37 – Animal Nutrition
adequate diet satisfies three needs: fuel
(chemical energy for all the cellular work of the body); the organic raw
materials animals use in biosynthesis (carbon skeletons to make many of
their own molecules); and essential nutrients (substances the animal cannot
make for itself from any raw material)
obtain the fuel that powers the work of their body cells from the oxidation
of organic molecules and the monomers are used to generate ATP by cellular
must meet their basal metabolic rate to sustain life.
in more calories that it consumes causes the body to store the excess
calories. For example, the
liver and muscle cells store energy in the form of glycogen.
If the glycogen stores are full, the excess calories are stored as
undernourished person is one whose diet is deficient in calories.
When starvation for calories begins, the body breaks down its own
proteins for fuel, muscles decrease in size and the brain becomes deficient
and often the damage is irreversible.
common feedback mechanism regulates fate storage and use in mammals.
A hormone called leptin produced by the adipose cells.
An increase in adipose tissue increases leptin levels in the brain
and this cues the brain to depress appetite and increase energy-consuming
muscular activity and body-heat production.
Conversely, loss of body fat decreases leptin levels in the blood
signaling the brain to increase appetite and weight gain.
- A. Heterotrophs
do not always produce the raw materials it needs to continue growth and
development so essential nutrients must be obtained.
essential nutrient is vitamin C or ascorbic acid.
animal lacking these essential nutrients is said to be malnourished
instead of undernourished.
are four classes of essential nutrients
be obtained from food in prefabricated form.
amino acids are essential in the human diet
that lacks one or more essential amino acid results in a protein
deficiency and often causes physical and mental development problems.
of these come from eggs, cheese and animal products.
unsaturated fatty acids
acid is an example
to make some of the phospholipid found in membranes.
molecules required in small amounts.
vitamins are essential
include B complex for coenzyme activity, Vitamin C for synthesis of
are excreted through the urine.
are vitamins A, D, E, and K.
is used in the visual pigments of the eyes
aids in calcium absorption and bone formation
is not fully understood but seems to protect the phospholipids
is required for blood clotting
is not excreted but are deposited in body fat.
nutrients required in very small amounts.
is needed for functioning of nerves, muscles and formation of bones.
is used in the formation of ATP and nucleic acids.
is used in the Cytochromes involved in cellular respiration and
zinc, copper, manganese, selenium, and molybdenum are cofactors for
main stages of food processing
is the act of eating
is the process of breaking down food molecules into bits small enough to
absorb. Macromolecules cannot
be used directly because they are too large to pass through the membranes.
This is catalyzed by hydrolytic enzymes and is usually preceded by
mechanical fragmentation of food.
is the taking up of small molecules like amino acids from the digestive
is the removal of undigested material out of the digestive compartment.
occurs in specialized compartments
vacuoles contain enzymes that break down food without digesting the
cell’s own cytoplasm.
digest their meals in food vacuoles usually after phagocytosis or
food vacuoles fuse with lysosomes to have this occur.
most animals, at least some hydrolysis occurs by extracellular digest,
which occurs in compartments that are continuous with the outside of the
body plans have digestive sacs with signal openings called
gastrovascular cavities that function in both digestion and distribution
digestive tracts or alimentary canals have two openings, a mouth and an
moves in one direction and it can be organized into specialized
ingested through the mouth and pharynx passes through an esophagus
that leads to a crop, gizzard, or stomach.
Crops and stomachs normally store the food and gizzards tend to
Mammalian Digestive System
of an alimentary canal with various accessory glands that secrete
digestive juices into canals through ducts.
is the rhythmic waves of contraction by smooth muscles in the wall of the
canal that pushes the food along the tract.
are used to close off the tube like drawstrings and regulate the passage
glands are three pairs of salivary glands, the pancreas, the liver, and
the gall bladder.
begins in the oral cavity
and chemical digestion takes place here.
or chewing the food is the mechanical breakdown of the food making it
easier to swallow and increases the surface area.
presence of food in the oral cavity triggers a nervous reflex for the
salivary glands to deliver saliva through ducts in the oral cavity.
is dissolved in the saliva, which protects the soft lining of the mouth
from abrasion and lubricates the food.
