1. The Digestive System

2. The principal structure of the digestive system
Alimentary canal
gastrointestinal (GI) tract
-Irregular tube open at 2 ends
About 29 feet long
Food is broken down and then absorbed through the walls
Mechanical & Chemical digestion

3. Main and Accessory Organs of the Digestive System
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Teeth & tongue
Salivary glands
Liver
Gallbladder
Pancreas
Veriform appendix

4. Mouth/oral cavity Lined with mucous membrane
Roof has hard (front) and soft (rear) palates
Uvula prevents food/liquid from entering nasal cavity
Teeth for physical digestion
Salivary glands -secrete saliva w/ enzymes

5. Pharynx Functions in respiration and digestion 5 inches long
Serves as hallway for food and air
3 segments - see diagram

6. Esophagus Connects to stomach 10 inches long
Peristalsis - pushing food toward stomach
Epiglottis prevents food from entering windpipe

7. Stomach Pouch for food to enter after chewed
Enters thru the esophageal sphincter (rings of muscle tissue)
Muscle fibers run lengthwise, around and obliquely (STRONG)
-Contraction mixes food with gastric juice into chyme (mechanical digestion)
Gastric glands secrete juice and HCl

8. Stomach

9. Small intestine 20 ft long 3 segments, duodenum, jejunum, ileum
Mucous layer contains 1000’s of microscopic glands that secretes digestive juice
Interior is not smooth - circular folds called plicae covered w/ 1000s of villi

10. Close up of small intestine
Villi project into interior of intestine
Inside rich in blood capillaries - why?
Microvilli greatly increase surface area & absorption of nutrients

11. Liver & Gall Bladder Liver secretes bile into gall bladder ducts
Bile breaks down fats to smaller molecules (emulsify)
When lipid enters duodenum it initiates mechanism that contracts gall bladder and forces bile into sm. Int.

12. Pancreas Lies behind stomach
Gland secretes pancreatic juice into ducts
Pancreatic juice contains enzymes that digest many types of foods.
Also contains sodium bicarbonate, alkaline, to neutralize stomach acid

13. Large Intestine 1.5 m/5 ft. long Undigested food and unabsorbed food
Bacteria acts on food here which allows some nutrient absorption
Water and salt are reabsorbed here
Waste excreted