ZOO 3210 Lecture 5: Digestion
2 May 2018
School
Department
Course
Professor
Link the structure and function of components of
complex digestive tracts
1.
Hummingbirds vs pythons: do digestive
structures and physiology vary with food intake?
2.
Learning Outcomes:
Note: we cannot synthesize 8 amino acids =
essential amino acids
!
Capacity to synthesize various amino acids and
vitamins varies from animal to animal
!
Evolved in terms of their nutritional needs
○
Feeding apparatus also varies (ex. Baleen vs tooth
whales)
!
Factors are linked and have evolved together
!
*see relations of nutrition, feeding, digestion, and
absorption in vertebrates and most types of
invertebrates
simple, short digestive tube (feed on
blood)
!
Lamprey:
○
contain spiral valve in intestine
(ileum) to increase surface area and
therefore have shorter intestine
!
Sharks:
○
contain pyloric ceca to increase
surface area (specialized
compartments; blind ended sacs
attached to digestive system that are
filled with bacteria and contribute to
digestion)
!
Actinopterygian (gar):
○
Amphibian (salamander)
○
Reptile (turtle)
○
crop (temporary storage compartment
located in foregut; take advantage of
a large amount of food),
!
proventriculus -secretes acid and
enzymes
!
Gizzard -grinds up food with pebbles
and stones in gizzard by compressing
food against stones
!
ceca -contains bacteria and increase
surface area
!
*do not have teeth -ability to grind
stuff is limited (--> proventriculus is
separated from ventriculus)
!
Avian:
○
digestive system is much longer and
broken up into specialized
compartments, optimized for
digestion of different food stuff (eat a
complex variety of different types of
food; omnivorous)
!
Mammal (pig):
○
Diversity
!
Spiral valve
○
Ceca
○
Crop
○
Specialized compartments increase the efficiency
of digestion, for example:
!
Have highly specialized multi-chambered
(4) STOMACH
○
Chamber allows the process of
fermentative breakdown and digestive
breakdown to be separated
○
Rumen
!
Reticulum -contains enzymes to
break down cellulose
!
Omasum -saliva is reabsorbed
!
Abomasum -glandular stomach
(enzymes and HCl); chemical
digestion
!
*see slide
○
Some mammals possess modifications that
improve the digestion of plant material:
ruminants
!
Note: differences in length of digestive
systems and in the development of the ceca
○
*cecum doesn’t really play a role in
carnivores (much smaller)
○
Carnivore digestive tracts have different
morphology than herbivore digestive tracts
!
Gut length and complexity is linked to diet
Mouth -ingestion; secretion of saliva
○
Pharynx -voluntary motility (& mouth)
○
*crop
○
Stomach (glandular) -acidic digestion;
secretion of enzymes & HCl
○
Foregut:
!
*enzymes here need neutral pH to
work
!
Absorption of food (and some water)
occurs in small intestine
!
Small intestine -basic digestion; secretion
(duodenum <-- pancreas)
○
Midgut:
!
Water and electrolyte absorption
!
Storage of wastes
!
Large intestine (colon)
○
Anus/cloaca -defecation
○
Hindgut:
!
General plan of vertebrate guts:
Note: muscular contractions throughout entire digestive
system is involved in motility
Occurs throughout digestive tract
!
Constriction in waves moves and
mixes food
!
Peristaltic contractions:
○
Oscillating contractions mixes chyme
in small intestine
!
Segmentation:
○
Outer longitudinal and inner circular smooth
muscles of the gut wall are involved in
mechanical digestion
!
*see slide
○
The pyloric sphincter is tightly closed when
the contraction reaches the sphincter,
tossing the remaining chyme backward into
the antrum
○
Waves create increase in pressure -->
closes sphincters
○
Ex. If chyme has low pH, wave
frequency decreases
!
If there is a lot of fat --> negative
feedback --> slows waves
!
Frequency of waves is regulated by
composition of chyme in duodenum
○
Gastric emptying involves peristaltic contractions
from the fundus to the antrum
!
Mechanical Digestion:
Carbohydrates --> dissaccharides -->
monosaccharides (polysaccharides)
1.
Protein --> polypeptides --> amino acids2.
Lipids --> small fat droplets --> triglycerides -->
glycerol or fatty acids
3.
Nucleic acids (DNA/RNA) --> nucleotides --> N
bases + phosphate + sugars
4.
Digestive processes: breakdown of macromolecules
*see process of chemical digestion
Mouth: polysaccharides are broken down
into smaller polysaccharides and
disaccharides by salivary amylase
○
Lumen of small intestine: polysaccharides
are broken down into disaccharides by
pancreatic amylase
○
Epithelial cells of small intestine:
disaccharides (maltose, sucrose, lactose)
are broken down into monosaccharides
(glucose, galactose) by disaccharidases
○
Carbohydrates:
!
Stomach: proteins are broken down into
peptides via pepsin
○
Proteins are broken down into
peptides via trypsin and
chymotrypsin
!
Large peptides are broken down into
amino acids by carboxypeptidase
!
Lumen of small intestine:
○
Large peptides are broken down into
amino acids by amino peptidase
!
Dipeptides are broken down into
amino acids by dipeptidase
!
Epithelial cells of small intestine:
○
Proteins:
!
Lumen of small intestine: triglycerides and
other lipids are degraded into fatty acids
and monoglycerides by lipase
○
Fats:
!
Lumen of small intestine: DNA/RNA are
broken down into nucleotides by pancreatic
nucleases
○
Epithelial cells of small intestine:
nucleotides are broken down by
nucleotidases, nucleosidases and
phosphatases into nitrogenous bases, 5C
sugars and phosphates
○
Nucleic acids:
!
Chemical digestion occurs in different segments of the
GI tract:
Lumen of intestine: all enzymes come from
pancreas
!
*note: enzymes are compartmentalized
Folds in intestinal wall
○
Villi
○
Microvilli (brush border membranes)
○
Surface area of…1.
Fructose enter cells via diffusion
through GLUT 5
!
Galactose and glucose are transported
into cell with Na+ via co-transporter
SGLT1
!
Glucose, galactose and fructose are
moved across basolateral membrane
via GLUT 2
!
Na+-K+ -ATPase creates
electrochemical gradient on
basolateral membrane
!
Sugars
○
Amino acids
○
*see slide
Water soluble vitamins
○
Transport proteins for…2.
Bile salt create micelle with FA inside
○
At apical membrane, micelle breaks apart
and allows the diffusion of FA into the
epithelial cell
○
FA and glycerol combine to form
triacylglycerols
○
Triacylglycerols combine with proteins to
produce chylomicrons
○
Chylomicrons are secreted into the villus
interior by the Golgi apparatus via vesicles
○
Availability of bile salts and Golgi apparatus for
transport of lipids
3.
Nutrient Absorption depends on:
03/20/18
Link diet, feeding apparatus, digestion and
absorption
1.
Link diet and kidney structure 2.
Hummingbirds:
!
Learning Outcomes:
Food: solid (whole animals), carnivores
○
Frequency: infrequent feeders
○
Python
!
Food: liquid diet, herbivores
○
Frequency: frequent feeders
○
Hummingbird
!
Heart rate ~1,260 beats/min
!
Wing beat ~80x/sec
○
They have the highest known mass
specific metabolic rate when
hovering
!
Mass-specific oxygen consumption
rate in hovering Anna's and rufous
hummingbirds is 30-40 mL O2/g/h
!
Birds of the same size of
mammals have significantly
higher metabolic rates
"
*recall: birds have higher internal
temperatures
!
Metabolic rate: with body mass ~3-4g
○
Environmental temperature
!
Food reserves (i.e. flower density)
!
Torpor: can be daily, but depends on…
○
Must increase fat reserves
before and stop to refuel
"
Ex. Rufous migrates from pacific
northwest to Mexico (>3200 km)
!
Migration:
○
Basic Facts of Hummingbirds:
!
Ex. Rufous: 14-18 feeding bouts/hour
(every 3-4 minutes)
!
Feed frequently
○
50-200 ul/feed --> 4-5x body weight
each day
!
Take in a high volume of nectar
○
Sucrose (20-25%)
!
Water
!
Electrolytes
!
Amino acids
!
Vitamins and other compounds
!
Nectar consists of:
○
Hummingbird Diet:
!
Tongue picks up liquid, calorie-dense
nectar that cannot be grasped and do this at
a very high rate (17 Hz, or ~60ms/lick)
○
Gravity should increase nectar-
uptake rates at downward
facing flowers --> no evidence
"
Rate of capillary action
will be less with high
sugar content (inverse
relationship)
!
Maximum energy intake
should occur with lower
density nectar (lower sugar
concentration) --> no evidence
"
If true, predictions:
!
Testing 1833 Hypothesis: hummingbird
tongue tips are loaded with nectar by means
of capillary rise (i.e. the tongue fills
passively via capillary action when in
contact with the nectar)
○
Distal portion (last 10 mm) of tongue
is bifurcated with each side forming a
groove
!
Tongue tips are supported by rods
that have membranous edges (i.e.
lamellae)
!
During feeding, the position of rods
and lamellae rotate and trap nectar
!
Retraction of bifurcated tongue tips
back into the bill, and rolling of
membranous lamellae traps nectar
!
Formation of conical shaped tongue
tip when tongue is withdrawn from
nectar prevents fluid from dripping
out
!
The process results purely from
the structural configuration of
the tongue tips
"
Nectar trapping by the lamellae does
not require any muscular work
!
Fluid at the tip is driven into the
tongue's grooves by pumping forces
resulting from re-expansion of a
collapsed section
!
