Download Lecture #10 – Animal Nutrition and Digestion

Lecture #9 – Animal Nutrition and
Digestion
1
Key Concepts:
• Animals are heterotrophic!
• Nutritional needs – what animals get from
food
• Food processing
• The human digestive system
2
Critical Thinking
• Is this animal approaching the fruit or the
flower???
• Why???
3
Critical Thinking
• Is this animal approaching the fruit or the
flower???
• Why???
4
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
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Critical Thinking
• Why do we eat??? Specifically, what do
we get from food???
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Critical Thinking
• Why do we eat??? Specifically, what do
we get from food???
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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
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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
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Why we eat – carbon skeletons
• Animals need organic carbon scaffolds to
build our own organic molecules – such
as???
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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 can’t make organic molecules
from CO2
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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
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Essential Amino Acids
• Most animals use the same 20 amino acids
to make what???
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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
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Human vegetarian diets must mix plant
groups to obtain all essential amino acids
Chart – essential amino acids; overlap between grains and legumes
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Grains and legumes mixed provide all essential amino acids – cultural traditions prevent protein deficiencies
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????
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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
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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
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Critical Thinking
• Which category of vitamin is more likely to
accumulate and become toxic – water
soluble or fat soluble??? Why???
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Critical Thinking
• Which category of vitamin is more likely to
accumulate and become toxic – water
soluble or fat soluble??? Why???
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Table – essential vitamins; sources and functions
Study
table in
text
for a
general
understanding
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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
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Mineral Functions???
•
•
•
•
•
•
•
•
Calcium –
Phosphorous –
Sulfur –
Potassium –
Chlorine –
Sodium –
Magnesium –
Iron –
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Mineral Functions???
•
•
•
•
•
•
•
•
Calcium –
Phosphorous –
Sulfur –
Potassium –
Chlorine –
Sodium –
Magnesium –
Iron –
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Food Processing
• Ingestion
• Digestion
• Absorption
• Elimination
Diagram – food procession in a small mammal
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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
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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
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
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Sponges digest food in vacuoles that fuse with
lysosomes containing hydrolytic enzymes
Diagram – sponges and their choanocytes
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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
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Jellies and flatworms start digestion in
gastrovascular cavities; finish in food vacuoles
Diagram – two cell
layers in cnidarians
Images – a jellyfish and a flatworm
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Jellies and flatworms start digestion in
gastrovascular cavities; finish in food vacuoles
32
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
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
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???
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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
Tubular system allows
for specialization and
efficiency
• Specialization based on
habitat and diet
• Both divergent and
convergent patterns have
emerged
Diagram – development
of specialization in 2-hole
tubular digestive tracts in
earthworms, insects and
birds
All mammals have a cecum
Both earthworms and birds
have developed crops
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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
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Diagram – the human digestive tract
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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
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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
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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
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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
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• Controls passage of food into small intestine
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
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• Controls passage of food into small intestine
Diagram – the somach lining and secreting cells
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Ulcers…..
• Stomach lining replaces itself by mitosis
about every 3 days
• Lesions still sometimes occur
• Ulcer risk factors???
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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!!
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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
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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
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• Controls passage of food into small intestine
Diagram – the cells lining the stomach, secretion
of digestive juices
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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
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Diagram – the human small intestine
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Four levels of folding function to
increase surface area – tube,
interior folds, villi, microvilli
Diagram – levels of folding in the human small intestine
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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
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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
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Pancreas secretes enzymes and
bicarbonate; liver secretes bile
Diagram – the pancreas, liver and gall bladder; structure and function
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Digestive enzymes and substrates
Chart – digestive enzymes; point of secretion and substrate; same
on next slide
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Most digestion in duodenum (1st 25cm)
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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
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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
60
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 monoglycerides
• These monomers form
into micelles
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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)
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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
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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
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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
65
Critical Thinking
• Where will the levels of
blood sugar and other
nutrients vary the most???
66
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
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Diagrams – the cecum in omnivores
(humans) vs. specialized herbivores
(koalas)
68
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
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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
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Diagram – the human digestive tract with the large intestine highlighted
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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 microorganisms that can digest cellulose (animals
lack cellulases)
Enlarged ceca (first feces are re-eaten)
Esophageal pouches (crops in some birds, the
“stomachs” of ruminants)
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Critical Thinking
•
•
•
•
How might diet affect tooth evolution?
Carnivores –
Herbivores –
Omnivores –
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Critical Thinking
•
•
•
•
How might diet affect tooth evolution?
Carnivores –
Herbivores –
Omnivores –
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Ripping, crushing and
shredding teeth
Diagram – differences in tooth structure
Biting and grinding teeth
Combo of teeth for
biting, tearing, grinding
and crushing
75
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 microorganisms that can digest cellulose (animals
lack cellulases)
Enlarged ceca (first feces are re-eaten)
Esophageal pouches (crops in some birds, the
“stomachs” of ruminants)
76
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
77
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 microorganisms that can digest cellulose (animals
lack cellulases)
Enlarged ceca (first feces are re-eaten)
Esophageal pouches (crops in some birds, the
“stomachs” of ruminants)
78
Extra compartments house symbiotic
micro-organisms – food is often
regurgitated and / or re-consumed
Diagram – the digestive system of a cow
79
Review – Key Concepts:
• Animals are heterotrophic!
• Nutritional needs
Energy
Carbon skeletons
Essential nutrients
• Food processing
• The human digestive system
• Diet as a selection pressure
80