Transcript digestion - KingSNC2D

DIGESTIVE
SYSTEM

Digestion: process by which food and
drink are broken down into smallest parts
so that body can use them to build and
nourish cells and provide energy
Why is digestion important?
 Our food and drink must be changed into
smaller molecules of nutrients before they
can be absorbed into the blood and
carried to cells throughout the body.
What nutrients do organisms need
and Why?
MACROMOLECULES
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Carbohydrates for short and long-term energy
Fats/Lipids for long-term energy
Proteins for building organisms own proteins
(performing important cellular functions,
growth & repair)
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If starving, proteins can be used for energy, but that is
not their primary function
Nucleic acids are synthesized by the organism,
they are not usually obtained by feeding
(function of nucleic acids is to store genetic
information)
Organization of Complexity
Cell
Tissue:
The smallest
A group of
structural unit
cells that
of an organism
works
that is capable
 together to 
of independent
perform a
functioning,
specialized
task
Organs:
Organ
A structure
system:
composed of
A group of
different
organs that
tissues
 work together
specialized to
to perform a
carry out a
specialized
specific
function
function
Digestive System
TISSUES OF THE STOMACH
4 Stages of Food Processing
INGESTION (nutrients IN)
 DIGESTION (break down of larger
molecules into smaller molecules)
 ABSORPTION (from intestine into blood)
 EGESTION, EXCRETION, ELIMINATION
(wastes OUT)
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Types of digestion
1)
Physical/Mechanical Digestion: is the
physical breakdown of food by chewing,
crushing in the mouth and grinding in the
stomach. This is done primarily to increase
surface area for exposure to digestive
chemicals.
2) Chemical digestion: which is the
breakdown of food by chemical substances
such as bile, acids, and enzymes. This
process starts in the mouth (saliva contains
amylase), continues in the stomach
(secretes acid and enzymes) and is
completed in the small intestine.
ENZYMES
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Are proteins
Are catalysts (chemicals that speed up the rate of
a reaction without being consumed themselves)
Function best at a specific pH and temperature
Are highly specific for their substrate
Eg. Maltase catalyzes the hydrolysis of maltose
into 2 glucose, but NOT the breakdown of
Lactose, which would be catalyzed by lactase
Optimal Temperature & pH
ENZYME ANIMATION
http://highered.mcgrawhill.com/sites/0072495855/student_vie
w0/chapter2/animation__how_enzyme
s_work.html
OPEN TUBE
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Two openings: one mouth & one anus
Human Digestive System
Organs of Digestive System
Animation

http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter26/animation__organs_of_digestio
n.html
DIGESTIVE TRACT
MOUTH
A. Teeth - physical break down of
food
B. Saliva secreted by 3 pairs of
salivary glands
Contains the enzyme amylase,
which begins chemical
digestion of starch
C. Tongue helps mix food and
saliva, moistens (lubricates)
food and forming it into a ball
(bolus) so it can be easily
swallowed.
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A.
B.
Esophagus
(passage way)
Entire length is lined with
muscles that contract in a wave
like action called peristalsis.
Peristalsis helps push food down
towards your stomach. This is
why you can even swallow food
while hanging upside down!!!
Many small glands are located in
the back of the -throat and in the
walls of the esophagus. These
produce mucin, a lubricant that
eases the travel of food to the
stomach.
C. A valve or sphincter,
called the cardiac
sphincter is located at
the end of the
esophagus. It
ensures that food that
has entered the
stomach can not
move back into the
esophagus (if it does
it is- called reflux or
heart burn)
Stomach
(storage and digestion of proteins)
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J-shaped storage and digestive organ.
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Entrance to the stomach is through the cardiac
sphincter, exit through the pyloric sphincter
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Consists of three (3) layers of muscle churning aids physical breakdown. Churns
food into "chyme"
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Acid environment (pH 2) due to hydrochloric
acid (HCI). This kills bacteria and activates
enzymes. Eg pepsinogen -> becomes pepsin
(digests proteins)
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Small intestine
most chemical digestion occurs
here therefore most enzyme
activity occurs here
Purpose is to complete chemical
digestion (pH 8) and to absorb
nutrients into blood (amino acids
& monosaccharides) or lymph
(fatty acids & glycerol).
it is approximately 6-7 metres
long composed of three
sections: duodenum, jejunum,
ileum
Unabsorbed material exits via
the ileo-cecal valve which opens
into the large intestine
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The entire surface is covered with finger like projections
called villi which in turn are covered with smaller
projections called microvilli – increase surface area for
absorption
Amino acids & monosaccharides are absorbed into the
capillaries, but fatty acids and glycerol are absorbed into
the lacteal, part of the lymphatic system, eventually they
too enter the circulatory system
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Large intestine
Purpose is to re-absorb water
and to remove indigestible
waste e.g. fibre
7 litres of water/day are
reabsorbed
Waste/feces becomes more
solid as it is moved along due
to peristalsis
If peristalsis occurs too quickly,
water cannot be reabsorbed
into the body and remains in
the feces causing diarrhea.
If peristalsis occurs too slowly,
too much water may be
removed resulting in
constipation.
Colon is home to many
beneficial bacteria like E. coli,
which allow us to absorb
certain vitamins
Accessory Organs
STOMACH
3 Accessory organs aid chemical
digestion in the small intestine
1) Pancreas
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Many enzymes are made here which enter the
small intestine through the common bile duct.
These include lipases, proteases (trypsin,
chymotrypsin, carboxypeptidase),
carbohydrases (maltase, lactase) and lipases.
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It secretes bicarbonate, a base which
neutralizes the stomach acid.
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It also produces insulin and glucagon which
are hormones (NOT DIGESTIVE ENZYMES),
that travel through the blood and aid in
managing blood-sugar levels.
2) Liver
 The liver produces bile salts, a soapy
emulsifier that breaks large globules of
fat into smaller ones, thereby increasing
surface area for lipase enzymes to act.
3) Gall bladder
 Attached to the liver, it stores bile until
signaled to release it into the bile duct. It
then travels through the common bile
duct together with pancreatic juices into
the small intestine.
HOMEWORK
 Read pages 56 to 58
 See powerpoint on wiki
 Complete the Handout (see table 2.1 on
page 65)
 Answer page 63 #1 - 5, 8 - 13
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