This pumping mechanism fills the
tongue's grooves an order of
magnitude faster than a capillary
could
!
*see slides
!
New morphological and biomechanical
data:
○
Nectar trapping and pumping allows
for longue loading rates that are
compatible with known licking rates
(due to pressure differences)
!
Conclusion: capillary rise is not the main
mechanisms operating during hummingbird
drinking
○
Hummingbird Ingestion:
!
I.e. transformation of sucrose into
glucose and fructose via sucrase
!
*see slide
!
In brush border of small intestine
epithelial cell --> cytosol
!
Hummingbirds have very high rates of
sugar hydrolysis
○
*requires favourable
concentration gradient
"
Fructose enters the epithelial cells of
the villus in the same intestine by
passive facilitated diffusion via the
GLUT-5 transporter
!
*does not depend on
favourable concentration
gradient
"
Glucose is absorbed into the
epithelial cells by Na+ and energy-
dependent secondary active transport
located at the luminal membrane
!
Fructose and glucose exit the cell at
the basal membrane by passive
facilitated diffusion via GLUT-2
!
Carbohydrate absorption:
○
Hummingbirds have the highest known rate
of carrier-mediated glucose absorption
○
Hyperbolic curve (plateaus at ~
2 umol/g/min at 25mM)
"
Draw a graph to fit this scenario
!
Vmax = 2 umol/g/min
"
What is Vmax?
!
Km = 4mM (1/2 Vmax = 1
umol/g/min)
"
What is Km?
!
*possible exam question: active transport
of glucose across intestinal wall in Anna's
hummingbird in response to glucose
concentrations follow Michaelis-Menten
kinetics. Transport rates are saturated at
25-50mM glucose and are half-saturated at
~4 mM glucose
○
*see gastrointestinal tract
!
Food is 100% cleared from the crop
in 20 minutes
!
Food is 100% cleared from the
remaining GI tract in 40 min
!
The very simple diet of hummingbird
does not require a lot of time for
processing (60 min)
!
Reduces their feeding rate for
storage of excess nectar
"
The presence of a crop confers
foraging flexibility reducing
meals/time
!
To deal with the massive water
intake, water is absorbed by the
intestine and filtered via the kidneys
!
Retention in the gut: how long does it take
to process the nectar?
○
If this is true, animals would eat less
when offered food with a higher
energy content
!
Design experiment with
different sources of water with
varying amounts of sugar and
measure food intake
"
Test in hummingbirds:
!
Amount of sucrose in each
source
"
Amount of sucrose they ate at
each source (volume taken up
by bird; determine energy that
it contains)
"
Data collected:
!
Suggests that
hummingbirds defend a
constant rate of energy
intake
!
Negative correlation between
food intake and sugar
concentration (linear negative
slope in first graph)
"
Not exclusive to nectar-
feeding birds, similar
relationships have been
observed in a variety of
animal species
!
Reciprocal relationship
between nutrient density and
food intake (straight horizontal
line in second graph)
"
Expected results:
!
Theory among biologists that animals
regulate food intake to maintain a constant
flux of nutrients
○
Hummingbird Digestion:
!
Vs. medulla and major vasculature
!
Kidney consists mostly of cortex (~90% of
kidney)
○
Do not need to retain water (liquid
diet)?
!
Shorter loops of Henle due to little
volume in medulla -->cannot have
large concentration gradient (required
to concentrated urine)
!
Typical urine osmolarity is low
○
Low ability to produce concentrated urine
○
Hummingbird Kidney Anatomy:
!
Do digestive structures and physiology vary with food
intake (in animals that consume different diets at
different intervals)?
03/22/18
Why study pythons?1.
What is the sequence of events after a meal?2.
Synthesize information on multiple physiological
systems to explain postprandial digestion in
pythons
3.
Learning Outcomes:
Eat infrequently
!
Eat solid food
!
Eat high protein diets
!
Eat whole prey (complex diet to digest)
!
Low resting metabolic rate
!
Long gut food retention time
!
Large size of individual meals
!
Why are pythons an interesting contrast to
hummingbirds in terms of digestive physiology?
Can reach 6m and 100kg
○
One of largest snakes
!
Native to SE Asia
○
Established in southern Florida
○
Distribution:
!
Every 1-2 months when active
○
Can fast for 18 months
○
Frequency of meals:
!
Consume 25-160% of their body mass
○
Size of meals:
!
Basic facts of pythons:
Jaw does not detach
○
Two lower jaws can move independent of
each other because they are attached by an
elastic ligament
○
Multi-hinged jaw joint allows pythons to
consume prey that are several times wider
than their own head
○
Ingestion:
!
1 day post feeding: skeleton is
completely intact within the python's
stomach; 27% of stomach contents
have moved on
!
3 days post feeding: 73% of stomach
contents have disappeared
!
6 days post feeding: skeleton has
been completely broken down and
passed into small intestine
!
8-14 days post feeding: small
intestine is cleared
!
14 days post feeding: defecation
!
Daily x-ray images of a python digestion a
rat that was equal to 25% of the snakes
body mass:
○
Retention time of a meal:
!
Python Digestion:
SDA is the "work of digestion" or the additional
amount of O2 consumed during the full digestion
of a meal over and above the standard metabolic
rate
!
In man, there is a 30% increase in metabolic rate
after a meal
!
In fish, the SDA is ~160-240% (1.6-2.4 fold) for
1-3 days after meal
!
*large meals have higher SDA for a longer
period
○
In general, the magnitude of SDA is proportional
to meal size and larger in animals that freed
infrequently
!
Specific Dynamic Action (SDA):
Pythons have a 17-45 fold increase in
metabolic rate after a meal (25-100% of
body mass)
○
This is the largest SDA for any vertebrate
○
Note: SDA is proportional to the size of the
meal
○
In animals that feed infrequently, a meal will
cause the digestive system to upregulate = the
"feeding response"
!
Feeding Response in Pythons:
Upregulates the proliferation and
cellular activity
!
Gene expression of Frizzled-4 increases
after eating
○
Inhibitor of genes associated with
cell proliferation and differentiation
!
Gene expression of TCF7L2 decreases after
eating
○
1367 showed increased expression
!
1122 showed decreased expression
!
In only 6 hours after a meal (after 30 days
of fasting), the expression of ~2500 genes
in the midgut was modified
○
Molecular
!
Cellular
!
Tissue
!
HCL (parietal cells)
"
Pepsinogen is produced
in a inactive form in the
lumen of the stomach
and then is activated into
pepsin
!
Pepsin is responsible for
breaking large proteins
down into smaller ones
!
Pepsinogen (chief cells)
"
In carnivores, the stomach secretes
two key compounds that initiate the
digestion of proteins:
!
To save energy, this system is
only activated after a meal is
consumed
"
Unlike mammals, pythons do not
maintain a steady baseline rate of
acid production during fasting
!
*see slide
"
The potassium proton ATPase
pump is critical for HCl
secretion
"
Disadvantage: large
amounts of bicarbonate
will be present in
blood --> increase in
blood pH
!
HCO3-is sent into the blood
when H+ are secreted into the
stomach lumen
"
Gastric pH rapidly drops after
feeding in pythons, remains very
acidic during digestion, and rises
upon completion of gastric digestion
!
Stomach pH decreases
"
Blood pH increases
"
Blood [HCO3-] increases
"
Overall, following a meal…
!
= post proandial alkaline tide
"
Metabolic alkalosis (acid-base
disturbance; in blood) are most
pronounced in big carnivores
!
Stomach
○
Because it is the site of
absorption
"
When pythons eat a meal after a long
fast, the small intestine almost
doubles in mass by day 3
!
Surface of microvilli have
enzymes that are able to break
down the food into absorbable
units with transporters
"
The microvilli will increase in length
following a meal, peaking at day 3 =
postprandial lengthening
!
Note: upregulation of form and
function in small intestine precedes
entrance of chyme
!
All enzyme activity increases
after the digestion of the meal,
along with the transport of
nutrients (leucine and proline)
"
Note: trypsin and APN from
the pancreas
"
There is synchronous regulatory
responses of components in both
protein and carbohydrate digestion
and absorption (aminopeptidase-N
aka APN)
!
Small intestine
○
Organ
!
Whole animal
!
Post-prandial changes in the digestive system of
pythons occurs at all levels of organization
Link abundance of enzymes and chemical
breakdown
○
*see slide
!
Chemical digestion occurs in different segments of the
GI tract
Gastric pepsin, pancreatic enzymes and brush
border aminopeptidase hydrolyze proteins into
amino acids and small peptides
!
Some amino acids (e.g. proline) are absorbed in
the epithelial cells by Na+ and energy-dependent
secondary active transport via a symporter on the
luminal surface
!
Other amino acids (e.g. leucine) and small
peptides are absorbed into the epithelial cells by
Na+ and energy-dependent secondary active
transporters via antiporters
!
Amino acids exit the cell at the basal surface by
facilitated diffusion via carriers (passively) -->
circulatory system
!
*see slide
!
If they were passive transporters, they
would always be moving amino acids down
their concentration gradients
○
Secondary active transporters will work
whether gradient is favourable or not
○
--> need a larger amount in digestive-
tract lumen
!
If these were passive, the ability to move
these things would be limited
○
All amino acid transporters are upregulated
following meal (increases transport
capacity)
○
Note:
!
