1. Most animals ingest chunks of food
Figure 21.1E

2. 21

3. 21.2 Overview: Food processing occurs in four stages
Small molecules
Pieces of food
Nutrient molecules enter body
cells
Chemical breakdown (enzymatic hydrolysis)
Mechanical breakdown
Undigested material
Food 1
INGESTION 2
DIGESTION 3
ABSORPTION 4
ELIMINATION
Figure 21.2

4. TEETH
Incisors
Canine
Premolars
Molars
“Wisdom” tooth
Tongue
Salivary glands
Opening of a salivary gland duct
Figure 21.5

5. HUMAN DIGESTIVE SYSTEM
21.4 The human digestive system consists of an alimentary canal and accessory glands
When food is swallowed, it is moved through the alimentary canal by peristalsis
Peristalsis is rhythmic muscle contraction in the walls of the digestive tract
Ringlike sphincter muscles regulate the passage of food

6. Oral cavity
Mouth
Tongue
Pharynx
Salivary glands
Esophagus
Liver
Stomach
Pyloric sphincter
Stomach
Gall- bladder
Small intestine
Pancreas
Small intestine
Large intestine
Rectum
Anus
Figure 21.4

7. 21.8 The stomach stores food and breaks it down with acid and enzymes
The stomach mixes food with gastric juice
The gastric juice contains pepsin, which begins the hydrolysis of protein

8. 21

9. 21

10. 21.10 The small intestine is the major organ of chemical digestion and nutrient absorption
Alkaline pancreatic juice neutralizes stomach acids
Its enzymes digest polysaccharides, proteins, nucleic acids, and fats
Bile emulsifies fat droplets for attack by pancreatic enzymes
It is made in the liver and stored in the gall bladder

11. Duodenum of small intestine Pancreas
Bile
Liver
Gall- bladder
Stomach
Bile
Acid chyme
Duodenum of small intestine
Pancreas
Figure 21.10A

12. Nutrients pass through the epithelium of the villi and into the blood
The lining of the small intestine is folded and covered with tiny, fingerlike villi
Villi increase the absorptive surface
Nutrients pass through the epithelium of the villi and into the blood
The blood flows to the liver
The liver can store nutrients and convert them to other substances the body can use

14. 21.11 The large intestine reclaims water
Undigested material passes to the large intestine, or colon
Water is absorbed
Feces are produced
Large intestine (colon)
End of small intestine
Small
intestine
Rectum
Anus
Nutrient flow
Appendix
Cecum
Figure 21.11

15. INTERIOR OF INTESTINE
Blood vessel with blood en route to the liver
Nutrient absorption
Nutrient absorption
Microvilli
Epithelial cells
Lumen
Muscle layers
Blood capillaries
Circular folds
Villi
Lymph vessel
EPITHELIAL CELLS
Nutrient absorption
INTESTINAL WALL
VILLI
Figure 21.10B