DIGESTIVE SYSTEM

15 JULY 2021

DIGESTIVE
SYSTEM

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NURSULIANA BINTI MD ASRI D20181083297

Simple Digestion

Some of the simplest forms of Intracellular digestion

life (protists and sponges) eliminates the need for a gut or
have no gut and thus carry other cavity in which to
out intracellular digestion. chemically digest food.
Tiny food particles are taken At the same time, however,
into the cell directly from the intracellular digestion limits an
environment by diffusion or animal’s size and complexity—
endocytosis. only very small pieces of food
Digestion begins in a food can be used.

vacuole where lysosomal

enzymes break the small

particles into constituent

nutrients.

Aplysina archeri (Stove Pipe Sponge)

Like all other sponges, the Stove
Pipe Sponge obtains its food by
filter feeding and digests it
through intracellular digestion.
Its constant circulation of water
allows for the removal of
wastes.

Leucettusa lancifer (Flask Sponge)

The Flask Sponge obtains its
food by pulling in water
through its pores and filtering
out food particles.
Like all sponges, the Flask
Sponge digests through
intracellular digestion and
removes wastes through its
constant circulation of water.

The gastrovascular cavity is a structure found in primitive animal
phyla. It is responsible for both the digestion of food and the
transport of nutrients throughout the body. The cavity has only
one opening to the environment. Food goes in and waste comes
out that same opening, making it a two-way digestive tract.
By contrast, organisms that have a mouth on one end with an
anus on the other end have a one-way digestive tract, called an
alimentary canal. Food goes in the mouth, while waste comes out
the anus. There are two phyla under Kingdom Animalia that
possess a gastrovascular cavity which is cnidaria and
platyhelminthes

Montastrea Cavernosa (Great Star Coral)
Polyps obtain food by preying on small organisms such as
plankton and fish. It obtains its food by using its tentacles to
catch and paralyze its prey.
Once the prey is paralyzed, it is brought into the mouth and
gastrovascular cavity where it is to be digested

Once digested, the mouth opens and wastes are released.

Platyhelminthes is Latin for flatworms. Some type of
platyhelminthes are flatworms, tapeworms and flukes.
Flatworms display bilateral symmetry, meaning the left and
right halves are mirror images of one another.

Maritigrella crozierae
(The Tiger Flatworm)

The intestine of the tiger
flatworm is lined by phagocytic
cells which capture the food
particles that have been
partially digested by enzymes
in the gut and complete the
digestion process.
The nutrients then diffuse
through the body of the tiger
flatworm.

Seudoceros bicolor (The two-
colored flatworm)

Like all other flatworms,
the two colored
flatwrom eats and
excretes in the same
opening.

The alimentary canal is compartmentalized for different
digestive functions and consists of one tube with a
mouth at one end and an anus at the other.
Once the food is ingested through the mouth, it passes
through the esophagus and is stored in an organ called
the crop
Then it passes into the gizzard where it is churned and
digested.
From the gizzard, the food passes through the intestine
and nutrients are absorbed.
Most other invertebrates like segmented worms
(earthworms), arthropods (grasshoppers), and
arachnids (spiders) have alimentary canals.

Lumbricus terrestris (Common
Earthworm)

An earthworm obtains its food
by feeding on live and dead
organic matter in soil.
When food enters the
earthworm's mouth, its pharynx
pumps the food into its
esophagus where it is then
passed into the gizzard.
Strong muscular contractions
take place in the gizzard
allowing for the food to be
ground and for mineral particles
to be ingested.
After the gizzard, the food moves
to the intestines where different
enzymes are released to digest
proteins, cellulose, fats, and
complex carbohydrates.
Nutrients are then absorbed,
and wastes are released through
the anus.
Like all members of the Annelida
phylum, the earthworm's
digestive system is a single
straight tube from its mouth to
its anus.

A monogastric organism has a simple single-chambered
stomach, compared with a ruminant organism.
Examples of monogastric animals include omnivores such as
humans, rats, and pigs, carnivores such as dogs and cats, and
herbivores such as horses and rabbits.
Herbivores with monogastric digestion can digest cellulose in
their diets by way of symbiotic gut bacteria.

Monogastric digestive

systems begin with the

ingestion of food into their

mouth.

The tongue and the teeth

gather feed and break it

down into smaller pieces in

order to make it easier for

the animal to digest.

Food travels down the

esophagus, which is a long

tube that carries the feed

from the mouth to the

stomach.

The stomach serves as a

reservoir for short term

storage and digestion where

enzymes break down the feed

components so that they may

enter and be absorbed into

the blood stream.

Any remaining undigested

food travels into the small

intestine, where it is broken

down further.

After the small intestine has

removed all available

nutrients from the feed, the

remaining material is passed

into the large intestine and

finally excreted from the

body through the rectum or

anus.

In many animals, the mechanical action involves chewing;
however, because birds do not have teeth, their bodies use
other mechanical action.
The chemical action includes the release of digestive enzymes
and fluids from various parts of the digestive system.
After being released from food during digestion, nutrients are
absorbed and distributed throughout the animal’s body.

The firtst step is food
passes from the crop to
the first of two stomachs,
called the proventriculus,
which contains digestive
juices that break down
food.
From the proventriculus,
the food enters the
second stomach, called
the gizzard, which grinds
food.
Some birds swallow
stones or grit, which are
stored in the gizzard, to
aid the grinding process.
Birds do not have
separate openings to
excrete urine and feces.
Instead, uric acid from
the kidneys is secreted
into the large intestine
and combined with waste
from the digestive
process.
This waste is excreted
through an opening called
the cloaca.

Ruminants are animals with four-part stomachs, which allows them to
chew food more than once.
When a ruminant is feeding, it does so in a series of quick bites, giving
the food no more than a cursory chew between its molar teeth, mixing
it with large quantities of saliva (several hundred litres per day in
domestic cattle) and then swallowing it into the first of the chambers,
the rumen.
Here powerful muscles churn it with the microbes that start the
fermentation process.
The food ferments, generating methane and carbon dioxide which are
eructed.
The microbes start to break down the cellulose of the cell walls into
sugars, thereby releasing other nutrients from inside the cells.
The microbes use some of these nutrients for their own metabolism,
and in doing so generate fatty acids, which the ruminant can absorb
into its blood through the wall of the rumen and can use in its own
metabolism.

Some animals, such as camels and alpacas, are pseudo-
ruminants.
The digestive enzymes of these animals cannot break down
cellulose, but microorganisms present in the digestive system
can.
Therefore, the digestive system must be able to handle large
amounts of roughage and break down the cellulose. Pseudo-
ruminants have a three-chamber stomach in the digestive
system.
However, their cecum—a pouched organ at the beginning of
the large intestine containing many microorganisms that are
necessary for the digestion of plant materials—is large and is
the site where the roughage is fermented and digested.
These animals do not have a rumen but have an omasum,
abomasum, and reticulum.

SURPRISING FACTS ABOUT
THE DIGESTIVE SYSTEM

Some animals have

stomachs with multiple

compartments.

Cows and other

"ruminants" — including

giraffes, deer and cattle

— have four-chambered

stomachs, which help

them digest their plant-

based food.

But some animals —

including seahorses,

lungfishes and

platypuses — have no

stomach.

Their food goes from the

esophagus straight to

the intestines.

When you eat
something, the food
doesn't simply fall
through your esophagus
and into your stomach.
The muscles
in your esophagus
constrict and relax in a
wavelike manner called
peristalsis, pushing the
food down through the
small canal and into the
stomach.
Because of peristalsis,
even if you were to eat
while hanging upside
down, the food would
still be able to get to
your stomach.