Amino Acid Absorption:
Average glucose uptake raises significantly
more 24 after meal vs fasting state in
snakes that have been infrequently feeding
(~+0.5 vs ~+0.15)
○
During fasting, the average glucose uptake
is lower in snakes infrequently feeding (~
0.1 vs ~0.2) --> smaller capacity
○
The average glucose uptake is higher 24
hours after feeding in snakes that
infrequently feed (~0.6 vs ~0.35)
○
The average glucose uptake increased 24
hours after feeding in both groups
○
Describe the results (4)
!
Conserve energy needed for glucose
uptake (uses ATP) in snakes that are
infrequently feeding
!
Baseline capacity for picking up glucose
from the lumen of the intestine is higher in
frequently feeding snakes
○
Adaptive strategy in infrequently feeding
snake is to upregulate genes associated with
glucose uptake (ex. Transporters)
○
Provide an explanation for these findings
!
Possible exam question:
03/27/18
Digestion entails an integrated effort across
multiple organs
1.
Luminal content and gastrointestinal hormones
regulate and coordinate the feeding response
2.
The feeding response has an adaptive value in
infrequent feeders
3.
Learning Outcomes:
All happens simultaneously
○
Involves both a substantial metabolic investment
and the coordinated interactions of several tissues
!
Increased heart rate, blood flow, and heart mass
(rbc cell volume increases)
!
Increase blood pH
○
Increase blood HCO3-
○
Blood:
!
Increase O2 uptake by 6.7x
○
Lung:
!
Increase mass
○
Liver:
!
Increase mass
○
Increase HCL and pepsin
○
Stomach:
!
Decrease mass --> release of bile (allows
lipids to be absorbed)
○
Gall bladder:
!
Increase in mass
○
Pancreas:
!
Increase mass
○
Increase microvilli length and cell volume
○
Small intestine:
!
Increasing capacity to secrete
HCl (skeleton) and pepsin
(protein) for digestion
"
Stomach (~50%)
!
Need more ATP for
transporters and enzymes via
oxidative phosphorylation
"
Lungs (~50%)
!
Need more oxygen at tissues to
create ATP
"
Heart (~50%)
!
Increase capacity for enzymes
and
"
Pancreas (~60%)
!
Increased capacity for
absorbable units to be
converted back into storage
forms
"
Liver (~70%)
!
Due to increased need to break
down protein (nitrogen)
"
Direct result of the
production of HCl
!
Balance acids-bases: HCO3-is
increased in blood (post
prandial alkaline tide)
"
Kidneys (~100%)
!
Intestinal mucosa (~160%)
!
Rationale for each increase in size:
○
*Note: all organs increase rapidly in mass upon
feeding by at least 50%
!
Heart is first organ to increase
○
The Burmese python coordinates feeding and
fasting responses across organs and tissues and
this is reflected in the collective changes in their
mass and function
!
Python digestion entails an integrated effort:
The 40% increase in postprandial ventricular
mass due to increased myosin gene expression
and presumably increase in contractile elements
!
DNA per unit of mass decreased
○
The increase in ventricular mass is due to
increase in hypertropy (cell volume) NOT
hyperplasia (cell number)
!
How does the python heart undergo hypertrophy
following a meal?
Luminal content (e.g. amino acid)
○
CCK
"
Glucagon
"
GIP
"
Insulin (stimulates uptake and
storage of nutrients into cells)
"
Increase in…
!
Gastrointestinal hormones
○
Two types of signals appear to be involved in
regulating GI morphology and activity
!
CCK and GIP secretion from the midgut
are stimulated by acidity and exposure to
nutrients
○
CCK stimulates the pancreas and gall
bladder to secrete enzymes and bile
○
GIP and CCK inhibit gastric acid secretion,
gastric emptying and muscle contraction
○
*see slide
○
Gastrointestinal hormones:
!
Need to meet both needs: store nutrients
but need huge amount of energy to build up
organ mass after fasting
○
Glucagon --> increase glucose in blood -->
increased breakdown of molecules into
energy
○
Insulin --> increase glucose uptake -->
store nutrients and molecules
○
Paradoxical increase in glucagon and insulin:
!
Enormous changes occur in the anatomy
and physiology of infrequently feeding
pythons after a meal
○
In contrast, human SDA increases by
0.3 fold (30%) and SDA coefficient
is 9% of energy taken in
!
Ex. In pythons, SDA increases up to 44
fold, and the relative cost of digestion
(SDA coefficient) is ~32% energy taken in
○
Hypothesis: "feeding response" is an
adaptation to conserve energy during
digestive quiescence
!
Prediction: infrequent feeders will
have a lower SMR than frequent
feeders
!
*see slide
!
Larger rates of increase
in infrequent feeders -->
larger cost of digestion
!
SMR, SDA coefficient and
factorial increase in four
frequently and four
infrequently feeding snake
species
"
Al animals were red rodent
meals equivalent to 25% of
snake's body mass
"
Study:
!
Infrequent feeders save on
maintenance costs
"
--> increase in organ size
!
Infrequent feeders incur larger
start up costs and cost of
digestion with each meal
"
Conclusions:
!
What is the advantage of this feeding
response?
○
Adaptive Value:
!
Pros: decrease SDA
!
Cons: increase SMR
!
Frequent, small meals:
○
Pros: decrease SMR
!
Cons: increase SDA
!
Infrequent, large meals:
○
Actively foraging snake
"
Meals are ~15% of body mass,
every ~10 days
"
Coachwhip:
!
An ambush-hunting snake
"
Meals are ~25% of body mass,
every ~6 weeks
"
Sidewinder:
!
1-4 weeks: total energetic cost
in sidewinder > coachwhip
"
4 weeks: total energetic cost in
sidewinder = coachwhip
"
>4 weeks: total energetic cost
in coachwhip > sidewinder
"
Experiment: animals are fed the same
size meal at the same intervals
!
Sidewinder has less energetic
costs than coachwhip is meal
interval is > 5 weeks
"
Coachwhip has less energetic
costs than the sidewinder if
meal interval is < 3 weeks
"
Energetic costs are equal if
meal interval in ~4 weeks
"
Conclusions:
!
Are these trade-offs observed in the field:
○
Cost-Benefit Analysis of Feeding Frequency in
Snakes
!
The "Feeding Response"
Digestion
#$%&'()*+, -)&.$, /0+,12/3
/1405,6-
Link the structure and function of components of
complex digestive tracts
1.
Hummingbirds vs pythons: do digestive
structures and physiology vary with food intake?
2.
Learning Outcomes:
Note: we cannot synthesize 8 amino acids =
essential amino acids
!
Capacity to synthesize various amino acids and
vitamins varies from animal to animal
!
Evolved in terms of their nutritional needs
○
Feeding apparatus also varies (ex. Baleen vs tooth
whales)
!
Factors are linked and have evolved together
!
*see relations of nutrition, feeding, digestion, and
absorption in vertebrates and most types of
invertebrates
simple, short digestive tube (feed on
blood)
!
Lamprey:
○
contain spiral valve in intestine
(ileum) to increase surface area and
therefore have shorter intestine
!
Sharks:
○
contain pyloric ceca to increase
surface area (specialized
compartments; blind ended sacs
attached to digestive system that are
filled with bacteria and contribute to
digestion)
!
Actinopterygian (gar):
○
Amphibian (salamander)
○
Reptile (turtle)
○
crop (temporary storage compartment
located in foregut; take advantage of
a large amount of food),
!
proventriculus -secretes acid and
enzymes
!
Gizzard -grinds up food with pebbles
and stones in gizzard by compressing
food against stones
!
ceca -contains bacteria and increase
surface area
!
*do not have teeth -ability to grind
stuff is limited (--> proventriculus is
separated from ventriculus)
!
Avian:
○
digestive system is much longer and
broken up into specialized
compartments, optimized for
digestion of different food stuff (eat a
complex variety of different types of
food; omnivorous)
!
Mammal (pig):
○
Diversity
!
Spiral valve
○
Ceca
○
Crop
○
Specialized compartments increase the efficiency
of digestion, for example:
!
Have highly specialized multi-chambered
(4) STOMACH
○
Chamber allows the process of
fermentative breakdown and digestive
breakdown to be separated
○
Rumen
!
Reticulum -contains enzymes to
break down cellulose
!
Omasum -saliva is reabsorbed
!
Abomasum -glandular stomach
(enzymes and HCl); chemical
digestion
!
*see slide
○
Some mammals possess modifications that
improve the digestion of plant material:
ruminants
!
Note: differences in length of digestive
systems and in the development of the ceca
○
*cecum doesn’t really play a role in
carnivores (much smaller)
○
Carnivore digestive tracts have different
morphology than herbivore digestive tracts
!
Gut length and complexity is linked to diet
Mouth -ingestion; secretion of saliva
○
Pharynx -voluntary motility (& mouth)
○
*crop
○
Stomach (glandular) -acidic digestion;
secretion of enzymes & HCl
○
Foregut:
!
*enzymes here need neutral pH to
work
!
Absorption of food (and some water)
occurs in small intestine
!
Small intestine -basic digestion; secretion
(duodenum <-- pancreas)
○
Midgut:
!
Water and electrolyte absorption
!
Storage of wastes
!
Large intestine (colon)
○
Anus/cloaca -defecation
○
Hindgut:
!
General plan of vertebrate guts:
Note: muscular contractions throughout entire digestive
system is involved in motility
Occurs throughout digestive tract
!
Constriction in waves moves and
mixes food
!
Peristaltic contractions:
○
Oscillating contractions mixes chyme
in small intestine
!
Segmentation:
○
Outer longitudinal and inner circular smooth
muscles of the gut wall are involved in
mechanical digestion
!
