1. Lecture #9 – Animal Nutrition and Digestion

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

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

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

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

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

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. 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
Diagram – bioenergetics and the fate of food

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

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

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

14. Essential Amino Acids Most animals use the same 20 amino acids to make
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. Human vegetarian diets must mix plant groups to obtain all essential amino acids
Chart – essential amino acids; overlap between grains and legumes
Grass and legumes mixed provide all essential amino acids – cultural traditions prevent protein deficiencies
Grains and legumes mixed provide all essential amino acids – cultural traditions prevent protein deficiencies

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. 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

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

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

21. for a general under-standing
Study table in text
for a general under-standing
Table – essential vitamins; sources and functions
Don’t memorize, just grasp significance

22. Minerals Inorganic elements Many different functions
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. Mineral Functions??? Calcium – Phosphorous – Sulfur – Potassium –
Chlorine –
Sodium –
Magnesium –
Iron –

24. Some Mineral Functions
Calcium –
Phosphorous –
Sulfur –
Potassium –
Chlorine –
Sodium –
Magnesium –
Iron –

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

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. Evolution of Compartmentalization
Food digestion must be contained
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. Evolution of Compartmentalization
Food digestion must be contained
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. Sponges digest food in vacuoles that fuse with lysosomes containing hydrolytic enzymes
Diagram – sponges and their choanocytes

30. Evolution of Compartmentalization
Food digestion must be contained
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. Jellies and flatworms start digestion in gastrovascular cavities; finish in food vacuoles
Diagram – two cell layers in cnidarians
Images – a jellyfish and a flatworm

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

33. Evolution of Compartmentalization
Food digestion must be contained
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

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

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

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???

39. Tubular system allows for specialization and efficiency
Diagram – development of specialization in 2-hole tubular digestive tracts in earthworms, insects and birds
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. 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
Schematic diagram – the human digestive system

41. Diagram – the human digestive tract

42. 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
Diagram – the oral cavity, pharynx and esophagus; same diagram on next two slides

43. 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)
Diagram – specifically the function of the epiglottis

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. 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. 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. Diagram – the somach lining and secreting cells

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

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

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. 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
Partly based on liquidity of food – drink water to get over the over-stuffed feeling

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

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 600m2!!
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. Diagram – the human small intestine

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

56. Increased surface area, especially of transport epithelia, is a hallmark of large, complex, multi-dimensional animals
Factoids from humans:
Lungs have 100 m2 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. 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 600m2!!
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. Pancreas secretes enzymes and bicarbonate; liver secretes bile
Diagram – the pancreas, liver and gall bladder; structure and function

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

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

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 600m2!!
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. Monomers cross into epithelial cells, then into interstitial fluid, then into the lymph or bloodstream
Diagram – close-up of villi and microvilli
Some transport is facilitated, some active
Each villus includes lymph and blood vessels

63. Fat Digestion Fats are hydrophobic
Diagram – fat digestion process; same next slide
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. 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. Intestinal blood vessels drain directly into the hepatic portal vein
Nutrients get sent straight to the liver for metabolic processing
Diagram – how blood vessels absorb nutrients; same next slide

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

68. Critical Thinking
Where will the levels of blood sugar and other nutrients vary the most???

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
Cecum is very large in herbivores. Last point from October 2007 P&C review of a Duke study on appendix function. Adaptive value in sparse populations where individuals can’t pick up germs from other people (as in before we were overpopulated), or in areas that still suffer from intestinal diseases that cause diarrhea (cholera, dysentery) that clear out the gut bacteria.

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

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

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

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

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

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. 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
Diagram – differences in the digestive tract of carnivore vs. herbivore

80. Cecum in magenta…..

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

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!!!!