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The Human Body: From Food to Fuel
Chapter 4
The Gastrointestinal Tract
• Organization– Mouth anus– Accessory
organs• Salivary
glands, liver, pancreas, gallbladder
Organization of theGastrointestinal Tract
• Functions– Ingestion– Transport– Secretion– Absorption– Movement– Elimination
Organization of the Gastrointestinal Tract
• Layers– Mucosa– Circular muscle– Longitudinal
muscle– Spincter
Overview of Digestion
• Physical movement– Peristalsis– Segmentation
• Chemical breakdown– Enzymes– 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
• Liver– Produces bile– “Chemical factory”
• Gallbladder– Stores and secretes bile
• Pancreas– Secretes bicarbonate– Secretes 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
• 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, ileum
– 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– Digestion
• Nutrient digestion already complete
• Some digestion of fiber by bacteria
– Absorption• Water• Sodium, potassium, 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
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, Defense
• Nervous system– Regulates GI activity
• Enteric nervous system• Autonomic nervous system
• Hormonal system– Increases or decreases GI activity
Signaling Systems: Command, Control, 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
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
Nutrition and GI Disorders
• Irritable bowel syndrome– Stress and certain foods aggravate the
symptoms– Controlled by diet and lifestyle
modifications• Reduce stress
Nutrition and GI Disorders
• Colorectal cancer– Fiber-rich diet may reduce risk
• Gas– Most foods that contain
carbohydrates can cause
• Ulcers– Bacterial cause (H. Pylori)
Nutrition and GI Disorders
• Functional dyspepsia– Chronic pain in the upper abdomen– Treat with medicine and stress-reduction