*see slide
○
The pyloric sphincter is tightly closed when
the contraction reaches the sphincter,
tossing the remaining chyme backward into
the antrum
○
Waves create increase in pressure -->
closes sphincters
○
Ex. If chyme has low pH, wave
frequency decreases
!
If there is a lot of fat --> negative
feedback --> slows waves
!
Frequency of waves is regulated by
composition of chyme in duodenum
○
Gastric emptying involves peristaltic contractions
from the fundus to the antrum
!
Mechanical Digestion:
Carbohydrates --> dissaccharides -->
monosaccharides (polysaccharides)
1.
Protein --> polypeptides --> amino acids2.
Lipids --> small fat droplets --> triglycerides -->
glycerol or fatty acids
3.
Nucleic acids (DNA/RNA) --> nucleotides --> N
bases + phosphate + sugars
4.
Digestive processes: breakdown of macromolecules
*see process of chemical digestion
Mouth: polysaccharides are broken down
into smaller polysaccharides and
disaccharides by salivary amylase
○
Lumen of small intestine: polysaccharides
are broken down into disaccharides by
pancreatic amylase
○
Epithelial cells of small intestine:
disaccharides (maltose, sucrose, lactose)
are broken down into monosaccharides
(glucose, galactose) by disaccharidases
○
Carbohydrates:
!
Stomach: proteins are broken down into
peptides via pepsin
○
Proteins are broken down into
peptides via trypsin and
chymotrypsin
!
Large peptides are broken down into
amino acids by carboxypeptidase
!
Lumen of small intestine:
○
Large peptides are broken down into
amino acids by amino peptidase
!
Dipeptides are broken down into
amino acids by dipeptidase
!
Epithelial cells of small intestine:
○
Proteins:
!
Lumen of small intestine: triglycerides and
other lipids are degraded into fatty acids
and monoglycerides by lipase
○
Fats:
!
Lumen of small intestine: DNA/RNA are
broken down into nucleotides by pancreatic
nucleases
○
Epithelial cells of small intestine:
nucleotides are broken down by
nucleotidases, nucleosidases and
phosphatases into nitrogenous bases, 5C
sugars and phosphates
○
Nucleic acids:
!
Chemical digestion occurs in different segments of the
GI tract:
Lumen of intestine: all enzymes come from
pancreas
!
*note: enzymes are compartmentalized
Folds in intestinal wall
○
Villi
○
Microvilli (brush border membranes)
○
Surface area of…1.
Fructose enter cells via diffusion
through GLUT 5
!
Galactose and glucose are transported
into cell with Na+ via co-transporter
SGLT1
!
Glucose, galactose and fructose are
moved across basolateral membrane
via GLUT 2
!
Na+-K+ -ATPase creates
electrochemical gradient on
basolateral membrane
!
Sugars
○
Amino acids
○
*see slide
Water soluble vitamins
○
Transport proteins for…2.
Bile salt create micelle with FA inside
○
At apical membrane, micelle breaks apart
and allows the diffusion of FA into the
epithelial cell
○
FA and glycerol combine to form
triacylglycerols
○
Triacylglycerols combine with proteins to
produce chylomicrons
○
Chylomicrons are secreted into the villus
interior by the Golgi apparatus via vesicles
○
Availability of bile salts and Golgi apparatus for
transport of lipids
3.
Nutrient Absorption depends on:
03/20/18
Link diet, feeding apparatus, digestion and
absorption
1.
Link diet and kidney structure 2.
Hummingbirds:
!
Learning Outcomes:
Food: solid (whole animals), carnivores
○
Frequency: infrequent feeders
○
Python
!
Food: liquid diet, herbivores
○
Frequency: frequent feeders
○
Hummingbird
!
Heart rate ~1,260 beats/min
!
Wing beat ~80x/sec
○
They have the highest known mass
specific metabolic rate when
hovering
!
Mass-specific oxygen consumption
rate in hovering Anna's and rufous
hummingbirds is 30-40 mL O2/g/h
!
Birds of the same size of
mammals have significantly
higher metabolic rates
"
*recall: birds have higher internal
temperatures
!
Metabolic rate: with body mass ~3-4g
○
Environmental temperature
!
Food reserves (i.e. flower density)
!
Torpor: can be daily, but depends on…
○
Must increase fat reserves
before and stop to refuel
"
Ex. Rufous migrates from pacific
northwest to Mexico (>3200 km)
!
Migration:
○
Basic Facts of Hummingbirds:
!
Ex. Rufous: 14-18 feeding bouts/hour
(every 3-4 minutes)
!
Feed frequently
○
50-200 ul/feed --> 4-5x body weight
each day
!
Take in a high volume of nectar
○
Sucrose (20-25%)
!
Water
!
Electrolytes
!
Amino acids
!
Vitamins and other compounds
!
Nectar consists of:
○
Hummingbird Diet:
!
Tongue picks up liquid, calorie-dense
nectar that cannot be grasped and do this at
a very high rate (17 Hz, or ~60ms/lick)
○
Gravity should increase nectar-
uptake rates at downward
facing flowers --> no evidence
"
Rate of capillary action
will be less with high
sugar content (inverse
relationship)
!
Maximum energy intake
should occur with lower
density nectar (lower sugar
concentration) --> no evidence
"
If true, predictions:
!
Testing 1833 Hypothesis: hummingbird
tongue tips are loaded with nectar by means
of capillary rise (i.e. the tongue fills
passively via capillary action when in
contact with the nectar)
○
Distal portion (last 10 mm) of tongue
is bifurcated with each side forming a
groove
!
Tongue tips are supported by rods
that have membranous edges (i.e.
lamellae)
!
During feeding, the position of rods
and lamellae rotate and trap nectar
!
Retraction of bifurcated tongue tips
back into the bill, and rolling of
membranous lamellae traps nectar
!
Formation of conical shaped tongue
tip when tongue is withdrawn from
nectar prevents fluid from dripping
out
!
The process results purely from
the structural configuration of
the tongue tips
"
Nectar trapping by the lamellae does
not require any muscular work
!
Fluid at the tip is driven into the
tongue's grooves by pumping forces
resulting from re-expansion of a
collapsed section
!
This pumping mechanism fills the
tongue's grooves an order of
magnitude faster than a capillary
could
!
*see slides
!
New morphological and biomechanical
data:
○
Nectar trapping and pumping allows
for longue loading rates that are
compatible with known licking rates
(due to pressure differences)
!
Conclusion: capillary rise is not the main
mechanisms operating during hummingbird
drinking
○
Hummingbird Ingestion:
!
I.e. transformation of sucrose into
glucose and fructose via sucrase
!
*see slide
!
In brush border of small intestine
epithelial cell --> cytosol
!
Hummingbirds have very high rates of
sugar hydrolysis
○
*requires favourable
concentration gradient
"
Fructose enters the epithelial cells of
the villus in the same intestine by
passive facilitated diffusion via the
GLUT-5 transporter
!
*does not depend on
favourable concentration
gradient
"
Glucose is absorbed into the
epithelial cells by Na+ and energy-
dependent secondary active transport
located at the luminal membrane
!
Fructose and glucose exit the cell at
the basal membrane by passive
facilitated diffusion via GLUT-2
!
Carbohydrate absorption:
○
Hummingbirds have the highest known rate
of carrier-mediated glucose absorption
○
Hyperbolic curve (plateaus at ~
2 umol/g/min at 25mM)
"
Draw a graph to fit this scenario
!
Vmax = 2 umol/g/min
"
What is Vmax?
!
Km = 4mM (1/2 Vmax = 1
umol/g/min)
"
What is Km?
!
*possible exam question: active transport
of glucose across intestinal wall in Anna's
hummingbird in response to glucose
concentrations follow Michaelis-Menten
kinetics. Transport rates are saturated at
25-50mM glucose and are half-saturated at
~4 mM glucose
○
*see gastrointestinal tract
!
Food is 100% cleared from the crop
in 20 minutes
!
Food is 100% cleared from the
remaining GI tract in 40 min
!
The very simple diet of hummingbird
does not require a lot of time for
processing (60 min)
!
Reduces their feeding rate for
storage of excess nectar
"
The presence of a crop confers
foraging flexibility reducing
meals/time
!
To deal with the massive water
intake, water is absorbed by the
intestine and filtered via the kidneys
!
Retention in the gut: how long does it take
to process the nectar?
○
If this is true, animals would eat less
when offered food with a higher
energy content
!
Design experiment with
different sources of water with
varying amounts of sugar and
measure food intake
"
Test in hummingbirds:
!
Amount of sucrose in each
source
"
Amount of sucrose they ate at
each source (volume taken up
by bird; determine energy that
it contains)
"
Data collected:
!
Suggests that
hummingbirds defend a
constant rate of energy
intake
!
Negative correlation between
food intake and sugar
concentration (linear negative
slope in first graph)
"
Not exclusive to nectar-
feeding birds, similar
relationships have been
observed in a variety of
animal species
!
Reciprocal relationship
between nutrient density and
food intake (straight horizontal
line in second graph)
"
Expected results:
!
Theory among biologists that animals
regulate food intake to maintain a constant
flux of nutrients
○
Hummingbird Digestion:
!
Vs. medulla and major vasculature
!
Kidney consists mostly of cortex (~90% of
kidney)
○
Do not need to retain water (liquid
diet)?
!
Shorter loops of Henle due to little
volume in medulla -->cannot have
large concentration gradient (required
to concentrated urine)
!
Typical urine osmolarity is low
○
Low ability to produce concentrated urine
○
Hummingbird Kidney Anatomy:
!
