DIGESTIVE SYSTEM

1. DIGESTIVE SYSTEM Describe the path food takes through the digestive system. Identify organs of the digestive system and describe their function.

2. What is digestion? • Digestion: the process of breaking down food into molecules the body can use. • Mechanical: physically changing the size of the food. • grinding teeth • churning action of stomach • Chemical: changing the chemical nature of the nutrients. amylase working on starch

3. Gastrointestinal Track • Also known as the “Alimentary Canal.” • Hollow series of organs that food passes through.

4. First stop: The Mouth Teeth provide surface for mechanical digestion. • Molars—grinding • Incisor—biting • Canine—piercing • Bicuspid—grinding Tongue • Keeps food in place • Push bolus back in mouth

5. Mouth Anatomy • Hard Palate: bony and hard roof of the mouth. • Soft Palate: Area just behind the hard palate that separates the mouth cavity from pharynx. • Uvula: Dangles in that back of the throat and catches bacteria and dirt particles (can be destroyed by bulimia).

6. Pharynx: Passageway for both food and air • Epiglottis: a thin flap that prevents food from entering the esophagus.

7. Esophagus • 25 cm long tube that connects the pharynx to the stomach. • Has two layers of muscle: circular and longitudinal. • Peristalsis: series of rhythmic muscle contractions that pushes food through digestive system.

8. Stomach • Site of mechanical and chemical digestion. • Made of three layers of smooth muscle that twist and turn the stomach (causing churning action and “growling” sound). • Covered by a thick layer of mucus to protect the lining from stomach acid.

9. Inside the Stomach • Rugae: thick, wrinkled membrane inside to increase surface area. • Dotted with gastric pits that release pepsin and HCl acid (chemical digestion).

10. Leaving the Stomach • After 3 to 4 hours. • Chyme: paste like substance that contains everything that was not already broken down by pepsin. • Consistency of toothpaste. • Peristalsis forces chyme out of stomach and into small intestine.

11. Small Intestine • 7 m long! • Most important organ in digestive system because most chemical digestion and absorption of nutrients occurs here. • Enzymes continue to break down fats, carbohydrates and proteins. • Absorbed by villi which are filled with many capillaries to transfer the nutrients to the blood stream.

12. Large Intestine • Main function is to absorb water. • 4 parts: • Ascending colon • Transverse colon • Descending colon • Sigmoid colon

13. End of the Line… • Rectum: stores feces until peristalsis moves it out. • Anus: last sphincter muscle.

14. Accessory Organs • Just as important as the main digestive organs. • Food does NOT pass through them: • Salivary Glands • Liver • Pancreas • Gall Bladder

15. Salivary Glands • Adds amylase to mouth during initial stages of digestion. • Amylase: an enzyme that breaks down large starch molecules. Starch  Smaller Carbohydrates

16. Liver • Important in blood sugar homeostasis. • Stores glucose as glycogen and produces bile. • Bile: a brown chemical that emulsifies fat and neutralizes acids. Remember: Glycogen is a complex carbohydrate (polysaccharide).

17. Pancreas • Second most important organ in digestive system • Makes a cocktail of enzymes that are deposited into the small intestine. • Pancreatic amylase • Trypsin (proteins) • Lipase (lipids)

18. Gal Bladder • Stores bile until needed. • Connects to liver. • Problems • Gallstones • Cholesterol deposits

19. Stomach Problems • Stomach Ulcers: stomach acid “eats” a hole through the lining of stomach due to diet, stress or some bacterial infections. • Heartburn: Cardiac sphincter doesn’t close all the way so gastric fluid splashes up from stomach onto esophagus.

20. Large Intestine Problems • Appendicitis: obstruction in appendix. • Diarrhea: not enough water is absorbed due to irritation from drugs, stress, bacteria or parasites. • Constipation: too much water absorbed.