Lecture 9 – Animal Nutrition and Digestion

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
• These are the 4 main categories of macromolecules
  common to all forms of life
• Animals cant make organic molecules from CO2

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
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
Study table in text for a general under-standing
Table essential vitamins sources and functions
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
Mineral Functions???

• Calcium
• Phosphorous
• Sulfur
• Potassium
• Chlorine
• Sodium
• Magnesium
• Iron

24
Mineral Functions???

• Calcium
• Phosphorous
• Sulfur
• Potassium
• Chlorine
• Sodium
• Magnesium
• Iron

25
Food Processing

• Ingestion
• Digestion

• Absorption
• 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
• 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
Jellies and flatworms start digestion in
gastrovascular cavities finish in food vacuoles
Images a jellyfish and a flatworm
Diagram two cell layers in cnidarians
32
Jellies and flatworms start digestion in
gastrovascular cavities finish in food vacuoles
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
• More complex animals have a digestive tube with
  an opening for ingestion and one for elimination

34
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

35
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???

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
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

38
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
39
Diagram the human digestive tract
40
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
41
Oral cavity, pharynx and esophagus allow for
chewing and swallowing food

• Epiglottis tips down to direct food from pharynx
  to esophagus (so you dont breathe your food)

Diagram specifically the function of the
epiglottis
42
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

43
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

44
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

45
Diagram the somach lining and secreting cells
46
Ulcers..

• Stomach lining replaces itself by mitosis about
  every 3 days
• Lesions still sometimes occur
• Ulcer risk factors???

47
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!!
48
Other animals can get ulcers, too

• From a students extra credit ?
• Causes include stress, diet, genetic
  abnormalities, microbial infections, very finely
  ground grains, heredity, bile reflux that
  destroys stomach lining

49
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

50
Diagram the cells lining the stomach, secretion
of digestive juices
51
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

52
Diagram the human small intestine
53
Four levels of folding function to increase
surface area tube, interior folds, villi,
microvilli
Diagram levels of folding in the human small
intestine
54
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

55
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

56
Pancreas secretes enzymes and bicarbonate liver
secretes bile
Diagram the pancreas, liver and gall bladder
structure and function
57
Digestive enzymes and substrates
Chart digestive enzymes point of secretion and
substrate same on next slide
58
Most digestion in duodenum (1st 25cm)
59
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

60
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

61
Fat Digestion
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

62
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)

63
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
64
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

65
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
66
Critical Thinking

• Where will the levels of blood sugar and other
  nutrients vary the most???

67
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

68
Diagrams the cecum in omnivores (humans) vs.
specialized herbivores (koalas)
69
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, Bs, folic acid,
  biotin)
• Some produce stinky gasses as a byproduct of
  metabolism

70
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

71
Diagram the human digestive tract with the
large intestine highlighted
72
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)

73
Critical Thinking

• How might diet affect tooth evolution?
• Carnivores
• Herbivores
• Omnivores

74
Critical Thinking

• How might diet affect tooth evolution?
• Carnivores
• Herbivores
• Omnivores

75
Ripping, crushing and shredding teeth Biting
and grinding teeth Combo of teeth for biting,
tearing, grinding and crushing
Diagram differences in tooth structure
76
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)

77
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
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
Extra compartments house symbiotic
micro-organisms food is often regurgitated and
/ or re-consumed
Diagram the digestive system of a cow
80
Review Key Concepts

• Animals are heterotrophic!
• Nutritional needs
• Energy
• Carbon skeletons
• Essential nutrients
• Food processing
• The human digestive system
• Diet as a selection pressure