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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