Chapter 3 The Human Body: From Food to Fuel

Taste and Smell: The Beginnings of Our Food Experience Sight, smell, thought, taste, and sound Trigger a set of responses that prepare the digestive tract to receive food

The Gastrointestinal Tract Variety of functions, including: Ingestion of food Transport of ingested food Secretion of digestive enzymes, acid, mucus, and bile Absorption of end products of digestion Movement of undigested material Elimination of digestive waste products

The Gastrointestinal Tract Several layers to the GI tract, including Mucosa Circular muscle Longitudinal muscle Sphincters

Overview of Digestion Physical movement Peristalsis Wavelike, muscular contractions Transport food and nutrients along the GI tract Segmentation Series of muscular contractions in the small intestines Divides and mixes the chyme

Overview of Digestion Chemical breakdown Enzymes Proteins that catalyze chemical reactions Other secretions Acid Base Bile Mucus

Overview of Absorption The road to nutrition absorption Passive diffusion Facilitated diffusion Active transport

Assisting Organs Salivary glands Moisten food Supply enzymes

Assisting Organs Liver Produces bile “Chemical factory” “Dynamic warehouse”

Assisting Organs Gallbladder Stores and secretes bile Pancreas Secretes bicarbonate Secretes digestive enzymes

Putting it All Together: Digestion and Absorption Mouth Enzymes Salivary amylase acts on starch Lingual lipase acts on fat Saliva Moistens food for swallowing

Putting it All Together: Digestion and Absorption Esophagus Transports food to stomach Esophageal sphincter

Putting it All Together: Digestion and Absorption Stomach Hydrochloric acid prepares protein for digestion and activates enzymes Pepsin begins protein digestion Gastric lipase has some fat digestion Gastrin (hormone) stimulates gastric secretion and movement Intrinsic factor is needed for absorption of vitamin B12

Putting it All Together: Digestion and Absorption Small intestine Sections of small intestine Duodenum, jejunum, and ileum Nutrient digestion Bicarbonate neutralizes stomach acid Pancreatic and intestinal enzymes Carbohydrates Fat Protein

Putting it All Together: Digestion and Absorption Small intestine Absorption Folds, villi, and microvilli expand absorptive surface Most nutrients absorbed here Fat-soluble nutrients go into lymph Other nutrients go into blood

Putting it All Together: Digestion and Absorption Large intestine Sections Cecum, colon, rectum, anal canal Digestion Peristaltic movement is slow, taking 18–24 hours for material to travel Some digestion of fiber by bacteria

Putting it All Together: Digestion and Absorption Large Intestine Absorption Water Sodium, potassium, and chloride Vitamin K (produced by bacteria) Elimination

Circulation of Nutrients Vascular system Veins and arteries Carries oxygen and nutrients to tissues Removes wastes Lymphatic system Vessels that drain lymph Empties into the bloodstream near the neck

Circulation of Nutrients Excretion and elimination Lungs Excrete water and carbon dioxide Kidneys filter blood Excrete waste; maintain water and ion balance

Signaling Systems: Command, Control, and Defense Nervous system Regulates GI activity Enteric nervous system Autonomic nervous system Hormonal system Increases or decreases GI motility and secretions Influence your appetite

Signaling Systems: Command, Control, and Defense Immune system Protects us from foreign invaders Role of GI tract Barrier Immune response Natural killer cells Macrophages Location of lymphoid tissues Lymphocytes Antibodies

Influences on Digestion and Absorption Psychological influences Taste, smell, and presentation of food Chemical influences Type of protein you eat and the way it is prepared Bacterial influences Hydrochloric acid kills most bacteria

Nutrition and GI Disorders Constipation Hard, dry, infrequent stools Reduced by high fiber, fluid intake, exercise Diarrhea Loose, watery, frequent stools Symptom of diseases/infections Can cause dehydration Broth, tea, toast, and other low-fiber foods can help reduce

Nutrition and GI Disorders Diverticulosis Pouches along colon High-fiber diet reduces formation Heartburn and GERD Reduced by smaller meals, less fat Smoking weakens the esophageal sphincter Being overweight often worsens symptoms

Nutrition and GI Disorders Irritable bowel syndrome Causes abdominal pain, diarrhea or constipation, and cramps Stress and certain foods aggravate the symptoms Can usually be controlled by diet and lifestyle modifications Stress management

Nutrition and GI Disorders Colorectal cancer Fiber-rich diet may reduce risk Gas Most foods that contain carbohydrates can cause Ulcers Pain in the upper abdomen Can cause nausea, vomiting, loss of appetite, and weight loss Bacterial cause (H. pylori)

Nutrition and GI Disorders Functional dyspepsia Chronic pain in the upper abdomen Treat with medicine and stress reduction