Animal Nutrition/Digestion

1. Animal Nutrition/Digestion Chapter 41 & IB Topic 6.1

2. Introduction • Physiology: how and why the parts of the body function the way they do • Anatomy: the study of the structure. • Structure and function • Physiology is an experimental science • Cells of organisms function best in a constant internal environment

3. Digestion • The body needs to get essential nutrients • An essential step because the bulk of food taken in consists of insoluble molecules • Too large to cross the gut wall and enter the blood stream • The bulk of our diet consists of: carbohydrates, lipids, and proteins • Must be hydrolyzed • Food cannot be said to have truly entered the body until it has been digested and absorbed

4. The five steps of nutrition • 1. Ingestion • 2. Digestion • 3. Absorption • 4. Assimilation • 5. Egestion/elimination

5. Ingestion • Food is taken into the mouth for processing in the gut

6. Digestion • Process of breaking food down into molecules small enough for the body to absorb • Mechanical digestion • Teeth (mastication) and muscular walls of the gut (peristalsis: waves of contraction and relaxation • Increases surface area • Chemical digestion • Enzymes (mainly in the stomach and intestine)

7. Absorption • Soluble products of digestion are absorbed into blood circulation system

8. Assimilation • Products of digestion absorbed from blood into body cells (such as liver and muscle cells) and used or stored

9. Egestion or elimination • Undigested food and dead cells from the lining of the gut, together with bacteria from the gut flora, expelled from the body as feces

10. Enzymes (remember … ) • Huge contributor in chemical digestion • Digestion enzymes are protein catalysts produced in specialized cells in glands associated with the gut • Enzymes speed up the breakdown of insoluble food substances • Remember pH and temperature • Think homeostasis

11. What you need to know:

12. Lets take a trip down the alimentary canal … • 1. The oral cavity • 2. The stomach • 3. The small intestine • 4. The large intestine

13. Also reference Figure 41.13 in your text

14. The oral cavity • Mechanical and chemical manipulation of food • Saliva moistens food and helps prevent tooth decay by buffering/neutralizing acids • Also contains antibacterial agents • The pharynx • Opens both to the windpipe (trachea) and esophagus • When we swallow, the windpipe moves up and the glottis is covered by the epiglottis • The esophagus • Food travels down the esophagus to the stomach • Peristalsis

15. The stomach • J-shaped, pouch-like organ that hangs inferior to the diaphragm in the upper left portion of the abdominal cavity • 1-2 L capacity • The wall of the stomach is elastic, so large meals can be swallowed quickly, stored, and then gradually released into the small intestine • The wall of the stomach is muscular and contracts rhythmically to squeeze the food, mixing it and breaking it into smaller lumps

16. Functions of the stomach • Gastric glands secrete gastric juices (includes HCL) • HCL has a pH of 1.5-2.0 • Good for protein digestion (protease) • Goblet cells secrete mucus • Prevents autolysis • Chyme • Semi-liquid • A typical meal may spend up to 4 hours in the stomach

17. The small intestine • Completion of digestion of carbohydrates, lipids, and proteins • Useful products are absorbed • In humans, about 5 meters long • The inner-most layer contains finger-like projections called villi

18. Digestion in the small intestine • Food enters the first part (duodenum) a little at a time • The chyme meets bile from the bile duct and the pancreatic juice from the pancreas • Bile neutralizes the acidity of the chyme • Bile lowers the surface tension of large fat globules (emulsification) • Pancreatic juice contains several enzymes: amylase, lipase, and protease

19. Absorption in the small intestine • The products of digestion (monomers, minerals, vitamins) are absorbed as they make contact with the villi • Efficient because the villi drastically increase the surface area of the small intestine • Active transport • Products of digestion are taken into cells • Protein pump molecules

20. Assimilation follows absorption • The fate of absorbed nutrients is called assimilation • In the villi: • Sugars are passed into the capillary network, then to the liver • Amino acids are passed into the capillary network, then to the liver (make new proteins) • Lipids are absorbed as fatty acids and glycerol into the lacteal vessels  lymphatic system  blood circulation

22. The large intestine • No villi; surface area is increased by numerous folds • At this point, most of the useful nutrients have been absorbed • What remains: • Undigested matter (plant fiber), mucus, dead intestinal cells, bacteria, mineral ions, and water • In the colon, water and mineral salts (Na+, Cl-) are absorbed • What remains is now called feces • Bacteria compose about 50% of feces (so wash your hands!) • Bile pigments color the feces

23. Animations • http://www.pennhealth.com/health_info/animationplayer/ • Digestion • Peristalsis • Heartburn • Ulcers

24. Lets Model A Trip Down the Alimentary Canal … • Students will be assigned a portion of the digestive system • Arrange yourselves in the proper order • Pink Koosh ball will represent a piece of food • As the “food” passes from person to person down the digestive system, the student who is holding the ball will state the function of their body part in processing the food. • In some cases, the food may not reach you – you are a vital, accessory organ

25. Small Group Discussion • What would be the consequences if a person’s stomach was surgically removed, or did not function properly? • What about: • Small intestine • Large intestine • Pancreas • Gall bladder • Liver • Teeth and/or tongue • Salivary glands • Which of these digestive organs could you live without? What accommodations would you need to make to maintain good nutrition and digestive function? Which of these organs are absolutely impossible to live without?