Transcript Animal nutrition - University of Texas at Austin

Animal nutrition
• Animal diet needs
• Overview of food processing
• Evolutionary adaptations of vertebrate
digestive systems
Animal diet needs
• It must provide fuel for cellular work
• It must supply the organic raw materials
needed to construct organic molecules
• Essential nutrients that the animal cannot
make from raw materials must be provided
in its food
Fuel for cellular work
• Most of the energy budget from food goes
into ATP production
• Nearly all of an animal’s ATP generation is
based on the oxidation of energy-rich
molecules: carbohydrates, proteins, and
fats
Raw materials for biosynthesis
• When an animal takes in more calories
than it needs to produce ATP, excess can
be used for biosynthesis
• Animals can fabricate a great variety of
organic molecules from a source of
organic carbon and organic nitrogen
Nutrients in preassembled form
• Animals require 20 amino acids
– And can synthesize about half of them
• The remaining amino acids, the essential
amino acids
– Must be obtained from food in preassembled
form
• Protein in animal products are complete in
amino acid make up
• Most plant proteins are incomplete
Essential amino acids for adults
Methionine
Valine
Threonine
Phenylalanine
Corn (maize)
and other grains
Leucine
Isoleucine
Tryptophan
Figure 41.10
Lysine
Beans
and other
legumes
• Animals can synthesize most of the fatty
acids they need
• The essential fatty acids are certain
unsaturated fatty acids
• Vitamins are organic molecules
– Required in the diet in small amounts
• Minerals are simple inorganic nutrients
– Usually required in small amounts
Overview of food processing
• The four steps of food processing
– Ingestion, digestion, absorption, elimination
• Digestive systems in animals
Food processing
• The four stages of
Smallfood processing
molecules
Pieces
of food
Mechanical
digestion
Chemical digestion
(enzymatic hydrolysis)
Nutrient
molecules
enter body
cells
Undigested
material
Food
1 INGESTION
Figure 41.12
2 DIGESTION
3 ABSORPTION
4
ELIMINATION
• Sponges digest their food entirely by the
intracellular mechanism
5 Choanocytes. The spongocoel
is lined with feeding cells called
choanocytes. By beating flagella,
the choanocytes create a current that
draws water in through the porocytes.
Azure vase sponge (Callyspongia
plicifera)
4 Spongocoel. Water
passing through porocytes
enters a cavity called the
spongocoel.
3 Porocytes. Water enters
the epidermis through
channels formed by
porocytes, doughnut-shapd
cells that span the body wall.
2 Epidermis. The outer
layer consists of tightly
packed epidermal cells.
Figure 33.4
1 Mesohyl. The wall of this
simple sponge consists of
two layers of cells separated
by a gelatinous matrix, the
mesohyl (“middle matter”).
Flagellum
Collar
Food particles
in mucus
Choanocyte
Osculum
Phagocytosis of
food particles
Spicules
Water
flow
Amoebocyte
6 The movement of the choanocyte
flagella also draws water through its
collar of fingerlike projections. Food
particles are trapped in the mucus
coating the projections, engulfed by
phagocytosis, and either digested or
transferred to amoebocytes.
7 Amoebocyte. Amoebocytes
transport nutrients to other cells of
the sponge body and also produce
materials for skeletal fibers (spicules).
• 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
Figure 41.13
Mesenchyme
• Animals with a more complex body plan
– Have a digestive tube with two openings, a
mouth and an anus
• This digestive tube
– Is called a complete digestive tract or an
alimentary canal
Alimentary canals
The human digestive system
From mouth to stomach: the swallowing reflex and esophageal peristalsis (Layer 3)
Secretion of gastric juice
• Gastric ulcers, lesions in the lining
– Are caused mainly by the bacterium
Helicobacter pylori
Bacteria
Figure 41.18
1 µm
Mucus
layer of
stomach
The duodenum
• The enormous microvillar surface
– Is an adaptation that greatly increases the
rate of nutrient absorption
Microvilli
(brush border)
Vein carrying blood to
hepatic portal vessel
Figure 41.23
Blood
capillaries
Epithelial
cells
Muscle layers
Villi
Epithelial cells
Large
circular
folds
Lacteal
Key
Nutrient
absorption
Intestinal wall
Villi
Lymph
vessel
• Amino acids and sugars
– Pass through the epithelium of the small
intestine and enter the bloodstream
• After glycerol and fatty acids are absorbed
by epithelial cells
– They are recombined into fats within these cells
• 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
Figure 41.24
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.
Enzymatic digestion in the human digestive system
• The large intestine, or colon
– Is connected to the small intestine
Figure 41.25
• A major function of the colon
– Is to recover water that has entered the
alimentary canal
• The wastes of the digestive tract, the feces
– Become more solid as they move through the
colon
– Pass through the rectum and exit via the anus
• The colon houses various strains of the
bacterium Escherichia coli
– Some of which produce various vitamins
Evolutionary adaptations of
vertebrate digestive systems
• Ingestion adaptations
• Digestion adaptations
Dentition and diet
The digestive tracts of a carnivore (coyote) and a herbivore (koala) compared
Symbiotic Adaptations
• Many herbivorous animals have
fermentation chambers
– Where symbiotic microorganisms digest
cellulose
• The most elaborate adaptations for an
herbivorous diet
– Have evolved in the animals called ruminants
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
Figure 41.28
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.