1. Digestion

2. Digestive Tract (passageway through digestive system) Mouth, including teeth & salivary glands Pharynx (larynx/esophageal fork at the end) Esophagus Stomach Small Intestine Large Intestine In order that food travels through digestive system Rectum

3. Mouth Salivary glands Stomach Pancreas Large intestine Small intestine Pharynx Esophagus Liver Gallbladder Rectum

5. Digestion  The function of the digestive system… …is to help convert foods into simpler molecules that can be absorbed and used by the cells of the body. This occurs mechanically as well as chemically.

6. The Mouth The Mouth (mech. & chem.)  Chewing begins mechanical digestion, which is the physical breakdown of food into smaller pieces.  Mechanical digestion occurs in both the mouth and the stomach. Chewing one’s food more lessens the work needed by the stomach.

7. The Mouth  The teeth cut, tear, and crush food into small fragments.  As the teeth cut and grind the food, salivary glands secrete saliva, which moistens food and makes it easier to chew.

8. The Esophagus Saliva is slippery and helps ease food down the esophagus. It’s the start of chemical digestion and helps compress food into a bolus. Saliva contains amylase, an enzyme that breaks the chemical bonds in starches and releases sugars.

9. The Esophagus  From the throat, the chewed food passes through the esophagus, or food tube, into the stomach.  Food is moved along by contractions of smooth muscle.  These contractions, known as peristalsis, squeeze the food through the esophagus into the stomach.

10. The Esophagus Peristalsis Esophagus Bolus Stomach Muscles contracted

11. The Stomach  Food from the esophagus empties into the stomach.  The stomach continues mechanical and chemical digestion.  Contractions of smooth muscle churn food.

12. The Stomach  Chemical Digestion  The stomach lining has millions of gastric glands that release substances into the stomach. Some glands produce mucous, which lubricates and protects the stomach wall. Other glands produce hydrochloric acid (HCl), which makes the stomach contents very acidic. Other glands produce pepsin, an enzyme that digests protein.

13. The Stomach

14.  Mechanical Digestion  The stomach contracts to churn fluids and food, gradually producing a mixture known as chyme.  Every so often, the pyloric valve between the stomach and small intestine opens and chyme flows into the small intestine.

15. The Small Intestine  As chyme is pushed through the pyloric valve, it enters the duodenum.  The duodenum is the first of three parts of the small intestine, and is where most digestive enzymes enter the intestine.  Most chemical digestion and absorption of nutrients occurs in the small intestine.

16. Accessory Digestive Organs ry Structures of Digestion Liver Gallbladder Duodenum Bile duct Pancreas Pancreatic duct To rest of small intestine

17. The Pancreas During digestion, the pancreas:  produces enzymes that break down carbohydrates, proteins, lipids, and nucleic acids.  produces sodium bicarbonate, a base that neutralizes stomach acid so that these enzymes can be effective.

18. The Liver & Gallbladder Assisting the pancreas is the liver, which produces bile. Bile dissolves and disperses droplets of fat in fatty foods. This enables enzymes to break down smaller fat molecules. Bile is stored in the gallbladder.

19. The Small Intestine Absorption in the Small Intestine  The small intestine is adapted for the absorption of nutrients.  The folded surfaces of the small intestine are covered with fingerlike projections called villi.

20. Absorption in the Small Intestine The Small Intestine Small intestine Circular folds Villi Villus Epithelial cells Capillaries Lymph vessel Vein Artery

21. Absorption in the Small Intestine Cell surfaces of villi have more projections called microvilli. These provide an enormous surface area for the absorption of nutrient molecules. Slow, wavelike contractions of smooth muscles move the chyme along this surface.

22. Absorption in the Small Intestine Nutrient molecules are absorbed into the cells lining the small intestine. Most products of carbohydrate and protein digestion are absorbed into the capillaries in the villi. Molecules of undigested fat are absorbed by lymph vessels.

23. The Large Intestine  When the chyme leaves the small intestine, it enters the large intestine, or colon.  The large intestine removes water from the chyme.  Water is absorbed quickly, leaving undigested materials behind.  Concentrated waste material passes through the rectum and is eliminated from the body.

24. Digestive System Disorders Based on your knowledge of the digestive system… …can you describe these common disorders?? When stomach acid enters the esophagus. It “burns” because the esophagus is not as well-lined. When the large intestine does not absorb enough water, leaving the fecal matter saturated. When the large intestine absorbs too much water, leaving the fecal matter arid and difficult to pass through the tract. Heartburn is…? Diarrhea is…? Constipation is…?

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26. Copyright Pearson Prentice Hall

27. 38– 2 Copyright Pearson Prentice Hall  Food is moved through the esophagus into the stomach by  air pressure.  muscle contractions.  gravity.  swallowing.

28. 38– 2 Copyright Pearson Prentice Hall  A gland that has both endocrine and exocrine functions is the  liver.  spleen.  pancreas.  gallbladder.

29. 38– 2 Copyright Pearson Prentice Hall  The enzyme in saliva that begins the digestion of starch is  amylase.  pepsin.  lysozyme.  peptidase.

30. 38– 2 Copyright Pearson Prentice Hall  Stomach muscles contract to churn and mix stomach fluids and food, producing a mixture known as  chyme.  amylase.  bile.  acid.

31. 38– 2 Copyright Pearson Prentice Hall  Absorption of vitamins, minerals, and digested food molecules takes place in the  stomach.  small intestine.  large intestine.  duodenum.

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