Do digestive structures and physiology vary with food
intake (in animals that consume different diets at
different intervals)?
03/22/18
Why study pythons?1.
What is the sequence of events after a meal?2.
Synthesize information on multiple physiological
systems to explain postprandial digestion in
pythons
3.
Learning Outcomes:
Eat infrequently
!
Eat solid food
!
Eat high protein diets
!
Eat whole prey (complex diet to digest)
!
Low resting metabolic rate
!
Long gut food retention time
!
Large size of individual meals
!
Why are pythons an interesting contrast to
hummingbirds in terms of digestive physiology?
Can reach 6m and 100kg
○
One of largest snakes
!
Native to SE Asia
○
Established in southern Florida
○
Distribution:
!
Every 1-2 months when active
○
Can fast for 18 months
○
Frequency of meals:
!
Consume 25-160% of their body mass
○
Size of meals:
!
Basic facts of pythons:
Jaw does not detach
○
Two lower jaws can move independent of
each other because they are attached by an
elastic ligament
○
Multi-hinged jaw joint allows pythons to
consume prey that are several times wider
than their own head
○
Ingestion:
!
1 day post feeding: skeleton is
completely intact within the python's
stomach; 27% of stomach contents
have moved on
!
3 days post feeding: 73% of stomach
contents have disappeared
!
6 days post feeding: skeleton has
been completely broken down and
passed into small intestine
!
8-14 days post feeding: small
intestine is cleared
!
14 days post feeding: defecation
!
Daily x-ray images of a python digestion a
rat that was equal to 25% of the snakes
body mass:
○
Retention time of a meal:
!
Python Digestion:
SDA is the "work of digestion" or the additional
amount of O2 consumed during the full digestion
of a meal over and above the standard metabolic
rate
!
In man, there is a 30% increase in metabolic rate
after a meal
!
In fish, the SDA is ~160-240% (1.6-2.4 fold) for
1-3 days after meal
!
*large meals have higher SDA for a longer
period
○
In general, the magnitude of SDA is proportional
to meal size and larger in animals that freed
infrequently
!
Specific Dynamic Action (SDA):
Pythons have a 17-45 fold increase in
metabolic rate after a meal (25-100% of
body mass)
○
This is the largest SDA for any vertebrate
○
Note: SDA is proportional to the size of the
meal
○
In animals that feed infrequently, a meal will
cause the digestive system to upregulate = the
"feeding response"
!
Feeding Response in Pythons:
Upregulates the proliferation and
cellular activity
!
Gene expression of Frizzled-4 increases
after eating
○
Inhibitor of genes associated with
cell proliferation and differentiation
!
Gene expression of TCF7L2 decreases after
eating
○
1367 showed increased expression
!
1122 showed decreased expression
!
In only 6 hours after a meal (after 30 days
of fasting), the expression of ~2500 genes
in the midgut was modified
○
Molecular
!
Cellular
!
Tissue
!
HCL (parietal cells)
"
Pepsinogen is produced
in a inactive form in the
lumen of the stomach
and then is activated into
pepsin
!
Pepsin is responsible for
breaking large proteins
down into smaller ones
!
Pepsinogen (chief cells)
"
In carnivores, the stomach secretes
two key compounds that initiate the
digestion of proteins:
!
To save energy, this system is
only activated after a meal is
consumed
"
Unlike mammals, pythons do not
maintain a steady baseline rate of
acid production during fasting
!
*see slide
"
The potassium proton ATPase
pump is critical for HCl
secretion
"
Disadvantage: large
amounts of bicarbonate
will be present in
blood --> increase in
blood pH
!
HCO3-is sent into the blood
when H+ are secreted into the
stomach lumen
"
Gastric pH rapidly drops after
feeding in pythons, remains very
acidic during digestion, and rises
upon completion of gastric digestion
!
Stomach pH decreases
"
Blood pH increases
"
Blood [HCO3-] increases
"
Overall, following a meal…
!
= post proandial alkaline tide
"
Metabolic alkalosis (acid-base
disturbance; in blood) are most
pronounced in big carnivores
!
Stomach
○
Because it is the site of
absorption
"
When pythons eat a meal after a long
fast, the small intestine almost
doubles in mass by day 3
!
Surface of microvilli have
enzymes that are able to break
down the food into absorbable
units with transporters
"
The microvilli will increase in length
following a meal, peaking at day 3 =
postprandial lengthening
!
Note: upregulation of form and
function in small intestine precedes
entrance of chyme
!
All enzyme activity increases
after the digestion of the meal,
along with the transport of
nutrients (leucine and proline)
"
Note: trypsin and APN from
the pancreas
"
There is synchronous regulatory
responses of components in both
protein and carbohydrate digestion
and absorption (aminopeptidase-N
aka APN)
!
Small intestine
○
Organ
!
Whole animal
!
Post-prandial changes in the digestive system of
pythons occurs at all levels of organization
Link abundance of enzymes and chemical
breakdown
○
*see slide
!
Chemical digestion occurs in different segments of the
GI tract
Gastric pepsin, pancreatic enzymes and brush
border aminopeptidase hydrolyze proteins into
amino acids and small peptides
!
Some amino acids (e.g. proline) are absorbed in
the epithelial cells by Na+ and energy-dependent
secondary active transport via a symporter on the
luminal surface
!
Other amino acids (e.g. leucine) and small
peptides are absorbed into the epithelial cells by
Na+ and energy-dependent secondary active
transporters via antiporters
!
Amino acids exit the cell at the basal surface by
facilitated diffusion via carriers (passively) -->
circulatory system
!
*see slide
!
If they were passive transporters, they
would always be moving amino acids down
their concentration gradients
○
Secondary active transporters will work
whether gradient is favourable or not
○
--> need a larger amount in digestive-
tract lumen
!
If these were passive, the ability to move
these things would be limited
○
All amino acid transporters are upregulated
following meal (increases transport
capacity)
○
Note:
!
Amino Acid Absorption:
Average glucose uptake raises significantly
more 24 after meal vs fasting state in
snakes that have been infrequently feeding
(~+0.5 vs ~+0.15)
○
During fasting, the average glucose uptake
is lower in snakes infrequently feeding (~
0.1 vs ~0.2) --> smaller capacity
○
The average glucose uptake is higher 24
hours after feeding in snakes that
infrequently feed (~0.6 vs ~0.35)
○
The average glucose uptake increased 24
hours after feeding in both groups
○
Describe the results (4)
!
Conserve energy needed for glucose
uptake (uses ATP) in snakes that are
infrequently feeding
!
Baseline capacity for picking up glucose
from the lumen of the intestine is higher in
frequently feeding snakes
○
Adaptive strategy in infrequently feeding
snake is to upregulate genes associated with
glucose uptake (ex. Transporters)
○
Provide an explanation for these findings
!
Possible exam question:
03/27/18
Digestion entails an integrated effort across
multiple organs
1.
Luminal content and gastrointestinal hormones
regulate and coordinate the feeding response
2.
The feeding response has an adaptive value in
infrequent feeders
3.
Learning Outcomes:
All happens simultaneously
○
Involves both a substantial metabolic investment
and the coordinated interactions of several tissues
!
Increased heart rate, blood flow, and heart mass
(rbc cell volume increases)
!
Increase blood pH
○
Increase blood HCO3-
○
Blood:
!
Increase O2 uptake by 6.7x
○
Lung:
!
Increase mass
○
Liver:
!
Increase mass
○
Increase HCL and pepsin
○
Stomach:
!
Decrease mass --> release of bile (allows
lipids to be absorbed)
○
Gall bladder:
!
Increase in mass
○
Pancreas:
!
Increase mass
○
Increase microvilli length and cell volume
○
Small intestine:
!
Increasing capacity to secrete
HCl (skeleton) and pepsin
(protein) for digestion
"
Stomach (~50%)
!
Need more ATP for
transporters and enzymes via
oxidative phosphorylation
"
Lungs (~50%)
!
Need more oxygen at tissues to
create ATP
"
Heart (~50%)
!
Increase capacity for enzymes
and
"
Pancreas (~60%)
!
Increased capacity for
absorbable units to be
converted back into storage
forms
"
Liver (~70%)
!
Due to increased need to break
down protein (nitrogen)
"
Direct result of the
production of HCl
!
Balance acids-bases: HCO3-is
increased in blood (post
prandial alkaline tide)
"
Kidneys (~100%)
!
Intestinal mucosa (~160%)
!
Rationale for each increase in size:
○
*Note: all organs increase rapidly in mass upon
feeding by at least 50%
!
Heart is first organ to increase
○
The Burmese python coordinates feeding and
fasting responses across organs and tissues and
this is reflected in the collective changes in their
mass and function
!
Python digestion entails an integrated effort:
The 40% increase in postprandial ventricular
mass due to increased myosin gene expression
and presumably increase in contractile elements
!
DNA per unit of mass decreased
○
The increase in ventricular mass is due to
increase in hypertropy (cell volume) NOT
hyperplasia (cell number)
!
How does the python heart undergo hypertrophy
following a meal?
Luminal content (e.g. amino acid)
○
CCK
"
Glucagon
"
GIP
"
Insulin (stimulates uptake and
storage of nutrients into cells)
"
Increase in…
!
Gastrointestinal hormones
○
Two types of signals appear to be involved in
regulating GI morphology and activity
!
CCK and GIP secretion from the midgut
are stimulated by acidity and exposure to
nutrients
○
CCK stimulates the pancreas and gall
bladder to secrete enzymes and bile
○
GIP and CCK inhibit gastric acid secretion,
gastric emptying and muscle contraction
○
*see slide
○
Gastrointestinal hormones:
!
