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FOOD & DIGESTION
DIGESTION
Functions of Digestive System
• Breaks down food into molecules
• Molecules are absorbed into
blood and carried throughout the
body
• Wastes are eliminated from the
body
Parts of the digestive system
Parts of the digestive system
 Two main parts:
 Alimentary canal – continuous
coiled hollow tube
 Accessory digestive organs
Organs of the alimentary canal
 Mouth
 Pharynx
 Esophagus
 Stomach
 Small intestine
 Large intestine
 Anus
Processes of the Mouth
 Mastication (chewing) of food
 Mixing masticated food with saliva
 Initiation of swallowing by the tongue
 Allowing for the sense of taste
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 14.7
Saliva
• Saliva helps break down starch into simple
sugars.
• moistens the food allowing easier passage
through the gastrointestinal tract.
• Secreted from glands - under the tongue
and at the back of the mouth.
• The sight, smell, taste or even the thought
of food - increase the amount of saliva
secreted.
Pharynx Function
 Serves as a passageway for air and
food
 Food movement is by alternating
contractions of the muscle layers
(peristalsis)
 Epiglottis shuts the air passage while
swallowing.
Esophagus
 Runs from pharynx to stomach through
the diaphragm
 Conducts food by peristalsis
(slow rhythmic squeezing)
 Passageway for food only (respiratory
system branches off after the pharynx)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Stomach Functions
 Acts as a storage tank for food
 Site of food breakdown
 Chemical breakdown of protein begins
 Delivers chyme (processed food) to the
small intestine
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Small Intestine
 The body’s major digestive organ
 Site of nutrient absorption into the blood
 Duodenum
 Attached to the stomach
 Curves around the head of the pancreas
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Large Intestine
 Larger in diameter, but shorter than the
small intestine
 Frames the internal abdomen
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Functions of the Large Intestine
 Absorption of water
 Eliminates indigestible food from the
body as feces
 Does not participate in digestion of food
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Structures of the Large Intestine
 Colon
 Rectum
 Anus – external
Body opening
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Task- 2.6
• Draw and label the parts of the human
digestive system.
Digestion
• Process by which the
body breaks down food
into small nutrient
molecules
Two Kinds of
Digestion
• Mechanical
And
Chemical
Mechanical Digestion
• Foods are physically broken
down into smaller pieces.
• Begins when you take your
first bite of food
• Your teeth are the first stage
in mechanical digestion
Chemical Digestion
• Chemicals produced by the body
break foods into smaller chemical
building blocks.
• Begins in the mouth
• Accomplished by enzymes
What are enzymes?
• Catalysts that speed up a reaction by
“short cut route” so that the reaction
happens fast !!
• Enzymes – protein that speeds up
chemical reactions in the body.
• Enzymes are highly substrate
specific.
• Names end with an ‘–ase’
Our food is made up of:
• Carbohydrates: Bread, Pasta, Potato
• Protein: Meat, Nuts, Lentils
• Fats: Butter, Milk
Our body needs to digest them – turn
them into a form that can be
absorbed into the blood and used by
cells. Enzymes make this possible.
Look closely at the 3 digestion
equations:
Enzymes that work on carbohydrates:
Amylase + Starch
Enzyme (in pasta, bread )
(in saliva)
Maltose
(a form of sugar that is
absorbed by the body )
Enzymes that work on Proteins:
Protease + Proteins
Enzyme
(eg. In meat, nuts)
Amino Acids
(the body can absorb
them in the stomach)
Enzymes that work on Fats:
Lipase enzyme +
(secreted by pancreas)
Fats
Fatty Acids + Glycerol
(Butter)
(can be absorbed into body)
http://www.youtube.com/watch?v=qDEVBMldiY8&feature=related
Enzyme action animation
Task-2.7
• Complete the table:
Sl.No:
Name of the
enzyme
Carbohydrase
Amylase
Protease
Lipase
Peptidase
Sucrase
Pepsin
Maltase
lactase
Substrate
Reaction it aids/ function Found in
What is digestion?
