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Animal Nutrition

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Chapter 41
Animal Nutrition
Dietary Categories of Animals
пЃ® Herbivores
eat mainly autotrophs (plants
and algae)
пЃ® Carnivores eat other animals
пЃ® Omnivores regularly consume animals as
well as plants or algal matter
Basic Nutritional Needs
пЃ® Regardless of what an animal eats, an adequate
diet must satisfy three nutritional needs
пЃ®
пЃ®
пЃ®
Fuel for all cellular work
The organic raw materials for biosynthesis
Essential nutrients, substances such as vitamins
that the animal cannot make for itself
Feeding Mechanisms
SUSPENSION FEEDERS
SUBSTRATE FEEDERS
Feces
Baleen
Caterpillar
FLUID FEEDERS
BULK FEEDERS
Suspension feeders shift small particles from water
Substrate feeders live in or on their food source
Bulk feeders eat largish pieces of food
Fluid feeders …well that is pretty obvious
Bioenergetics - basics
пЃ® Energy Budget can be viewed as the flow of
food energy into and out of the animal
пЃ® ATP is the energy currency of life
 Nearly all of an animal’s ATP generation
пЃ®
Is based on the oxidation of energy-rich
molecules: carbohydrates, proteins, and fats
Glucose Regulation as an Example
of Homeostasis
пЃ® Animals store excess calories as glycogen in
the liver and muscles and as fat
пЃ® When fewer calories are taken in than are
expended … fuel is taken out of storage and
oxidized
пЃ® Glucose is a major fuel for cells
пЃ®
Its metabolism, regulated by hormone action,
is an example of homeostasis
Glucose Metabolism
1 When blood glucose
level rises, a gland called
the pancreas secretes insulin,
a hormone, into the blood.
2 Insulin enhances the
transport of glucose into body
cells and stimulates the liver
and muscle cells to store
glucose as glycogen. As a
result, blood glucose level
drops.
STIMULUS:
Blood glucose
level rises
after eating.
Homeostasis
Glucose
90mg/dl
4 Glucagon promotes
the breakdown of
glycogen in the
liver and the
release of glucose
into the blood,
increasing blood
glucose level.
STIMULUS:
Blood glucose
level drops
below set point.
3 When blood glucose
level drops, the pancreas
secretes the hormone
glucagon, which opposes
the effect of insulin.
Caloric Imbalance
пЃ® Undernourishment
пЃ®
Occurs in animals when their diets are chronically deficient
in calories
пЃ® Overnourishment
пЃ®
пЃ®
пЃ®
пЃ®
Results from excessive food intake
Leads to the storage of excess calories as fat
Obesity contributes to a number of health problems,
including diabetes, cardiovascular disease, and colon and
breast cancer
Some Stats on US Obesity
пЃ®
пЃ®
пЃ®
пЃ®
пЃ®
58 Million Overweight; 40 Million Obese; 3 Million morbidly Obese
Eight out of 10 over 25's Overweight
78% of American's not meeting basic activity level recommendations
25% completely Sedentary
76% increase in Type II diabetes in adults 30-40 yrs old since 1990
Regulation of Body Weight
Hormones and appetite
пЃ® Several hormones regulate
both long-term and short-term
appetite by affecting a “satiety center” in the brain
Secreted by the stomach
wall, ghrelin is one of the
signals that triggers feelings
of hunger as mealtimes
approach. In dieters who lose
weight, ghrelin levels increase,
which may be one reason
it’s so hard to stay on a diet.
Produced by adipose (fat)
tissue, leptin suppresses
appetite as its level increases.
When body fat decreases,
leptin levels fall, and appetite
increases.
Ghrelin
The hormone PYY,
secreted by the small
intestine after meals,
acts as an appetite
suppressant that
counters the appetite
stimulant ghrelin.
Insulin
Leptin
PYY
A rise in blood sugar level
after a meal stimulates
the pancreas to secrete
insulin
In addition to its other
functions, insulin suppresses
appetite by acting on the brain.
