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Nutrition, Metabolism, and Body Temperature Regulation
Anatomy and Physiology I (BIOL 2401 )
Texas A&M University-Corpus Christi
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Nutrition, Metabolism, and Body Temperature
Regulation
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)
- Grains, fruits, vegetables, meats and fish, and milk products
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
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
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”
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
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
Prostaglandins function in:
- Smooth muscle contraction
- Control of blood pressure
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
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., stress, burns, infection, or injury)
Hormonal control
- Anabolic hormones accelerate protein synthesis
Vitamins
Organic compounds needed for growth and good health
They are crucial in helping the body use nutrientsand 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 - B 12 additionally requires gastric intrinsic factor to be absorbed
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
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
- 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
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
Two important coenzymes are nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD)
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
Mechanisms of ATP Synthesis: Oxidative Phosphorylation
- Uses the chemiosmotic process whereby the movement of substances across a membrane is coupled to chemical reactions
- 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 thsynthase, energy is captured and attaches phosphategroups to ADP (torough ATP make ATP)
Carbohydrate Metabolism
- Since all carbohydrates are transformed into glucose, it is essentially glucose metabolism
- Oxidation of glucose is shown by the overall reaction:
C 6 H 12 O 6 + 6O 2 à 6H 2 O + 6CO 2 + 36ATP + heat
- Occurs in three pathways
- Glycolysis
- Krebs cycle
- The electron transport chain and oxidative phosphorylation
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
Glycolysis: Phase 1 and 2
Sugar activation
- Two ATP molecules activate glucose into
Decarboxylation
- Carbon is removed from pyruvic acid
- Carbon dioxide is released
Oxidation
- Hydrogen atoms are removed from pyruvic acid
- NAD+is reduced to NADH + H+
Formation of acetyl CoA – the resultant acetic acid is combined with coenzyme A, a sulfur-containing coenzyme, toform acetyl CoA
Krebs Cycle
- An eight-step cycle in which acetic acid is decarboxylated and oxidized, generating: - Three molecules of NADH + H+ - One molecule of FADH 2 - Two molecules of CO 2 - One molecule of ATP
- For each molecule of glucose entering glycolysis, two molecules of acetyl CoA enter the Krebs cycle
Electron Transport Chain
Food (glucose) is oxidized and the hydrogen:
- Are transported by coenzymes NADH and FADH 2
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
Hypothetical 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-c 1 - Cytochrome oxidase (a-a 3 ) - The electrons are shuttled from one acceptor to the next
- 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
Electronic Energy Gradient
- 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
- Catabolism of fats involves two separate pathways
- Glycerol pathway
- Fatty acids pathway
- Glycerol is converted to glyceraldehyde phosphate
- Glyceraldehyde is ultimately converted into acetylCoA
- Acetyl CoA enters the Krebs cycle
- 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
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
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)
Lipid Metabolism: Synthesis of Structural Materials
- Phospholipids are important components of myelin and cell membranes
- The liver:
- Synthesizes lipoproteins for transport of cholesterol and fats
- Makes tissue factor, a clotting factor
- Synthesizes cholesterol for acetyl CoA
- Uses cholesterol for forming bile salts
- Certain endocrine organs use cholesterol for synthesizing steroid hormones
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
Deaminated amino acids are converted into:
- Pyruvic acid
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
State of the Body
- The body exists in a dynamic catabolic-anabolic state
- Organic molecules (except DNA) are continuously broken down and rebuilt
- The body’s total supply of nutrients constitutes its nutrient pool
- Amino acid pool – body’s total supply of free amino acids is the source for:
- Resynthesizing body proteins
- Forming amino acid derivatives
- Gluconeogenesis
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
Absorptive 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
Absorptive 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
Principal Pathways of the Absorptive State
In muscle
- Amino acids become protein
Glucose becomes unavailable to most body cells
Metabolic acidosis, protein wasting, and weight loss results as fats and tissue proteins are used for energy
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
Principle Pathways in the Postabsorptive State
In muscle:
- Protein is broken down to amino acids
- Glycogen is converted to ATP and pyruvic acid (lactstates) ic acid in anaerobic
In the liver:
- Amino acids, pyruvic acid, stored glycogen, and fatglucose are converted into
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
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
- 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
Liver Metabolism
- Hepatocytes carry out over 500 intricate metabolic functions
- A brief summary of liver functions
- Packages fatty acids to be stored and transported
- Synthesizes plasma proteins
Nutrition, Metabolism, and Body Temperature Regulation
Course: Anatomy and Physiology I (BIOL 2401 )
University: Texas A&M University-Corpus Christi
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