2. Animal Nutrition Chapter 41

3. Animals are heterotrophs They eat for three reasons: To obtain fuel for cell processes To get carbon to build organic molecules To get nutrients they cannot make

4. Why do we eat? There is a homeostatic mechanism at work Blood glucose levels help determine when we should eat

5. 1. After a meal, blood glucose levels rise. 2. This triggers the beta cells in the pancreas to make insulin 3. Insulin levels rise, making cells use available glucose 4. Blood glucose levels fall. 5. This triggers the alpha cells in the pancreas to make glucagon 6. Blood sugar levels rise as stored glucose is released into blood- stream

6. Animals feed in different ways Most are opportunistic feeders Carnivores, herbivores and omnivores

7. Feeding Adaptations Suspension feeders: sift food particles from the water Substrate feeders: live on their food source Fluid feeders: suck nutrient- rich liquid from host organisms Bulk feeders: eat large particles of food

8. Stages of Food Processing There are 4 stages you need to be familiar with

9. 1. Ingestion The act of taking food into the body From http://www.barefootbushman.com/images/water_python_eating_egg.jpg

10. 2. Digestion Process of breaking down food into particles small enough to absorb Achieved with enzymes

11. 3. Absorption Molecules that have been broken down are absorbed by the digestive system Nutrients travel to blood stream to be distributed to whole body From http://www.slp-slimming.co.uk/images/digestion2.jpg

12. 4. Elimination Waste products of digestion are expelled from the body Contains undigested parts of food

13. Digestion happens in specialized compartments Intracellular: Digestion occurs in food vacuoles Ex. paramecium Extracellular: Digestion occurs outside cells Is possible to eat larger food items this way Ex. Hydra eating Daphnia

14. Human Digestive Tract

15. Generalized Structure of the Tract Throughout the digestive tract, the general structure is like that shown at right

17. Mouth Mechanical digestion by teeth and tongue happens here Saliva secreted to lubricate food Salivary amylase to digest starches to smaller polysaccharides From http://training.seer.cancer.gov/module_anatomy/images/illu_mouth.jpg

18. Swallowing and the esophagus Food is formed into a bolus-a ball of food and is pushed back by the tongue into pharynx Peristalsis moves bolus down esophagus to stomach

19. Stomach Mechanical and chemical digestion happen here— chyme produced pH of stomach is low to facilitate protein digestion by pepsin From http://www.yourdictionary.com/images/ahd/jpg/A4stomac.jpg

20. Cells of the stomach Chief cells: secrete pepsinogen Parietal cells: secrete HCl Pepsinogen is converted to pepsin in presence of HCl

21. Sphincters and the Stomach The stomach has two sphincters: Cardiac: controls food entrance into stomach Pyloric: controls food entrance into duodenum From http://trc.ucdavis.edu/mjguinan/apc100/modules/digestive/mammal/images/ stomach00.jpg

22. Small intestine: duodenum More than 6 m in length Majority of digestion and absorption takes place here Chyme mixes with bile, enzymes and secretions from duodenum, pancreatic secretions

23. What is secreted? Liver: produces bile Gall bladder: stores bile Pancreas: makes bicarbonate ions, lipase Duodenum: produces hydrolytic enzymes

24. Enzymes of digestion

25. Digestion of Fats Fats are hydrophobic, thus digestion is difficult Bile salts emulsify large fat particles into smaller globules Pancreatic lipase surrounds smaller globules and digests them

26. Absorption of Fats Glycerol and fatty acids are absorbed by epithelial cells Remade into fats, and mixed with cholesterol, then coated with special proteins Form small globules called chylomicrons absorbed by lacteals

27. Absorption of Nutrients The small intestine is lined with villi Each villus has capillaries and a lacteal Nutrients are absorbed and carried to the hepatic portal vein

28. Hepatic portal system Hepatic portal vein: Major blood vessel that goes to the liver The liver uses absorbed nutrients in the manufacture of other organic molecules

29. Large Intestine Responsible for water recovery and absorption Produces feces Mutualistic bacteria reside here

30. Rectum and anus Fecal matter is stored here until expelled through the anus To process an entire meal takes from 16-24 hours in humans