Need to meet both needs: store nutrients
but need huge amount of energy to build up
organ mass after fasting
○
Glucagon --> increase glucose in blood -->
increased breakdown of molecules into
energy
○
Insulin --> increase glucose uptake -->
store nutrients and molecules
○
Paradoxical increase in glucagon and insulin:
!
Enormous changes occur in the anatomy
and physiology of infrequently feeding
pythons after a meal
○
In contrast, human SDA increases by
0.3 fold (30%) and SDA coefficient
is 9% of energy taken in
!
Ex. In pythons, SDA increases up to 44
fold, and the relative cost of digestion
(SDA coefficient) is ~32% energy taken in
○
Hypothesis: "feeding response" is an
adaptation to conserve energy during
digestive quiescence
!
Prediction: infrequent feeders will
have a lower SMR than frequent
feeders
!
*see slide
!
Larger rates of increase
in infrequent feeders -->
larger cost of digestion
!
SMR, SDA coefficient and
factorial increase in four
frequently and four
infrequently feeding snake
species
"
Al animals were red rodent
meals equivalent to 25% of
snake's body mass
"
Study:
!
Infrequent feeders save on
maintenance costs
"
--> increase in organ size
!
Infrequent feeders incur larger
start up costs and cost of
digestion with each meal
"
Conclusions:
!
What is the advantage of this feeding
response?
○
Adaptive Value:
!
Pros: decrease SDA
!
Cons: increase SMR
!
Frequent, small meals:
○
Pros: decrease SMR
!
Cons: increase SDA
!
Infrequent, large meals:
○
Actively foraging snake
"
Meals are ~15% of body mass,
every ~10 days
"
Coachwhip:
!
An ambush-hunting snake
"
Meals are ~25% of body mass,
every ~6 weeks
"
Sidewinder:
!
1-4 weeks: total energetic cost
in sidewinder > coachwhip
"
4 weeks: total energetic cost in
sidewinder = coachwhip
"
>4 weeks: total energetic cost
in coachwhip > sidewinder
"
Experiment: animals are fed the same
size meal at the same intervals
!
Sidewinder has less energetic
costs than coachwhip is meal
interval is > 5 weeks
"
Coachwhip has less energetic
costs than the sidewinder if
meal interval is < 3 weeks
"
Energetic costs are equal if
meal interval in ~4 weeks
"
Conclusions:
!
Are these trade-offs observed in the field:
○
Cost-Benefit Analysis of Feeding Frequency in
Snakes
!
The "Feeding Response"
Digestion
#$%&'()*+, -)&.$, /0+,12/3 /1405,6-
Link the structure and function of components of
complex digestive tracts
1.
Hummingbirds vs pythons: do digestive
structures and physiology vary with food intake?
2.
Learning Outcomes:
Note: we cannot synthesize 8 amino acids =
essential amino acids
!
Capacity to synthesize various amino acids and
vitamins varies from animal to animal
!
Evolved in terms of their nutritional needs
○
Feeding apparatus also varies (ex. Baleen vs tooth
whales)
!
Factors are linked and have evolved together
!
*see relations of nutrition, feeding, digestion, and
absorption in vertebrates and most types of
invertebrates
simple, short digestive tube (feed on
blood)
!
Lamprey:
○
contain spiral valve in intestine
(ileum) to increase surface area and
therefore have shorter intestine
!
Sharks:
○
contain pyloric ceca to increase
surface area (specialized
compartments; blind ended sacs
attached to digestive system that are
filled with bacteria and contribute to
digestion)
!
Actinopterygian (gar):
○
Amphibian (salamander)
○
Reptile (turtle)
○
crop (temporary storage compartment
located in foregut; take advantage of
a large amount of food),
!
proventriculus -secretes acid and
enzymes
!
Gizzard -grinds up food with pebbles
and stones in gizzard by compressing
food against stones
!
ceca -contains bacteria and increase
surface area
!
*do not have teeth -ability to grind
stuff is limited (--> proventriculus is
separated from ventriculus)
!
Avian:
○
digestive system is much longer and
broken up into specialized
compartments, optimized for
digestion of different food stuff (eat a
complex variety of different types of
food; omnivorous)
!
Mammal (pig):
○
Diversity
!
Spiral valve
○
Ceca
○
Crop
○
Specialized compartments increase the efficiency
of digestion, for example:
!
Have highly specialized multi-chambered
(4) STOMACH
○
Chamber allows the process of
fermentative breakdown and digestive
breakdown to be separated
○
Rumen
!
Reticulum -contains enzymes to
break down cellulose
!
Omasum -saliva is reabsorbed
!
Abomasum -glandular stomach
(enzymes and HCl); chemical
digestion
!
*see slide
○
Some mammals possess modifications that
improve the digestion of plant material:
ruminants
!
Note: differences in length of digestive
systems and in the development of the ceca
○
*cecum doesn’t really play a role in
carnivores (much smaller)
○
Carnivore digestive tracts have different
morphology than herbivore digestive tracts
!
Gut length and complexity is linked to diet
Mouth -ingestion; secretion of saliva
○
Pharynx -voluntary motility (& mouth)
○
*crop
○
Stomach (glandular) -acidic digestion;
secretion of enzymes & HCl
○
Foregut:
!
*enzymes here need neutral pH to
work
!
Absorption of food (and some water)
occurs in small intestine
!
Small intestine -basic digestion; secretion
(duodenum <-- pancreas)
○
Midgut:
!
Water and electrolyte absorption
!
Storage of wastes
!
Large intestine (colon)
○
Anus/cloaca -defecation
○
Hindgut:
!
General plan of vertebrate guts:
Note: muscular contractions throughout entire digestive
system is involved in motility
Occurs throughout digestive tract
!
Constriction in waves moves and
mixes food
!
Peristaltic contractions:
○
Oscillating contractions mixes chyme
in small intestine
!
Segmentation:
○
Outer longitudinal and inner circular smooth
muscles of the gut wall are involved in
mechanical digestion
!
*see slide
○
The pyloric sphincter is tightly closed when
the contraction reaches the sphincter,
tossing the remaining chyme backward into
the antrum
○
Waves create increase in pressure -->
closes sphincters
○
Ex. If chyme has low pH, wave
frequency decreases
!
If there is a lot of fat --> negative
feedback --> slows waves
!
Frequency of waves is regulated by
composition of chyme in duodenum
○
Gastric emptying involves peristaltic contractions
from the fundus to the antrum
!
Mechanical Digestion:
Carbohydrates --> dissaccharides -->
monosaccharides (polysaccharides)
1.
Protein --> polypeptides --> amino acids2.
Lipids --> small fat droplets --> triglycerides -->
glycerol or fatty acids
3.
Nucleic acids (DNA/RNA) --> nucleotides --> N
bases + phosphate + sugars
4.
Digestive processes: breakdown of macromolecules
*see process of chemical digestion
Mouth: polysaccharides are broken down
into smaller polysaccharides and
disaccharides by salivary amylase
○
Lumen of small intestine: polysaccharides
are broken down into disaccharides by
pancreatic amylase
○
Epithelial cells of small intestine:
disaccharides (maltose, sucrose, lactose)
are broken down into monosaccharides
(glucose, galactose) by disaccharidases
○
Carbohydrates:
!
Stomach: proteins are broken down into
peptides via pepsin
○
Proteins are broken down into
peptides via trypsin and
chymotrypsin
!
Large peptides are broken down into
amino acids by carboxypeptidase
!
Lumen of small intestine:
○
Large peptides are broken down into
amino acids by amino peptidase
!
Dipeptides are broken down into
amino acids by dipeptidase
!
Epithelial cells of small intestine:
○
Proteins:
!
Lumen of small intestine: triglycerides and
other lipids are degraded into fatty acids
and monoglycerides by lipase
○
Fats:
!
Lumen of small intestine: DNA/RNA are
broken down into nucleotides by pancreatic
nucleases
○
Epithelial cells of small intestine:
nucleotides are broken down by
nucleotidases, nucleosidases and
phosphatases into nitrogenous bases, 5C
sugars and phosphates
○
Nucleic acids:
!
Chemical digestion occurs in different segments of the
GI tract:
Lumen of intestine: all enzymes come from
pancreas
!
*note: enzymes are compartmentalized
Folds in intestinal wall
○
Villi
○
Microvilli (brush border membranes)
○
Surface area of…1.
Fructose enter cells via diffusion
through GLUT 5
!
Galactose and glucose are transported
into cell with Na+ via co-transporter
SGLT1
!
Glucose, galactose and fructose are
moved across basolateral membrane
via GLUT 2
!
Na+-K+ -ATPase creates
electrochemical gradient on
basolateral membrane
!
Sugars
○
Amino acids
○
*see slide
Water soluble vitamins
○
Transport proteins for…2.
Bile salt create micelle with FA inside
○
At apical membrane, micelle breaks apart
and allows the diffusion of FA into the
epithelial cell
○
FA and glycerol combine to form
triacylglycerols
○
Triacylglycerols combine with proteins to
produce chylomicrons
○
Chylomicrons are secreted into the villus
interior by the Golgi apparatus via vesicles
○
Availability of bile salts and Golgi apparatus for
transport of lipids
3.
Nutrient Absorption depends on:
03/20/18
Link diet, feeding apparatus, digestion and
absorption
1.
Link diet and kidney structure 2.
Hummingbirds:
!
Learning Outcomes:
Food: solid (whole animals), carnivores
○
Frequency: infrequent feeders
○
Python
!
