Biochemistry and Physiology test 3

Digestion of Carbohydrates

• Monosaccharides are the simplest carbohydrates and cannot be further hydrolyzed
• Examples of monosaccharides include Glucose, Fructose, and Galactose
• Disaccharides are composed of two monosaccharide units
• Examples of disaccharides include Maltose (Glucose + Glucose), Lactose (Glucose + Galactose), and Sucrose (Glucose + Fructose)
• Oligosaccharides contain a small number (2-10) of monosaccharide units
• Polysaccharides are large polymers of monosaccharides
• Examples of polysaccharides include Starch, Glycogen, and Cellulose

Lipid Digestion

• Focus on enzymes, location, products, emulsification, bile acid function, and absorption

Monosaccharides

• Monosaccharides exist in both linear (Fischer projection) and cyclic (Haworth projection) forms
• Cyclic structures form due to hemiacetal or hemiketal formation
• Glucose forms a six-membered pyranose ring.
• Fructose forms a five-membered furanose ring

Protein Digestion

• Focus on enzymes, location, and products

Physical Properties

• Colorless, crystalline solids that are soluble in water but insoluble in nonpolar solvents

Chemical Properties

• Can be oxidized to form carboxylic acids
• Can be reduced to form sugar alcohols (e.g., glucose → sorbitol)
• Can form glycosidic bonds to create disaccharides and polysaccharides

Enzymes, Location, and Products

• Stomach: Pepsin (activated by HCl) hydrolyzes proteins into polypeptides
• Small Intestine:
  • Pancreatic Proteases:
    • Trypsin & Chymotrypsin: Cleave peptide bonds into smaller peptides
    • Carboxypeptidase: Removes terminal amino acids
    • Aminopeptidase & Dipeptidase: Cleave peptides into free amino acids
  • Absorption: Free amino acids are absorbed via Na+-dependent active transport

Protein Digestion in Ruminants vs. Non-Ruminants

• Ruminants:
  • Rumen microbes digest dietary protein, producing microbial protein
  • Microbial proteases degrade proteins into peptides & ammonia
  • Microbes synthesize new proteins from ammonia and volatile fatty acids
  • Rumen Undegradable Protein (RUP) passes to the small intestine for absorption
• Non-Ruminants: Rely on gastric and pancreatic enzymes for protein digestion

Material Transfer and Membranes

• Focus on chemical composition, function, structural elements (proteins, carbohydrates, and lipids) of membranes, types of transport, and examples

Chemical Composition of Membranes

• Composed of lipids, proteins, and carbohydrates
• Lipids consist of phospholipids, sphingolipids, and cholesterol
• Proteins include integral and peripheral proteins
• Carbohydrates are present as glycolipids and glycoproteins, important for cell recognition

Structural Elements of Membranes

• Phospholipid Bilayer: Hydrophilic heads face outward, hydrophobic tails face inward
• Proteins:
  • Integral Proteins: Embedded in the membrane, help in transport
  • Peripheral Proteins: Attached to membrane surfaces, involved in signaling
• Carbohydrates: Attached to proteins (glycoproteins) or lipids (glycolipids), crucial for cell recognition

Types of Membrane Transport

• Passive Transport (No energy required)
  • Diffusion: Movement from high to low concentration
  • Facilitated Diffusion: Uses carrier or channel proteins
  • Osmosis: Water movement through the membrane (via aquaporins)
• Active Transport (Requires energy – ATP)
  • Primary Active Transport: Direct use of ATP (e.g., Sodium-Potassium (Na+/K+) Pump: 3 Na+ out, 2 K+ in)
  • Secondary Active Transport: Uses energy from another molecule's concentration gradient (e.g., glucose transport)
• Endocytosis & Exocytosis (Bulk Transport)
  • Endocytosis: Engulfing substances into the cell
  • Exocytosis: Releasing substances out of the cell

Carbohydrates

• Focus on classification, linear and cyclic structures, properties, reducing/non-reducing disaccharides/polysaccharides, bonds, qualitative tests of carbohydrates
• Starch (plant storage form of glucose)
• Amylose: Unbranched, α-1,4 glycosidic bonds
• Amylopectin: Branched, α-1,4 and α-1,6 glycosidic bonds
• Glycogen (animal storage form of glucose): Similar to amylopectin but more highly branched (every 8–12 glucose units)
• Cellulose (structural component in plants): β-1,4 glycosidic bonds; indigestible by humans

