Chapter 22a Metabolism and Energy Balance. About this Chapter Appetite and satiety Energy balance...

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

Figure 22-1

Peptides Regulate the Feeding Center

Table 22-1

Many Peptides Alter Food Intake

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 rate1 - Age and gender2 - Amount of lean muscle mass3 - Activity level4 - 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 body1 - 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 fates1. 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

Figure 22-2

CarbohydratesFats

Free fatty acids + glycerol

Fatstores

Glucose

Excess glucose

Glycogenstores

Aminoacids

Proteins

DIET

Lipogenesis

Brainmetabolism

Range of normalplasma glucose

Gluconeogenesis

Bodyprotein

Glycogenolysis

GlycogenesisProtein

synthesis

Metabolism inmost tissues

Free fattyacid pool

Urine

Excess nutrients

Lipolysis

Glucose pool

Amino acidpool

Lip

og

enes

is

Figure 22-2 (1 of 4)

Carbohydrates

Fatstores

Glucose

Excess glucose

Glycogenstores

DIET

Lipogenesis

Brainmetabolism


Glycogenolysis

Glycogenesis


Urine

Glucose pool

Glucose Metabolism

• Most plasma glucose is used for immediate energy production, or is stored as glycogen

Fats


Fatstores

DIET


Free fattyacid pool

Excess nutrients

Lipolysis

Lip

og

enes

is


Fat Metabolism

• Free fatty acids are used for immediate energy production, or are stored as fat molecules in adipose tissue

Aminoacids

Proteins

DIET


Gluconeogenesis

Bodyprotein

Proteinsynthesis

Glucose pool

Amino acidpool


Amino Acid Metabolism

• Amino acids are used for building needed body proteins. Excess amino acids are converted into glucose by the liver.

Summary of Metabolism


CarbohydratesFats


Fatstores

Glucose

Excess glucose

Glycogenstores

Aminoacids

Proteins

DIET

Lipogenesis

Brainmetabolism


Gluconeogenesis

Bodyprotein

Glycogenolysis

GlycogenesisProtein

synthesis


Free fattyacid pool

Urine

Excess nutrients

Lipolysis

Glucose pool

Amino acidpool

Lip

og

enes

is

Biochemical Pathways for Energy Production

• Overview of Pathways

Figure 22-3

Glucose

Someaminoacids

Someaminoacids

Lactate

Glycogen

Glucose 6-phosphate

Liver only

Fatty acids

Electron transportsystem

CO2

NH3

+ H2OO2 26-28

CoAKetone bodies (in liver)

Glycerol

2

ATP

Pyruvate

Pyruvate

Acetyl CoA

NH3

Cytoplasm

Mitochondria

Citric acidcycle ATP

ATP2

Interconversions of Glucose


Glucose

Glycogen

Glucose 6-phosphate

Liver only

Cytoplasm

Mitochondria

Glycolysis is Catabolism of Glucose


Glucose

Glycogen

Glucose 6-phosphate

Liver only

Pyruvate

Cytoplasm

Mitochondria

ATP2

Some Amino Acids Can Also Supply Pyruvate


Glucose

Someaminoacids

Glycogen

Glucose 6-phosphate

Liver only

Glycerol

Pyruvate

NH3

Cytoplasm

Mitochondria

ATP2

Anaerobic Metabolism Produces Lactate


Glucose

Someaminoacids

Lactate

Glycogen

Glucose 6-phosphate

Liver only

Glycerol

Pyruvate

Pyruvate

NH3

Cytoplasm

Mitochondria

ATP2

Mitochondria and the Citric Acid Cycle


Glucose

Someaminoacids

Lactate

Glycogen

Glucose 6-phosphate

Liver only

CO2

CoA

Glycerol

2

Pyruvate

Pyruvate

Acetyl CoA

NH3

Cytoplasm

Mitochondria


ATP2

Fatty Acids and Some Amino Acids Enter Here


Glucose

Someaminoacids

Someaminoacids

Lactate

Glycogen

Glucose 6-phosphate

Liver only

Fatty acids

CO2

NH3


Glycerol

2

Pyruvate

Pyruvate

Acetyl CoA

NH3

Cytoplasm

Mitochondria


ATP2

Electron Transport System


Glucose

Someaminoacids

Someaminoacids

Lactate

Glycogen

Glucose 6-phosphate

Liver only

Fatty acids

Electron transportsystem

CO2

NH3

+ H2OO2 26-28


Glycerol

2

ATP

Pyruvate

Pyruvate

Acetyl CoA

NH3

Cytoplasm

Mitochondria


ATP2

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

Figure 22-5

Dietaryfats

apo

Chylomicron

MonoglyceridesPhospholipidsFree fatty acids (FFA)Cholesterol

FFA

FFA

CM

CM

CMremnants

Lymph

Bileduct

Blood Adipose cells

Most cells

Liver

Intestinallumen

Intestinalcells

lpl

Glycerol

HDL-C LDL-C

Cholesterol + FFA + Lipoproteins

Lipoproteincomplexes

Bile salts

Metabolized

Reassembleto triglycerides

(TG)

TGstorage

Lipolysis by lipases

FFA oxidizedfor energy

Cholesterolfor synthesis

KEYapo=apoproteinslpl=lipoprotein lipaseLDL=low-density lipoproteinHDL = high-density lipoproteinC=cholesterol

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

Figure 22-7

Liverglycogen

stores

Energyproduction

Energy production

Free fattyacids

Free fattyacids

Glycerol

Aminoacids

KetonebodiesGlucose

Adipose lipidsbecome freefatty acids andglycerol thatenter blood.

Muscle glycogen can be used for energy.Muscles also use fatty acids and breakdown their proteins to amino acids thatenter the blood.

Liver glycogenbecomes glucose.

Brain can useonly glucose andketones for energy.

or

Triglyceride stores

Glycogen

Pyruvate

Lactate

Energy production

Glucose

Proteins

Ketonebodies

-oxidationGlycogenolysis

Gluconeogenesis

Gluconeogenesis

1 2

34



Liverglycogen

stores

Free fattyacids

KetonebodiesGlucose

1

Energyproduction





Liverglycogen

stores

Free fattyacids

Free fattyacids

Glycerol

KetonebodiesGlucose


Triglyceride stores

Gluconeogenesis

1 2

Energyproduction





Liverglycogen

stores

Free fattyacids

Free fattyacids

Glycerol

Aminoacids

KetonebodiesGlucose



or

Triglyceride stores

Glycogen

Pyruvate

Lactate

Energy production

Proteins

Gluconeogenesis

Gluconeogenesis

1 2

3

Energyproduction





Liverglycogen

stores

Energy production

Free fattyacids

Free fattyacids

Glycerol

Aminoacids

KetonebodiesGlucose



Brain can useonly glucose andketones for energy.

or

Triglyceride stores

Glycogen

Pyruvate

Lactate

Energy production

Glucose

Proteins

Ketonebodies

Gluconeogenesis

Gluconeogenesis

1 2

34

Energyproduction



Chapter 22a Metabolism and Energy Balance. About this Chapter Appetite and satiety Energy balance...

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Transcript of Chapter 22a Metabolism and Energy Balance. About this Chapter Appetite and satiety Energy balance...