Food: liquid diet, herbivores
○
Frequency: frequent feeders
○
Hummingbird
!
Heart rate ~1,260 beats/min
!
Wing beat ~80x/sec
○
They have the highest known mass
specific metabolic rate when
hovering
!
Mass-specific oxygen consumption
rate in hovering Anna's and rufous
hummingbirds is 30-40 mL O2/g/h
!
Birds of the same size of
mammals have significantly
higher metabolic rates
"
*recall: birds have higher internal
temperatures
!
Metabolic rate: with body mass ~3-4g
○
Environmental temperature
!
Food reserves (i.e. flower density)
!
Torpor: can be daily, but depends on…
○
Must increase fat reserves
before and stop to refuel
"
Ex. Rufous migrates from pacific
northwest to Mexico (>3200 km)
!
Migration:
○
Basic Facts of Hummingbirds:
!
Ex. Rufous: 14-18 feeding bouts/hour
(every 3-4 minutes)
!
Feed frequently
○
50-200 ul/feed --> 4-5x body weight
each day
!
Take in a high volume of nectar
○
Sucrose (20-25%)
!
Water
!
Electrolytes
!
Amino acids
!
Vitamins and other compounds
!
Nectar consists of:
○
Hummingbird Diet:
!
Tongue picks up liquid, calorie-dense
nectar that cannot be grasped and do this at
a very high rate (17 Hz, or ~60ms/lick)
○
Gravity should increase nectar-
uptake rates at downward
facing flowers --> no evidence
"
Rate of capillary action
will be less with high
sugar content (inverse
relationship)
!
Maximum energy intake
should occur with lower
density nectar (lower sugar
concentration) --> no evidence
"
If true, predictions:
!
Testing 1833 Hypothesis: hummingbird
tongue tips are loaded with nectar by means
of capillary rise (i.e. the tongue fills
passively via capillary action when in
contact with the nectar)
○
Distal portion (last 10 mm) of tongue
is bifurcated with each side forming a
groove
!
Tongue tips are supported by rods
that have membranous edges (i.e.
lamellae)
!
During feeding, the position of rods
and lamellae rotate and trap nectar
!
Retraction of bifurcated tongue tips
back into the bill, and rolling of
membranous lamellae traps nectar
!
Formation of conical shaped tongue
tip when tongue is withdrawn from
nectar prevents fluid from dripping
out
!
The process results purely from
the structural configuration of
the tongue tips
"
Nectar trapping by the lamellae does
not require any muscular work
!
Fluid at the tip is driven into the
tongue's grooves by pumping forces
resulting from re-expansion of a
collapsed section
!
This pumping mechanism fills the
tongue's grooves an order of
magnitude faster than a capillary
could
!
*see slides
!
New morphological and biomechanical
data:
○
Nectar trapping and pumping allows
for longue loading rates that are
compatible with known licking rates
(due to pressure differences)
!
Conclusion: capillary rise is not the main
mechanisms operating during hummingbird
drinking
○
Hummingbird Ingestion:
!
I.e. transformation of sucrose into
glucose and fructose via sucrase
!
*see slide
!
In brush border of small intestine
epithelial cell --> cytosol
!
Hummingbirds have very high rates of
sugar hydrolysis
○
*requires favourable
concentration gradient
"
Fructose enters the epithelial cells of
the villus in the same intestine by
passive facilitated diffusion via the
GLUT-5 transporter
!
*does not depend on
favourable concentration
gradient
"
Glucose is absorbed into the
epithelial cells by Na+ and energy-
dependent secondary active transport
located at the luminal membrane
!
Fructose and glucose exit the cell at
the basal membrane by passive
facilitated diffusion via GLUT-2
!
Carbohydrate absorption:
○
Hummingbirds have the highest known rate
of carrier-mediated glucose absorption
○
Hyperbolic curve (plateaus at ~
2 umol/g/min at 25mM)
"
Draw a graph to fit this scenario
!
Vmax = 2 umol/g/min
"
What is Vmax?
!
Km = 4mM (1/2 Vmax = 1
umol/g/min)
"
What is Km?
!
*possible exam question: active transport
of glucose across intestinal wall in Anna's
hummingbird in response to glucose
concentrations follow Michaelis-Menten
kinetics. Transport rates are saturated at
25-50mM glucose and are half-saturated at
~4 mM glucose
○
*see gastrointestinal tract
!
Food is 100% cleared from the crop
in 20 minutes
!
Food is 100% cleared from the
remaining GI tract in 40 min
!
The very simple diet of hummingbird
does not require a lot of time for
processing (60 min)
!
Reduces their feeding rate for
storage of excess nectar
"
The presence of a crop confers
foraging flexibility reducing
meals/time
!
To deal with the massive water
intake, water is absorbed by the
intestine and filtered via the kidneys
!
Retention in the gut: how long does it take
to process the nectar?
○
If this is true, animals would eat less
when offered food with a higher
energy content
!
Design experiment with
different sources of water with
varying amounts of sugar and
measure food intake
"
Test in hummingbirds:
!
Amount of sucrose in each
source
"
Amount of sucrose they ate at
each source (volume taken up
by bird; determine energy that
it contains)
"
Data collected:
!
Suggests that
hummingbirds defend a
constant rate of energy
intake
!
Negative correlation between
food intake and sugar
concentration (linear negative
slope in first graph)
"
Not exclusive to nectar-
feeding birds, similar
relationships have been
observed in a variety of
animal species
!
Reciprocal relationship
between nutrient density and
food intake (straight horizontal
line in second graph)
"
Expected results:
!
Theory among biologists that animals
regulate food intake to maintain a constant
flux of nutrients
○
Hummingbird Digestion:
!
Vs. medulla and major vasculature
!
Kidney consists mostly of cortex (~90% of
kidney)
○
Do not need to retain water (liquid
diet)?
!
Shorter loops of Henle due to little
volume in medulla -->cannot have
large concentration gradient (required
to concentrated urine)
!
Typical urine osmolarity is low
○
Low ability to produce concentrated urine
○
Hummingbird Kidney Anatomy:
!
Do digestive structures and physiology vary with food
intake (in animals that consume different diets at
different intervals)?
03/22/18
Why study pythons?1.
What is the sequence of events after a meal?2.
Synthesize information on multiple physiological
systems to explain postprandial digestion in
pythons
3.
Learning Outcomes:
Eat infrequently
!
Eat solid food
!
Eat high protein diets
!
Eat whole prey (complex diet to digest)
!
Low resting metabolic rate
!
Long gut food retention time
!
Large size of individual meals
!
Why are pythons an interesting contrast to
hummingbirds in terms of digestive physiology?
Can reach 6m and 100kg
○
One of largest snakes
!
Native to SE Asia
○
Established in southern Florida
○
Distribution:
!
Every 1-2 months when active
○
Can fast for 18 months
○
Frequency of meals:
!
Consume 25-160% of their body mass
○
Size of meals:
!
Basic facts of pythons:
Jaw does not detach
○
Two lower jaws can move independent of
each other because they are attached by an
elastic ligament
○
Multi-hinged jaw joint allows pythons to
consume prey that are several times wider
than their own head
○
Ingestion:
!
1 day post feeding: skeleton is
completely intact within the python's
stomach; 27% of stomach contents
have moved on
!
3 days post feeding: 73% of stomach
contents have disappeared
!
6 days post feeding: skeleton has
been completely broken down and
passed into small intestine
!
8-14 days post feeding: small
intestine is cleared
!
14 days post feeding: defecation
!
Daily x-ray images of a python digestion a
rat that was equal to 25% of the snakes
body mass:
○
Retention time of a meal:
!
Python Digestion:
SDA is the "work of digestion" or the additional
amount of O2 consumed during the full digestion
of a meal over and above the standard metabolic
rate
!
In man, there is a 30% increase in metabolic rate
after a meal
!
In fish, the SDA is ~160-240% (1.6-2.4 fold) for
1-3 days after meal
!
*large meals have higher SDA for a longer
period
○
In general, the magnitude of SDA is proportional
to meal size and larger in animals that freed
infrequently
!
Specific Dynamic Action (SDA):
Pythons have a 17-45 fold increase in
metabolic rate after a meal (25-100% of
body mass)
○
This is the largest SDA for any vertebrate
○
Note: SDA is proportional to the size of the
meal
○
In animals that feed infrequently, a meal will
cause the digestive system to upregulate = the
"feeding response"
!
Feeding Response in Pythons:
Upregulates the proliferation and
cellular activity
!
Gene expression of Frizzled-4 increases
after eating
○
Inhibitor of genes associated with
cell proliferation and differentiation
!
Gene expression of TCF7L2 decreases after
eating
○
1367 showed increased expression
!
1122 showed decreased expression
!
In only 6 hours after a meal (after 30 days
of fasting), the expression of ~2500 genes
in the midgut was modified
○
Molecular
!
Cellular
!
Tissue
!
HCL (parietal cells)
"
Pepsinogen is produced
in a inactive form in the
lumen of the stomach
and then is activated into
pepsin
!
Pepsin is responsible for
breaking large proteins
down into smaller ones
!
Pepsinogen (chief cells)
"
In carnivores, the stomach secretes
two key compounds that initiate the
digestion of proteins:
!
To save energy, this system is
only activated after a meal is
consumed
"
Unlike mammals, pythons do not
maintain a steady baseline rate of
acid production during fasting
!
*see slide
"
The potassium proton ATPase
pump is critical for HCl
secretion
"
Disadvantage: large
amounts of bicarbonate
will be present in
blood --> increase in
blood pH
!