Glycolysis

• Focus on the first and second stages of glycolysis: Reactions, enzymes, energy producing or using reactions

Fehling's/Benedict's Test

• For reducing sugars; positive result is a brick-red precipitate (Cu2O)

Iodine Test

• For starch detection; starch reacts with iodine to give a blue-black color; glycogen may give a reddish-brown color

Stages and Reactions

• Stage 1: Energy Investment Phase (Reactions 1-5)
  • Glucose → Glucose-6-Phosphate (G6P)
    • Enzyme: Hexokinase/Glucokinase (in liver)
    • Consumes 1 ATP
  • G6P → Fructose-6-Phosphate (F6P)
    • Enzyme: Phosphoglucose Isomerase
  • F6P → Fructose-1,6-Bisphosphate (F1,6BP)
    • Enzyme: Phosphofructokinase-1 (PFK-1)
    • Consumes 1 ATP
  • F1,6BP → Glyceraldehyde-3-Phosphate (G3P) + Dihydroxyacetone Phosphate (DHAP)
    • Enzyme: Aldolase
  • DHAP → G3P
    • Enzyme: Triose Phosphate Isomerase
• Net: -2 ATP used
• Stage 2: Energy Payoff Phase (Reactions 6-10)
  • G3P → 1,3-Bisphosphoglycerate (1,3-BPG)
    • Enzyme: Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH)
    • Produces NADH
  • 1,3-BPG → 3-Phosphoglycerate (3PG)
    • Enzyme: Phosphoglycerate Kinase
    • Generates 2 ATP (substrate-level phosphorylation)
  • 3PG → 2-Phosphoglycerate (2PG)
    • Enzyme: Phosphoglycerate Mutase
  • 2PG → Phosphoenolpyruvate (PEP)
    • Enzyme: Enolase
  • PEP → Pyruvate
    • Enzyme: Pyruvate Kinase
    • Generates 2 ATP (substrate-level phosphorylation)
• Net: +4 ATP, +2 NADH, +2 Pyruvate
• Overall ATP Yield: +2 ATP per glucose

Pyruvate

• Focus on fates in aerobic and anaerobic conditions: Conditions, main reason of lactate production, reactions, enzymes, products

Aerobic Conditions

• Pyruvate is converted into Acetyl-CoA by the Pyruvate Dehydrogenase Complex (PDC)
• Acetyl-CoA enters the Krebs cycle (Citric Acid Cycle) for further oxidation
• Products: CO2, NADH, and Acetyl-CoA

Anaerobic Conditions

• Pyruvate is converted into Lactate by Lactate Dehydrogenase
• This regenerates NAD+, allowing glycolysis to continue
• Main reason for lactate production: To regenerate NAD+ for glycolysis in the absence of oxygen

Oxidative Decarboxylation of Pyruvate

• Focus on enzymes, coenzymes, mechanism, products, regenerated/non-regenerated coenzymes

Enzymes and Coenzymes

• Enzyme Complex: Pyruvate Dehydrogenase Complex (PDC)
• Coenzymes Involved:
  • Thiamine Pyrophosphate (TPP) – (Bound to E1)
  • Lipoamide – (Bound to E2)
  • Coenzyme A (CoA) – (Substrate for E2)
  • FAD (Flavin Adenine Dinucleotide) – (Bound to E3)
  • NAD (Nicotinamide Adenine Dinucleotide) – (Substrate for E3)

Mechanism of Reaction

• E1: Pyruvate Decarboxylation
  • Pyruvate reacts with TPP, leading to the formation of Hydroxyethyl-TPP
  • CO2 is released
• E2: Acetyl Transfer to CoA
  • The hydroxyethyl group is oxidized and transferred to lipoamide
  • The acetyl group is then transferred to Coenzyme A (CoA) forming Acetyl-CoA
• E3: Regeneration of Lipoamide
  • FAD oxidizes lipoamide, regenerating its disulfide form
  • NAD+ oxidizes FADH2, producing NADH + H+

Products

• Acetyl-CoA (enters the Krebs Cycle)
• NADH (goes to the electron transport chain)
• CO2 (exhaled as a waste product)

Regenerated and Non-Regenerated Coenzymes

• Regenerated: Lipoamide, FAD
• Non-Regenerated: NADH, Acetyl-CoA

Krebs Cycle

• Focus on precursors and products, reactions and enzymes, reactions where energy is produced, and reactions where oxidative decarboxylation occurs

