Chapters 7 & 8 Metabolism & Energy Balance METABOLISM Metabolism – the sum total of all chemical...

Chapters 7 & 8

Metabolism & Energy Balance

METABOLISMMetabolism – the sum total of all chemical

reactions that take place in living cellsMetabolic Organs

• Digestive System – to ingest, digest & absorb nutrients

• Liver – the “control panel” and most active processing center in the body

1. Receives absorbed nutrients first2. Manufactures important compounds3. Detoxifies drugs & metabolic

wastes

METABOLISM • Pancreas

1. Secretes digestive enzymes2. Produces insulin & other

hormones involved in glucose regulation

• Heart & Blood Vessels 1. Carry nutrients & O2 to cells2. Return cell wastes

• Kidneys1. Filter wastes2. Produce important body

compounds

ENERGY METABOLISM

• After absorption, 2 processes occur:1. Anabolism – “building reactions”

to create larger molecules Example:

Glucose>>>Glycogen2. Catabolism – “breakdown

reactions” to release energy Example: Glycogen>>>Glucose

Chemical Reactions

Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning

ENERGY METABOLISM• Energy Metabolism – how the body obtains

& uses energy from foods or body stores• Nutrients in the body that generate energy

1. CHO>>>Glucose (liver converts fructose & galactose to glucose)

2. Fat (Triglycerides)>>>Glycerol & Fatty Acids

3. Protein>>>Amino Acids

ENERGY PATHWAYS• Glucose breakdown pathway =

glycolysis1. The 6- carbon glucose is split

in half forming two 3-carbon compunds that are converted to glucose

2. The net yield of one glucose molecule is two pyruvate molecules

3. This process does not require oxygen and is reversible


Glycolysis: Glucose-to-Pyruvate

Glucose• The fate of pyruvate

– Anaerobic vs. aerobic pathways Anaerobic

-Pyruvate converted to lactic acid in the muscles

-Lactic acid converted to glucose in the liver (Cori cycle)

-The glucose can travel back to the muscles

-Used when the body needs energy quickly


Glucose Aerobic

- Pyruvate converted to acetyl CoA

- This process is irreversible- Acetyl CoA may be used to synthesize fat or to generate ATP (the TCA cycle)

- Slower energy expenditure but can be sustained longer


The TCA Cycle


The Final Pathway - Electron Transport Chain and ATP Synthesis

ENERGY PATHWAYS

Fat (triglycerides) breakdown pathway>>>Glycerol & Fatty acids

1. Glycerol can be used to make glucose or to form pyruvate and then Acetyl CoA

FATTY ACIDS

2. Fatty Acids can be oxidized to form Acetyl CoA and then proceed through TCA cycle

-Fatty acids cannot form pyruvate so they cannot be converted to glucose


Fats Enter the Energy Pathway

ENERGY PATHWAYS • Protein breakdown pathway:

1. Amino acids must be deaminated to lose their nitrogen-containing amino group

2. Then ~50% of amino acids are converted to Pyruvate

3. Others are converted to Acetyl CoA or enter the TCA cycle directly

Amino Acids• Amino acids-to-acetyl CoA


ENERGY PATHWAYS• Amino acids are only used for energy if:

-Consumed in excess -Inadequate energy is available from carbohydrate or the body is given only fat forcing the breakdown of protein tissue to make glucose


The Paths of Pyruvate & Acetyl CoA

ENERGY BUDGET• Feasting – when a person eats more

than he/she needs, excess energy will be stored as:1. Glycogen – excess carbohydrate2. Body fat – excess carbohydrate,

fat, protein, or alcohol3. Metabolism favors fat formation

especially when the excess energy is derived from dietary fat

Economics of Feasting


Energy Budget

• Fasting – when a person doesn’t eat enough, the body draws on its energy stores (glycogen & fat) to meet its constant demand

• If a person chooses not to eat, he/she is fasting; if not by choice, he/she is starving

• The body makes no such distinction

ENERGY BUDGET • During a fast or starvation, glucose will be released from stored glycogen to fuel the

brain & central nervous system1. Glycogen stores will only last ~1/2

day2. Other cells in the body can use

stored fat, but the brain requires glucose; thus, body proteins begin rapid breakdown to supply glucose to brainREMEMBER: Fatty acids cannot form glucose

ENERGY BUDGET Eventually, the nervous system adapts to using

stored body fat.1. AcetlyCoAs combine to form ketones

(acidic compounds that arise from the incomplete breakdown of fat)

2. High blood ketone levels (ketonemia) + ketones in urine (ketonuria) = ketosis

3. Protein continues to breakdown, but at a slower rate to conserve vital protein tissues as long as possible

Economics of Fasting


ENERGY BUDGET• As fasting continues:

1. Metabolism slows 2. Appetite is suppressed

3. Wasting of lean body tissue occurs

4. Susceptibility to disease increases

5. Body temperature drops

Chapters 7 & 8 Metabolism & Energy Balance METABOLISM Metabolism – the sum total of all chemical...

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