Lesson 2: The Human Alimentary Canal

1. Lesson 2: The Human Alimentary Canal

2. The Human Alimentary Canal … includes the entire tube from the mouth all the way to the anus

3. Human Alimentary Canal • Mouth • Pharynx • Esophagus • Stomach • Small intestine • Large intestine • Rectum • Anus

4. Accessory Organs • Salivary glands • Secrete saliva • Liver • Secretes bile • Gallbladder • Stores and concentrates bile • Pancreas • Secretes digestive enzymes …Organs that are involved in digestion but that food does not pass directly through

5. Types of Digestion • Physical Digestion: • Food is physically broken down • Example – Teeth chew food • Chemical Digestion: • Food is broken down by acids, bases or enzymes in the human alimentary canal • Example – HCl in stomach

6. Mouth (Oral Cavity) • Site of Ingestion • Salivary Amylase breaks carbohydrates into simpler sugars ??? What type of digestion takes place in the mouth? Physical? Chemical?

7. Saliva • Produced by salivary glands at back of mouth and under tongue • Saliva includes • Salivary amylase (enzyme) • Bicarbonate (buffer) • Mucins (bind food into bolus) • Water

8. Salivary Glands • Accessory Organ found at back of mouth and under tongue • Releases salivary amylase into the mouth

9. Once chewed, food is called a bolus Swallowing Tongue forces food into pharynx Epiglottis closes off the trachea to prevent choking (breathing temporarily stops) Bolus moves into oesophagus

10. Pharynx (The throat) • No physical or chemical digestion occurs here • Links in with the respiratory system

11. Esophagus • Function: to transport food from mouth to the stomach • Food considered a BOLUS at this stage • wet ball of chewed food How does the bolus get from the mouth to the stomach?

12. Peristalsis Peristalsis: waves of muscular contraction that move food along the human alimentary canal

13. Discuss the types of digestion occurring in the stomach… Stomach • Muscular sac-like organ • Lined with a thick protective mucus • The stomach lining secretes Gastric Juices that contain: • Hydrochloric Acid • Pepsinogen (inactive form of pepsin) • Mucus

14. Chemical Digestion in the Stomach • Pepsinogen is activated by the acid HCl in the stomach and becomes pepsin • Pepsin chemically digests protein into amino acids

15. Physical Digestion • Food is mixed and moved by waves of stomach contractions (peristalsis) • Becomes Chyme – thick liquid made of partially digested food and stomach juices

16. Small Intestine • Over 6.5 meters long • Duodenum • First 10 cm of small intestine

17. What happens in the small intestine? • Pancreatic juices neutralise acidic chyme • Digestion is completed in duodenum • Liver secretes bile, via gallbladder, which emulsifies fats • Pancreas secretes various enzymes which complete the breakdown of protein, carbs and fats • Absorption takes place of digested products into bloodstream

18. LIVER produces bile which breaks up the larger fats (emulsification) GALLBLADDER stores the bile until needed

19. Large Intestine • Function: to absorb water into blood • Also the site of vitamin K production • End section: rectum & anus

20. Stages of Digestion YOU DECIDE! Look at your diagram of the Digestive System. Where does each stage of digestion take place? Hint: Some stages take place at multiple locations… • Ingestion – the process by which food is taken into the body • Digestion - the process of breaking up complex substances into simpler substances. • Absorption – the process by which digested food diffuses into blood • Assimilation - the conversion or incorporation of absorbed simple food into the complex substances that are useful in our bodies • Egestion - the elimination of undigested food (faeces) from the body

21. Warning: Do not confuse Egestion with Excretion Egestion – removal of undigested food (faeces) via the anus Excretion – removal of waste products of metabolism (like urine, carbon dioxide, sweat)