Role of Leptin
пЃ® Mice that inherit a defect in the gene for leptin
become very obese
Obesity and Evolution
пЃ® The problem of
maintaining weight
may partly stem from
our evolutionary past
when fat hoarding was
a means of survival
What’s in the Diet
 An animal’s diet must supply
пЃ® Fuel (energy)
пЃ®
Carbon skeletons
пЃ®
пЃ®
Essential nutrients
Supplied in preassembled form
пЃ® An animal that is malnourished is missing one or
more essential nutrients in its diet
Malnutrition is much more common than undernutrition in
human populations
пЃ®
пЃ®
To build the complex molecules it needs to grow,
maintain itself, and reproduce an animal must obtain
organic precursors (carbon skeletons) from its food
Mineral deficiencies
пЃ® Herbivorous animals may suffer mineral deficiencies
if they graze on plants in soil lacking key minerals
Essential Amino Acids
пЃ® Animals require 20 amino acids
пЃ®
пЃ®
They can synthesize about half of them from the
other molecules they obtain from their diet
The remaining amino acids, the essential amino
acids, must be obtained from food in preassembled
form
Protein Deficiency
пЃ® A diet that provides insufficient amounts of
one or more essential amino acids causes a
form of malnutrition called protein deficiency
Kwashiorkor- enough calories but
protein is very deficient
Essential Amino Acids
пЃ® Complete proteins provide all essential AAs
in their proper proportions
пЃ® Incomplete proteins do not
пЃ®
пЃ®
Most plant proteins are incomplete in amino acid makeup
So individuals who must eat only plant proteins need to eat a
variety to ensure that they get all the essential amino acids
Essential amino acids for adults
Beans
Methionine
and other
legumes
Valine
Together corn and beans
would provide all 8 of the
essential amino acids for
humans
Threonine
Phenylalanine
Corn (maize)
and other grains
Leucine
Isoleucine
Tryptophan
Lysine
пЃ® Some animals have adaptations that help them through periods
when their bodies demand extraordinary amounts of protein
пЃ® Penguins use their muscle protein as an AA source for building
new proteins when their replace feathers after molting
Essential Fatty Acids
пЃ® Animals can synthesize most of the fatty
acids they need
пЃ® The essential fatty acids are certain
unsaturated fatty acids (linoleic acid in
humans)
пЃ® Deficiencies in fatty acids are rare
Vitamins
пЃ® Vitamins are organic molecules required in
the diet in small amounts
пЃ® 13 vitamins essential to humans have been
identified
пЃ® Vitamins are grouped into two categories
пЃ®
пЃ®
Fat-soluble (A, D, E, and K)
Water-soluble
Minerals
пЃ® Minerals are simple inorganic nutrients usually
required in small amounts
Food Processing
пЃ® The main stages of food processing
пЃ® Ingestion: Intake of food
пЃ® Digestion: Process of breaking food down
into molecules small enough to absorb
пЃ®
пЃ®
пЃ®
Involves enzymatic hydrolysis of polymers into
their monomers
Absorption: The uptake of nutrients by body
cells
Elimination: occurs as undigested material
passes out of the digestive compartment
Food Processing
пЃ® The four stages Small
of food processing
molecules
Pieces
of food
Mechanical
digestion
Chemical digestion
(enzymatic hydrolysis)
Nutrient
molecules
enter body
cells
Undigested
material
Food
1 INGESTION
2 DIGESTION
3 ABSORPTION
4
ELIMINATION
Digestive Compartments
пЃ® Most animals process food in
specialized compartments
пЃ® Intracellular digestion
пЃ®
Food particles are engulfed by endocytosis
and digested within food vacuoles
пЃ® Extracellular digestion
пЃ®
Is the breakdown of food particles outside
cells
Gastrovascular Cavity
пЃ® Animals with simple body plans have a gastrovascular cavity
that functions in both digestion and distribution of nutrients
Tentacles
Mouth
Food
Gastrovascular
cavity
Epidermis
Mesenchyme
Gastrodermis
Nutritive
muscular
cells
Flagella
Gland cells
Food vacuoles
Hydra (a cnidarian)
Mesenchyme
Digestive Tube
пЃ® Animals with a more complex body plan
пЃ®
Have a digestive tube with two openings, a mouth
and an anus
пЃ® This digestive tube is called a complete digestive
tract or an alimentary canal
Organization of Digestive Tube
пЃ® The digestive tube can be organized into specialized regions
that carry out digestion and nutrient absorption in a stepwise
fashion
Pharynx
Earthworm. The digestive tract of
an earthworm includes a muscular
pharynx that sucks food in through the
mouth. Food passes through the
esophagus and is stored and moistened
in the crop. The muscular gizzard, which
contains small bits of sand and gravel,
pulverizes the food. Digestion and
absorption occur in the intestine,
which has a dorsal fold, the typhlosole,
that increases the surface area for
nutrient absorption.
