Digestion

2. Digestion • All animals are heterotrophs • Different modes of feeding evolved • Modes of feeding (structure-function) can be used as an evolutionary evidence • Compartmentalization

4. Intracellular vs. Extracellular • Intracellular- occurs within food vacuoles • E.g. food vacuoles in Paramecium, amoebocytes of sponge • Extracellular- occurs within specialized compartments • Incomplete vs. complete

5. Incomplete • A single opening is present for both entrance of food and exit of wastes • Gastrovascular cavity of Cnidarians • Gastrodermis- has specialized cells that secrete digestive enzymes • Hydrolysis of macromolecules is intracellular

6. Incomplete Obelia sp.

7. Complete • Opening of food is different from exit of waste materials • Specialized regions of the alimentary canal • Complexity varies in each phylum • Extracellular hydrolysis of food

8. Complete Bos taurus

9. Modes of feeding • Herbivore • Carnivore • Omnivore • Dentition • Alimentary canal

10. Modes of Feeding • Suspension feeders • Substrate feeders • Fluid feeders • Bulk feeders

11. Modes of Feeding

12. Symbiotic Relationship • Vertebrates acquired symbiotic relationship with microscopic organisms in processing food • E.g. Ruminants, Humans, termites

13. Four Main Stages of Food Processing • Ingestion • Large oral cavity • Digestion • Mechanical vs. Chemical • Absorption • Elimination

14. Digestion in Humans • Primary organs of digestion • Mouth, pharynx, esophagus, stomach, small intestine, large intestine • Accessory glands of digestion • Salivary glands, pancreas, liver, gall bladder

15. Digestion in Humans • Mouth- functions: ingestion and digestion • Digestion begins in the Oral Cavity • Mechanical and Chemical digestion • Salivary amylase- breaks down polysaccharide and glycogen • Saliva- also fxns as antibacterial agent and neutralizes acidity of foods

16. Pharynx • Upper portion of the throat • Where air and digested food meet • Digested ball (bolus) of food enters • Epiglottis- acts as a seal to prevent food from entering the air passages

17. Esophagus • Upper portion- striated muscle • Lower portion- smooth muscle • Connects the pharynx to the stomach • Peristalsis • Goblet cells- specialized cells that lines the esophagus • Release mucus that covers the bolus

18. Peristalsis • Wave-like motion responsible for the movement of digested food in the alimentary canal

19. Stomach • Stores and digests food • Cardiac sphincter- prevents backflow • Pyloric sphincter- regulates entrance of acidic chyme to the small intestine • Secretes digestive juice • Mixed with food through churning of the stomach through smooth muscle contractions

20. Stomach • Chief cells- secretes pepsinogen • Parietal cells- secrete HCl • HCl- disrupts the extracellular matrix of plant and animal cell • Pepsin- active form of pepsinogen • Hydrolyzes proteins • Works best in an acidic environment

21. Stomach • Stomach lining is protected • First, pepsinogen is only activated when secreted into the lumen due to the action of the acidic HCl (pepsinogen activation-positive feedback) • Secondly, presence of goblet cells that secrete mucus • product- acid chyme

22. Stomach

23. Small Intestine • Major organ of digestion and absorption • Longest section of the alimentary canal • Divided into three sections:duodenum, jejunum, ileum • Duodenum- site of mixing of acidic chyme and other digestive juices (digestion) • Jejunum and Ileum- absorption

24. Small Intestine • Carbohydrate digestion • Protein Digestion • Nucleic Acid Digestion • Fatty Acid Digestion

25. Carbohydrate digestion • Starch, glycogen and other polysaccharides that were digested in the mouth is further digested • Pancreatic amylase • Maltase- splits maltose into its glucose units • Disaccharides- absorbed by intestinal epithelium

26. Protein digestion • Trypsin and Chymotrypsin- breakdown large polypeptide chain like pepsin • Dipeptidase- split small peptides • Carboxypeptidase- breakdown polypeptides in its carboxyl end • Aminopeptidase- breakdown peptidase in its nitrogenous end • Enteropeptidase- activates pancreatic enzymes

27. Protein digestion • Intestinal enzymes- aminopeptidase, enteropeptidase • Pancreatic enzymes- Trypsinogen, Procarboxypeptidase, Chymotrypsinogen • Enteropeptidase- activates Trypsinogen • Trypsin- activates Procarboxypeptidase, Chymotrypsinogen

28. Nucleic Acid Digestion • Nucleases- hydrolyze nucleic acids • Exonucleases- hydrolyze nucleic acids on its terminal • Endonucleases- hydrolyze nucleic acids within • Other enzymes hydrolyze the nucleotides into its components

29. Fatty acid digestion • Bile salts- emulsify undigested fats in the duodenum • Emulsification- inc SA of fat molecules • Lipase- digests fat molecules

30. Absorption • Villus- folds found in the small intestine • Microvillus- microscopic fingerlike projections that increases the absorption of materials • Each villus is connected to a capillary (BV) network and lacteals(Lymphatic system)

31. Transport of nutrients • Passive Diffusion • Active transport • Nutrients that were absorbed are transformed into what the body needs • Chylomicron- small globule that is a combination of fats, cholesterol, coated with proteins

32. Hormones that regulate digestion • Gastrin-stimulated by gastric juices • Inhibited by low pH • stimulates secretion of gastric juice • Enterogastrones- group of enzymes found in the duodenum • Cholecystokinin (CCK)- stimulated by fats and amino acids • Stimulates gall bladder to release bile • Secretin- stimulated by the acidic chyme • Stimulates pancreas to release bicarbonates • If chyme is rich in fats, it stimulates the duodenum to release other enzymes to slows down digestion in the stomach

33. Large Intestine • Also called the colon • Cecum – small pouch that has different fxns • Appendix- small cecum found in man • Rectum- portion of the large intestine that temporarily stores feces • Main fxn of colon is to reabsorb water • Feces- waste that was formed after digestion • Compactness depends on water that was reabsorbed

34. Large Intestine • Intestinal Bacteria- common example is E. coli • Have mutualistic relationship with host • Generate methane or hydrogen sulfide • Some produce vitamins that are needed by the body

35. Nutrition • Nutritionally adequate diet • composed of: • fuel (chemical energy) • organic raw materials (carbon skeletons) • essential nutrients (substances the animal cannot make)

36. Balancing the fuel • Homeostatic mechanism balances the animal’s fuel • ATPs that were produced are budgeted depending on the energy requirements • Fats have the highest amount of ATP • Glucose conversion is an example of homeostatic mechanism

37. Caloric Imbalance • Undernourishment • Calorie deficiency • Overnourishment • Excessive calorie intake- results to obesity • Malnourishment • Deficient in any essential nutrients

38. Essential Nutrients • Essential Amino Acids • Essential Fatty Acids • Vitamins • Minerals

39. Essential Amino Acids • Tryptophan, methionine, Valine, Threonine, Phenylalanine, Leucine, Isoleucine, Lysine, Histidine (infants) • Deficiency in one of these may result into protein deficiency

40. Essential Fatty Acids • Essential Fatty Acids belong to the unsaturated fatty acid groups • An example is linoleic acid • Deficiencies are rare

41. Vitamins • Organic molecules that are required relatively in small amount • Two types: • Water-soluble • B vits, C • Fat-soluble • A, D, E, K

42. Minerals • Inorganic nutrients that are required in small amounts • E.g. Calcium, Phosphorous, Sodium, etc.

43. Balance diet • what enters= what leaves • It is easier to take in calories in the body than to burn it • The food pyramid serves as a guide in the kind of foods that should be taken in