Nutrition, Metabolism, and Body Temperature Regulation

1
Chapter 24

• Nutrition, Metabolism, and Body Temperature
  Regulation

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)

3
USDA Food Guide Pyramid
Figure 24.1a
4
Nutrition
Figure 24.1b
5
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

6
Carbohydrates

• 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

7
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

8
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

9
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

10
Lipids

• Prostaglandins function in
• Smooth muscle contraction
• Control of blood pressure
• Inflammation
• Cholesterol stabilizes membranes and is a
  precursor of bile salts and steroid hormones

11
Lipids Dietary Requirements

• Higher for infants and children than for adults
• The American Heart Association suggests that
• Fats should represent less than 30 of ones
  total caloric intake
• Saturated fats should be limited to 10 or less
  of ones total fat intake
• Daily cholesterol intake should not exceed 200 mg

12
Proteins

• Complete proteins that meet all the bodys amino
  acid needs are found in eggs, milk, milk
  products, meat, and fish
• Incomplete proteins are found in legumes, nuts,
  seeds, grains, and vegetables

13
Proteins

• 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

14
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

15
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

16
Essential Amino Acids
Figure 24.2
17
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

18
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

19
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

20
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

21
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

22
Metabolism

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

23
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

24
Figure 24.3
25
Oxidation-Reduction (Redox) Reactions

• 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)

26
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 24.4a
27
Mechanisms of ATP Synthesis Oxidative
Phosphorylation

• Uses the chemiosmotic process whereby the
  movement of substances across a membrane is
  coupled to chemical reactions

28
Mechanisms of ATP Synthesis Oxidative
Phosphorylation

• 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)

29
Mechanisms of ATP Synthesis Oxidative
Phosphorylation
Figure 24.4b
30
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 36 ATP heat
• Glucose is catabolized in three pathways
• Glycolysis
• Krebs cycle
• The electron transport chain and oxidative
  phosphorylation

31
Carbohydrate Catabolism
Figure 24.5
32
Glycolysis

• A three-phase pathway in which
• 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

33
Glycolysis
Electron trans- port chain and
oxidative phosphorylation
Glycolysis
Krebs cycle
ATP
ATP
ATP
Glucose
Key
2 ATP
Phase 1 Sugar activation
Carbon atom
Inorganic phosphate
Pi
2 ADP
Fructose-1,6- bisphosphate
P
P
Phase 2 Sugar cleavage
Dihydroxyacetone phosphate
Glyceraldehyde phosphate
P
P
Pi
2 NAD
4 ADP
2
NADHH
4 ATP
Phase 3 Sugar oxidation and formation of ATP
2 Pyruvic acid
2
NADHH
O2
O2
2 NAD
To Krebs cycle (aerobic pathway)
2 Lactic acid
Figure 24.6
34
Glycolysis Phase 1 and 2

• Phase 1 Sugar activation
• Two ATP molecules activate glucose into
  fructose-1,6-diphosphate
• Phase 2 Sugar cleavage
• Fructose-1,6-bisphosphate is cleaved into two
  3-carbon isomers
• Bishydroxyacetone phosphate
• Glyceraldehyde 3-phosphate

35
Glycolysis Phase 3

• 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

36
Glycolysis Phase 3

• The final products are
• Two pyruvic acid molecules
• Two NADH H molecules (reduced NAD)
• A net gain of two ATP molecules

37
Krebs Cycle Preparatory Step

• Occurs in the mitochondrial matrix and is fueled
  by pyruvic acid and fatty acids

38
Krebs Cycle Preparatory Step

• Pyruvic acid is converted to acetyl CoA in three
  main steps
• Decarboxylation
• Carbon is removed from pyruvic acid
• Carbon dioxide is released

39
Krebs Cycle Preparatory Step

• Oxidation
• Hydrogen atoms are removed from pyruvic acid
• NAD is reduced to NADH H
• Formation of acetyl CoA the resulting acetic
  acid is combined with coenzyme A, a
  sulfur-containing coenzyme, to form acetyl CoA

40
Krebs Cycle

• An eight-step cycle in which each acetic acid is
  decarboxylated and oxidized, generating
• Three molecules of NADH H
• One molecule of FADH2
• Two molecules of CO2
• One molecule of ATP
• For each molecule of glucose entering glycolysis,
  two molecules of acetyl CoA enter the Krebs cycle