Esophagus Crop
Esophagus
Intestine
Crop
Pharynx
Anus
Mouth
Gizzard
Intestine
Typhlosole
Lumen of intestine
Foregut
Grasshopper. A grasshopper has several
digestive chambers grouped into three
main regions: a foregut, with an esophagus
and crop; a midgut; and a hindgut. Food is
moistened and stored in the crop, but most
digestion occurs in the midgut. Gastric ceca,
pouches extending from the midgut,
absorb nutrients.
Gizzard
Midgut
Esophagus
Hindgut
Crop
Esophagus
Rectum
Midgut
Anus
Hindgut
Mouth
Crop
Gastric ceca
Esophagus
Bird. Many birds have three separate chambers—
the crop, stomach, and gizzard—where food is
pulverized and churned before passing into the
intestine. A bird’s crop and gizzard function very
much like those of an earthworm. In most birds,
chemical digestion and absorption of nutrients
occur in the intestine.
Gizzard
Mouth
Intestine
Crop
Stomach
Esophagus
Crop
Anus
Stomach
Gizzard
Intestine
Mammalian Digestive System
A Tour of the Tube
Overview of the System
Tongue
Salivary
glands
Salivary
glands
Cardiac
orifice
Oral cavity
Parotid gland
Sublingual gland
Mouth
Pharynx
Submandibular gland
Esophagus
Esophagus
Pyloric
sphincter
Liver
Ascending
portion of
large intestine
Stomach
Gallbladder
Gallbladder
Liver
Pancreas
Stomach
Small
intestines
Pancreas
IIeum
of small
intestine
Small intestine
Duodenum of
small intestine
Large intestine
Rectum
Large
intestines
Rectum
Anus
A schematic diagram of
the human digestive system
Appendix
Anus
Cecum
Food is pushed along the digestive tract by peristalsis … Rhythmic
waves of contraction of smooth muscles in the wall of the canal
The Oral Cavity, Pharynx, and
Esophagus
пЃ® Oral cavity
пЃ® Food is lubricated and digestion begins
пЃ® Teeth chew food into smaller particles that are
exposed to salivary amylase, initiating the
breakdown of starch
пЃ® Tongue forms the food bolus and pushes it to the
pharynx
пЃ® Pharynx (throat)
пЃ® The common passage way for air and ingesta
пЃ® Esophagus
пЃ® Conducts food from the pharynx down to the
stomach by peristalsis
From Mouth to Stomach
4 The esophageal
sphincter relaxes,
allowing the
bolus to enter the
esophagus.
Epiglottis
up
Bolus of food
Tongue
Glottis
down
and open
Epiglottis
up
Pharynx
Esophageal
Epiglottis
sphincter
down
contracted
Glottis
Larynx
Trachea
Esophagus
To lungs
To stomach
1 When a person is not
swallowing, the esophageal
sphincter muscle is contracted,
the epiglottis is up, and the
glottis is open, allowing air
to flow through the trachea
to the lungs.
Glottis up
and closed
2 The swallowing
reflex is triggered
when a bolus of
food reaches the
pharynx.
Esophageal
sphincter
relaxed 5 After the food
Esophageal
sphincter
contracted
has entered the
esophagus, the
larynx moves
downward and
opens the
breathing
passage.
Relaxed
muscles
Contracted
muscles
3 The larynx, the
upper part of the
6 Waves of muscular
respiratory tract,
contraction
moves upward and
(peristalsis)
tips the epiglottis
move the bolus
over the glottis,
down the esophagus
preventing food
to the stomach.
from entering the
trachea.
Relaxed
muscles
Stomach
GERD
пЃ® Gastroesophageal reflux disease (GERD)
пЃ®
Better known as heartburn
The Stomach
пЃ® Stomach
пЃ® Stores food
пЃ® Secretes gastric juice, which converts a meal to acid chyme
пЃ® Gastric juice
пЃ® Hydrochloric acid
пЃ® Pepsin (enzyme)
пЃ® Mucus (which coated the stomach lining and protects the
cells from acidity
Stomach structure
Gastric gland
пЃ® Goblet (mucus) cells
Esophagus
Cardiac orifice
пЃ® Chief cells
pepsinogen
пЃ® Parietal cells
пЃ®
HCl
Interior surface of stomach.
