∞ a group of organs working together to convert food into energy
and basic nutrients to feed the entire body.
∞ made up of the digestive tract—a series of hollow organs joined in
a long, twisting tube from the mouth to the anus—and other organs
that help the body break down and absorb food.
∞ contains a layer of smooth muscle that
helps break down food and move it along
the tract.
∞ From the word digestio which means
from, dis means apart and gerere is to
carry
Digestive Tract
NUTRITION
•
includes all of those processes by which an animal takes in, digests, absorbs, stores
and uses food (nutrients) to meet its metabolic needs
• Nutrients in the food an animal consumes provide the necessary chemicals for
growth, maintenance and energy production
• Autotrophs – green plants and photosynthetic protists can synthesize all their
own food
• From the word auto, self and trophe, nourishing
• Heterotrophs – those animals that cannot synthesize their own food thus they
obtain them by consuming other organisms or their product
• From the word heteros, another or different and trophe, nourishing
• Herbivores – animals that subsist entirely on plant materials
• Herba, plants and vorare, to eat
• Carnivores – animals that eat only meat
• Caro which means flesh
• Omnivores – humans and some animals that eat both plants and animals
• Omnius means all
• Insectivores – eat primarily arthropods
NUTRIENTS IN HETEROTROPHS
• Macronutrients- needed in large quantities, includes
carbohydrates, lipids, and proteins
sugar
Neutral
fats
starches
glucose
glycolysis
glycerol
Amino
acids
steroids
Steroids the
animal
needs
Fatty acids
Proteins the
animal needs
Nitrogen
waste
Other lipids the
animal needs
Acetyl-CoA
Carbon
compounds
Krebs
cycle
Electron
transport
chain
ATP
energy
• Micronutrients- needed in small quantities
• Essential minerals- are macrominerals
needed in relatively large amounts
MINERAL
MAJOR PHYSIOLOGICAL
ROLES
MINERAL
MAJOR PHYSIOLOGICAL
ROLES
Calcium
Component of bone and teeth;
for normal blood clotting
Potassium
Chlorine
Principal negative ion in
extracellular; needed to
produce stomach HCl;
important in acid-base balance
Major positive ion in cells;
influences muscle
contraction and neuron
excitability
Magnesium
Component of many
coenzyme; needed for normal
neuron and muscle function
Sodium
Phosphorus
Major constituent of bones,
blood plasma; needed for
energy metabolism; part of
DNA, RNA, ATP, energy
metabolism
Principal positive ion in
extracellular fluid;
important in fluid balance;
essential for conduction of
action potentials, active
transport
Sulfur
Protein structure;
detoxification reactions and
other metabolic activity
• Microminerals- known as trace minerals,
animals need these in very small amounts
MINERAL
PHYSIOLOGICAL ROLES
Cobalt
Copper
Fluorine
Iodine
Iron
MINERAL
PHYSIOLOGICAL ROLES
Component of vitamin B12;
essential for red blood cell
production
Manganese
Component of many
enzymes; essential for
melanin and hemoglobin
synthesis; part of
cytochromes
Activates many enzymes;
an enzyme essential for
urea formation and parts
of the Krebs cycle
Molybdenum
Constituent of some
enzymes
Selenium
Needed in fat metabolism
Zinc
Component of at least 70
enzymes; needed for
wound healing and
fertilization
Component of bone and
teeth; prevents tooth decay
Component of thyroid
hormones
Component of hemoglobin,
myoglobin, enzymes, and
cytochromes
• Vitamins- the general term for a number of chemically unrelated , organic
substances that occur in many foods in small amounts and are necessary for
normal metabolic functioning
• Water soluble vitamin- such as vitamin B and C are coenzymes needed in
metabolism
• Fat soluble vitamin- such as vitamins A, D, E, K that are limited to the
vertebrates
• Intracellular digestiontiny food particles are taken into the body wall cells by endocytosis,
digestive enzyme in the vacuole then break the small particles into
constituent molecules
• Extracellular digestionthe enzymatic breakdown of larger pieces of food into constituent
molecules, in special organ or cavity and then can take part in energy metabolism
ANIMAL STRATEGIES FOR GETTING
AND USING FOOD
• Continuous Feeders- sessile animals