41
Cytosol
Pyruvic acid from glycolysis
Electron transport chain and oxidative phosphory
lation
Glycolysis
Krebs cycle
NAD
CO2
Mitochondrion (fluid matrix)
NADHH
CoA
Acetyl CoA
ATP
ATP
ATP
Oxaloacetic acid
Citric acid
(pickup molecule)
NADHH
(initial reactant)
CoA
NAD
Isocitric acid
Malic acid
NAD
Krebs cycle
CO2
NADHH
Fumaric acid
a-Ketoglutaric acid
CoA
CO2
FADH2
NAD
Succinic acid
NADHH
Succinyl-CoA
FAD
Key
CoA
GDP
Pi
Carbon atom
GTP
Inorganic phosphate
Pi
Coenzyme A
CoA
ADP
ATP
Figure 24.7
42
Electron Transport Chain

• Food (glucose) is oxidized and the released
  hydrogens
• Are transported by coenzymes NADH and FADH2
• Enter a chain of proteins bound to metal atoms
  (cofactors)
• Combine with molecular oxygen to form water
• Release energy
• The energy released is harnessed to attach
  inorganic phosphate groups (Pi) to ADP, making
  ATP by oxidative phosphorylation

43
Mechanism of Oxidative Phosphorylation

• The hydrogens delivered to the chain are split
  into protons (H) and electrons
• The protons are pumped across the inner
  mitochondrial membrane by
• NADH dehydrogenase (FMN, Fe-S)
• Cytochrome b-c1
• Cytochrome oxidase (a-a3)
• The electrons are shuttled from one acceptor to
  the next

44
Mechanism of Oxidative Phosphorylation

• Electrons are delivered to oxygen, forming oxygen
  ions
• Oxygen ions attract H to form water
• H pumped to the intermembrane space
• Diffuses back to the matrix via ATP synthase
• Releases energy to make ATP

45
Electron transport chain and oxidative phosphory
lation
Glycolysis
Krebs cycle
ATP
ATP
ATP
H
H
H
H
Core
Intermembrane space
Cyt c
e-
e
-
Q
1
3
2

Inner mitochondrial membrane
1 2
2
H



O2
H2O
FAD
FADH2
ADP

ATP
Pi
NADH H

NAD
(carrying from food)
e
-
H
Mitochondrial matrix
Electron Transport Chain
ATP Synthase
Figure 24.8
46
Electronic Energy Gradient

• The transfer of energy from NADH H and FADH2
  to oxygen releases large amounts of energy
• This energy is released in a stepwise manner
  through the electron transport chain

47
Electronic Energy Gradient

• The electrochemical proton gradient across the
  inner membrane
• Creates a pH gradient
• Generates a voltage gradient
• These gradients cause H to flow back into the
  matrix via ATP synthase

48
Figure 24.9
49
ATP Synthase

• The enzyme consists of three parts a rotor, a
  knob, and a rod
• Current created by H causes the rotor and rod to
  rotate
• This rotation activates catalytic sites in the
  knob where ADP and Pi are combined to make ATP

50
Structure of ATP Synthase
Figure 24.10
51
Summary of ATP Production
Figure 24.11
52
Glycogenesis and Glycogenolysis

• Glycogenesis formation of glycogen when glucose
  supplies exceed cellular need for ATP synthesis
• Glycogenolysis breakdown of glycogen in
  response to low blood glucose

Figure 24.12
53
Gluconeogenesis

• The process of forming sugar from noncarbohydrate
  molecules
• Takes place mainly in the liver
• Protects the body, especially the brain, from the
  damaging effects of hypoglycemia by ensuring ATP
  synthesis can continue

54
Lipid Metabolism

• Most products of fat metabolism are transported
  in lymph as chylomicrons
• Lipids in chylomicrons are hydrolyzed by plasma
  enzymes and absorbed by cells
• Only neutral fats are routinely oxidized for
  energy

55
Lipid Metabolism

• Catabolism of fats involves two separate pathways
• Glycerol pathway
• Fatty acids pathway

56
Lipid Metabolism

• Glycerol is converted to glyceraldehyde phosphate
• Glyceraldehyde is ultimately converted into
  acetyl CoA
• Acetyl CoA enters the Krebs cycle

57
Lipid Metabolism

• Fatty acids undergo beta oxidation which
  produces
• Two-carbon acetic acid fragments, which enter the
  Krebs cycle
• Reduced coenzymes, which enter the electron
  transport chain

