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 obtains and utilizes nutrients for energy, growth, and maintenance. Proper nutrition involves a balance of macronutrients and micronutrients, while metabolism encompasses all chemical reactions that sustain life.

Nutrition: Definitions and Concepts

Key Terms

• Nutrition: The study of nutrients in food, how the body uses them, and the relationship between diet, health, and disease.

• Malnutrition: A deficiency or imbalance in nutrient intake.

• Macronutrients: Nutrients required in large amounts (carbohydrates, fats, proteins).

• Micronutrients: Nutrients required in small amounts (vitamins, minerals).

Major Macronutrients

Macronutrients provide energy and are essential for body structure and function. Each has unique dietary sources and physiological roles.

Nutrient	Dietary Sources	Functions
Carbohydrate	Fruits, honey, grains, vegetables	Primary energy source; builds other carbohydrates
Fat (Lipid)	Meat, vegetable oils, dairy	Energy storage, cell membrane structure, steroid hormone synthesis
Protein	Meat, eggs, dairy, vegetables	Builds body structures, enzymes, hormones; energy source if needed

Metabolism: Overview and Pathways

Definitions

• Metabolism: The sum of all chemical reactions in the body, including catabolism and anabolism.

• Catabolism: Breakdown of molecules to release energy.

• Anabolism: Synthesis of complex molecules from simpler ones.

Carbohydrate Metabolism

Carbohydrates are the body's preferred energy source. Glucose metabolism occurs in three main stages:

1. Glycolysis: Anaerobic breakdown of glucose to pyruvic acid in the cytoplasm, yielding 2 ATP.

2. Citric Acid Cycle (Krebs Cycle): Aerobic process in mitochondria converting acetyl CoA to CO2 and high-energy electrons.

3. Electron Transport System (ETS): Uses electrons to generate most ATP (about 32-34 ATP per glucose).

ATP: The Energy Currency

Adenosine triphosphate (ATP) stores and transfers energy for cellular processes. Energy from nutrient catabolism is used to synthesize ATP, which is then used for cellular work.

Blood Glucose Regulation

Blood glucose levels are tightly regulated, primarily by the hormone insulin, which lowers blood glucose by promoting cellular uptake and storage as glycogen. Normal fasting blood glucose is 80–110 mg/100 mL.

Fat and Protein Metabolism

• Fat Metabolism: Fats are catabolized for energy and can be converted to glucose. Excess fat is stored as adipose tissue.

• Protein Metabolism: Proteins are used for energy only when carbohydrates and fats are insufficient. Gluconeogenesis converts amino acids to glucose.

Amino Acids: Essential and Nonessential

The body requires 20 amino acids; some are essential (must be obtained from diet), others are nonessential (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

Vitamins and Minerals

Vitamins

Vitamins are organic compounds required in small amounts for normal metabolism. Deficiency (avitaminosis) or excess (hypervitaminosis) can cause disease. Many vitamins act as coenzymes.

Vitamin	Dietary Source	Function	Deficiency Consequence
Vitamin A	Green/yellow vegetables, dairy	Maintains epithelial tissue, vision	Night blindness
Vitamin C	Citrus fruits, vegetables	Collagen synthesis, antioxidant	Scurvy
Vitamin D	Dairy, sunlight	Calcium absorption	Rickets

Minerals

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

Mineral	Dietary Source	Function	Deficiency Symptoms
Calcium	Dairy, legumes, vegetables	Bone formation, nerve/muscle function	Bone degeneration
Iron	Meat, eggs, vegetables	Oxygen transport (hemoglobin)	Anemia

Regulation of Food Intake and Metabolic Rate

Appetite Regulation

Food intake is regulated by the hypothalamus, which contains appetite and satiety centers. Various hormones and neural signals stimulate or inhibit appetite.

Stimulate Appetite	Inhibit Appetite	Source
Endogenous opioid peptides, Ghrelin	Leptin, Insulin, Cholecystokinin	Hypothalamus, GI tract, pancreas

Basal and Total Metabolic Rate

Basal metabolic rate (BMR) is the energy expended at rest in a neutral environment. Total metabolic rate (TMR) includes BMR plus energy used for activity and digestion. Factors affecting metabolic rate include age, sex, body composition, thyroid hormone levels, and temperature.

Metabolic and Eating Disorders

Common Disorders

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

• Bulimia: Cycles of overeating followed by self-induced vomiting or fasting.

• Obesity: Excessive body fat, may be related to metabolic or eating disorders.

• Protein-Calorie Malnutrition (PCM): Includes marasmus (overall deficiency) and kwashiorkor (protein deficiency with adequate calories).

Body Temperature Regulation

Thermoregulation

The hypothalamus maintains body temperature through mechanisms such as radiation, conduction, convection, and evaporation. Abnormal temperatures can result in fever, heat exhaustion, heatstroke, hypothermia, or frostbite.

Sample Review Questions

1. Which series of chemical reactions that break down glucose is anaerobic and takes place in the cytoplasm? Answer: Glycolysis

2. Identify the hormone that significantly lowers the blood glucose level. Answer: Insulin

3. An excess amount of cholesterol in the blood results in a condition called: Answer: Hypercholesterolemia

4. A vitamin C deficiency can lead to: Answer: Scurvy

5. The _____ rate is the rate at which food is catabolized under basal conditions. Answer: Basal metabolic rate

6. Which metabolic eating disorder is characterized by chronic refusal to eat, often because of an abnormal fear of becoming obese? Answer: Anorexia nervosa

7. Which condition related to body temperature is characterized by the inability to maintain a normal body temperature in extremely cold environments? Answer: Hypothermia