Reactions and Enzymes

• Acetyl-CoA + Oxaloacetate → Citrate
  • Enzyme: Citrate Synthase
• Citrate → Isocitrate
  • Enzyme: Aconitase
• Isocitrate → α-Ketoglutarate (Oxidative Decarboxylation, Produces NADH)
  • Enzyme: Isocitrate Dehydrogenase
• α-Ketoglutarate → Succinyl-CoA (Oxidative Decarboxylation, Produces NADH)
  • Enzyme: α-Ketoglutarate Dehydrogenase
• Succinyl-CoA → Succinate (Substrate-Level Phosphorylation, Produces GTP/ATP)
  • Enzyme: Succinyl-CoA Synthetase
• Succinate → Fumarate (Produces FADH2)
  • Enzyme: Succinate Dehydrogenase
• Fumarate → Malate
  • Enzyme: Fumarase
• Malate → Oxaloacetate (Produces NADH)
  • Enzyme: Malate Dehydrogenase

Energy-Producing Reactions

• NADH-producing reactions:
  • Isocitrate → α-Ketoglutarate
  • α-Ketoglutarate → Succinyl-CoA
  • Malate → Oxaloacetate
• FADH2-producing reaction:
  • Succinate → Fumarate
• ATP/GTP-producing reaction:
  • Succinyl-CoA → Succinate

Energy Yield of Glycolysis

• Focus on energy yield to pyruvate; to lactate; and to CO2/H2O

To Pyruvate

• Net ATP Gain: 2 ATP
• NADH Produced: 2 NADH

To Lactate

• 2 ATP (same as pyruvate stage, NADH is used to convert pyruvate to lactate)

To CO2 and H2O (Complete Oxidation)

• Glycolysis: 2 ATP, 2 NADH (5 ATP)
• Krebs Cycle (Per Glucose): 2 GTP, 6 NADH (15 ATP), 2 FADH2 (3 ATP)
• Total ATP Yield: ~30-32 ATP per glucose

Glycolysis to Pyruvate

• 2 ATP (net)
• 2 NADH (5 ATP if fully oxidized in mitochondria)

Glycolysis to Lactate (Anaerobic)

• 2 ATP (since NADH is used in lactate formation, no additional ATP)

Complete Oxidation to CO2 & H2O

• Glycolysis: 2 ATP + 2 NADH (5 ATP)
• Pyruvate → Acetyl-CoA: 2 NADH (5 ATP)
• Krebs Cycle (2 rounds): 6 NADH (15 ATP), 2 FADH2 (3 ATP), 2 GTP (2 ATP)
• Total: ~30-32 ATP per glucose molecule

Final Energy Yield

• Glycolysis → Pyruvate: 8 ATP
• Pyruvate → Acetyl-CoA: 6 ATP
• Acetyl-CoA → CO2 + H2O (Krebs Cycle): 24 ATP
• Total ATP (Complete Oxidation of Glucose): 38 ATP

Glycogenolysis

• Focus on stages, enzymes, debranching, and products

Stages & Enzymes

• Glycogen Phosphorylase:
  • Removes glucose from the non-reducing ends
  • Converts glycogen → Glucose-1-Phosphate
  • Stops 4 residues before a branch point
• Debranching Enzyme:
  • α(1,4) Transglycosylase shifts 3 glucose residues
  • α(1,6) Glucosidase hydrolyzes branch point glucose → Free Glucose
• Phosphoglucomutase:
  • Converts Glucose-1-Phosphate → Glucose-6-Phosphate

Products

• Glucose-6-Phosphate (for glycolysis or blood glucose regulation)
• Free Glucose (from branch points)

Glycogen Synthesis

• Focus on stages, enzymes, and branching
• Stages:
  • Glucose → Glucose-1-P (Enzyme: Phosphoglucomutase)
  • Glucose-1-P + UTP → UDP-Glucose (Enzyme: UDP-Glucose Pyrophosphorylase)
  • Glycogen Synthase forms α(1→4) glycosidic bonds
  • Branching Enzyme introduces α(1→6) branches

Pentose Phosphate Pathway

• Focus on stages, main reactions of the first oxidative stage, enzymes, and functions (NADPH, glutathione, glucose-6-phosphate dehydrogenase)