58
Lipid Metabolism
Figure 24.13
59
Lipogenesis and Lipolysis

• Excess dietary glycerol and fatty acids undergo
  lipogenesis to form triglycerides
• Glucose is easily converted into fat since acetyl
  CoA is
• An intermediate in glucose catabolism
• The starting molecule for the synthesis of fatty
  acids

60
Lipogenesis and Lipolysis

• Lipolysis, the breakdown of stored fat, is
  essentially lipogenesis in reverse
• Oxaloacetic acid is necessary for the complete
  oxidation of fat
• Without it, acetyl CoA is converted into ketones
  (ketogenesis)

61
Lipogenesis and Lipolysis
Figure 24.14
62
Lipid Metabolism Synthesis of Structural
Materials

• Phospholipids are important components of myelin
  and cell membranes

63
Lipid Metabolism Synthesis of Structural
Materials

• The liver
• Synthesizes lipoproteins for transport of
  cholesterol and fats
• Makes tissue factor, a clotting factor
• Synthesizes cholesterol for acetyl CoA
• Uses cholesterol to form bile salts
• Certain endocrine organs use cholesterol to
  synthesize steroid hormones

64
Protein Metabolism

• Excess dietary protein results in amino acids
  being
• Oxidized for energy
• Converted into fat for storage
• Amino acids must be deaminated prior to oxidation
  for energy

65
Protein Metabolism

• Deaminated amino acids are converted into
• Pyruvic acid
• One of the keto acid intermediates of the Krebs
  cycle
• These events occur as transamination, oxidative
  deamination, and keto acid modification

66
Amino Acid Oxidation
Figure 24.15
67
Oxidation of Amino Acids

• Transamination switching of an amine group from
  an amino acid to a keto acid (usually
  ?-ketoglutaric acid of the Krebs cycle)
• Typically, glutamic acid is formed in this process

68
Oxidation of Amino Acids

• Oxidative deamination the amine group of
  glutamic acid is
• Released as ammonia
• Combined with carbon dioxide in the liver
• Excreted as urea by the kidneys
• Keto acid modification keto acids from
  transamination are altered to produce metabolites
  that can enter the Krebs cycle

69
Synthesis of Proteins

• Amino acids are the most important anabolic
  nutrients, and they form
• All protein structures
• The bulk of the bodys functional molecules

70
Synthesis of Proteins

• Amounts and types of proteins
• Are hormonally controlled
• Reflect each life cycle stage
• A complete set of amino acids is necessary for
  protein synthesis
• All essential amino acids must be provided in the
  diet

71
Summary Carbohydrate Metabolic Reactions
Table 24.4.1
72
Summary Lipid and Protein Metabolic Reactions
Table 24.4.2
73
State of the Body

• The body exists in a dynamic catabolic-anabolic
  state
• Organic molecules (except DNA) are continuously
  broken down and rebuilt
• The bodys total supply of nutrients constitutes
  its nutrient pool

74
State of the Body

• Amino acid pool bodys total supply of free
  amino acids is the source for
• Resynthesizing body proteins
• Forming amino acid derivatives
• Gluconeogenesis

75
Carbohydrate/Fat and Amino Acid Pools
Figure 24.16
76
Interconversion Pathways of Nutrients

• Carbohydrates are easily and frequently converted
  into fats
• Their pools are linked by key intermediates
• They differ from the amino acid pool in that
• Fats and carbohydrates are oxidized directly to
  produce energy
• Excess carbohydrate and fat can be stored

77
Interconversion Pathways of Nutrients
Figure 24.17
78
Absoprtive and Postabsorptive States

• Metabolic controls equalize blood concentrations
  of nutrients between two states
• Absorptive
• The time during and shortly after nutrient intake
• Postabsorptive
• The time when the GI tract is empty
• Energy sources are supplied by the breakdown of
  body reserves

79
Absoprtive State

• The major metabolic thrust is anabolism and
  energy storage
• Amino acids become proteins
• Glycerol and fatty acids are converted to
  triglycerides
• Glucose is stored as glycogen
• Dietary glucose is the major energy fuel
• Excess amino acids are deaminated and used for
  energy or stored as fat in the liver

80
Absoprtive State
Figure 24.18a
81
Principal Pathways of the Absorptive State

• In muscle
• Amino acids become protein
• Glucose is converted to glycogen
• In the liver
• Amino acids become protein or are deaminated to
  keto acids
• Glucose is stored as glycogen or converted to fat

