Download PPT: Digestive System

HUMAN DIGESTION
Fun Facts
We eat about 500kg of food per year.
 1.7 liters of saliva is produced each day
 You can swallow even if you are standing on your head.
 Every day 11.5 liters of digested food, liquids and digestive
juices flow through the digestive system, but only 100mls is
lost in feces.
 Food stays in your stomach for 2-6 hours.
 Small intestine, 5-6 meters long
 Esophagus is 25 cm long
 The food stays in the small intestine from 1-4 hours
 The food stays at the colon for 10 hours or for a several
days
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Fart Facts
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Most of us pass somewhere between 200 and 2,000 ml of gas
per day (average, about 600 ml) in roughly 13-14 passages.
These emissions are composed of five gasses: nitrogen (N2),
oxygen (O2), carbon dioxide (CO2), hydrogen (H2), and
methane (CH4).
produce more gas than meat-eaters because the intestinal
enzymes
can't digest the cellulose in vegetables' cell walls
Does your poop float? If so, that means bacteria in your gut
are producing methane
The noise created by passing gas is not from the two buttocks
vibrating together, as many believe. The noise created occurs
as the gas passes through the anal sphincter. It's influenced by
a combination of the volume of gas, the force with which it's
expelled and the tightness of the anal sphincter.
Digestion
Digestion is the
breakdown of large,
complex organic
molecules into smaller
components that can
be used by the body.
 Molecules need to be
small enough to pass
across the membrane
of your intestine to
your blood stream
 Digestion animation
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Ingestion
Food enters the
human digestive tract
through the mouth
(aka oral cavity).
 Physical breakdown of
food begins with the
teeth grinding the food
and increasing its
surface area. An
increase surface area
allows for easier
chemical digestion
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Alimentary Canal
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The human digestive tract is
often referred to as the
alimentary canal.
The alimentary canal of a
normal adult is approximately
6.5 to 9 meters long.
It runs from mouth to anus!
What organs/structures make
up the alimentary canal?
Which contribute to digestion?
Which don’t?
Saliva
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Saliva is released from
the salivary glands and
begins chemical digestion
of starches. Saliva
contains the enzyme
salivary amylase which
breaks down starches
into simpler
carbohydrates.
Saliva also moistens and
lubricates food, making it
easier to swallow.
Swallowing
Esophagus
The bolus of food
moves down the
esophagus propelled
by wave-like muscular
contractions known as
peristalsis.
 Peristalsis moves food
all the way through
the gastrointestinal
tract.
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Stomach
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The stomach acts as a
temporary storage site for
food. Food usually
spends about 4 hours in
the stomach. It has
ridges which allow it to
expand to store about 1.5
litres of food.
The stomach is also the
site of initial protein
digestion.
Endoscopy
Stomach
Movement of food into and
out of the stomach is
controlled by circular muscles
known as sphincters.
 One at the top of the stomach
allows food from the
esophagus to enter and
prevents food from going back
up into the esophagus.
 Another located at the bottom
slowly releases partially
digested food into the small
intestine. The partially
digested food is called
chyme.
Stomach pyloris
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Stomach
Millions of cells lining the stomach secrete
various fluids known collectively as gastric fluids.
 Gastric fluid consists of mucus, hydrochloric
acid, pepsinogens (an enzyme) and other
substances.
 Mucus coats and protects the lining of the
stomach. Hydrochloric acid kills any harmful
substances that have been ingested and it also
converts pepsinogen into pepsin.
 Pepsin is a protein digesting enzyme that breaks
large protein chains into smaller chains.
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Stomach pH
The pH environment
of the stomach
normally ranges
between 2.0 and 3.0
on the pH scale.
 The high acidity
allows pepsin to work
and makes the HCL
effective at killing
pathogens
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Small and Large Intestine
The intestines are
named for their
diameter, not length.
 The small intestine is
up to 7 m in length
but only 2.5 cm in
diameter.
 The large intestine is
only 1.5 m in length
but 7.6 cm in
diameter.
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Small Intestine
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In mammals the length of
the small intestine is
directly related to their
diet.
Due to the fact that
meats are easier to digest
than plant materials,
carnivores (lion) will have
a shorter intestine than
herbivores (rabbit). The
length of the digestive
tract of omnivores falls
somewhere in the middle.
Anatomy of the Small Intestine
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The majority of chemical
digestion occurs in the
first of three sections of
the small intestine known
as the duodenum.
This section also contains
an opening from the bile
duct and pancreatic duct
through which bile and
pancreatic enzymes enter
the small intestine.
Small Intestine
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Food enters the small
intestine as a semi-solid
mixture known as
chyme. The chyme is
acidic due to the HCl in
the stomach so it needs
to be neutralized.
Pancreas
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The pancreas is an
accessory organ of the
digestive system. It
releases chemicals to aid
in digestion.
Secretin will stimulate the
pancreas to release a
solution containing
bicarbonate ion into the
small intestine where it
will neutralize the acidic
chyme and raise the pH
from 2.5 to 9.0. This
inactivates the pepsin.
Pancreas and Digestion
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The pancreas also releases digestive enzymes
that break down the three macromolecules:
carbohydrates, lipids and proteins.
Liver
The liver is a large
accessory organ of
the digestive system
that is constantly
producing a fluid
known as bile.
 Bile is stored in the
gall bladder until it is
needed in the small
intestine.
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Liver and Gall Bladder
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The presence of lipids in
the small intestine trigger
the release of bile from
the gall bladder.
Bile contains bile salts
that emulsifies fats which
means it breaks them
into smaller droplets so
they can be digested.
Absorption of Materials
Now that nutrients
are small enough they
need to be absorbed
into the blood stream
in the small intestine.
 Chemical digestion of
nutrients is completed
by the time it reaches
the large intestine.
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Large Intestine
The large intestine or
colon stores waste
products long enough
so that water can be
reabsorbed from the
wastes.
 Along with the water,
some inorganic salts,
minerals and vitamins
are absorbed.
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Large Intestine
The large intestine is
home to several
different types of
bacteria.
 These bacteria use
waste materials to
make vitamins B and
K. This is an example
of a symbiotic
relationship.
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Cellulose
Cellulose is more commonly
known as fiber. Fiber helps to
remove wastes and therefore
toxins from the body.
 Humans cannot digest
cellulose however it provides
bulk which promotes the
movement of the waste
products out of the colon.
 If you have a diet low in fiber
you will have fewer bowel
movements which means
toxins remain in your body for
longer periods of time.
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It all comes down to poo…