Lecture #10 – Animal Nutrition and Digestion
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Transcript 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 – such as
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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???
13
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???
19
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
21
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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Some 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
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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
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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
• 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
Problem
???
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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
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Hands On
• Be sure to examine specimens and
comment on structure-function
relationships
• Be sure to examine Cnidarians at the
aquarium and comment on structurefunction relationships
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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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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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Two hole tube digestive plan – essentially an open tube
that passes through the body
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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???
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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
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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
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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
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Critical Thinking
• Where will the levels of
blood sugar and other
nutrients vary the most???
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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)
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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
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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)
78
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
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Cecum in magenta…..
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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)
81
Extra compartments house symbiotic
micro-organisms – food is often
regurgitated and / or re-consumed
Diagram – the digestive system of a cow
82
Review – Key Concepts:
• Animals are heterotrophic!
• Nutritional needs
Energy
Carbon skeletons
Essential nutrients
• Food processing
• The human digestive system
• Diet as a selection pressure
83
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