Download Unit Four Digestive System

Unit Four
Digestive System
Lisa Michelek
Digestion
• Digestion is the process that changes food
into a form that can be used by the cells of
your body.
• Food is taken in and processed through your
digestive system before it can be used
by your body.
• The usable parts of food (nutrients) supply
you with the chemicals and
energy you need to survive.
• The digestive process begins
when food is taken into
the body – ingestion.
Digestion
• Digestion begins with the breakdown of food into smaller
pieces.
• This process is called mechanical digestion and it prepares
the food for chemical digestion.
• During chemical digestion, large complex food molecules are
chemically changed into smaller simpler molecules.
• In unicellular and other simple organisms, digestion is
intracellular.
– This means that digestion takes place in vacuoles inside
the cell of the organism.
• In larger, complex multicellular organisms, digestion is
extracellular.
Mechanical Digestion
• In most organisms, food must undergo a
mechanical breakdown called mechanical
digestion, where food is physically cut, ground,
and torn into smaller pieces.
• Mechanical digestion increases the surface
area of the food particles, which prepares them
for chemical digestion.
Chemical Digestion
• During chemical digestion, large organic
molecules are broken down into small simple
molecules by the chemical process of
hydrolysis.
• During hydrolysis water is added to large
complex molecules causing them to split into
simpler molecules that can be used by the cells.
• Each reaction in digestion is catalyzed by a
specific enzyme.
• These digestive enzymes help chemically break
down foods and must be present for digestion
to occur.
Chemical Digestion
• In all organisms, the complete chemical
digestion of large molecules produces the end
products shown in the below table.
Large Molecules
Enzymes
End Products
Carbohydrates
Maltase
Simple sugars
Lipids
Lipase
Fatty acids and
glycerol
Proteins
Protease
Amino acids
Chemical Digestion
• Chemical digestion does not completely break
down all food molecules.
• The organism may lack enzymes to digest
some types of food molecules, or there may not
be enough time for enzymes to digest the food
completely.
• When this happens, the organism must
eliminate indigestible or undigested materials.
• Egestion is the process by which heterotrophs
(organisms that cannot make their own food)
eliminate or remove food wastes from the body.
The Alimentary Canal
• The digestive system is made up
of a continuous one-way tube that
begins in the mouth and ends with
the anus.
• This tube is commonly called the
alimentary canal or
gastrointestinal (GI) tract.
• As food passes through the tube,
special areas of the tube
mechanically and
chemically change food.
The Alimentary Canal
• Food moves in one direction through the
alimentary canal by slow, rhythmic, muscular
contractions called peristalsis.
• After chemical digestion, the nutrients you eat
pass from the alimentary canal into all the cells
of the body.
The Alimentary Canal
• Ingestion takes place at the
mouth, which is also called the
oral cavity.
• This process begins mechanical
digestion, which increases the
surface area of the food.
• Chemical digestion also begins in
the mouth.
The Alimentary Canal
• The salivary
glands, located in
the oral cavity,
secrete saliva.
• Saliva has mucus
that moistens food
making it easier to
swallow.
The Alimentary Canal
• Saliva also contains the enzyme ptyalin.
• Ptyalin starts the chemical digestion of
starches.
– The starch in bread is changed into maltose, a
disaccharide (double sugar).
– You can check this for yourself by chewing
a piece of bread for a few minutes.
– When the starch in the bread is changed
to sugar, you will notice a sweet taste.
The Alimentary Canal
• Besides aiding in mechanical digestion, the
tongue is important during the tasting and
swallowing of food.
• There are little groups of cells
located in the tongue and roof
of the mouth called taste buds.
• Four basic kinds of taste are
sweet, sour, salty, and bitter.
The Alimentary Canal
• After food is swallowed, it goes into the esophagus.
• The esophagus or gullet is a tube that moves food
from the mouth to the stomach by peristalsis.
• No additional chemical digestion begins in the
esophagus.
• The chemical action of saliva continues in the
esophagus until the food reaches the stomach.
• The esophagus produces a slimy material called
mucus.
• Mucus lubricates (moistens) food so it slides down
esophagus more easily.
The Stomach
• The stomach is a muscular,
J-shaped organ.
• Mechanical digestion occurs
when stomach muscles
churn and mash food.
• The food becomes a thick
soupy mixture called chyme.
