Chapter 22a

advertisement
Chapter 22a
Metabolism and
Energy Balance
About this Chapter
•
•
•
•
•
Appetite and satiety
Energy balance
Metabolism
Homeostatic control of metabolism
Regulation of body temperature
Appetite and Satiety
• Food intake is carefully controlled
• Two competing behavioral states
• Appetite (or hunger) = desire for food
• Satiety = sense of fullness (or satisfaction)
• Hypothalamus contains two key control
centers
• Feeding center
• Satiety center
Four Types of Input to the Hypothalamus
•
•
•
•
Neural input from the cerebral cortex
Neural input from the limbic system
Peptide hormones from the GI tract
Adipocytokines from adipose tissue
Two Theories for Regulation of Food Intake
• Glucostatic theory
• Theory proposes that blood glucose levels
ultimately control the feeding and satiety
centers
• Lipostatic theory
• Theory proposes that the level of body fat
regulates the feeding and satiety centers
• Recent discovery of several peptides
(especially leptin and neuropeptide Y) seems
to support this theory
Peptides Regulate the Feeding Center
Figure 22-1
Many Peptides Alter Food Intake
Table 22-1
Energy Balance - The Key to Weight Control
• Energy input = energy output
• Energy output = work  heat
• Three categories of work done by our cells
• Membrane transport
• Mechanical work
• Chemical work = building molecules, including
synthesis of energy storage molecules
• Short-term energy storage (ATP)
• Long-term energy storage (glycogen, fat)
Energy Balance
• Methods for measuring energy use
• Direct calorimetry
• Measures the energy content of food
• Fat 9 Kcal/g / protein and CHO ~ 4 Kcal/g
• Indirect calorimetry
• Estimates metabolic rate as a measure of energy
use
• Oxygen consumption
• Carbon dioxide production
• Ratio of CO2 to O2 (RQ or RER)
Metabolic Rate
• Basal metabolic rate (BMR) is most common
measure of metabolic rate
• Six factors affecting metabolic rate
1 - Age and gender
2 - Amount of lean muscle mass
3 - Activity level
4 - Energy intake (diet) – fat vs protein thermogenesis
5 – Hormones – thyroid hormone thyroxin
6 - Genetics
• Only energy intake and level of physical
activity can be voluntarily changed
Two Chemical Forms of Energy Storage
• Glycogen (highly branched polymer of
glucose)
• Stored glycogen binds water
• Liver glycogen is used to regulate blood
glucose
• Muscle glycogen is used to power muscle
contraction
• Fat (triglycerides)
• Fats have higher energy content per gram
• Little water is required for fat storage
• Energy in fats is harder and slower to access
Metabolism
• Metabolism is all of the chemical reactions in the
body
1 - Extract energy from nutrients
2 - Use energy for work and synthesis
3 - Store excess energy
• Two types of metabolic pathways
• Anabolic pathways build large molecules
• Catabolic pathways break down large molecules
• Metabolism can be divided into two states
• Absorptive (“fed”) state is anabolic
• Post-absorptive (“fasted”) state is catabolic
Metabolic Fates and Nutrient Pools
• Ingested biomolecules have three fates
1. Immediate use in energy production
2. Synthesis into needed macromolecules
3. Storage for later use in energy production
• Nutrient pools are available for immediate
use
• Free fatty acids
• Plasma glucose pool
• Amino acid pool
Know definitions of:
Glycogenesis / glycogenolysis / lipogenesis / lipolysis / ketosis
Overview of Metabolism
DIET
Fats
Carbohydrates
Proteins
Lipogenesis
Free fatty acids + glycerol
Fat
stores
Glucose
Glycogenesis
Lipogenesis
Excess glucose
Glycogen
stores
Lipolysis
Excess nutrients
Metabolism in
most tissues
Body
protein
Urine
Glycogenolysis
Glucose pool
Free fatty
acid pool
Amino
acids
Protein
synthesis
Gluconeogenesis
Range of normal
plasma glucose
Amino acid
pool
Brain
metabolism
Figure 22-2
Glucose Metabolism
DIET
Carbohydrates
Fat
stores
Glucose
Lipogenesis
Excess glucose
• Most plasma
glucose is used
for immediate
energy
production, or is
Glycogenesis
stored as
glycogen
Glycogen
stores
Urine
Glycogenolysis
Glucose pool
Range of normal
plasma glucose
Metabolism in
most tissues
Brain
metabolism
Figure 22-2 (1 of 4)
Fat Metabolism
DIET
Fats
Lipogenesis
Free fatty acids + glycerol
Fat
stores
Lipolysis
• Free fatty acids
are used for
immediate energy
production, or are
stored as fat
molecules in
adipose tissue
Free fatty
acid pool
Excess nutrients
Metabolism in
most tissues
Figure 22-2 (2 of 4)
Amino Acid Metabolism
DIET
• Amino acids are
used for building
needed body
proteins. Excess
amino acids are
converted into
glucose by the
liver.
