Chapters 7 & 8 Metabolism & Energy Balance

METABOLISM  Metabolism – the sum total of all chemical reactions that take place in living cells  Metabolic Organs Digestive System – to ingest, digest & absorb nutrients Liver – the “control panel” and most active processing center in the body 1. Receives absorbed nutrients first 2. Manufactures important compounds 3. Detoxifies drugs & metabolic wastes

METABOLISM Pancreas 1. Secretes digestive enzymes 2. Produces insulin & other hormones involved in glucose regulation Heart & Blood Vessels 1. Carry nutrients & O2 to cells 2. Return cell wastes Kidneys 1. Filter wastes 2. Produce important body compounds

ENERGY METABOLISM After absorption, 2 processes occur: 1. Anabolism – “building reactions” to create larger molecules Example: Glucose>>>Glycogen 2. Catabolism – “breakdown reactions” to release energy Example: Glycogen>>>Glucose

Chemical Reactions Copyright 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 = glycolysis 1. 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

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

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

Copyright 2005 Wadsworth Group, a division of Thomson Learning The TCA Cycle

Copyright 2005 Wadsworth Group, a division of Thomson Learning 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

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

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

Copyright 2005 Wadsworth Group, a division of Thomson Learning The Paths of Pyruvate & Acetyl CoA

Copyright 2005 Wadsworth Group, a division of Thomson Learning

ENERGY BUDGET Feasting – when a person eats more than he/she needs, excess energy will be stored as: 1. Glycogen – excess carbohydrate 2. Body fat – excess carbohydrate, fat, protein, or alcohol 3. Metabolism favors fat formation especially when the excess energy is derived from dietary fat

Economics of Feasting Copyright 2005 Wadsworth Group, a division of Thomson Learning

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 system 1. Glycogen stores will only last ~1/2 day 2. Other cells in the body can use stored fat, but the brain requires glucose; thus, body proteins begin rapid breakdown to supply glucose to brain REMEMBER: 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 Copyright 2005 Wadsworth Group, a division of Thomson Learning

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