HCO3-is sent into the blood
when H+ are secreted into the
stomach lumen
"
Gastric pH rapidly drops after
feeding in pythons, remains very
acidic during digestion, and rises
upon completion of gastric digestion
!
Stomach pH decreases
"
Blood pH increases
"
Blood [HCO3-] increases
"
Overall, following a meal…
!
= post proandial alkaline tide
"
Metabolic alkalosis (acid-base
disturbance; in blood) are most
pronounced in big carnivores
!
Stomach
○
Because it is the site of
absorption
"
When pythons eat a meal after a long
fast, the small intestine almost
doubles in mass by day 3
!
Surface of microvilli have
enzymes that are able to break
down the food into absorbable
units with transporters
"
The microvilli will increase in length
following a meal, peaking at day 3 =
postprandial lengthening
!
Note: upregulation of form and
function in small intestine precedes
entrance of chyme
!
All enzyme activity increases
after the digestion of the meal,
along with the transport of
nutrients (leucine and proline)
"
Note: trypsin and APN from
the pancreas
"
There is synchronous regulatory
responses of components in both
protein and carbohydrate digestion
and absorption (aminopeptidase-N
aka APN)
!
Small intestine
○
Organ
!
Whole animal
!
Post-prandial changes in the digestive system of
pythons occurs at all levels of organization
Link abundance of enzymes and chemical
breakdown
○
*see slide
!
Chemical digestion occurs in different segments of the
GI tract
Gastric pepsin, pancreatic enzymes and brush
border aminopeptidase hydrolyze proteins into
amino acids and small peptides
!
Some amino acids (e.g. proline) are absorbed in
the epithelial cells by Na+ and energy-dependent
secondary active transport via a symporter on the
luminal surface
!
Other amino acids (e.g. leucine) and small
peptides are absorbed into the epithelial cells by
Na+ and energy-dependent secondary active
transporters via antiporters
!
Amino acids exit the cell at the basal surface by
facilitated diffusion via carriers (passively) -->
circulatory system
!
*see slide
!
If they were passive transporters, they
would always be moving amino acids down
their concentration gradients
○
Secondary active transporters will work
whether gradient is favourable or not
○
--> need a larger amount in digestive-
tract lumen
!
If these were passive, the ability to move
these things would be limited
○
All amino acid transporters are upregulated
following meal (increases transport
capacity)
○
Note:
!
Amino Acid Absorption:
Average glucose uptake raises significantly
more 24 after meal vs fasting state in
snakes that have been infrequently feeding
(~+0.5 vs ~+0.15)
○
During fasting, the average glucose uptake
is lower in snakes infrequently feeding (~
0.1 vs ~0.2) --> smaller capacity
○
The average glucose uptake is higher 24
hours after feeding in snakes that
infrequently feed (~0.6 vs ~0.35)
○
The average glucose uptake increased 24
hours after feeding in both groups
○
Describe the results (4)
!
Conserve energy needed for glucose
uptake (uses ATP) in snakes that are
infrequently feeding
!
Baseline capacity for picking up glucose
from the lumen of the intestine is higher in
frequently feeding snakes
○
Adaptive strategy in infrequently feeding
snake is to upregulate genes associated with
glucose uptake (ex. Transporters)
○
Provide an explanation for these findings
!
Possible exam question:
03/27/18
Digestion entails an integrated effort across
multiple organs
1.
Luminal content and gastrointestinal hormones
regulate and coordinate the feeding response
2.
The feeding response has an adaptive value in
infrequent feeders
3.
Learning Outcomes:
All happens simultaneously
○
Involves both a substantial metabolic investment
and the coordinated interactions of several tissues
!
Increased heart rate, blood flow, and heart mass
(rbc cell volume increases)
!
Increase blood pH
○
Increase blood HCO3-
○
Blood:
!
Increase O2 uptake by 6.7x
○
Lung:
!
Increase mass
○
Liver:
!
Increase mass
○
Increase HCL and pepsin
○
Stomach:
!
Decrease mass --> release of bile (allows
lipids to be absorbed)
○
Gall bladder:
!
Increase in mass
○
Pancreas:
!
Increase mass
○
Increase microvilli length and cell volume
○
Small intestine:
!
Increasing capacity to secrete
HCl (skeleton) and pepsin
(protein) for digestion
"
Stomach (~50%)
!
Need more ATP for
transporters and enzymes via
oxidative phosphorylation
"
Lungs (~50%)
!
Need more oxygen at tissues to
create ATP
"
Heart (~50%)
!
Increase capacity for enzymes
and
"
Pancreas (~60%)
!
Increased capacity for
absorbable units to be
converted back into storage
forms
"
Liver (~70%)
!
Due to increased need to break
down protein (nitrogen)
"
Direct result of the
production of HCl
!
Balance acids-bases: HCO3-is
increased in blood (post
prandial alkaline tide)
"
Kidneys (~100%)
!
Intestinal mucosa (~160%)
!
Rationale for each increase in size:
○
*Note: all organs increase rapidly in mass upon
feeding by at least 50%
!
Heart is first organ to increase
○
The Burmese python coordinates feeding and
fasting responses across organs and tissues and
this is reflected in the collective changes in their
mass and function
!
Python digestion entails an integrated effort:
The 40% increase in postprandial ventricular
mass due to increased myosin gene expression
and presumably increase in contractile elements
!
DNA per unit of mass decreased
○
The increase in ventricular mass is due to
increase in hypertropy (cell volume) NOT
hyperplasia (cell number)
!
How does the python heart undergo hypertrophy
following a meal?
Luminal content (e.g. amino acid)
○
CCK
"
Glucagon
"
GIP
"
Insulin (stimulates uptake and
storage of nutrients into cells)
"
Increase in…
!
Gastrointestinal hormones
○
Two types of signals appear to be involved in
regulating GI morphology and activity
!
CCK and GIP secretion from the midgut
are stimulated by acidity and exposure to
nutrients
○
CCK stimulates the pancreas and gall
bladder to secrete enzymes and bile
○
GIP and CCK inhibit gastric acid secretion,
gastric emptying and muscle contraction
○
*see slide
○
Gastrointestinal hormones:
!
Need to meet both needs: store nutrients
but need huge amount of energy to build up
organ mass after fasting
○
Glucagon --> increase glucose in blood -->
increased breakdown of molecules into
energy
○
Insulin --> increase glucose uptake -->
store nutrients and molecules
○
Paradoxical increase in glucagon and insulin:
!
Enormous changes occur in the anatomy
and physiology of infrequently feeding
pythons after a meal
○
In contrast, human SDA increases by
0.3 fold (30%) and SDA coefficient
is 9% of energy taken in
!
Ex. In pythons, SDA increases up to 44
fold, and the relative cost of digestion
(SDA coefficient) is ~32% energy taken in
○
Hypothesis: "feeding response" is an
adaptation to conserve energy during
digestive quiescence
!
Prediction: infrequent feeders will
have a lower SMR than frequent
feeders
!
*see slide
!
Larger rates of increase
in infrequent feeders -->
larger cost of digestion
!
SMR, SDA coefficient and
factorial increase in four
frequently and four
infrequently feeding snake
species
"
Al animals were red rodent
meals equivalent to 25% of
snake's body mass
"
Study:
!
Infrequent feeders save on
maintenance costs
"
--> increase in organ size
!
Infrequent feeders incur larger
start up costs and cost of
digestion with each meal
"
Conclusions:
!
What is the advantage of this feeding
response?
○
Adaptive Value:
!
Pros: decrease SDA
!
Cons: increase SMR
!
Frequent, small meals:
○
Pros: decrease SMR
!
Cons: increase SDA
!
Infrequent, large meals:
○
Actively foraging snake
"
Meals are ~15% of body mass,
every ~10 days
"
Coachwhip:
!
An ambush-hunting snake
"
Meals are ~25% of body mass,
every ~6 weeks
"
Sidewinder:
!
1-4 weeks: total energetic cost
in sidewinder > coachwhip
"
4 weeks: total energetic cost in
sidewinder = coachwhip
"
>4 weeks: total energetic cost
in coachwhip > sidewinder
"
Experiment: animals are fed the same
size meal at the same intervals
!
Sidewinder has less energetic
costs than coachwhip is meal
interval is > 5 weeks
"
Coachwhip has less energetic
costs than the sidewinder if
meal interval is < 3 weeks
"
Energetic costs are equal if
meal interval in ~4 weeks
"
Conclusions:
!
Are these trade-offs observed in the field:
○
Cost-Benefit Analysis of Feeding Frequency in
Snakes
!
The "Feeding Response"
Digestion
#$%&'()*+, -)&.$, /0+,12/3 /1405,6-
Document Summary
Link the structure and function of components of complex digestive tracts. *see relations of nutrition, feeding, digestion, and absorption in vertebrates and most types of invertebrates. Note: we cannot synthesize 8 amino acids = essential amino acids. Capacity to synthesize various amino acids and vitamins varies from animal to animal. Gut length and complexity is linked to diet. Lamprey: simple, short digestive tube (feed on blood) Sharks: contain spiral valve in intestine (ileum) to increase surface area and therefore have shorter intestine. Actinopterygian (gar): contain pyloric ceca to increase surface area (specialized compartments; blind ended sacs attached to digestive system that are filled with bacteria and contribute to digestion) Avian: crop (temporary storage compartment located in foregut; take advantage of a large amount of food), proventriculus - secretes acid and enzymes. Gizzard - grinds up food with pebbles and stones in gizzard by compressing food against stones ceca - contains bacteria and increase surface area.