Proteins
Amino
acids
Protein
synthesis
Body
protein
Glucose pool
Gluconeogenesis
Range of normal
plasma glucose
Amino acid
pool
Figure 22-2 (3 of 4)
Summary of Metabolism
DIET
Fats
Carbohydrates
Proteins
Lipogenesis
Free fatty acids + glycerol
Fat
stores
Glucose
Glycogenesis
Lipogenesis
Excess glucose
Glycogen
stores
Lipolysis
Excess nutrients
Metabolism in
most tissues
Body
protein
Urine
Glycogenolysis
Glucose pool
Free fatty
acid pool
Amino
acids
Protein
synthesis
Gluconeogenesis
Range of normal
plasma glucose
Amino acid
pool
Brain
metabolism
Figure 22-2 (4 of 4)
Biochemical Pathways for Energy Production
• Overview of
Pathways
Glycogen
Glucose 6-phosphate
Glucose
Liver only
Glycerol
2
ATP
NH3
Some
amino
acids
Lactate
Pyruvate
Cytoplasm
Mitochondria
Pyruvate
Fatty acids
Acetyl CoA
CoA
Ketone bodies (in liver)
CO2
Citric acid
cycle
2
Electron transport
system
NH3
O2
26-28 ATP
ATP
Some
amino
acids
+ H2O
Figure 22-3
Interconversions of Glucose
Glycogen
Glucose 6-phosphate
Glucose
Liver only
Cytoplasm
Mitochondria
Figure 22-3 (1 of 7)
Glycolysis is Catabolism of Glucose
Glycogen
Glucose 6-phosphate
Glucose
Liver only
2 ATP
Pyruvate
Cytoplasm
Mitochondria
Figure 22-3 (2 of 7)
Some Amino Acids Can Also Supply Pyruvate
Glycogen
Glucose 6-phosphate
Glucose
Liver only
Glycerol
2 ATP
NH3
Some
amino
acids
Pyruvate
Cytoplasm
Mitochondria
Figure 22-3 (3 of 7)
Anaerobic Metabolism Produces Lactate
Glycogen
Glucose 6-phosphate
Glucose
Liver only
Glycerol
2 ATP
NH3
Some
amino
acids
Pyruvate
Lactate
Cytoplasm
Mitochondria
Pyruvate
Figure 22-3 (4 of 7)
Mitochondria and the Citric Acid Cycle
Glycogen
Glucose 6-phosphate
Glucose
Liver only
Glycerol
2 ATP
NH3
Some
amino
acids
Lactate
Pyruvate
Cytoplasm
Mitochondria
Pyruvate
Acetyl CoA
CoA
CO2
Citric acid
cycle
2
ATP
Figure 22-3 (5 of 7)
Fatty Acids and Some Amino Acids Enter Here
Glycogen
Glucose 6-phosphate
Glucose
Liver only
Glycerol
2 ATP
NH3
Some
amino
acids
Lactate
Pyruvate
Cytoplasm
Mitochondria
Pyruvate
Fatty acids
Acetyl CoA
CoA
Ketone bodies (in liver)
CO2
Citric acid
cycle
2
NH3
ATP
Some
amino
acids
Figure 22-3 (6 of 7)
Electron Transport System
Glycogen
Glucose 6-phosphate
Glucose
Liver only
Glycerol
2 ATP
NH3
Some
amino
acids
Lactate
Pyruvate
Cytoplasm
Mitochondria
Pyruvate
Fatty acids
Acetyl CoA
CoA
Ketone bodies (in liver)
CO2
Citric acid
cycle
2
Electron transport
system
NH3
O2
26-28 ATP
ATP
Some
amino
acids
+ H2O
Figure 22-3 (7 of 7)
Metabolism: Push-Pull Control
• Metabolic balance can shift when enzyme
activity is controlled
Figure 22-4
Metabolism: Fates of Nutrients in the Fed State
Table 22-2
Transport and Fate of Dietary Fats
Dietary
fats
Intestinal
lumen
Monoglycerides
Phospholipids
Free fatty acids (FFA)
Cholesterol
apo
Intestinal
cells
CM
Chylomicron
FFA
Lymph
Adipose cells
Blood
Bile
duct
Lipolysis by lipases
CM
lpl
FFA
Glycerol
Reassemble
to triglycerides
(TG)
TG
storage
CM
