This document provides an overview of the digestive system, including the main organs and their functions. It describes how food moves through the digestive tract via peristalsis and is broken down through mechanical and chemical digestion. The major organs involved are the mouth, esophagus, stomach, small intestine, large intestine, and accessory organs like the liver, gallbladder and pancreas. Each organ contributes to further breaking down food into smaller molecules that can be absorbed into the bloodstream.

1. Introduction to the
Digestive System

2. Digestion
Animals cannot ingest macromolecules
made by other animals and use them
directly
2 kinds:
Mechanical digestion
Chemical digestion

3. Vertebrate Digestive System
Food moves through digestive tract
by peristalsis:
Mouth  pharynx esophagus 
stomach 
small intestine  large intestine  anus
Accessory organs:
 Salivary glands
 Liver
 Gall bladder
 Pancreas

4. Layers of digestive tract

5. Mouth
Start of food processing
Mechanical digestion – teeth
Incisors
Canines
Premolars
Molars

6. Chemical digestion:
Salivary glands secrete 1 L saliva/day
Salivary amylase

7. Pharynx and Esophagus
Bolus moves through pharynx
Epiglottis covers trachea during swallowing
Esophagus leads to stomach
Peristalsis moves food along

9. Stomach
Ring of sphincter muscle relaxes and
allows bolus to enter stomach
As stomach fills, rugae of stomach smooth
out

10. Chemical Digestion in Stomach
Gastric glands in mucosa secrete:
HCl
Intrinsic factor
Pepsinogen (converts to pepsin in presence of acidic
gastric juice)
Pepsin, main digestive enzyme of stomach,
breaks down large proteins into short
polypeptides

11. Food spends 3-4 hours in stomach
Muscle contraction churns food
Salivary amylase works until stomach becomes
too acidic
Partly digested food becomes chyme
Peristalsis releases chyme in spurts through
pylorus into small intestine

12. Protection of Stomach
Lining of stomach secretes large amounts
of alkaline mucus
Epithelial cells are tightly joined to prevent
leaking

13. Small Intestine
In human, approx. 17
feet long
Divided into 3 regions:
duodenum, jejunum, and
ileum
Lining is folded and
composed of villi and
microvilli

14. Digestion in Small Intestine
Bile, secreted by liver, mechanically digests fats
Enzymes secreted by small intestine and
pancreas:
Polypeptides and peptides
Trypsin, chymotrypsin, peptidases
Completion of carbohydrate digestion
Pancreatic amylase, maltase, sucrase, lactase
Digestion of fat droplets
lipase

15. Absorption of Nutrients
Nutrients must pass through epithelium to reach
blood or lymph
Simple diffusion, facilitated diffusion, active
transport

16. Large Intestine
Approx. 4 feet long
Includes cecum and appendix, a blind
pouch
Sections include ascending,
transverse, descending & sigmoid
colon
Ends at rectum & anus

17. Functions of Large Intestine
Undigested material and unabsorbed
chyme passes slowly through large
intestine
Water and sodium are absorbed
Bacteria in large intestine feed and produce
vitamin K and some B vitamins for use by
host