1. The Digestive System

2. Digestive System
Also known as the gastrointestinal (GI) tract or alimentary canal
Long tube open at both ends
Also has accessory organs
Nutrients absorbed, waste eliminated
Converts food into useable form

3. Mouth
Salivary Glands
Esophagus
Liver
Stomach
Gallbladder
Pancreas
Small Intestine
Large Intestine
Appendix
Anus

4. 4 Steps to Nutrient Intake
Ingestion
Digestion
- Prepares food for absorption
- Mechanical and chemical breakdown of food
Absorption
- Small intestine
Elimination

5. Two Types of Digestion
Mechanical
Chemical

6. Mechanical Digestion Physical breakdown of food Movement of food
Mouth (chewing) and stomach (churning)
Movement of food
Peristalsis - wavelike involuntary muscle contractions

7. Chemical Digestion In mouth, stomach, small intestine
Chemicals (e.g., HCl) and enzymes break down complex molecules
e.g., Amylase in saliva - enzyme that breaks down starch (a carbohydrate)

8. Enzymes
Break down substances
Protein catalysts
Specific to substrates

9. Oral Cavity (Mouth)
Mechanical digestion (teeth) and chemical digestion (saliva with enzymes)
Bolus of food forms and passes through pharynx into esophagus
Epiglottis prevents food from entering trachea
Bolus

10. Esophagus Muscular tube that connects pharynx to stomach
Peristaltic contractions move food to stomach
Cardiac sphincter at junction prevents food in stomach from going back into esophagus

11. Stomach J-shaped muscular organ to churn and squeeze
Acts as a reservoir for food (1.5 L)
Rugae (folds) allow for expansion
Movement of food controlled by two sphincters:
Cardiac sphincter: Between the stomach & the esophagus
Pyloric sphincter: Between the stomach & the small intestine
Cardiac sphincter

12. Stomach
Digestion turns bolus into chyme – paste-like partially digested food
Secretes HCl (pH of 2)
Destroys microbes and breaks down food
Primarily digests protein
Pepsin, an enzyme only active at low pH

13. Small Intestine Major site of digestion and absorption
80% of nutrient absorption occurs here – diffusion
About 6 m long, SMALLER diameter than large intestine, 3 sections
Bile produced by liver breaks down fats
Enzymes secreted by pancreas break down carbs,
fats and proteins

14. Structure of Small Intestine
Microvilli
Villus
Villi and microvilli - increase surface area, maximize absorption

15. Duodenum First section of small intestine
Receives pancreatic secretions for further chemical digestion
Basic pH
Bile from gall bladder and bicarbonate ions from pancreas neutralize acidic chyme from stomach

16. Jejunum and Ileum
Make up the other two sections of the small intestine.
Where most nutrient absorption takes place.
Peristaltic contractions continue to propel chyme through tract.

17. Large Intestine
About 1.5 m long and has a LARGER diameter than the small intestine.
Consists of four sections:
Caecum
Colon
Rectum
Anus.

18. Large Intestine Main function is to reabsorb water
Bacteria produce vitamins which are absorbed
Compacts unabsorbed material into feces
Defecation:
Rectal sphincter passes feces into rectum for temporary storage
Anal sphincter passes feces from rectum out anus

19. Animated Digestion Video!
Graphic Digestion Video!