Digestion is the breakdown of
large insoluble molecules into
smaller soluble molecules which can
pass through the wall of the gut
into the blood.
How does it start?
•
First you chew something with your teeth.
Which makes it have a larger surface
area
•
Enzyme in your saliva called amylase
starts breaking the carbohydrate into
sugar. The food is then pushed down the
oesophagus to the stomach by
PERISTALSIS.
What’s that???
Peristalsis is the contraction
and relaxation of the circular
muscles in the wall of the gut.
When the muscle relaxes
the food drops down and
when it contracts at the
top the food at the
bottom is pushed down
The food is then in the stomach,
the food is churned around by
More waves of peristalsis to make
it into mush, and it mixes
with gastric juice.
IN THE STOMACH
Gastric juice contains and enzyme called Protease
which breaks down, yup you guessed it, protein,
into amino acids.
It also contains hydrochloric acid which kill
bacteria and makes the optimum PH for this
enzyme, meaning it will work at its best at a lower
PH. The food is then released a little bit at a time
into the duodenum, which is the first part of the
small intestine.
IN THE INTESTINE
The duodenum DOES NOT produce any digestive
juices, but has 2 poured into it!
*Did you know the small intestine is 6m long?*
One of the juices comes from the pancreas.
PANCREATIC JUICE, It contains carbohydrase,
protease and lipase.
What does each one do?
The other digestive juice is call BILE. Which is
made by the liver and stored in a bag called the gall
bladder. It is NOT AN ENZYME, but it neutralises
the acid that was added in the stomach. This helps
the small intestine work more effectively.
Bile also helps emulsify the fats.
What’s emulsify mean?
It means to make the fats into smaller
blobs to make their surface area
larger. So that the lipase can digest
quicker.
The food is now a semi-liquid like a
smoothie! And it passes into the second
part of the small intestine called the
ileum.
The walls of the ileum make a digestive
juice which contains
carbohydrase, protease and lipase.
These enzymes complete the digestion of
• fats to fatty acids and glycerol
• Complex sugars to simple sugars
• protein to amino acids
The ileum is specially adapted for
absorption, passing digested food into
the blood. It is very long to allow time
for digestion. It has a very large surface
area due to the presence of villi (finger
like projections) and microvilli.
This allows rapid diffusion of the products
of digestion. Since villi walls are only one cell
thick, this helps speed up the diffusion.
Each Villus has a blood vessel and a lymph
vessel to carry the food away.
All the food which cannot be digested
ends up in the large intestine. It enters
into the colon where most of the water is
reabsorbed into the blood. The
indigestible remains form a semi solid
faeces which is stored in the rectum.
Eventually it is passed out the anus.
Absorption
• Occurs after food has
been digested.
• Process by which nutrient
molecules pass through
the wall of the digestive
system into the blood
Summary of the phases of digestion
Ingestion - this is the physical intake of
foodstuff into the gastrointestinal tract.
Digestion - a series of physical and chemical
processes which begin in the mouth, but take
place mainly in the stomach and small intestine.
Absorption - the passage of the digested food
substances across the gastro-intestinal lining, or
mucosa, into the blood and lymph.
Elimination - the excretion, or elimination, of
those food substances that cannot be digested
(such as cellulose) or without any nutritional value
in the faeces.
Some interesting facts on digestive
system
•People do not have conscious control over
the muscles in the oesophagus. Even if
someone is upside down, the food will be
passed on to the stomach.
•The stomach is an expandable sack made up
of three different layers of muscles where
the bolus will be churned for a few minutes
or up to 2 or 3 hours.
• The duodenum is about 25
centimetres long and in the shape of a
horse shoe.
• Fat can take from 3 to 5 hours to be
broken down and absorbed.
• Dietary fibre aids peristalsis because
it increases the bulk of the bolus or
chyme being moved along.
• The villi have a surface area of about
30m2, this is equivalent to the size of
a tennis court!
Task-2.8
• Describe step wise the digestion of a
chicken sandwich, tracing its journey
through the various organs .