Chapter 24: Nutrition, Metabolism, and Body Temperature Regulation

Nutrients

Substance in food needed for growth, maintenance, and repair, which include proteins, carbohydrates, fats, vitamins, minerals, and water.

Macronutrients

Three major nutrients that make up the bulk of ingested food.

Micronutrients

Two nutrients that are required, but in small amounts.

Essential Nutrients

Molecules that must be eaten because the body cannot synthesize these from other nutrients.

Complete Proteins

Contain all nine essential amino acids in the proportions needed by the body.

Incomplete Proteins

Lack one or more of the nine essential amino acids.

Carbohydrates

Primary source of energy (glucose is used in cellular respiration to produce ATP).

Proteins

Growth and repair of tissues, enzyme and hormone production, immune function, and energy when needed.

Fats (Lipids)

Long-term energy storage, insulation, cell membrane structure, and hormone synthesis.

Vitamins

Act as coenzymes in metabolic reactions, support immune function, promote cell growth, and maintain overall health.

Minerals

Structural components (e.g., calcium in bones), fluid balance, nerve signaling, and enzymatic reactions.

Water

Essential for all biochemical reactions, regulates temperature, transports nutrients, removes waste, and lubricates joints.

Metabolism

Metabolism refers to the sum of all chemical reactions occurring within an organism to maintain life.

Catabolism

Breakdown of large molecules into smaller ones, releasing energy.

Anabolism

Synthesis of large molecules from small ones, requiring energy.

Essential Amino Acids

Certain amino acids that the body cannot produce and must be obtained from food.

Sources of Carbohydrates

Grains (bread, rice, pasta), fruits, vegetables, legumes, dairy products.

Sources of Proteins

Meat, poultry, fish, eggs, dairy, legumes, nuts.

Sources of Fats

Oils, butter, avocados, nuts, seeds, fatty fish.

Sources of Vitamins

Fruits, vegetables, dairy, lean meats, whole grains.

Sources of Minerals

Dairy (calcium), meat (iron, zinc), fruits and vegetables (potassium, magnesium), salt (sodium).

Sources of Water

Drinking water, fruits, vegetables, soups, beverages.

Catabolism

Hydrolysis of complex structures to simpler ones, releasing energy.

Cellular respiration

Breaking down glucose to produce ATP.

Catabolic Reactions

Involves the breakdown of complex molecules into simpler ones, releasing energy in the form of ATP.

Digestion

Large macronutrients (carbohydrates, proteins, fats) are broken down into smaller molecules.

Glycolysis

Breakdown of glucose into pyruvate, producing ATP (2) and NADH.

Krebs Cycle

Pyruvate is further broken down into Acetyl-CoA, generating energy carriers (NADH, FADH₂), and produces ATP (2).

Oxidative Phosphorylation

Energy carriers donate electrons to produce ATP (26-28) efficiently.

Anabolism

The process of using ATP to build complex molecules needed for growth, repair, and maintenance.

Protein Synthesis

Amino acids combine to form proteins (enzymes, hormones, muscle tissue).

Glycogenesis

Excess glucose is stored as glycogen in the liver and muscles.

Lipogenesis

Fatty acids are converted into stored fat for long-term energy.

DNA & RNA Synthesis

Nucleotides combine to form genetic material for cell replication.

Insulin

Promotes glucose uptake and storage (anabolism).

Glucagon

Stimulates the breakdown of stored glycogen to release glucose (catabolism).

Thyroid Hormones (T3, T4)

Regulate overall metabolic rate.

Epinephrine (Adrenaline)

Increases energy release during stress.

Glycogenolysis

The hormone glucagon and epinephrine signal glycogenolysis, breaking down glycogen into glucose-1-phosphate.

Gluconeogenesis

When carbohydrate intake is low, the body needs an alternative glucose source.