Stages & Reactions

• Oxidative Stage (Irreversible)
  • Glucose-6-Phosphate → Ribulose-5-Phosphate
    • Enzyme: Glucose-6-Phosphate Dehydrogenase (G6PD)
    • Products: NADPH & CO2
• Non-Oxidative Stage (Reversible)
  • Converts 3-7 carbon sugars for biosynthetic use
  • Provides Ribose-5-Phosphate for nucleotide synthesis

Functions

• NADPH production:
  • Used for fatty acid synthesis (liver, adipose tissue)
  • Maintains glutathione in its reduced form (antioxidant in RBCs)
• Glucose-6-Phosphate Dehydrogenase Deficiency:
  • Leads to hemolysis in RBCs due to oxidative stress

Gluconeogenesis

• Focus on similarities/differences between glycolysis/gluconeogenesis & non-reversible reactions/enzymes

Differences from Glycolysis

• Not a simple reversal of glycolysis
• Bypasses 3 irreversible steps:

1. Pyruvate → Phosphoenolpyruvate (PEP):

• Pyruvate Carboxylase converts Pyruvate → Oxaloacetate
• PEP Carboxykinase (PEPCK) converts Oxaloacetate → PEP

2. Fructose-1,6-Bisphosphate → Fructose-6-Phosphate:

• Enzyme: Fructose-1,6-Bisphosphatase

3. Glucose-6-Phosphate → Glucose:

• Enzyme: Glucose-6-Phosphatase (in ER of liver/kidney)

Precursors for Glucose Synthesis

• Lactate (from anaerobic glycolysis)
• Amino Acids (mainly Alanine)
• Glycerol (from triglyceride breakdown)

Metabolism

• Focus on energy/substance transformations, anabolic/catabolic processes, ATP structure, ATP's role in energy metabolism

ATP Structure

• Adenine + Ribose + Three Phosphate groups

Role

• Anabolic Reactions: Provides energy for biosynthesis
• Catabolic Reactions: ATP is regenerated via glycolysis, Krebs cycle, and oxidative phosphorylation

Substrate-Level Phosphorylation

• Focus on macroergic compounds and examples
• Definition & Mechanism: Substrate-level phosphorylation is the direct formation of ATP by transferring a phosphoryl group from a high-energy intermediate to ADP
• This process does not require oxygen and occurs in:
  • Glycolysis
  • Krebs Cycle (TCA Cycle)

Examples

• Glycolysis:
  • 1,3-Bisphosphoglycerate + ADP → 3-Phosphoglycerate + ATP
    • Enzyme: Phosphoglycerate Kinase
  • Phosphoenolpyruvate (PEP) + ADP → Pyruvate + ATP
    • Enzyme: Pyruvate Kinase
• Krebs Cycle:
  • Succinyl-CoA + GDP → Succinate + GTP
  • Enzyme: Succinyl-CoA Synthetase

Oxidative Phosphorylation

• Focus on respiratory chain enzymes, their localization in the cell, respiratory chain dehydrogenases/cytochrome coenzymes, their structure, equations of redox reactions in the respiratory chain, and proton transport across the membrane
• Definition: Oxidative phosphorylation is the formation of ATP using energy derived from the transfer of electrons in the Electron Transport Chain (ETC)
• Requires oxygen as the final electron acceptor

Enzymes & Complexes in the Respiratory Chain

• Complex I (NADH-CoQ Reductase): Transfers electrons from NADH → Coenzyme Q (Ubiquinone); pumps 4 H+ into the intermembrane space
• Complex II (Succinate-CoQ Reductase): Transfers electrons from FADH2 → Coenzyme Q; does not pump protons
• Complex III (CoQ-Cytochrome c Reductase): Transfers electrons from CoQ → Cytochrome c; pumps 4 H+
• Complex IV (Cytochrome c Oxidase): Transfers electrons from Cytochrome c → O2; final step: O2 is reduced to H2O; pumps 2 H+

Proton Transport & ATP Synthesis

• Electron movement generates a proton gradient across the inner mitochondrial membrane
• This creates the proton motive force (PMF)
• ATP Synthase (Complex V) uses this gradient to produce ATP

ATP Synthase

• Focus on the principle of action and energy effect of oxidation of reduced dehydrogenases