also contains buffers to prevent tooth decay and antibacterial agents
may kill much of the bacteria that enters.
amylase is also release that begins the digestion of carbohydrates by
breaking down starch and glycogen.
tongue tastes the food and manipulates it during chewing helping form the
food into a ball called a bolus, which is then pushed to the pharynx.
is the intersection of the esophagus and trachea.
causes the top of the trachea to move up so that its opening the glottis
is covered by a cartilaginous flap called the epiglottis and forces the
food to move into the esophagus
food from the pharynx to the stomach.
squeezes the bolus along. (It
is possible to eat while standing on your head because of these reactions.
Reverse peristalsis is regurgitation.)
muscles at the top are striated and voluntary.
amylase continues its digestion of starch.
sphincter is used to control movement into the stomach.
on the left side of the abdominal cavity, just below the diaphragm.
a very elastic wall and can accommodate about 2L of food and water.
epithelium secretes gastric juice that mixes with food and has a pH of 2.
disrupts the extracellular matrix that binds cells together and kills
any other bacteria present.
is an enzyme that begins the breakdown of proteins by breaking the peptide
bonds adjacent to specific amino acids and works best in a strong acidic
cells located in gastric pits synthesize and secrete pepsin in an inactive
form called pepsinogen, which is converted by HCl to pepsin.
(This is a positive feedback)
coating of mucus secreted by the epithelial cells protects the lining from
being destroyed and the epithelium is constantly replacing the cells
gastric ulcer is caused by bacteria and can be treated using antibiotics
but may worsen if the lining is destroyed faster than it can be
contents of the stomach are mixed every 20 seconds by the smooth muscles
and becomes known as chyme.
backflow of chyme into the esophagus is called heartburn.
the junction of the small intestine and the stomach is the pyloric
digestion takes place here.
responsible for absorption
pancreas, liver, and gall bladder contribute to the digestion.
first 25cm is called the duodenum
pancreas produces several enzymes as well as bicarbonate, which act as a
buffer to neutralize the acid from the stomach.
liver produces bile, which is a mixture, stored in the gallbladder until
contains no enzymes but bile salts that act as detergents and aid in
the digestion and absorption of fats.
in the oral cavity by amylase, which breaks down polysaccharides.
in the small intestine using pancreatic amylases.
break down the disaccharides into monosaccharides in the epithelium of the
small intestine and are then absorbed into the blood stream
in the stomach with the conversion of pepsinogen to pepsin due to HCl.
the lumen of the small intestine, trypsin, chymotrypsin, carboxypeptidase
and aminopeptidase digest the polypeptides into amino acids
digest the small peptides in the epithelium of the intestine into amino
in the lumen of the small intestine where DNA and RNA are catalyzed by
nucleases into nucleotides
process is completed in the epithelium of the small intestine by
place in the lumen of the small intestine.
salts turn fat globules into fat droplets.
then digest the fat droplets into glycerol, fatty acids, and glycerides.
must cross the lining of the digestive tract
circular folds bear fingerlike projections that contain villi and each of
the epithelial cells of a villus contains microvilli.
the core of each villus is a net of capillaries and a small vessel of the
lymphatic system called a lacteal.
are absorbed into the capillaries or lacteals.
the transport is passive like with fructose but amino acids, peptides,
vitamins, and glucose must be actively transported.
capillaries and veins drain nutrients into the hepatic portal vessel,
which leads to the liver, which has access to amino acids and sugars
blood that leaves the liver may have a very different balance of nutrients
than it did initially.
help regulate digestion
ensure that digestive secretions are present only when needed.
hormone gastrin recirculates the blood stream back to the stomach wall and
stimulates the secretin of gastric juice.
are secreted by the wall of the duodenum.
acidic pH of the chyme stimulates the release of secretin, which causes
the pancreas to secrete the bicarbonate to buffer the acid.
(CCK) is secreted in response to amino acid and fat presence and causes
the gallbladder to release bile and pancreatic enzymes.
known as the colon
main function is to reabsorb water that has entered the canal.
waste or feces becomes more solid as it moves through the colon by
much water reabsorbed causes constipation.
enough water absorbed causes diarrhea.