• Discontinuous Feeders- mobile animals
• Suspension Feeders- removal of suspended food particles from the
surrounding water by some sort of capture, trapping or filtration
structure
• Depositor Feeders- omnivorous animals obtain their nutrients from the
sediments of soft-bottom habitats (muds and sands) or terrestrial
soils
• Herbivory- consumption of macroscopic plants, it requires the ability to
bite and chew large of plant matter
• Herba, herb and vorare means to eat
• Predation- requires the capture of live prey
• Motile stalkers- actively pursue their prey
• Lurking predators- sit and wait for their prey to come within seizing distance
• Sessile opportunists- are not very mobile, they can only capture prey when
the prey organism comes into contact with them
• Grazing carnivores- move about the substrate picking up small organisms
• Surface Nutrient Absorption
• free-living and endoparasitic protozoa, cestode worms, endoparasitic
gastropods and crustaceans- lack mouths and digestive sytems so they
absorb nutrients across their body surface
• Pogonophoran worms- absorb some nutrients from sea water across
their body surface and also supplement their nutrition with organic
carbon that symbiotic bacteria fix within the pogonophoran’s tissue
• Fluid Feeders- animals that feed on biological fluids that are rich in nutrients
• The gastrovascular cavity of cnidarians,
such as hydra, in an incomplete
digestive tract because its mouth serve
as the entry and exit point for food and
waste.
• Extracellular digestion occur in
gastrovascular cavity while intracellular
digestion occur in food vacuole.
• Gastrovascular cavity – is a gut where
digestion takes place in invertebrates.
Incomplete digestive tract is a tract
that has one opening for entrance
and exit.
Complete digestive tract is a tract
with the development of the anus
for exit of wastes.
Platyhelminthes(planarian) has also
incomplete digestive tract.
The ingestion of planarian occur in
pharynx, sticks it out of its mouth and
sucks in food.
Nematodes have a
complete digestive
tract, it has mouth
pharynx and anus.
Protozoa
• Some protozoa may be autotrophic,
saprozoic, heterotrophic (ingestion
processes).
• Ciliated protozoan uses its cilia to direct
food toward the cytostome (mouth).
• The excess water do not go within the
digestion but go in the cytoplasm. The pH is
acidic.
• The lysosomes of the protozoa delivers
digestive enzymes and the nutrients are
absorbed in the cytoplasm, at this time the
pH is alkaline or basic.
• The waste vacuole moves to the cytopyge
(anus).
I
n
s
e
c
t
s
• Grasshopper is one of the example of the
insects with complete digestive tract and
extracellular digestion.
• Mastication – breaking up the food. In this
process saliva was mixed.
• During feeding the food, goes in mouth,
esophagus and crop.
• Crop – function as a food storage organ.
• The midgut or the
stomach secretes
enzymes such as lipases
and carbohydrases.
• Large particles returned
to the crop for further
processing while the
small particles enter at
the gastric caeca, where
extracellular digestion
takes place.
• Undigested food is
moved along the
intestine and passes
into the rectum, where
water and ions are
absorbed.
• The digested food or
the solid fecal pellets
pass out via anus.
∞ Food begins its journey through
the digestive system in the mouth.
∞ Inside the mouth are many
accessory organs that aid in the
digestion of food—the tongue, teeth,
and salivary glands. Teeth chop food
into small pieces, which are
moistened by saliva before the
tongue and other muscles push the
food into the pharynx.
Teeth
Tongue
Salivary
Glands
∞ a funnel-shaped tube connected to
the posterior end of the mouth.
∞ responsible for the passing of
masses of chewed food from the
mouth to the esophagus.
∞ plays an important role in the
respiratory system, as air from the
nasal cavity passes through the
pharynx on its way to the larynx and
eventually the lungs.
∞ it contains a flap of tissue known as
the epiglottis that acts as a switch to
route food to the esophagus and air
to the larynx.
∞ a muscular tube connecting the
pharynx to the stomach that is part of
the upper gastrointestinal tract.
