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