Chapter 3: Human Body Organization, Digestion, and Food-Related Disorders

Organization of the Human Body

Basic Cell Structure

The human body is organized hierarchically, beginning with the cell, the basic unit of life. Cells group together to form tissues, which then form organs and organ systems.

• Cell: The smallest structural and functional unit of an organism. Contains organelles such as the nucleus, mitochondria, and endoplasmic reticulum.

• Tissue: Groups of similar cells performing a specific function (e.g., muscle, epithelial, connective, nervous tissue).

• Organ: Structures composed of two or more tissue types working together (e.g., stomach, liver).

• Organ System: Groups of organs that perform related functions (e.g., digestive system).

Satiety and Hunger Regulation

Satiety Value of Nutrients and Types of Foods

Satiety refers to the feeling of fullness and the suppression of hunger after eating. Different nutrients and foods have varying effects on satiety.

• Proteins have the highest satiety value, followed by fats, then carbohydrates.

• High-fiber foods and foods with high water content increase satiety.

• Solid foods generally provide more satiety than liquids.

Organs and Hormones Involved in Hunger Regulation

• Organs: The hypothalamus in the brain is the primary regulator of hunger and satiety. The stomach and small intestine also play roles by releasing hormones.

• Hormones:

  • Ghrelin: Produced by the stomach; stimulates hunger.

  • Leptin: Produced by adipose (fat) tissue; signals satiety and reduces appetite.

  • Cholecystokinin (CCK): Released by the small intestine; promotes satiety.

  • Peptide YY (PYY): Released by the small intestine; reduces appetite.

  • Insulin: Released by the pancreas; involved in satiety signaling.

Anatomy and Physiology of the Digestive System

Anatomy of the GI Tract

The gastrointestinal (GI) tract is a continuous tube from the mouth to the anus, responsible for digestion and absorption of nutrients.

• Mouth → Esophagus → Stomach → Small Intestine (duodenum, jejunum, ileum) → Large Intestine (colon) → Rectum → Anus

Accessory Organs to the GI Tract

• Liver: Produces bile for fat digestion.

• Gallbladder: Stores and releases bile.

• Pancreas: Produces digestive enzymes and bicarbonate; releases insulin and glucagon.

Difference Between Digestion, Absorption, and Excretion

• Digestion: The mechanical and chemical breakdown of food into smaller components.

• Absorption: The process by which nutrients pass from the GI tract into the blood or lymph.

• Excretion: The elimination of indigestible substances and waste products from the body.

Functions of the Liver

Important Roles of the Liver

• Metabolizes carbohydrates, proteins, and fats.

• Detoxifies harmful substances.

• Stores vitamins and minerals (e.g., vitamin A, iron).

• Produces bile for fat digestion.

• Regulates blood glucose levels.

Small Intestine: Structure and Function

Structure and Function

• Composed of three sections: duodenum, jejunum, ileum.

• Primary site for digestion and absorption of nutrients.

• Contains villi and microvilli to increase surface area for absorption.

Types of Absorption in the Small Intestine

• Passive diffusion: Movement of nutrients from high to low concentration without energy.

• Facilitated diffusion: Movement via a carrier protein, no energy required.

• Active transport: Movement against a concentration gradient, requires energy (ATP).

• Endocytosis: Cell engulfs particles or fluids.

Neuromuscular Components of the GI Tract

• Peristalsis: Rhythmic contractions that move food through the GI tract.

• Segmentation: Contractions that mix and break down food in the intestines.

• Enteric nervous system: Network of nerves controlling GI function.

Gastrointestinal Disorders

Heartburn vs. GERD

• Heartburn: A burning sensation in the chest caused by acid reflux into the esophagus.

• GERD (Gastroesophageal Reflux Disease): Chronic condition where acid reflux occurs frequently, potentially damaging the esophagus.

Nutrition-Related Recommendations for GERD

• Avoid trigger foods (e.g., spicy, fatty, or acidic foods).

• Eat smaller, more frequent meals.

• Maintain a healthy weight.

• Avoid lying down after eating.

• Limit caffeine and alcohol intake.

Peptic Ulcers: Causes and Symptoms

• Causes: Helicobacter pylori infection, chronic use of NSAIDs, excessive acid production.

• Symptoms: Burning stomach pain, nausea, vomiting, bloating.

Food Intolerances and Allergies

Food Intolerance vs. Food Allergy

• Food Intolerance: Non-immune response to food, often due to enzyme deficiency (e.g., lactose intolerance).

• Food Allergy: Immune system reaction to a food protein (allergen).

Symptoms and Causes

• Food Intolerance Symptoms: Gas, bloating, diarrhea, abdominal pain.

• Food Allergy Symptoms: Hives, swelling, difficulty breathing, anaphylaxis.

• Causes of Food Intolerances: Enzyme deficiencies, sensitivity to food additives, reactions to naturally occurring chemicals.

Nutrition Facts Label and Allergens

• Food labels must list major allergens (e.g., milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, soybeans).

• Allergens are often highlighted in bold or in a separate statement.

Gluten and Celiac Disease

Gluten and Its Components

• Gluten: A protein found in wheat, barley, and rye.

• Composed mainly of gliadin and glutenin proteins.

Celiac Disease: Symptoms, Diagnosis, and Treatment

• Symptoms: Diarrhea, weight loss, fatigue, abdominal pain, anemia, skin rash.

• Diagnosis: Blood tests for specific antibodies (e.g., anti-tTG), intestinal biopsy.

• Treatment: Lifelong adherence to a strict gluten-free diet.

Table: Comparison of Food Intolerance and Food Allergy

Feature	Food Intolerance	Food Allergy
Immune System Involvement	No	Yes
Common Symptoms	GI symptoms (bloating, gas, diarrhea)	Hives, swelling, anaphylaxis
Onset	Gradual	Immediate or within hours
Amount Needed to Trigger	Large amount	Small amount
Examples	Lactose intolerance	Peanut allergy

Additional info: Academic context and definitions have been expanded for clarity and completeness. Table content inferred and summarized for study purposes.