82
Principal Pathways of the Absorptive State

• In adipose tissue
• Glucose and fats are converted and stored as fat
• All tissues use glucose to synthesize ATP

83
Principal Pathways of the Absorptive State
Figure 24.18b
84
Insulin Effects on Metabolism

• Insulin controls the absorptive state and its
  secretion is stimulated by
• Increased blood glucose
• Elevated amino acid levels in the blood
• Gastrin, CCK, and secretin

85
Insulin Effects on Metabolism

• Insulin enhances
• Active transport of amino acids into tissue cells
  
• Facilitated diffusion of glucose into tissue

86
Insulin Effects on Metabolism
Figure 24.19
87
Diabetes Mellitus

• A consequence of inadequate insulin production or
  abnormal insulin receptors
• Glucose becomes unavailable to most body cells
• Metabolic acidosis, protein wasting, and weight
  loss result as fats and tissue proteins are used
  for energy

88
Postabsorptive State

• The major metabolic thrust is catabolism and
  replacement of fuels in the blood
• Proteins are broken down to amino acids
• Triglycerides are turned into glycerol and fatty
  acids
• Glycogen becomes glucose
• Glucose is provided by glycogenolysis and
  gluconeogenesis
• Fatty acids and ketones are the major energy
  fuels
• Amino acids are converted to glucose in the liver

89
Postabsorptive State
Figure 24.20a
90
Principle Pathways in the Postabsorptive State

• In muscle
• Protein is broken down to amino acids
• Glycogen is converted to ATP and pyruvic acid
  (lactic acid in anaerobic states)

91
Principle Pathways in the Postabsorptive State

• In the liver
• Amino acids, pyruvic acid, stored glycogen, and
  fat are converted into glucose
• Fat is converted into keto acids that are used to
  make ATP
• Fatty acids (from adipose tissue) and ketone
  bodies (from the liver) are used in most tissue
  to make ATP
• Glucose from the liver is used by the nervous
  system to generate ATP

92
Principle Pathways in the Postabsorptive State
Figure 24.20b
93
Hormonal and Neural Controls of the
Postabsorptive State

• Decreased plasma glucose concentration and rising
  amino acid levels stimulate alpha cells of the
  pancreas to secrete glucagon (the antagonist of
  insulin)
• Glucagon stimulates
• Glycogenolysis and gluconeogenesis
• Fat breakdown in adipose tissue
• Glucose sparing

94
Influence of Glucagon
Figure 24.21
95
Hormonal and Neural Controls of the
Postabsorptive State

• In response to low plasma glucose, the
  sympathetic nervous system releases epinephrine,
  which acts on the liver, skeletal muscle, and
  adipose tissue to mobilize fat and promote
  glycogenolysis

96
Liver Metabolism

• Hepatocytes carry out over 500 intricate
  metabolic functions

97
Liver Metabolism

• A brief summary of liver functions
• Packages fatty acids to be stored and transported
• Synthesizes plasma proteins
• Forms nonessential amino acids
• Converts ammonia from deamination to urea
• Stores glucose as glycogen, and regulates blood
  glucose homeostasis
• Stores vitamins, conserves iron, degrades
  hormones, and detoxifies substances

98
Cholesterol

• Is the structural basis of bile salts, steroid
  hormones, and vitamin D
• Makes up part of the hedgehog molecule that
  directs embryonic development
• Is transported to and from tissues via
  lipoproteins

99
Cholesterol

• Lipoproteins are classified as
• HDLs high-density lipoproteins have more
  protein content
• LDLs low-density lipoproteins have a
  considerable cholesterol component
• VLDLs very low density lipoproteins are mostly
  triglycerides

100
Cholesterol
Figure 24.22
101
Lipoproteins

• The liver is the main source of VLDLs, which
  transport triglycerides to peripheral tissues
  (especially adipose)
• LDLs transport cholesterol to the peripheral
  tissues and regulate cholesterol synthesis
• HDLs transport excess cholesterol from peripheral
  tissues to the liver
• Also serve the needs of steroid-producing organs
  (ovaries and adrenal glands)

102
Lipoproteins

• High levels of HDL are thought to protect against
  heart attack
• High levels of LDL, especially lipoprotein (a),
  increase the risk of heart attack