The interior surface of the
stomach wall is highly folded
and dotted with pits leading
into tubular gastric glands.
Gastric gland. The gastric
Stomach
Pyloric
sphincter
5 Вµm
пЃ®
Small
intestine
Folds of
epithelial
tissue
Epithelium
3
Pepsinogen
2
HCl
glands have three types of cells
that secrete different components
of the gastric juice: mucus cells,
chief cells, and parietal cells.
Pepsin (active enzyme)
1 Pepsinogen and HCI
are secreted into the
lumen of the stomach.
1
2 HCl converts
pepsinogen to pepsin.
Mucus cells secrete mucus,
which lubricates and protects
the cells lining the stomach.
Chief cells secrete pepsinogen, an inactive form of the
digestive enzyme pepsin.
Parietal cell
Parietal cells secrete
hydrochloric acid (HCl).
Chief cell
3 Pepsin then activates
more pepsinogen,
starting a chain
reaction. Pepsin
begins the chemical
digestion of proteins.
Gastric Ulcers
пЃ® Caused mainly by the bacterium Helicobacter
pylori
Bacteria
1 Вµm
Mucus
layer of
stomach
The Small Intestine
пЃ® Small intestine
пЃ®
пЃ®
пЃ®
Longest section of the alimentary canal (six
meters in humans)
The major organ of digestion and absorption
Sections
пЃ®
пЃ®
пЃ®
Duodenum
Jejunum
Ileum
Enzymatic Action in the Small
Intestine
пЃ® In the duodenum acid chyme from the stomach mixes
with digestive juices from the pancreas, liver,
gallbladder, and intestine itself
Pancreatic enzymes
Liver
Trypsin and
Chymotrypsisn
Bile
Lipases
Gallbladder
Amylase
Stomach
Bile salts aid in
the digestion and
absorption of
lipids via
Emulsification
Nucleases
Acid chyme
Intestinal
juice
Pancreatic juice
Pancreas
Duodenum of
small intestine
The intestinal brush
border produces a variety
of enzymes that contribute
to digestion
Enzymatic digestion
Protein digestion
Carbohydrate digestion
Oral cavity,
pharynx,
esophagus
Polysaccharides
(starch, glycogen)
Nucleic acid digestion
Fat digestion
Disaccharides
(sucrose, lactose)
Salivary amylase
Smaller polysaccharides,
maltose
Stomach
Proteins
Pepsin
Small polypeptides
Lumen of
small intestine
Polysaccharides
Pancreatic amylases
Maltose and other
disaccharides
Polypeptides
Pancreatic trypsin and
chymotrypsin (These proteases
cleave bonds adjacent to certain
amino acids.)
Smaller
polypeptides
DNA, RNA
Pancreatic
nucleases
Nucleotides
Pancreatic carboxypeptidase
Small peptides
Disaccharidases
Monosaccharides
Amino acids
Fat droplets (A coating of
bile salts prevents small droplets from coalescing into
larger globules, increasing
exposure to lipase.)
Glycerol, fatty
acids, glycerides
Nucleotidases
Nucleosides
Dipeptidases, carboxypeptidase, and aminopeptidase
(These proteases split
off one amino acid at a time, working from opposite
ends of a polypeptide.)
Bile salts
Pancreatic lipase
Amino acids
Epithelium
of small
intestine
(brush
border)
Fat globules (Insoluble in
water, fats aggregate as
globules.)
Nucleosidases
and
phosphatases
Nitrogenous bases,
sugars, phosphates
Hormonal Regulation of Digestion
пЃ® Hormones help coordinate the secretion of digestive juices into
the alimentary canal
Enterogastrone secreted by
the duodenum inhibits peristalsis
and acid secretion by the stomach,
thereby slowing digestion when
acid chyme rich in fats enters the
duodenum.
Liver
Enterogastrone
Gallbladder
CCK
Gastrin
recirculates via the bloodstream
back to the stomach, where it
stimulates the production
of gastric juices.