Mechanism of ATP Synthase

• Location: Inner mitochondrial membrane
• Structure:
  • Fo Subunit: Proton channel that allows H+ back into the matrix
  • F1 Subunit: Catalyzes ATP synthesis from ADP + Pi
• Mechanism (Chemiosmotic Theory)
  • Protons flow through Fo due to the proton gradient
  • F1 subunit rotates, inducing conformational changes
  • ATP is synthesized from ADP and Pi

Energy Yield of Oxidative Phosphorylation

• NADH oxidation → 3 ATP
• FADH2 oxidation → 2 ATP
• Total ATP yield per glucose molecule (including glycolysis, Krebs cycle, oxidative phosphorylation) = 38 ATP

Utilization of Organic Nutrients

• Focus on metabolism of organic nutrients, absorptive and postabsorptive states, and carbohydrate/protein/lipid metabolism

Metabolism

• Refers to all chemical reactions in the body
• Consists of:
  • Catabolism: Breaking down complex molecules to release energy
  • Anabolism: Using energy to synthesize large molecules

Energy Source

• During digestion, energy is transferred to the body as glucose, fatty acids, and amino acids
• Some molecules are used for synthesis, while others are oxidized, producing CO2, H2O, and heat

Absorptive State (Anabolic)

• Body gets energy by oxidizing nutrients absorbed from the intestine
• Carbohydrates, fats, and proteins are used for growth and energy storage

Postabsorptive State (Catabolic)

• Energy is mobilized from body stores
• Liver produces glucose via Glycogenolysis (breakdown of glycogen) & Gluconeogenesis (conversion of lactate, pyruvate, amino acids, and glycerol into glucose)

Carbohydrate Metabolism

• Non-Ruminants: Starch/glycogen broken into monosaccharides (glucose, galactose, fructose); glucose is main monosaccharide absorbed
• Herbivores: Cellulose is the main carbohydrate
• Ruminants: Cellulose is converted to volatile fatty acids (VFAs) by microbes
• Simple-Stomached Herbivores: Cellulose metabolism occurs in the large intestine

Liver's Role

• Stores glucose as glycogen or converts it to lipids
• Maintains blood glucose levels through Glycogenolysis and Gluconeogenesis
• Glucose sparing (using lipids as energy)

Protein Metabolism

• Liver Functions:
  • Converts amino acids to glucose or fatty acids
  • Produces albumin, enzymes, and clotting factors
  • Deamination: Converts amino acids to keto acids, used for energy or stored as fat
  • Transamination: Converts amino acids into non-essential amino acids
  • Urea Cycle: Converts toxic ammonia (NH3) into urea for excretion
• Ruminants: Microbial proteins are synthesized in the forestomach; dietary amino acid composition is less important

Lipids Metabolism

• Triglycerides are the major storage form of energy
• Lipids are transported in the blood
• Chylomicrons transport dietary lipids
• VLDL (Very Low-Density Lipoproteins) transport liver-produced lipids

Lipid Metabolism

• Lipolysis releases fatty acids for energy
• Glucose Sparing: During fasting, tissues switch to fat metabolism

Regulation of Organic Nutrient Metabolism

• Hormonal Control:
  • Insulin: Lowers glucose and fatty acids in plasma
  • Glucagon: Stimulates glycogenolysis and gluconeogenesis
  • Cortisol: Stimulates gluconeogenesis
  • Epinephrine: Stimulates glycogenolysis
  • Growth Hormone: Mobilizes fatty acids
• Nervous System Control:
  • Sympathetic Nervous System: Increases glucose release
  • Parasympathetic Nervous System: Stimulates insulin secretion

Regulation of Body Temperature

• Normal body temperature in mammals: 36.5–39.5°C (varies by species) & Birds: 38-42°C
• Measurement: Usually taken rectally with an electronic or liquid thermometer
• Hyperthermia is excess heat production or reduced heat loss
  • Occurs during exercise, infections (fever), pregnancy, and lactation
• Hypothermia is when heat loss exceeds heat production
  • Common in newborns, old animals, and small breeds
  • Risk factors: Wet fur, prolonged exposure to cold, and inadequate fat/hair coat

Clinical Signs of Hypothermia

• Shivering, slow breathing, lethargy, and low blood pressure
• Severe cases: Muscle stiffness, dilated pupils, and coma

Heat Balance

• Balance between heat production and heat loss to maintain body temperature, heat input must equal heat output

Heat Production

• Basal metabolism: The body's normal energy use
• Shivering: Involuntary muscle contractions to generate heat
• Non-Shivering Thermogenesis: Brown Adipose Tissue (BAT) is present in newborns and hibernating animals
• Sympathetic Nervous System increases fat oxidation
• Thyroid Hormones increase metabolism and heat production

