1. 1 Lecture #9 – Animal Nutrition and Digestion

2. 2 Key Concepts: Animals are heterotrophic! Nutritional needs – what animals get from food Food processing The human digestive system

3. 3 Critical Thinking Is this animal approaching the fruit or the flower??? Why???

4. 4 Critical Thinking Is this animal approaching the fruit or the flower??? The flower!!! Why??? Butterflies pollinate while drinking nectar; frugivores eat fruits and distribute seeds!

5. 5 Animals are always consumers Only photosynthesis can convert solar energy to usable chemical energy Plants store chemical energy Animals eat plants (or other animals) ….of course this is somewhat simplified…. but NO animals are autotrophic

6. 6 Critical Thinking Why do we eat??? Specifically, what do we get from food???

7. 7 Critical Thinking Why do we eat??? Specifically, what do we get from food??? Energy Carbon skeletons Essential nutrients  Amino acids  Fatty acids  Vitamins  Minerals

8. 8 Why we eat – energy Animals generate ATP by aerobic respiration Main substrate is carbohydrates  Fats are also used  Proteins are used as a “last resort” Digestion converts consumed polymers to the monomers used in respiration

9. 9 Diagram – bioenergetics and the fate of food Remember bioenergetics Managing the energy budget is essential to maintaining animal function ATP powers basal metabolism, other activities; maintains homeostasis; etc… Animals must eat to make ATP

10. 10 Why we eat – carbon skeletons Animals need organic carbon scaffolds to build our own organic molecules – such as???

11. 11 Why we eat – carbon skeletons Animals need organic carbon scaffolds to build our own organic molecules – such as carbohydrates, lipids, proteins and nucleic acids These are the 4 main categories of macromolecules common to all forms of life Animals can’t make organic molecules from CO 2

12. 12 Why we eat – essential nutrients Molecules that animals cannot make at all  Do not have the right biosynthetic pathways Must be eaten in pre-assembled form Some common to all animals; some specialized  Essential amino acids  Essential fatty acids  Vitamins  Minerals

13. 13 Essential Amino Acids Most animals use the same 20 amino acids to make what???

14. 14 Essential Amino Acids Most animals use the same 20 amino acids to make proteins (including enzymes!) Most animals can only synthesize about half Remaining amino acids must be consumed  All animal proteins are complete – contain all the essential amino acids  All plant proteins are incomplete – missing some of the essential amino acids

15. 15 Chart – essential amino acids; overlap between grains and legumes Human vegetarian diets must mix plant groups to obtain all essential amino acids Grains and legumes mixed provide all essential amino acids – cultural traditions prevent protein deficiencies

16. 16 Essential Fatty Acids Some unsaturated fatty acids cannot be synthesized Most animals (especially humans!) get adequate essential fatty acids from their diet We use fatty acids for????

17. 17 Essential Fatty Acids Some unsaturated fatty acids cannot be synthesized Most animals (especially humans!) get adequate essential fatty acids from their diet We use fatty acids for  Phospholipid membranes  Energy storage  Cushioning and insulation  Steroids and some hormones

18. 18 Vitamins Organic molecules used in small quantities Water soluble vitamins usually function as coenzymes Fat soluble vitamins function in nutrient absorption, as antioxidants, etc.. Deficiencies are rare with an adequate, balanced diet

19. 19 Critical Thinking Which category of vitamin is more likely to accumulate and become toxic – water soluble or fat soluble??? Why???

20. 20 Critical Thinking Which category of vitamin is more likely to accumulate and become toxic – water soluble or fat soluble??? Why??? Water soluble vitamins dissolve in blood  Excesses are filtered and excreted in urine Fat soluble vitamins dissolve into our adipose tissue  Excesses are stored in fat and can become toxic

21. 21 Table – essential vitamins; sources and functions Study table in text for a general under- standing

22. 22 Minerals Inorganic elements  Some required in small amounts; some in larger  Requirements vary by taxon Many different functions  Some metabolic; some structural Know top 8 minerals and their main functions

23. 23 Mineral Functions??? Calcium – Phosphorous – Sulfur – Potassium – Chlorine – Sodium – Magnesium – Iron –

24. 24 Some Mineral Functions Calcium – bones and teeth; nerve and muscle fx. Phosphorous – bones and teeth; ATP; nucleic acids; membranes Sulfur – in some amino acids Potassium – pH and solute balance; nerve fx. Chlorine – pH and solute balance; nerve fx. Sodium – pH and solute balance; nerve fx. Magnesium – enzyme cofactor Iron – hemoglobin; e - carrier; enzyme cofactor

