1 Lecture #9 – Animal Nutrition and Digestion
Mar 30, 2015
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 carbohydratesFats are also usedProteins are used as a “last resort”
• Digestion converts consumed polymers to the monomers used in respiration
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
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 allDo not have the right biosynthetic pathways
• Must be eaten in pre-assembled form• Some common to all animals; some
specializedEssential amino acidsEssential fatty acidsVitaminsMinerals
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 consumedAll animal proteins are complete – contain all
the essential amino acidsAll plant proteins are incomplete – missing
some of the essential amino acids
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
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
Table – essential vitamins; sources and functions
Study table in
textfor a
general under-
standing
22
Minerals
• Inorganic elementsSome required in small amounts; some in
largerRequirements vary by taxon
• Many different functionsSome 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
Diagram – food procession in a small mammal
Food Processing• Ingestion• Digestion
• Absorption
• Elimination
26
Evolution of Compartmentalization
• Food digestion must be containedWhy???
• Earliest containment structures are food vacuolesSponges digest entirely intra-cellularly
• Most animals digest at least partly outside the cellsSimplest body plans have a digestive sac with one
openingMore 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
vacuolesSponges digest entirely intra-cellularly
• Most animals digest at least partly outside the cellsSimplest body plans have a digestive sac with one
openingMore 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
vacuolesSponges digest entirely intra-cellularly
• Most animals digest at least partly outside the cellsSimplest body plans have a digestive sac with one
openingMore complex animals have a digestive tube with an
opening for ingestion and one for elimination
29
Diagram – sponges and their choanocytes
Sponges digest food in vacuoles that fuse with lysosomes containing hydrolytic enzymes
30
Evolution of Compartmentalization
• Food digestion must be contained• Earliest containment structures are food
vacuolesSponges digest entirely intra-cellularly
• Most animals digest at least partly outside the cellsSimplest body plans have a digestive sac with one
openingMore complex animals have a digestive tube with an
opening for ingestion and one for elimination
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
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
vacuolesSponges digest entirely intra-cellularly
• Most animals digest at least partly outside the cellsSimplest 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 containedAvoids digestion of body cells and tissues
• Earliest containment structures are food vacuolesSponges digest entirely intra-cellularly
• Most animals digest at least partly outside the cellsSimplest body plans have a digestive sac with one
openingMore 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
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 emergedAll mammals have a cecumBoth earthworms and birds
have developed crops
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
Diagram – the human digestive tract
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
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
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 hydrolysisStomach 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 hydrolysisStomach 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 hydrolysisStomach lining protected from self-digestion by
thick mucus and secretion of inactive pepsin precursor
• Controls passage of food into small intestine
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 intestineEnzymatic hydrolysis
• Most absorption occurs in the latter 5.75m of the small intestine
54
Diagram – the human small intestine
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
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 intestineEnzymatic hydrolysis
• Most absorption occurs in the latter 5.75m of the small intestine
58
Diagram – the pancreas, liver and gall bladder; structure and function
Pancreas secretes enzymes and bicarbonate; liver secretes bile
59
Chart – digestive enzymes; point of secretion and substrate; same on next slide
Digestive enzymes and substrates
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 intestineEnzymatic hydrolysis
• Most absorption occurs in the latter 5.75m of the small intestine
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
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
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
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
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
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
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 functionlessAppendix contributes to immune function, but
is dispensable Appendix may function to repopulate intestines with
beneficial bacteria after intestinal infections
70
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 lumenAdditional water is consumed in dietSI and LI together absorb ~ 90% Inflammation of LI reduces water absorption diarrhea
• LI also houses both commensal and mutualistic bacteriaLive on undigested or unabsorbed materialsProduce 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 materialsWaste includes LOTS of bacteria; cellulose40% of the dry weight of feces is bacteria
• Feces are stored in the rectum• When the “time” comes, feces are eliminated
through the anusSphincter muscles control eliminationOne is voluntary, one involuntarySome, 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
Diagram – differences in tooth structure
Ripping, crushing and shredding teeth
Biting and grinding teeth
Combo of teeth for biting, tearing, grinding and crushing
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
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…..
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
Diagram – the digestive system of a cow
Extra compartments house symbiotic micro-organisms – food is often
regurgitated and / or re-consumed
83
Review – Key Concepts:
• Animals are heterotrophic!• Nutritional needs
EnergyCarbon skeletonsEssential 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!!!!