Nutrition and Metabolism: Study Notes for Anatomy & Physiology

Nutrition and Metabolism

Introduction to Nutrition and Metabolism

Nutrition and metabolism are fundamental concepts in Anatomy & Physiology, focusing on how the body acquires, processes, and utilizes nutrients for energy and growth. Proper nutrition involves a balance of macronutrients and micronutrients, while metabolism encompasses all chemical reactions that sustain life.

Nutrition: Definitions and Concepts

• Nutrition: The study of food and nutrients required for health.

• Malnutrition: Deficiency or imbalance in nutrient intake.

• Macronutrients: Carbohydrates, fats, and proteins—primary energy sources.

• Micronutrients: Vitamins and minerals—required in smaller amounts for normal function.

Metabolism: Catabolism and Anabolism

Metabolism is the sum of all chemical reactions in the body, divided into two main processes:

• Catabolism: Breakdown of molecules to release energy; requires oxygen.

• Anabolism: Building of complex molecules from simpler ones; uses energy.

Both processes are essential for cellular maintenance and growth.

Macronutrients and Their Metabolic Roles

Major Macronutrients

The three primary macronutrients are carbohydrates, fats, and proteins. Each plays a distinct role in metabolism and health.

Nutrient	Dietary Sources	Functions
Carbohydrate	Fruit, honey, grains	Energy source, builds other carbohydrates
Fat (Lipid)	Meat, vegetable oils, dairy	Energy, cell membrane stability, steroid hormone synthesis
Protein	Meat, eggs, dairy	Body structure, enzymes, neurotransmitters, energy

Carbohydrate Metabolism

Carbohydrates are the preferred energy source. Glucose metabolism involves three main steps:

1. Glycolysis: Occurs in cytoplasm, anaerobic, converts glucose to pyruvic acid.

2. Citric Acid Cycle (Krebs Cycle): Occurs in mitochondria, aerobic, produces CO2 and high-energy electrons.

3. Electron Transport System (ETS): Transfers electrons to produce ATP.

Energy is transferred to ATP, which is used for cellular work.

ATP: The Energy Currency

Adenosine Triphosphate (ATP) stores and releases energy for cellular processes. Energy from nutrient catabolism is used to convert ADP to ATP.

• ATP contains high-energy phosphate bonds.

• Energy is released when ATP is hydrolyzed to ADP.

$\text{ATP} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$

Blood Glucose Regulation

Blood glucose levels are tightly regulated, primarily by the hormone insulin. Insulin lowers blood glucose by promoting its uptake into cells and increasing glucose catabolism.

• Normal fasting blood glucose: 80–110 mg/100 mL.

• Insulin secretion increases after meals, reducing blood glucose.

Fat and Protein Metabolism

Fats are catabolized for energy and can be converted to glucose. Excess fat is stored as adipose tissue. Proteins are used for energy only when carbohydrate and fat stores are depleted. Gluconeogenesis converts amino acids to glucose.

Amino Acids: Essential and Nonessential

The body requires 20 amino acids; about half are essential and must be obtained from the diet. The rest are nonessential and can be synthesized by the body.

Essential (Indispensable)	Nonessential (Dispensable)
Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine	Alanine, Arginine, Asparagine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Glycine, Proline, Serine, Tyrosine

Micronutrients: Vitamins and Minerals

Vitamins

Vitamins are organic molecules required in small amounts for normal metabolism. Deficiency (avitaminosis) or excess (hypervitaminosis) can cause health problems.

• Most vitamins act as cofactors for enzymes.

• Vitamin A: Vision; Vitamin D: Calcium homeostasis; Vitamin E: Antioxidant.

Vitamin	Dietary Source	Functions	Deficiency Consequences
Vitamin A	Green/yellow vegetables	Maintains epithelial tissue	Night blindness
Vitamin C	Citrus fruits	Collagen synthesis	Scurvy

Minerals

Minerals are inorganic molecules essential for various physiological functions, including nerve conduction and enzyme activity.

Mineral	Dietary Source	Functions	Deficiency Symptoms
Calcium	Dairy, legumes	Bone formation, nerve function	Bone degeneration
Iron	Meat, vegetables	Oxygen transport	Anemia

Regulation of Food Intake and Metabolic Rate

Regulating Food Intake

Food intake is regulated by the appetite and satiety centers in the hypothalamus. Various factors stimulate or inhibit appetite.

Stimulate Appetite	Inhibit Appetite	Source
Endogenous opioid peptides, emotions, food sensations	Alpha-MSH, environmental stimuli, food sensations	Hypothalamus, nervous system
Cortisol, ghrelin	Cholecystokinin, insulin	Adrenal cortex, GI tract, liver, pancreas

Basal and Total Metabolic Rates

Basal Metabolic Rate (BMR): Energy expenditure at rest in a comfortable environment. Total Metabolic Rate (TMR): Total daily energy expenditure, including activity and food digestion.

• BMR is influenced by size, sex, body composition, age, thyroid hormone, and other factors.

• TMR includes BMR plus energy used for activity and food processing.

Metabolic and Eating Disorders

Metabolic Conditions

Disruptions in metabolism can result from genetic errors, hormonal imbalances, or complications of other conditions.

• Inborn errors of metabolism: Genetic enzyme deficiencies.

• Hormonal imbalances: Affect metabolic rate and nutrient processing.

Eating Disorders

• Anorexia nervosa: Chronic refusal to eat, often due to fear of obesity.

• Bulimia: Alternating periods of overeating and self-denial, sometimes with vomiting.

• Obesity: Excess body fat, may be a symptom of an eating disorder.

Protein-Calorie Malnutrition (PCM)

PCM results from insufficient calories and protein. Two advanced forms are:

• Marasmus: Overall lack of calories and protein, causing tissue wasting and electrolyte imbalance.

• Kwashiorkor: Lack of protein with sufficient calories, characterized by ascites and dermatitis.

Body Temperature Regulation

Thermoregulation

The hypothalamus regulates body temperature through mechanisms such as increased blood flow to the skin and heat loss by radiation, conduction, convection, and evaporation.

• Radiation: Heat waves from blood and skin.

• Conduction: Transfer of heat to the skin and environment.

• Convection: Transfer of heat to moving air.

• Evaporation: Heat loss via sweat vaporization.

Abnormal Body Temperature

• Fever: Elevated body temperature due to inflammation.

• Malignant hyperthermia: Genetic condition causing hyperthermia and muscle rigidity.

• Heat exhaustion: Fluid loss during overheating.

• Heatstroke: Failure of thermoregulation in hot environments.

• Hypothermia: Reduced body temperature in cold environments.

• Frostbite: Local tissue damage from extreme cold.

Additional Academic Context

Measuring Energy

Energy is measured in calories or joules. 1 kilocalorie (kcal) = 4.2 kilojoules (kJ). The calorie is the amount of energy needed to raise 1 g of water by 1°C.

Summary Table: Key Concepts

Concept	Definition
Nutrition	Intake and assimilation of nutrients
Metabolism	Sum of all chemical reactions in the body
Catabolism	Breakdown of molecules for energy
Anabolism	Building of molecules using energy
BMR	Basal metabolic rate—energy at rest
TMR	Total metabolic rate—total daily energy