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Chapter 41
Animal Nutrition
Types of Feeders
• Suspension feeders sift through water to obtain
small food particles
• Fluid feeders suck nutrients from a host
• Substrate feeders live on their food sources
• Bulk feeders eat large pieces of food
Nutritional Needs
To function properly an animal
needs to consume…
• Fuel.
• Organic raw materials for biosynthesis.
• Essential nutrients which can’t be synthesized
through biosynthesis.
• Animals synthesize ATP from other fuel sources
and use ATP to power many bodily functions.
• Animals oxidize carbohydrates, fats, and proteins in
that order as fuel for ATP synthesis.
• Severe situations regarding fuel consumption are…
– Undernourishment, a prolonged caloric deficit.
– Overnourishment (obesity), a prolongued surplus of fat in
a diet
Raw Organic Materials
• An Animal needs to synthesize complex chemicals
needed to function. This is called biosynthesis.
• Carbon skeletons and sources of organic nitrogen
are necessary to synthesize these molecules
• These are readily available in the environment
Essential Nutrients
• Essential Nutrients are important to bodily function
but cannot be synthesized by the animal. An
animal’s diet must provide these.
– Essential amino acids: 8 different monomers necessary for
protein synthesis
– Essential fatty acids: Certain unsaturated fatty acids.
– Vitamins: 13 different organic molecules which have a
wide array of bodily uses. They can be either water soluble
or fat soluble.
– Minerals: Inorganic compounds
• Malnutrition arises when an animal lacks essential
• Glucose Regulation is controlled by the antagonistic
hormones insulin and glucagon.
– Insulin: Stimulates blood glucose levels to drop
– Glucagon: Stimulates blood glucose levels to rise
• Hunger Regulation is controlled by four hormones
– Leptin, Insulin, and PYY suppress appetite
– Ghrelin increases appetite
Food Processing
Food Processing
Step 1: Ingestion of nutrients
Step 2: Digestion of macromolecules
Step 3: Absorption of monomers
Step 4: Elimination of undigested waste
Types of Digestion
• Intracellular digestion occurs when food is digested
in the vacuoles of cells
• Extracellular digestion occurs when some food is
digested in designated cavities outside of cells.
• There are two types of digestive cavities
– The gastrovascular cavity is a sac with a single opening
– The complete digestive tract (alimentary canal) has two
openings. Food only moves in one direction. This cavity
contains more specialized compartments for digestion.
• Hydrolytic Enzymes break down polymers and are
used in all types of digestion
The Mammalian
Digestive Tract
The Oral Cavity, Pharynx,
and Esophagus
• During chewing in the oral
cavity, salivary amylase
helps break down
• After chewing the tongue
shapes the food into a bolus
• The food is swallowed into
the Pharynx (throat) next
– The Pharynx opens to the
trachea and esophagus
• The epiglottis covers the
trachea when swallowing
• Peristalsis (rhythmic smooth
muscle contraction) moves
the food down the esophagus
The Stomach
• A sphincter called the
cardiac orifice regulates
entrance to the stomach.
• The stomach secretes
gastric juice.
– This mixes with the food
to form acid chyme.
• The acidity of the gastric
juice activates the
hydrolytic enzyme
• The pyloric sphincter
regulates flow of acid
chyme into the small
The Small Intestine
• The first 25 cm of this is the duodenum. In
the duodenum…
– Juices from the Pancreas buffer the acid chyme.
– The liver secretes bile salts to help digest fats
– The epithelium contains and secretes hydrolytic
• Structures in the epithelium called villi and
their appendages called microvilli help
absorb nutrients
– In the villi are capillary beds and lacteals from the
circulatory and lymphatic systems respectively
– The lacteals drain into larger lymphatic vessels
– The capillary beds drain into the hepatic portal
vein of the liver
The Large Intestine (Colon)
• A sphincter in a T-shaped junction controls the
entrance into the Large Intestine
• The colon reabsorbs most of the water which the
small intestine left in the mixture
• Undigested material moves through the colon by
way of peristalsis into the rectum
– The undigested material is now known as feces and is soon
Evolutionary Adaptations to
the Digestive System
• Carnivores have developed sharper teeth while
herbivores have developed broader and more rigid
• Herbivores have developed longer digestive tracts
• Herbivores have developed symbiotic relationships
with bacteria that digest cellulose