Heat Loss Mechanisms

• Radiation: Heat transfer by electromagnetic waves
• Conduction: Heat transfer via direct contact with objects
• Convection: Heat loss through moving air/water
• Evaporation: Sweating, panting, and wetting body surface

Thermoneutral Zone

• The most energy-efficient temperature range for an animal
• Outside the TNZ:
  • Too warm → Body must spend energy on cooling
  • Too cold → Body must spend energy on warming

Extreme Heat/Cold Conditions

• Hibernation: Some mammals lower body temperature to 4-8°C in winter
• Estivation: Heat dormancy in hot climates
• Body Temperature Regulation: Controlled by Reflexes:
  • Sensory Input: Skin, internal organs, and hypothalamus detect temperature changes
  • Integrating Center: Hypothalamus regulates body temperature
  • Motor Output:
    • Heat Stress: Sweating, panting, and increased blood flow to skin
    • Cold Stress: Shivering, reduced blood flow to skin, and increased hormone secretion

Bioenergetics and Growth

• Focus on absorption of energy substrates and metabolic rate
• Energy intake = Energy expenditure to maintain body functions

Energy Substrates

• Carbohydrates: Provide 4.1 kcal/gram
• Proteins: Provide 4.1 kcal/gram
• Lipids (Fats): Provide 9.3 kcal/gram

Metabolic Rate

• The total energy turnover in the body per unit time
• Factors affecting metabolic rate:
  • Body size (smaller animals have higher metabolic rates per unit weight)
  • Physical activity (exercise increases metabolism)
  • Environmental temperature (increases when cold or hot)
  • Reproductive status (pregnancy, lactation)
  • Hormones: Thyroid hormones/sympathetic nervous system increase metabolic rate
  • Starvation lowers metabolic rate.

Metabolic Rate Types

• Basal Metabolic Rate (BMR): Minimum energy required for basic life functions
• Fasting Metabolic Rate: Energy expenditure when an animal can move but is fasting
• Maintenance Metabolic Rate: Energy required to maintain body mass without production
• Field Metabolic Rate: Average daily metabolic rate under natural conditions

Energy Requirements

• Calculation of energy requirements of animals
• Production animals (e.g., dairy cows, laying hens, horses) require extra energy for work, growth, and milk/wool/egg production
• Formula: Total Energy Requirement = Maintenance Energy + Production Energy
• Measurement of metabolic rate.

Respiratory Quotient

• Definition: The ratio of CO2 produced / O2 consumed
• Indicates which energy substrate is being used:
  • Carbohydrates → RQ = 1.0
  • Proteins → RQ = 0.8
  • Lipids → RQ = 0.7
  • RQ > 1: Suggests anaerobic respiration is occurring

Heat Increment Digestion

• Definition: Increase in heat production after eating
• High in ruminants (50% of metabolizable energy due to fermentation)
• Lower in simple-stomached animals (10-30%)

Aerobic Metabolic Scope

• Definition: The ratio of maximum metabolic rate / maintenance metabolic rate
• During intense activity, animals can increase metabolic rate 25-35 times

Feed Energy Utilization

• Carnivores: Digest meat and fat efficiently (>80% metabolizable energy)
• Herbivores: Lose ~50% of feed energy in feces, urine, and methane
• Omnivores (e.g., pigs): Have energy utilization between herbivores and carnivores

Energy Storage

• Excess energy is stored as triglycerides

Energy Storage Examples

• Deer: Use fat stores for winter survival
• Migratory birds: Store fat before migration
• Lactating mammals: Use fat reserves for milk production
• Growth requires ATP (energy source) and nutrients for cell building (proteins, lipids, minerals)
• Fetal Growth:
  • Mammals: Nutrients come from the placenta
  • Birds: Nutrients come from the egg yolk
• Hormonal Control:
  • Fetal Stage: Insulin and T3 regulate growth
  • Postnatal Growth: Growth Hormone (GH) and Insulin-Like Growth Factor (IGF)

Aging Effects

• Reduced appetite, metabolic rate, muscle mass, and mental ability
• Cell number decreases over time
• Production animals are slaughtered before aging effects occur
• Companion animals/herbivores live longer and experience aging diseases.
• Aging accelerates when teeth wear down, affecting digestion