103
Plasma Cholesterol Levels

• The liver produces cholesterol
• At a basal level of cholesterol regardless of
  dietary intake
• Via a negative feedback loop involving serum
  cholesterol levels
• In response to saturated fatty acids

104
Plasma Cholesterol Levels

• Fatty acids regulate excretion of cholesterol
• Unsaturated fatty acids enhance excretion
• Saturated fatty acids inhibit excretion
• Certain unsaturated fatty acids (omega-3 fatty
  acids, found in cold-water fish) lower the
  proportions of saturated fats and cholesterol

105
Non-Dietary Factors Affecting Cholesterol

• Stress, cigarette smoking, and coffee drinking
  increase LDL levels
• Aerobic exercise increases HDL levels
• Body shape is correlated with cholesterol levels
• Fat carried on the upper body is correlated with
  high cholesterol levels
• Fat carried on the hips and thighs is correlated
  with lower levels

106
Body Energy Balance

• Bond energy released from catabolized food must
  equal the total energy output
• Energy intake equal to the energy liberated
  during the oxidation of food
• Energy output includes the energy
• Immediately lost as heat (about 60 of the total)
• Used to do work (driven by ATP)
• Stored in the form of fat and glycogen

107
Body Energy Balance

• Nearly all energy derived from food is eventually
  converted to heat
• Cells cannot use this energy to do work, but the
  heat
• Warms the tissues and blood
• Helps maintain the homeostatic body temperature
• Allows metabolic reactions to occur efficiently

108
Regulation of Food Intake

• When energy intake and energy outflow are
  balanced, body weight remains stable
• The hypothalamus releases peptides that influence
  feeding behavior
• Orexins are powerful appetite enhancers
• Neuropeptide Y causes a craving for carbohydrates
• Galanin produces a craving for fats
• GLP-1 and serotonin make us feel full and
  satisfied

109
Feeding Behaviors

• Feeding behavior and hunger depend on one or more
  of five factors
• Neural signals from the digestive tract
• Bloodborne signals related to the body energy
  stores
• Hormones, body temperature, and psychological
  factors

110
Nutrient Signals Related to Energy Stores

• High plasma levels of nutrients that signal
  depressed eating
• Plasma glucose levels
• Amino acids in the plasma
• Fatty acids and leptin

111
Hormones, Temperature, and Psychological Factors

• Glucagon and epinephrine stimulate hunger
• Insulin and cholecystokinin depress hunger
• Increased body temperature may inhibit eating
  behavior
• Psychological factors that have little to do with
  caloric balance can also influence eating
  behaviors

112
Control of Feeding Behavior and Satiety

• Leptin, secreted by fat tissue, appears to be the
  overall satiety signal
• Acts on the ventromedial hypothalamus
• Controls appetite and energy output
• Suppresses the secretion of neuropeptide Y, a
  potent appetite stimulant
• Blood levels of insulin and glucocorticoids play
  a role in regulating leptin release

113
Hypothalamic Command of Appetite
Figure 24.23
114
Metabolic Rate

• Rate of energy output (expressed per hour) equal
  to the total heat produced by
• All the chemical reactions in the body
• The mechanical work of the body
• Measured directly with a calorimeter or
  indirectly with a respirometer

115
Metabolic Rate

• Basal metabolic rate (BMR)
• Reflects the energy the body needs to perform its
  most essential activities
• Total metabolic rate (TMR)
• Total rate of kilocalorie consumption to fuel all
  ongoing activities

116
Factors that Influence BMR

• Surface area, age, gender, stress, and hormones
• As the ratio of surface area to volume increases,
  BMR increases
• Males have a disproportionately high BMR
• Stress increases BMR
• Thyroxine increases oxygen consumption, cellular
  respiration, and BMR

117
Regulation of Body Temperature

• Body temperature balance between heat
  production and heat loss
• At rest, the liver, heart, brain, and endocrine
  organs account for most heat production
• During vigorous exercise, heat production from
  skeletal muscles can increase 3040 times

118
Regulation of Body Temperature

• Normal body temperature is 36.2?C (98.2?F)
  optimal enzyme activity occurs at this
  temperature
• Temperature spikes above this range denature
  proteins and depress neurons

119
Regulation of Body Temperature
Figure 24.24
120
Core and Shell Temperature

• Organs in the core (within the skull, thoracic,
  and abdominal cavities) have the highest
  temperature
• The shell, essentially the skin, has the lowest
  temperature
• Blood serves as the major agent of heat transfer
  between the core and shell
• Core temperature remains relatively constant,
  while shell temperature fluctuates substantially
  (20?C40?C)

