid hormone increases BMR
o Hypothyroidism = lower than normal BMR
o Hyperthyroidism = higher than normal BMR
– Body surface area is important factor
o Greater surface area of skin, more heat lost
o More heat lost, more active body cells must be to maintain
temperature
75
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27.8a Metabolic Rate
• Total metabolic rate (TMR)
– BMR + metabolism associated with physical activity
– Depends on several factors
o Amount of skeletal muscle and its activity
– E.g., rapid increase during vigorous exercise
o Food intake
– E.g., increases following ingestion of a meal, but decreases after
absorption
o Changing environmental conditions
– Increases if exposed to cold temperature
76
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27.8b Temperature Regulation
• Temperature homeostasis
– Variable heat produced due to variable metabolic rate
– Body temperatures maintained within certain physiological
limits
o Near normal value of 98.6°F (37°C)
o Neural and hormonal controls
– Core body temperature
o Temperature of vital portions of body—head and torso
o Temperature kept relatively constant
o Maintained by allowing fluctuations in peripheral regions
77
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27.8b Temperature Regulation
• Nervous system control
– Mediated through hypothalamus
o Motor pathways to sweat glands, skeletal muscles, and
peripheral blood vessels
o Monitors temperature of blood
– With increase in body temperature
o Hypothalamus stimulates sweat glands
o Vasodilates peripheral vessels
78
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27.8b Temperature Regulation
• Nervous system control (continued)
– With decrease in body temperature
o Hypothalamus inhibits sweat glands
o Vasoconstricts peripheral vessels
o Induces skeletal muscles contraction to generate heat (shivering)
– Behavior changes initiated in cortex in response to
temperature
o E.g., putting on a coat if cold
o E.g., jumping into a pool when hot
79
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Nervous System
Control of Body
Temperature
Figure 27.9
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80
27.8b Temperature Regulation
• Hormonal control
– Mediated by multiple hormones
o Thyroid, epinephrine, norepinephrine, growth hormone, and
testosterone
– Thyroid hormone, most significant
o Establishes metabolic rate
o Raises body temperature by increasing rate of all cells
o If temperature drops, hypothalamus releases thyrotropin-releasing
hormone
o Stimulates thyroid-stimulating hormone from anterior pituitary
o Stimulates thyroid gland to release thyroid hormones
81
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Clinical View: Frostbite and Dry Gangrene
• Frostbite
̶ Damage to superficial cells due to extreme cold
̶ Skin white with possible loss of sensation
• Dry gangrene
̶ May be caused by severe frostbite
̶ Body part dry, distinct in color, shriveled
̶ Due to extensive vasoconstriction of blood vessels in
response to cold
̶ Oxygen deprivation and tissue death
82
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What did you
learn?
•
Which method of measuring BMR
is considered an indirect method?
•
What motor outputs are stimulated
by the hypothalamus in response to
a temperature decrease?
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83