The Process of Digestion

1. The Process of Digestion SBI3U

2. The Digestive System

3. Introduction The digestive system is used for breaking down food into nutrients which then pass into the circulatory system and are taken to where they are needed in the body.

4. Introduction There are four stages to food processing: Ingestion: taking in food Digestion: breaking down food into nutrients Absorption: taking in nutrients by cells Egestion: removing any leftover wastes

5. Human Digestive System Begins when food enters the mouth (oral cavity). It is physically broken down by the teeth (mechanical). It is chemically broken down by enzymes released from the salivary glands.

6. Human Digestive System The tongue moves the food around until it forms a ball called a bolus. The bolus is passed to the pharynx (throat) and the epiglottis makes sure the bolus passes into the esophagus and not down the trachea!

7. Human Digestive System The bolus passes down the esophagus by peristalsis. Peristalsis is a wave of muscular contractions that push the bolus down towards the stomach.

8. Human Digestive System To enter the stomach, the bolus must pass through the lower esophageal sphincter, a tight muscle that keeps stomach acid out of the esophagus.

9. Human Digestive System The stomach has folds called rugae and is a big muscular pouch which churns the bolus (physical digestion). The bolus is mixed with gastric juice, a mixture of stomach acid and enzymes (chemical digestion).

10. Human Digestive System The stomach does do some absorption too. Some medicines (i.e. aspirin), water and alcohol are all absorbed through the stomach. The digested bolus is now called chyme and it leaves the stomach by passing through the pyloric sphincter.

11. Human Digestive System Food is now in the small intestine. The majority of absorption occurs here. The liver and pancreas help the small intestine to maximize absorption. The small intestine is broken down into three parts:

12. Human Digestive System Duodenum Bile enters through the bile duct. It breaks down fats. The pancreassecretes pancreatic juiceto reduce the acidity of the chyme.

13. Human Digestive System • Jejunum • The jejunum is where the majority of absorption takes place. • It has tiny finger-like projections called villi lining it, which increase the surface area for absorbing nutrients.

14. Human Digestive System Each villi itself has tiny fingerlike projections called microvilli, which further increase the surface area for absorption.

15. Human Digestive System • Ileum • The last portion of the small intestine is the ileum, which has fewer villi and basically compacts the leftovers to pass through the caecuminto the large intestine.

16. Human Digestive System The large intestine(or colon) is used to absorb water from the waste material leftover and to produce vitamin K and some B vitaminsusing the helpful bacteria that live here.

17. Human Digestive System All leftover waste is compacted and stored at the end of the large intestine called the rectum. When full, the anal sphincter loosens and the waste, called feces, passes out of the body through the anus.

18. Chemical Digestion

19. Introduction Food cannot be broken down into small enough nutrients by physical digestion alone. Special enzymes in our body help chemically break down food into small nutrients.

20. Magic School Bus – “For Lunch” http://www.peteava.ro/id-538489-02-for-lunch

21. Enzymes • Enzymes are special proteins made at ribosomes. • There are different classes of enzymes: • Carbohydrases break down carbs • Proteinases break down proteins • Lipases break down lipids.

22. Enzymes These enzymes are secreted into the digestive system by special groups of secretory cells called glands. Glands are usually connected to the digestive system through special tubes called ducts.

23. Enzymes The item that an enzyme breaks down is called a substrate. The enzyme is not changed at all during this process. Every enzyme performs best under its own optimalconditions. This depends on temperature, pH and the presence/absence of certain ions or vitamins and minerals.

24. The Mouth • Three salivary glands produce saliva which contains: • Water and mucous: lubricates the food • Sodium bicarbonate: reduces the acidity of the bolus • Salivary amylase: enzyme that begins to break down carbohydrates

25. The Stomach Hydrochloricacid (HCl) kills off any invading bacteria or viruses. The enzyme pepsin breaks down proteins. The enzyme lipase breaks down lipids. Mucus protects the lining of the stomach from being eaten away by the acid.

26. The Pancreas • Produces and releases into the small intestine: • Enzymes that act on proteins, carbohydrates, and fats. • Bicarbonate solution to raise the pH of the chyme. • Produces and releases into the blood stream: • Insulin that converts glucose to glycogen, which gets stored in the body cells for later use.

27. The Liver • Makes bile, which aids in fat digestion • Most of the glycogen is stored here • Vitamins A, D, E, K are stored here • Detoxifies poisons that are ingested (including ethanol)‏ • Cirrhosis: breakdown of liver cells due to high levels of poisons.

28. The Gall Bladder • Stores the bile produced in the liver. • Releases bile into the small intestine. • Illnesses of the gall bladder include • Gall stones: crystals of bile salts around cholesterol. • Jaundice: collection of bile pigment in blood.

29. Digestion and Homeostasis A large meal activates receptors that churn the stomach and empty it faster. If the meal was high in fat, digestion is slowed, allowing time for the fat to be broken down. Hence why we feel fuller after eating a high fat meal.

30. Digestion and Homeostasis The Hormone Gastrin The endocrine, nervous, digestive and circulatory systems all work together to control digestion. Before we eat, smelling food releases saliva in our mouths and gastrinin our stomachs which prepares the body for a snack.

31. Hormones Hormones are chemical regulators, they also help control digestive enzymes. The hormone gastrin stimulates the digestive glands around the stomach. The hormone secretin stimulates the pancreas to release its enzymes which help neutralize the stomach contents as they enter the small intestine.