Glycogenesis

Storage of glucose as glycogen

Glycogenolysis

Breakdown of glycogen into glucose

Gluconeogenesis

Formation of new glucose from non-carbohydrates

Lipolysis

Breakdown of stored triglycerides into glycerol & fatty acids

Fatty Acid Activation

Fatty acids bind to CoA to form fatty acyl-CoA

Transport into mitochondria

Carnitine shuttle moves fatty acyl-CoA into mitochondria

Beta-oxidation

Fatty acids are broken down into acetyl-CoA

Krebs Cycle and ETC

Acetyl-CoA enters Krebs cycle, NADH/FADH₂ drive ATP production

Ketogenesis

Excess acetyl-CoA forms ketone bodies

Ketone bodies

Water-soluble molecules produced by the liver from acetyl-CoA when carbohydrate availability is low

Prolonged Fasting or Starvation

When glycogen stores in the liver are depleted, the body shifts to using fats for energy

Low-Carbohydrate Diet

A lack of dietary glucose forces the body to metabolize fat for energy, increasing ketone production

Uncontrolled Diabetes

In Type 1 diabetes, insulin deficiency prevents glucose uptake by cells, leading to excessive ketone production

Prolonged Exercise

Intense or prolonged physical activity depletes glycogen, leading to ketone production for energy

Starvation or Severe Caloric Restriction

The body shifts to fat metabolism due to a lack of food intake

Deamination

The amine (-NH₂) group is removed in the liver, forming ammonia, which is converted to urea for excretion

Conversion to Metabolic Intermediates

The remaining carbon skeleton enters the Krebs cycle or is used for gluconeogenesis

ATP Production

Amino acids generate NADH & FADH₂, which fuel the electron transport chain for ATP synthesis

Absorptive State

Occurs after eating (0-4 hours post-meal) where nutrients are absorbed, and energy is stored

Glucose in Absorptive State

Used for ATP or stored as glycogen (liver & muscles)

Fats in Absorptive State

Stored in adipose tissue as triglycerides

Fats

Stored in adipose tissue as triglycerides.

Amino Acids

Used for protein synthesis or energy if needed.

Insulin

Promotes glucose uptake, glycogenesis, and lipogenesis.

Post-Absorptive State (Fasting State)

Occurs when no nutrients are absorbed (4+ hours after a meal).

Glycogenolysis

Breakdown of glycogen.

Gluconeogenesis

New glucose production.

Lipolysis

Releases fatty acids for energy.

Ketogenesis

Occurs if glucose is very low.

Glucagon

Stimulates glucose release and fat breakdown.

Epinephrine

Stimulates glucose release and fat breakdown.

Cortisol

Stimulates glucose release and fat breakdown.

Cholesterol

Structural component of cell membranes.

Steroid hormones

Precursor for hormones like estrogen and testosterone.

Bile production

Needed for fat digestion.

Vitamin D synthesis

Supports the synthesis of vitamin D.

Hunger Signals

Controlled by the hypothalamus and influenced by hormones.

Ghrelin

A stomach hormone that increases appetite.

Low blood glucose

Stimulates eating.

Satiety Signals

Signals that suppress hunger.

Leptin

A hormone from fat cells that suppresses hunger.

Basal Metabolic Rate (BMR)

The energy needed at rest to maintain vital functions like breathing, circulation, and cell repair.

Total Metabolic Rate (TMR)

The rate of kilocalorie consumption to fuel all ongoing activities.

Heat Gain

Metabolism generates heat from the oxidation of nutrients.

Macronutrients

Carbohydrates, fats, and proteins that provide energy and structural components.

Micronutrients

Vitamins and minerals required in smaller amounts but critical for metabolic processes.

Calories

The unit of energy provided by foods.

Kilocalories (kcal)

Energy value of food measured in kilocalories.

Calorie

The amount of heat needed to raise the temperature of 1 kg of water by 1°C.

Dietary Calorie

One dietary 'Calorie' equals 1 kcal.