25. 25 Diagram – food procession in a small mammal Food Processing Ingestion Digestion Absorption Elimination

26. 26 Evolution of Compartmentalization Food digestion must be contained  Why??? Earliest containment structures are food vacuoles  Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells  Simplest body plans have a digestive sac with one opening  More complex animals have a digestive tube with an opening for ingestion and one for elimination

27. 27 Evolution of Compartmentalization Food digestion must be contained  Avoids digestion of body cells and tissues Earliest containment structures are food vacuoles  Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells  Simplest body plans have a digestive sac with one opening  More complex animals have a digestive tube with an opening for ingestion and one for elimination

28. 28 Evolution of Compartmentalization Food digestion must be contained  Avoids digestion of body cells and tissues Earliest containment structures are food vacuoles  Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells  Simplest body plans have a digestive sac with one opening  More complex animals have a digestive tube with an opening for ingestion and one for elimination

29. 29 Diagram – sponges and their choanocytes Sponges digest food in vacuoles that fuse with lysosomes containing hydrolytic enzymes

30. 30 Evolution of Compartmentalization Food digestion must be contained  Avoids digestion of body cells and tissues Earliest containment structures are food vacuoles  Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells  Simplest body plans have a digestive sac with one opening  More complex animals have a digestive tube with an opening for ingestion and one for elimination

31. 31 Images – a jellyfish and a flatwormDiagram – two cell layers in cnidarians Jellies and flatworms start digestion in gastrovascular cavities; finish in food vacuoles

32. 32 Jellies and flatworms start digestion in gastrovascular cavities; finish in food vacuoles Problem ???

33. 33 Evolution of Compartmentalization Food digestion must be contained  Avoids digestion of body cells and tissues Earliest containment structures are food vacuoles  Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells  Simplest body plans have a digestive sac with one opening – single opening for incoming food and outgoing waste is inefficient – food and waste mix  More complex animals have a digestive tube with an opening for ingestion and one for elimination

34. Hands On Be sure to examine specimens and comment on structure-function relationships Be sure to examine Cnidarians at the aquarium and comment on structure- function relationships 34

35. 35 Evolution of Compartmentalization Food digestion must be contained  Avoids digestion of body cells and tissues Earliest containment structures are food vacuoles  Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells  Simplest body plans have a digestive sac with one opening  More complex animals have a digestive tube with an opening for ingestion and one for elimination

36. 36 Critical Thinking The 2-hole tube body plan processes food sequentially – no mixing of incoming food and outgoing waste Can you think of another advantage for the 2-hole tube plan???

37. 37 Two hole tube digestive plan – essentially an open tube that passes through the body

38. 38 Critical Thinking The 2-hole tube body plan processes food sequentially – no mixing of incoming food and outgoing waste Can you think of another advantage for the 2-hole tube plan??? It allows for specialization along the digestive tract

39. 39 Diagram – development of specialization in 2-hole tubular digestive tracts in earthworms, insects and birds Tubular system allows for specialization and efficiency Specialization based on habitat and diet Both divergent and convergent patterns have emerged  All mammals have a cecum  Both earthworms and birds have developed crops

40. 40 Schematic diagram – the human digestive system The Human Digestive System Relatively straightforward adaptations to an omnivorous diet Tube running from mouth to anus with specialized regions for food processing, absorption, and elimination of wastes Accessory glands supply lubrication, digestive enzymes and other secretions

41. 41 Diagram – the human digestive tract

42. 42 Diagram – the oral cavity, pharynx and esophagus; same diagram on next two slides Oral cavity, pharynx and esophagus allow for chewing and swallowing food Teeth cut and grind Tongue mixes and pushes bolus to back Saliva lubricates food, protects the mouth lining, buffers pH, kills bacteria, and begins the digestion of carbohydrates

43. 43 Diagram – specifically the function of the epiglottis Oral cavity, pharynx and esophagus allow for chewing and swallowing food Epiglottis tips down to direct food from pharynx to esophagus (so you don’t breathe your food)

44. 44 Oral cavity, pharynx and esophagus allow for chewing and swallowing food Peristaltic contractions in esophagus push food to stomach Food does not fall by gravity – remember our quadruped ancestors… Sphincter (ring) muscles also control passage of food

