The Human Body:
From Food to Fuel
Chapter 4
The Gastrointestinal Tract
• Organization
– Mouth  anus
– Accessory
organs
• Salivary
glands, liver,
pancreas,
gallbladder
Organization of the
Gastrointestinal 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