• Chemical digestion also
occurs in the stomach.
The Stomach
• Glands in the stomach lining secrete gastric
juice and hydrochloric acid.
• Hydrochloric acid (HCl) destroys bacteria
normally present in food and provides the
proper pH for enzyme action.
• The gastric juice contains pepsin, an enzyme
that begins the chemical digestion of protein.
• Rennin is an enzyme that begins the chemical
digestion of milk protein.
The Small Intestine
• After three or four hours, partly
digested food leaves the stomach
and enters the small intestine.
• In the small intestine, food
digestion is completed and
digested nutrients are absorbed
into the bloodstream.
• Most chemical digestion takes
place in the small intestine,
not in the stomach.
The Small Intestine
• In the small intestine, digestion is
accomplished as a result of the
action of enzymes produced by
intestinal glands and the
pancreas.
• Bile, made by the liver, prepares
fats and oils for enzyme digestion
by breaking them down into
smaller pieces.
The Small Intestine
• This process greatly increases the
surface area of fat particles, thereby
speeding up fat digestion by
enzymes called lipases.
• The action of bile on fats is referred
to as a detergent effect, because
detergent also breaks up fat.
• Bile is stored in the gall bladder and
enters the small intestine through
the bile duct.
The Small Intestine
• Lining the inside of the small intestine are tiny
finger-like projections of the intestinal wall
known as villi.
• Villi increase the surface area of the small
intestine for the absorption of the end products
of digestion.
• End products are absorbed by the
process of
diffusion.
The Small Intestine
The Large Intestine
• Undigested foods (wastes) pass from the small
intestine into the large intestine.
• The large intestine is also called the colon.
• In the large intestine, water, some vitamins, and
minerals are absorbed into the blood stream.
• The remaining undigested
substances, called feces,
are stored in the lower
end of the large intestine
called the rectum.
• Feces are eliminated from the
body (egestion) through the anus.
End Products of Digestion
• The final compounds formed by digestion are
called end products.
• These molecules are small and chemically
simple so that they can be absorbed and used
by the body’s cells.
• Once the end products of digestion enter a cell,
the cell will use them as building blocks in the
synthesis (making) of complex compounds
(nutrients) necessary for life.
• This is done by the chemical process of
dehydration synthesis.
End Products of Digestion
• Dehydration synthesis is the opposite of
hydrolysis.
• Simple sugars are made into complex
carbohydrates, fatty acids and glycerol are
made into fats, and simple amino acids become
complex proteins.
• Excess water was absorbed by the large
intestine and what ever indigestible wastes
were formed will be egested through the anus.
Digestive System Disorders
• Ulcers
– An ulcer is an open, painful sore in the stomach
lining.
– Mucus, secreted by cells lining the surface of the
stomach, helps to protect the stomach lining from
hydrochloric acid.
– Open sores occur when there is too little
mucus or too much acid in the stomach.
– Ulcers can bleed and sometimes eat
completely through the stomach wall.
– Ulcers are treated with diet
and medication.
Digestive System Disorders
• Tooth Decay
– Mouth bacteria cause tooth decay.
– Brushing and flossing your teeth at least once a day
will help slow down the action of bacteria on food
caught between your teeth.
– Regular visits to your dentist are also very important
in preventing tooth decay and gum disease.
Digestive System Disorders
• Appendicitis
– Located near the beginning of the large intestine is
a small finger like projection called the appendix.
– An infection of the appendix is called appendicitis.
– Treatment for this very painful condition is surgical
removal of the appendix.
– If the appendix is not removed it may leak fluid into
the surrounding membranes and organs, possibly
leading to death.
Digestive System Disorders
• Diarrhea
– The condition in which the feces do not remain in
the large intestine long enough for the water to be
absorbed is called diarrhea.
– Diarrhea can be caused by bacteria or viruses,
emotional stress, or eating certain foods.
– If diarrhea lasts for a long time the body becomes
dehydrated (loss of water) resulting in weakness.
– Severe diarrhea can result in death.
Digestive System Disorders
• Constipation
– The opposite of diarrhea is constipation, a
condition where the feces remain in the colon too
long.
– Constipation can be caused by too little fiber or
water in the diet.
Digestive System Summary
• https://www.youtube.com/watch?v=lm3oIX
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