45. 45 Stomach continues the action… Stores food (very folded and stretchy) Muscle contractions mix food Lining secretes gastric juice  Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria  Pepsin begins protein hydrolysis  Stomach lining protected from self-digestion by thick mucus and secretion of inactive pepsin precursor Controls passage of food into small intestine

46. 46 Stomach continues the action… Stores food (very folded and stretchy) Muscle contractions mix food Lining secretes gastric juice  Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria  Pepsin begins protein hydrolysis  Stomach lining protected from self-digestion by thick mucus and secretion of inactive pepsin precursor Controls passage of food into small intestine

47. 47 Diagram – the somach lining and secreting cells

48. 48 Ulcers….. Stomach lining replaces itself by mitosis about every 3 days Lesions still sometimes occur Ulcer risk factors???

49. 49 Ulcers….. Stomach lining replaces itself by mitosis about every 3 days Lesions still sometimes occur Ulcer risk factors  Helicobacter pylori  Tobacco  Alcohol  Caffeine  Aspirin  Chocolate! Ouch!!

50. 50 Other animals can get ulcers, too From a student’s extra credit Causes include stress, diet, genetic abnormalities, microbial infections, very finely ground grains, heredity, bile reflux that destroys stomach lining

51. 51 Stomach continues the action… Stores food (very folded and stretchy) Muscle contractions mix food Lining secretes gastric juice  Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria  Pepsin begins protein hydrolysis  Stomach lining protected from self-digestion by thick mucus and secretion of inactive pepsin precursor Controls passage of food into small intestine

52. 52 Diagram – the cells lining the stomach, secretion of digestive juices

53. 53 The Small Intestine Completes digestion and absorbs monomers  Some absorption occurs in other parts of the digestive tract, but most in the SI More than 6m long Multiple levels of folding increase SA Surface area about 600m 2 !! Most digestion occurs in the first 25cm of the small intestine  Enzymatic hydrolysis Most absorption occurs in the latter 5.75m of the small intestine

54. 54 Diagram – the human small intestine

55. 55 Diagram – levels of folding in the human small intestine Four levels of folding function to increase surface area – tube, interior folds, villi, microvilli

56. 56 Increased surface area, especially of transport epithelia, is a hallmark of large, complex, multi-dimensional animals Factoids from humans: Lungs have 100 m 2 of surface area (almost 1/2 as big as room) Small intestine has surface area of a tennis court 80 km of tubules in a single kidney 100,000 km of blood vessels = almost 3X circumference of earth

57. 57 The Small Intestine Completes digestion and absorbs monomers  Some absorption occurs in other parts of the digestive tract, but most in the SI More than 6m long Multiple levels of folding increase SA Surface area about 600m 2 !! Most digestion occurs in the first 25cm of the small intestine  Enzymatic hydrolysis Most absorption occurs in the latter 5.75m of the small intestine

58. 58 Diagram – the pancreas, liver and gall bladder; structure and function Pancreas secretes enzymes and bicarbonate; liver secretes bile

59. 59 Chart – digestive enzymes; point of secretion and substrate; same on next slide Digestive enzymes and substrates

60. 60 Most digestion in duodenum (1 st 25cm)

61. 61 The Small Intestine Completes digestion and absorbs monomers  Some absorption occurs in other parts of the digestive tract, but most in the SI More than 6m long Multiple levels of folding increase SA Surface area about 600m 2 !! Most digestion occurs in the first 25cm of the small intestine  Enzymatic hydrolysis Most absorption occurs in the latter 5.75m of the small intestine

62. 62 Diagram – close-up of villi and microvilli Monomers cross into epithelial cells, then into interstitial fluid, then into the lymph or bloodstream Some transport is facilitated, some active Each villus includes lymph and blood vessels

63. 63 Diagram – fat digestion process; same next slide Fat Digestion Fats are hydrophobic Bile salts emulsify large fat droplets into smaller droplets  more surface area Lipase digestion produces fatty acids and mono- glycerides These monomers form into micelles

64. 64 Fat Absorbtion Micelles are tiny enough to diffuse into epithelial cells Monomers are recombined into fats in the epithelial cells Fats mix with cholesterol and are coated with proteins Resulting globules are transported into the lymph, and eventually into the blood (at shoulder ducts)

65. 65 Diagram – how blood vessels absorb nutrients; same next slide Intestinal blood vessels drain directly into the hepatic portal vein Nutrients get sent straight to the liver for metabolic processing

66. 66 Intestinal blood vessels drain directly into the hepatic portal vein From the liver, the blood goes straight to the heart for distribution throughout the body

67. 67 Diagram – circulation patterns in humans showing relationship between circulation and major organs Critical Thinking Where will the levels of blood sugar and other nutrients vary the most???