Stomach
Amino acids or fatty acids in the
duodenum trigger the release of
Gastrin from the stomach
Pancreas
cholecystokinin (CCK),
which stimulates the release of
digestive enzymes from the pancreas
and bile from the gallbladder.
Secretin
Duodenum
CCK
Key
Stimulation
Inhibition
Secreted by the duodenum,
secretin stimulates the pancreas
to release sodium bicarbonate,
which neutralizes acid chyme
from the stomach.
Small Intestine…Absorption of
Nutrients
пЃ® The small intestine has a huge surface area
due to the presence of villi and microvilli
Microvilli
(brush border)
Vein carrying blood to
hepatic portal vessel
Blood
capillaries
Epithelial
cells
Muscle layers
Epithelial cells
Large
circular
folds
Villi
Lacteal
Key
Nutrient
absorption
Intestinal wall
Villi
Lymph
vessel
The absorptive surface area of the small intestine is roughly 250 square meters - the size of a tennis court!
Absorption of Nutrients
пЃ® The core of each villus
пЃ® Contains a network of blood vessels and a
small vessel of the lymphatic system called a
lacteal
пЃ® Amino acids and sugars
пЃ® Pass through the epithelium of the small
intestine and enter the bloodstream
пЃ® After glycerol and fatty acids are absorbed by
epithelial cells
пЃ®
They are recombined into fats within these
cells
Fat absorption
пЃ® These fats are then mixed with cholesterol and
coated with proteins forming small molecules called
chylomicrons, which are transported into lacteals
Fat globule
1 Large fat globules are
emulsified by bile salts
in the duodenum.
Bile salts
Fat droplets
coated with
bile salts
Micelles made
up of fatty acids,
monoglycerides,
and bile salts
Epithelial
cells of
small
intestine
Lacteal
2 Digestion of fat by the pancreatic
enzyme lipase yields free fatty
acids and monoglycerides, which
then form micelles.
3 Fatty acids and monoglycerides leave micelles
and enter epithelial cells
by diffusion.
4 Chylomicrons containing fatty
substances are transported out
of the epithelial cells and into
lacteals, where they are carried
away from the intestine by lymph.
The Large Intestine
пЃ® Functions
пЃ® Recover water that has entered the alimentary canal
пЃ® Form compact and propel the feces to the anus
пЃ® The colon is home to a variety of bacteria including
Escherichia coli
Adaptations of the Mammalian
Digestive System
Variations in Dentition
пЃ® Mammals have specialized dentition that best enables them to
ingest their usual diet
Pointed incisor and canines.
Jagged premolars and molars
Incisors
Canines
(a) Carnivore
Molars
Premolars
Broad ridged surfaces for
grinding
Reduced/absent canines
(b) Herbivore
Chisel shaped incisors
Generalized/unspecialized
dentition
(c) Omnivore
Stomach and Intestinal Adaptations
пЃ® Herbivores generally have longer alimentary canals
than carnivores reflecting the longer time needed to
digest vegetation
Small intestine
Small
intestine
Stomach
Many large
carnivores
have large
very
expandable
stomachs
Cecum
Colon
(large
intestine)
Carnivore
Snakes can
“unhinge”
their jaws
Herbivore
Symbiotic Adaptations
пЃ® Many herbivorous animals have fermentation
chambers where symbiotic microorganisms
digest cellulose.
пЃ®
пЃ®
Horses, rabbits, and koalas have very large cecums
housing symbionts
Ruminants have large populations of symbiotic
prokaryotes and protozoa in their rumens and
reticulums
Ruminant Digestion
1
Rumen
. When the cow first chews and
swallows a mouthful of grass, boluses
(green arrows) enter the rumen.
2
Reticulum
. Some boluses
also enter the reticulum. In
both the rumen and the
reticulum, symbiotic prokaryotes
and protists (mainly ciliates) go
to work on the cellulose-rich
meal. As by-products of their
metabolism, the microorganisms
secrete fatty acids. The cow
periodically regurgitates and
rechews the cud (red arrows),
which further breaks down the
fibers, making them more
accessible to further microbial action.
Intestine
Esophagus
4
Abomasum
. The cud, containing great numbers of microorganisms,
finally passes to the abomasum for digestion by the cow�s own
enzymes (black arrows).
3
Omasum
. The cow then reswallows
the cud (blue arrows), which moves to
the omasum, where water is removed.
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