1. Dinner Is Served
Remember the last time you sat down to a dinner of your favorite foods? Recall everything that you did before you swallowed your first bite.
1. Why do you cut up your food?
2. What role do your teeth play in eating?
3. Saliva is the fluid that is found in your mouth. What role do you think it plays in eating?

2. Chapter 38.2 The Process of Digestion

3. Main Function
 Helps convert foods into simpler molecules that can be absorbed and used by the cells of the body
Built around a one-way tube (alimentary canal) that runs through the body

4. Organs of the Digestive System
The path that food travels:
Mouth  pharynx  esophagus  stomach  small intestine  large intestine  rectum  anus
 Several major accessory structures including the salivary glands, the pancreas and the liver add secretions to the digestive system.

5. Gallbladder (behind liver)
Digestive System
Mouth
Salivary glands
Stomach
Pancreas (behind stomach)
Large intestine
Small intestine
Rectum
Gallbladder (behind liver)
Liver
Esophagus
Pharynx

6. The Mouth Beginning of the digestive system
Mechanical digestion  physical breakdown large pieces into smaller pieces
Chewing – Teeth: cut, tear, crush food
Purpose is to increase surface area of food so that more enzymes can breakdown the molecules

7. The Mouth (Cont’d)
Chemical Digestion  large food molecules are broke down into smaller food molecules
Enzymes, acid
Salivary glands – produce saliva
Moistens food
Contains enzymes
Amylase  breaks down starches and releases sugars
Lysozyme  fights infection

8. Swallowing Food is pushed to the back of the throat
While chewing, the tongue pushes food up and back
Smashes food against the hard and soft pallet
Clump of food  bolus
Epiglottis  flap of tissue that blocks off the opening to the trachea, directing the food down the esophagus

9. Esophagus
Food tube
Connects pharynx and the stomach
Peristalsis  contractions of the smooth muscle squeeze the food through the esophagus into the stomach
Fig page 980

10. Stomach Large muscular sac Cardiac sphincter –
Site of chemical and mechanical digestion
Contracts to churn and mix stomach fluids together
Cardiac sphincter –
Ring of muscle that lets food into the stomach and prevents acid from entering the esophagus
Heartburn  painful, burning sensation, that results from the backflow of stomach acid

11. Mixture of stomach fluids and food  chyme
Stomach (cont’d)
Contains gastric glands
Produce mucus – protects the stomach
Produce hydrochloric acid - keeps stomach pH acidic
Produce pepsin – digests proteins
Works best in acidic conditions
Mixture of stomach fluids and food  chyme

12. Small Intestine 3 parts: duodenum, ileum, jejunum Functions:
Pyloric sphincter – separates stomach and small intestine
Functions:
Complete chemical digestion
Absorb nutrients

13. Pancreas
Pancreas and gall bladder release enzymes/fluids into small intestine
Pancreas
Produces hormones that regulate blood sugar
Produces enzymes that breakdown all the macromolecules
Produces sodium bicarbonate – neutralizes stomach acid and allows enzymes to function properly

14. Gall Bladder Gall bladder releases bile into the small intestine Bile
loaded with lipids and salts
Acts as a detergent to breakdown fats
Produced in the liver

15. Villi
Villi – fingerlike projections on the inside lining of the small intestine
Covered by microvilli
Provides an enormous surface area for the absorption of nutrient molecules
Once food is ready to leave it is nutrient free
Only cellulose, water, and other indigestible substances remain

16. Large Intestine
3 parts: ascending colon, transverse colon, descending colon
Contains bacteria that aids digestion
Functions:
Transports waste
Absorbs water

17. Enzymes in Digestion Site Mouth Stomach
Small intestine (from pancreas)
Small intestine
Enzyme
Role in Digestion
Salivary amylase
Pepsin
Amylase
Trypsin
Lipase
Maltase, sucrase, lactase
Peptidase
Breaks down starches into disaccharides
Breaks down proteins into large peptides
Continues the breakdown of starch
Continues the breakdown of protein
Breaks down fat
Breaks down remaining disaccharides into monosaccharides
Breaks down dipeptides into amino acids.

18. Digestive System Disorders
Peptic ulcers
Acids released by the stomach damage the organ’s own lining, producing a hole
Caused by Helicobacter pylori – bacteria
Diarrhea
Not enough water is absorbed
Constipation
Too much water is absorbed