remnants
HDL-C
Most cells
LDL-C
Liver
FFA oxidized
for energy
Cholesterol
for synthesis
Metabolized
Lipoprotein
complexes
Cholesterol + FFA + Lipoproteins
Bile salts
KEY
apo=apoproteins
lpl=lipoprotein lipase
LDL=low-density lipoprotein
HDL = high-density lipoprotein
C=cholesterol
Figure 22-5
High LDL-C Levels Increase Heart Disease Risk
• LDL-C takes cholesterol from liver to most
cells
• High LDL-C increases risk of atherosclerosis
• Many drugs try to lower cholesterol levels by
changing its metabolism
• Low HDL is another risk
factor for atheroslerosis
Figure 22-6
Fasted-State Metabolism
1 Liver glycogen
becomes glucose.
2 Adipose lipids
become free
fatty acids and
glycerol that
enter blood.
Liver
glycogen
stores
Free fatty
acids
Glycogenolysis
-oxidation
Energy
production
Glucose
Triglyceride stores
Free fatty
acids
Glycerol
Gluconeogenesis
Ketone
bodies
Energy production
Glycogen
Gluconeogenesis
Proteins
Pyruvate
or
Lactate
Glucose
Ketone
bodies
Energy production
4 Brain can use
only glucose and
ketones for energy.
Amino
acids
3 Muscle glycogen can be used for energy.
Muscles also use fatty acids and break
down their proteins to amino acids that
enter the blood.
Figure 22-7
Fasted-State Metabolism
1 Liver glycogen
becomes glucose.
Liver
glycogen
stores
Free fatty
acids
Glycogenolysis
-oxidation
Energy
production
Glucose
Ketone
bodies
Figure 22-7 (1 of 4)
Fasted-State Metabolism
1 Liver glycogen
becomes glucose.
2 Adipose lipids
become free
fatty acids and
glycerol that
enter blood.
Liver
glycogen
stores
Free fatty
acids
Glycogenolysis
-oxidation
Energy
production
Glucose
Triglyceride stores
Free fatty
acids
Glycerol
Gluconeogenesis
Ketone
bodies
Figure 22-7 (2 of 4)
Fasted-State Metabolism
1 Liver glycogen
becomes glucose.
2 Adipose lipids
become free
fatty acids and
glycerol that
enter blood.
Liver
glycogen
stores
Free fatty
acids
Glycogenolysis
-oxidation
Energy
production
Glucose
Triglyceride stores
Free fatty
acids
Glycerol
Gluconeogenesis
Ketone
bodies
Energy production
Glycogen
Gluconeogenesis
Proteins
Pyruvate
or
Lactate
Amino
acids
3 Muscle glycogen can be used for energy.
Muscles also use fatty acids and break
down their proteins to amino acids that
enter the blood.
Figure 22-7 (3 of 4)
Fasted-State Metabolism
1 Liver glycogen
becomes glucose.
2 Adipose lipids
become free
fatty acids and
glycerol that
enter blood.
Liver
glycogen
stores
Free fatty
acids
Glycogenolysis
-oxidation
Energy
production
Glucose
Triglyceride stores
Free fatty
acids
Glycerol
Gluconeogenesis
Ketone
bodies
Energy production
Glycogen
Gluconeogenesis
Proteins
Pyruvate
or
Lactate
Glucose
Ketone
bodies
Energy production
4 Brain can use
only glucose and
ketones for energy.
Amino
acids
3 Muscle glycogen can be used for energy.
Muscles also use fatty acids and break
down their proteins to amino acids that
enter the blood.
Figure 22-7 (4 of 4)
Download