Download Human Digestion

Human Digestion
© Lisa Michalek
Digestion
 Digestion is the process that changes food into a
form that can be used by your body cells.
 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 table below.
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 the mechanical digestion, the
tongue is important during the swallowing and
tasting 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 that it slides
down the 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.
 Some 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 is 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 burst and infect the
surrounding membranes and organs possibly leading to
death.