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Introduction to the Digestive System

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Presentation on theme: "Introduction to the Digestive System"— Presentation transcript:

1 Introduction to the Digestive System

2 Digestion Animals cannot ingest macromolecules made by other animals and use them directly 2 kinds: Mechanical digestion Chemical digestion

3 Vertebrate Digestive System
Food moves through digestive tract by peristalsis: Mouth  pharynx esophagus  stomach  small intestine  large intestine  anus Accessory organs: Salivary glands Liver Gall bladder Pancreas

4 Layers of digestive tract

5 Mouth Start of food processing Mechanical digestion – teeth Incisors
Canines Premolars Molars

6 Chemical digestion: Salivary glands secrete 1 L saliva/day
Salivary amylase

7 Pharynx and Esophagus Bolus moves through pharynx
Epiglottis covers trachea during swallowing Esophagus leads to stomach Peristalsis moves food along


9 Stomach Ring of sphincter muscle relaxes and allows bolus to enter stomach As stomach fills, rugae of stomach smooth out

10 Chemical Digestion in Stomach
Gastric glands in mucosa secrete: HCl Intrinsic factor Pepsinogen (converts to pepsin in presence of acidic gastric juice) Pepsin, main digestive enzyme of stomach, breaks down large proteins into short polypeptides

11 Food spends 3-4 hours in stomach
Muscle contraction churns food Salivary amylase works until stomach becomes too acidic Partly digested food becomes chyme Peristalsis releases chyme in spurts through pylorus into small intestine

12 Protection of Stomach Lining of stomach secretes large amounts of alkaline mucus Epithelial cells are tightly joined to prevent leaking

13 Small Intestine In human, approx. 17 feet long
Divided into 3 regions: duodenum, jejunum, and ileum Lining is folded and composed of villi and microvilli

14 Digestion in Small Intestine
Bile, secreted by liver, mechanically digests fats Enzymes secreted by small intestine and pancreas: Polypeptides and peptides Trypsin, chymotrypsin, peptidases Completion of carbohydrate digestion Pancreatic amylase, maltase, sucrase, lactase Digestion of fat droplets lipase

15 Absorption of Nutrients
Nutrients must pass through epithelium to reach blood or lymph Simple diffusion, facilitated diffusion, active transport

16 Large Intestine Approx. 4 feet long
Includes cecum and appendix, a blind pouch Sections include ascending, transverse, descending & sigmoid colon Ends at rectum & anus

17 Functions of Large Intestine
Undigested material and unabsorbed chyme passes slowly through large intestine Water and sodium are absorbed Bacteria in large intestine feed and produce vitamin K and some B vitamins for use by host

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