121
Mechanisms of Heat Exchange

• Four mechanisms
• Radiation loss of heat in the form of infrared
  rays
• Conduction transfer of heat by direct contact
• Convection transfer of heat to the surrounding
  air
• Evaporation heat loss due to the evaporation of
  water from the lungs, mouth mucosa, and skin
  (insensible heat loss)
• Evaporative heat loss becomes sensible when body
  temperature rises and sweating produces increased
  water for vaporization

122
Role of the Hypothalamus

• The main thermoregulation center is the preoptic
  region of the hypothalamus
• The heat-loss and heat-promoting centers comprise
  the thermoregulatory centers
• The hypothalamus
• Receives input from thermoreceptors in the skin
  and core
• Responds by initiating appropriate heat-loss and
  heat-promoting activities

123
Heat-Promoting Mechanisms

• Low external temperature or low temperature of
  circulating blood activates heat-promoting
  centers of the hypothalamus to cause
• Vasoconstriction of cutaneous blood vessels
• Increased metabolic rate
• Shivering
• Enhanced thyroxine release

124
Heat-Loss Mechanisms

• When the core temperature rises, the heat-loss
  center is activated to cause
• Vasodilation of cutaneous blood vessels
• Enhanced sweating
• Voluntary measures commonly taken to reduce body
  heat include
• Reducing activity and seeking a cooler
  environment
• Wearing light-colored and loose-fitting clothing

125
Skin blood vessels dilate capillaries become
flushed with warm blood heat radiates from skin
surface
Activates heat-loss center in hypothalamus
Body temper- ature decreases blood
temperature declines and hypo- thalamus
heat-loss center shuts off
Sweat glands activated secrete perspiration,
which is vaporized by body heat, helping to cool
the body
Blood warmer than hypothalamic set point
Stimulus Increased body temperature (e.g., when
exercising or the climate is hot)
Imbalance
Stimulus Decreased body temperature (e.g., due
to cold environmental temperatures)
Homeostasis normal body temperature
(35.8C38.2C)
Imbalance
Blood cooler than hypothalamic set point
Skin blood vessels constrict blood is diverted
from skin capillaries and withdrawn to deeper
tissues minimizes overall
heat loss from skin
surface
Body temper- ature increases blood
temperature rises and hypothala- mus
heat-promoting center shuts off
Activates heat- promoting center in hypothalamus
Skeletal muscles activated when more heat must be
generated shivering begins
Figure 24.26
126
Hyperthermia

• Normal heat loss processes become ineffective and
  elevated body temperatures depress the
  hypothalamus
• This sets up a positive-feedback mechanism,
  sharply increasing body temperature and metabolic
  rate
• This condition, called heat stroke, can be fatal
  if not corrected

127
Heat Exhaustion

• Heat-associated collapse after vigorous exercise,
  evidenced by elevated body temperature, mental
  confusion, and fainting
• Due to dehydration and low blood pressure
• Heat-loss mechanisms are fully functional
• Can progress to heat stroke if the body is not
  cooled and rehydrated

128
Fever

• Controlled hyperthermia, often a result of
  infection, cancer, allergic reactions, or central
  nervous system injuries
• White blood cells, injured tissue cells, and
  macrophages release pyrogens that act on the
  hypothalamus, causing the release of
  prostaglandins
• Prostaglandins reset the hypothalamic thermostat
• The higher set point is maintained until the
  natural body defenses reverse the disease process

129
Developmental Aspects

• Good nutrition is essential in utero as well as
  throughout life
• Lack of proteins needed for fetal growth and in
  the first three years of life can lead to mental
  deficits and learning disorders
• With the exception of insulin-dependent diabetes
  mellitus, children free of genetic disorders
  rarely exhibit metabolic problems
• In later years, non-insulin-dependent diabetes
  mellitus becomes a major problem

130
Developmental Aspects

• Many agents prescribed for age-related medical
  problems influence nutrition
• Diuretics can cause hypokalemia by promoting
  potassium loss
• Antibiotics can interfere with food absorption
• Mineral oil interferes with absorption of
  fat-soluble vitamins
• Excessive alcohol consumption leads to
  malabsorption problems, certain vitamin and
  mineral deficiencies, deranged metabolism, and
  damage to the liver and pancreas