68. 68 Critical Thinking Where will the levels of blood sugar and other nutrients vary the most??? The hepatic portal vein Levels are stabilized in the liver before blood is circulated to the rest of the body

69. 69 The large intestine, AKA the colon Connected to SI at T junction Dead-end of T is the cecum Appendix extends off cecum  Cecum functions as fermentation chamber in many animals, especially herbivores  Human cecum is small, relatively functionless  Appendix contributes to immune function, but is dispensable  Appendix may function to repopulate intestines with beneficial bacteria after intestinal infections

70. 70 Diagrams – the cecum in omnivores (humans) vs. specialized herbivores (koalas)

71. 71 The large intestine, AKA the colon Remainder of LI is ~ 1.5m Main function is to absorb water  7l of fluid is secreted into intestinal lumen  Additional water is consumed in diet  SI and LI together absorb ~ 90%  Inflammation of LI reduces water absorption  diarrhea LI also houses both commensal and mutualistic bacteria  Live on undigested or unabsorbed materials  Produce important vitamins (K, B’s, folic acid, biotin)  Some produce stinky gasses as a byproduct of metabolism

72. 72 The large intestine, AKA the colon Final section of LI is the rectum Feces are produced as water is absorbed from waste organic materials  Waste includes LOTS of bacteria; cellulose  40% of the dry weight of feces is bacteria Feces are stored in the rectum When the “time” comes, feces are eliminated through the anus  Sphincter muscles control elimination  One is voluntary, one involuntary  Some, but not complete control over defecation

73. 73 Diagram – the human digestive tract with the large intestine highlighted

74. 74 Diet is a selection pressure Dentition  Different tooth shapes for ripping and grinding Length of small intestine  Herbivores typically have much longer SI Other compartments and symbioses  Fermentation chambers that house micro- organisms that can digest cellulose (animals lack cellulases)  Enlarged ceca (first feces are re-eaten)  Esophageal pouches (crops in some birds, the “stomachs” of ruminants)

75. 75 Critical Thinking How might diet affect tooth evolution? Carnivores – Herbivores – Omnivores –

76. 76 Critical Thinking How might diet affect tooth evolution? Carnivores – eat meat only – puncture, rip, shred, crush Herbivores – eat plants only – bite, grind Omnivores – eat both – combo teeth

77. 77 Diagram – differences in tooth structure Ripping, crushing and shredding teeth Biting and grinding teeth Combo of teeth for biting, tearing, grinding and crushing

78. 78 Diet is a selection pressure Dentition  Different tooth shapes for ripping and grinding Length of small intestine  Herbivores typically have much longer SI Other compartments and symbioses  Fermentation chambers that house micro- organisms that can digest cellulose (animals lack cellulases)  Enlarged ceca (first feces are re-eaten)  Esophageal pouches (crops in some birds, the “stomachs” of ruminants)

79. 79 Diagram – differences in the digestive tract of carnivore vs. herbivore Most plant material is tough and fibrous – the longer digestive tract in herbivores allows more time and space for digestion and absorption of both nutrients and water

80. Cecum in magenta….. 80

81. 81 Diet is a selection pressure Dentition  Different tooth shapes for ripping and grinding Length of small intestine  Herbivores typically have much longer SI Other compartments and symbioses  Fermentation chambers that house micro- organisms that can digest cellulose (animals lack cellulases)  Enlarged ceca (first feces are re-eaten)  Esophageal pouches (crops in some birds, the “stomachs” of ruminants)

82. 82 Diagram – the digestive system of a cow Extra compartments house symbiotic micro-organisms – food is often regurgitated and / or re-consumed

83. 83 Review – Key Concepts: Animals are heterotrophic! Nutritional needs  Energy  Carbon skeletons  Essential nutrients Food processing The human digestive system Diet as a selection pressure

84. Hands On Begin your careful dissection of the rat Follow instructions in lab manual Answer questions on lab handout Be careful, delicate and precise!!!! 84