Chapter 41 Notes
Animal Nutrition
Nutritional Requirements
The flow of energy into and out of an
animal can be viewed as a “budget”
- most of the energy taken in is used to
produce ATP to power resting
metabolism and temperature regulation
- excess ATP can be used for
biosynthesis
Nutritional Requirements
In humans, the liver and muscle cells
store energy in the form of glycogen.
If glycogen stores are full, the excess is
usually stored as fat.
When fewer calories are taken in than
used, fuel is taken out of storage
deposits and oxidized.
Nutritional Requirements
Nutritional Requirements
Feedback mechanisms regulate fat
storage and use
- an increase in adipose tissue increases
leptin levels in the blood
- high levels of leptin cue the brain to
depress appetite and to increase
muscular activity and body-heat
production
Nutritional Requirements
In addition to providing fuel for ATP, a
diet must also supply the raw materials
needed for biosynthesis.
- organic precursors (carbon skeletons)
- essential amino acids
- essential fatty acids
- vitamins and minerals
Nutritional Requirements
Food Types and Feeding
Mechanisms
Even though animals are classified as
herbivores, carnivores, or
omnivores, they are opportunistic
feeders in that they eat foods outside
of their main dietary categories
Food Types and Feeding
Mechanisms
There are four main groups that animals
can be separated into based on the way
they feed
Suspension-feeders: animals that sift
food particles from water
Substrate-feeders: animals that live on
their food source, eating their way
through food
Food Types and Feeding
Mechanisms
Fluid-feeders: animals the survive by
sucking nutrient-rich fluids from a living
host
Bulk-feeders: animals that eat relatively
large pieces of food
Overview of Food Processing
The four main stages of food processing
are ingestion, digestion, absorption, and
elimination
Ingestion: the act of eating
Digestion: the process of breaking food
down into molecules small enough for
the body to absorb
- enzymatic hydrolysis
Overview of Food Processing
Absorption: the animal’s cells take up
small molecules such as amino acids
and simple sugars
Elimination: undigested material passes
out of the digestive compartment
Overview of Food Processing
Digestion occurs in specialized
compartments to reduce the risk of selfdigestion
Intracellular digestion: use of food
vacuoles where hydrolytic enzymes
break down food without digesting the
cell’s cytoplasm
Overview of Food Processing
Overview of Food Processing
Extracellular digestion: the breakdown
of food outside cells
Many animals with simple body plans
have gastrovascular cavities
- these function in both the digestion
and distribution of nutrients throughout
the body
Overview of Food Processing
Overview of Food Processing
Most animals have digestive tubes
extending between two openingscomplete digestive tracts or
alimentary canals
- the advantage is that animals can
ingest additional food before earlier
meals are completely digested
Overview of Food Processing
The Mammalian Digestive
System
The oral cavity, pharynx, and esophagus
initiate food processing
- the presence of food in the oral cavity
triggers the release of saliva.
-saliva contains amylase, the enzyme
that hydrolyzes starch
The Mammalian Digestive
System
The stomach stores food and performs
preliminary digestion
- the stomach secretes gastric juices
and mixes them with food by a
churning motion
- also present in the gastric juices is
pepsin, an enzyme that begins the
hydrolysis of proteins
The Mammalian Digestive
System
The Mammalian Digestive
System
The small intestine is the major organ of
digestion and absorption
- the first 25 cm of the small intestine is
called the duodenum. Here chyme
from the stomach is mixed with juices
from the pancreas, liver, and gall
bladder
The Mammalian Digestive
System
The Mammalian Digestive
System
- the pancreas produces hydrolytic
enzymes and an alkaline solution that
acts as a buffer to neutralize the low pH
of the chyme from the stomach
- the liver produces bile. Bile does not
contain enzymes, but acts as
detergents that aid in the digestion and
absorption of fats
The Mammalian Digestive
System
Carbohydrate digestion:
- begins with salivary amylase in the
oral cavity
- pancreatic amylase hydrolyzes starch,
glycogen, and other polysaccharides
into disaccharides
The Mammalian Digestive
System
Protein digestion:
- enzymes in the duodenum break apart
proteins into amino acids
- trypsin and chymotrypsin break the
peptide bonds
The Mammalian Digestive
System
Fat digestion:
- hydrolysis of fat is a special problem
because fat molecules are insoluble in
water
- bile salts work through
emulsification so that lipase can
break down fat molecules
The Mammalian Digestive
System
Most absorption occurs in the small
intestine
- s.i. has a large surface area due to the
folding of the lining into villi
- each villus has many microscopic
appendages called microvilli which
increase the rate of absorption
The Mammalian Digestive
System
- in the core of each villus is a net of
capillaries and a small vessel of the
lymphatic system called the lacteal
- nutrients are absorbed across the
intestinal epithelium and then across the
epithelium of the capillaries or lacteals
- nutrients then flow into the
bloodstream
The Mammalian Digestive
System