Anatomy and Function of the Digestive System

1. Anatomy and Function of the Digestive System Partnership for Environmental Education and Rural Health Texas A&M University peer.tamu.edu

2. Nutrition versus Digestion • Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed. • Recall the definition of nutrition. • Using these definitions, describe the relationship between nutrition and digestion and then share your answer with a neighbor.

3. The Digestive System • How many structures of the digestive system can you name?

4. Functions • Digestion - breaking down food by mechanical and enzymatic action in the stomach and intestines into substances that can be used by the body. • Absorption • Protection from microorganisms & noxious substances • Remove undigested material & waste • Immunological function • Metabolism • Endocrine functions

5. Types of Digestion • Mechanical Digestion- the physical break down of food into smaller pieces without changing its chemical structure. • Increases the surface area of food particles • Chemical Digestion- food is chemically broken down; its chemical structure is changed. • Enzymes and acids

6. Break It Down • What types of digestion are occurring in the following images?

7. Digestion Begins • Prehensile organs (lips, tongue) • Move food to the mouth • Mouth • Taste – accept or reject food • Mechanical digestion – mastication (chewing) • Mix digesta (food) with saliva

8. Saliva • Lubricates food with mucoproteins • Initiates enzymatic digestion • Salivary amylase – breaks down carbohydrates • Salivary lipase – breaks down lipids • Buffers stomach – prevents pH from rapidly changing Salivary glands

9. Esophagus • Muscular tube from pharynx to stomach • Peristalic (wave-like) contractions propel food down to stomach • Made of striated and smooth muscle • Ruminants have striated muscle throughout in order to regurgitate food.

10. Simple Stomach • Muscular bag that mixes food by peristalic contractions & holds for gradual release to small intestine • Digests proteins • Denatures (breaks apart) with hydrochloric acid • Enzymatic digestion with pepsin • Produces mucus to protect from acids • pH of stomach is about 2 • With out mucus develop ulcers • Absorption of alcohol and volatile fatty acids

12. Ruminants • What makes the ruminant stomach unique? • Identify the ruminant animals from the following images.

13. Ruminant Stomach • Occupies nearly ¾ of the abdominal cavity • 4 chambers • Reticulum – formation of bolus (cud) and regurgitation • Rumen - microbial digestion of feed and production of volatile fatty acids • Omasum – water and inorganic mineral absorption • Abomasum – “true stomach”, secretes acids and enzymes

15. Review Break #1: • What are the functions of the digestive system? • Give an example of the two types of digestion that occur in the digestive system. • What is the function of saliva? • How does food move down the esophagus? • Which part of the ruminant stomach is most like a simple stomach? Why?

16. Folds Upon Folds • What organ do you think is shown here? • What might be the purpose of the villi?

17. Small Intestine • Primary site for enzymatic digestion and nutrient absorption • Divided into 3 regions: • Duodenum – most digestive enzymes enter here • Jejunum • Ileum • Folded and lined with villi and microvilli – increases the surface area (therefore absorption efficiency) 600 fold

18. Pancreas, Liver and Gallbladder • Pancreas – adds enzymes and buffers to the duodenum • Enzymes digest starches, fats, and proteins • Produces insulin and glucagon • Liver – produces bile • Emulsifies large fat globules into a suspension of fine droplets for enhanced digestion • Gallbladder – stores bile • Horses have no gallbladder, bile is secreted directly into the stomach

19. click here for more information on the liver and pancreas

20. Why is the term “large” used to describe the large intestine?

21. Cecum • The start of the large intestine • Large in herbivores • Contains bacteria that aid in the enzymatic digestion of cellulose cecum

22. Large Intestine • Composed of the cecum, colon, and rectum • Bulks up and stores material • Absorbs water, volatile fatty acids, and some minerals • Site of microbial digestion • Digestion of cellulose producing volatile fatty acids – particularly important in non-ruminants • Synthesis of vitamin K and certain B vitamins

23. Review Break #2: • Where does the majority of digestion and absorption of nutrients occur? • What are the functions of the liver, pancreas, and gallbladder? • What are villi and what is their purpose? • Why is the large intestine so important to non-ruminants?

24. Fun Digestive Facts: • The domesticated dog’s digestive system is similar to a human's; except, the dog's intestinal tract is shorter, due to the amount of protein dogs consume. • Cows produce about 100 liters of saliva a day, humans produce about 1.5 • Sheep and goats produce gas at the rate of 5 liters per hour

25. Summarize it! • Take time to summarize the structure and function of the digestive system. • With a partner, go through each organ of the digestive system and tell its location and function. Be sure to say whether mechanical, chemical, or both types of digestion occur there. • Use the diagram in your notes or your flow chart to help!

26. References • Digestive Physiology of Herbivores • Applied Animal Nutrition • Feeding the Endurance Horse