∞ carries swallowed masses of chewed
food along its length.
*At the inferior end of the
esophagus is a muscular ring called the
lower esophageal sphincter or cardiac
sphincter. The function of this sphincter is
to close of the end of the esophagus and
trap food in the stomach.
∞ a muscular sac, located on the left
side of the abdominal cavity, just
inferior to the diaphragm.
∞the stomach is about the size of
their two fists placed next to each
other.
∞ acts as a storage tank for food so
that the body has time to digest
large meals properly.
∞ contains hydrochloric acid and
digestive enzymes that continue the
digestion of food that began in the
mouth.
Structures associated with the
Stomach:
∞Gastroesophageal Opening ∞Pyloric Sphincter
∞Pyloric Opening
∞Rugae
∞ a long, thin tube about 1 inch in diameter
and about 10 feet long that is part of
the lower gastrointestinal tract.
∞ located just inferior to the stomach and
takes up most of the space in the abdominal
cavity.
∞ coiled like a hose and the inside surface is
full of many ridges and folds.
*These folds are used to maximize
the digestion of food and absorption of
nutrients. By the time food leaves the small
intestine, around 90% of all nutrients have
been extracted from the food that entered
it.
∞ a roughly triangular accessory
organ of the digestive system located
to the right of the stomach, just
inferior to the diaphragm and
superior to the small intestine.
∞ weighs about 3 pounds
∞ the second largest organ in the
body.
∞ the main function of the liver in
digestion is the production of bile
and its secretion into the small
intestine.
∞ a small, pear-shaped organ located posterior to
the liver.
∞ used to store
and
recycle
excess bile from
the
small
intestine so that
it can be reused
for
the
digestion
of
subsequent
meals.
∞ a large gland located just
inferior and posterior to the
stomach.
∞ It is about 6 inches long
and shaped like short,
lumpy snake with its “head”
connected to the duodenum
and its “tail” pointing to the
left wall of the abdominal
cavity.
∞ secretes digestive enzymes
into the small intestine to
complete the chemical
digestion of foods.
∞ a long, thick tube about 2 ½
inches in diameter and about 5
feet long.
∞ located just inferior to the
stomach and wraps around the
superior and lateral border of
the small intestine.
∞ absorbs water and contains
many symbiotic bacteria that aid
in the breaking down of wastes
to extract some small amounts of
nutrients.
∞ Feces in the large intestine exit
the body through the anal canal.
Terms that must
be familiar with:
1. Chyme – semi fluid mixture
of
food
with
stomach
secretions.
2. Hydrochloric acid – has a pH
of 2.0 in the stomach; a
gastric gland that kills bacteria
and converts pepsinogen to
pepsin.
3. Pepsin – a gastric gland that
digest proteins.
4. Mucus – mucous cell that
protects stomach lining
5. Intrinsic factor – a gastric
gland that binds to B12 and
aids in its absorption
Regulation of
Stomach Secretions
21 of gastric secretions (gastric juice) are produced
each day.
a. Cephalic Phase- sensation of taste, smell of food,
stimulation of tactile receptors during the process
of chewing and swallowing and pleasant thoughts
of food stimulate centers.
b. Gastric Phase- a period during which the greatest
volume of gastric secretion occurs. It is activated
by the presence of food in the stomach.
*Gastrin
c. Intestinal phase- controlled by the entrance of
acidic chyme into the duodenum, which initiates
both neural and hormonal mechanisms.
*Secretin
*Cholecystokinin
The digestive system is responsible for taking whole foods and
turning them into energy and nutrients to allow the body to function, grow,
and repair itself.
The six primary processes of the digestive system include:
∞ Ingestion of food – eating
∞ Peristalsis – the involuntary, sequential muscular contractions that move
ingested nutrients along the digestive track
∞ Segmentation – mixing the contents in the digestive tract
∞ Secretion – the release of hormones, enzymes and specific ions and
chemicals that take part in digestion
∞ Digestion – the conversion of large nutrient particles or molecules into
small particles or molecules
∞ Absorption – the passage of usable nutrient molecules from the small
intestine into the bloodstream and lymphatic system for the final
passage to body cells