Download Digestion[1]

Energy from food:
The 7 food groups represent
large chemicals.
fats
proteins
minerals
vitamins
water
fibre
carbohydrates
These chemicals are often chains of smaller, more useful
chemicals, joined together.
Energy molecules in food
One example is carbohydrates.
Carbohydrates are made of long chains of identical
small sugar molecules.
sugar molecule
carbohydrate
Small sugar molecules
The small sugar molecules are very useful.
The body has to break these large food molecules up
into single or small chain sugar molecules. These are
used to make…
ENERGY
How can we release energy from food?
Problem One - releasing smaller sugars
Physical means like slicing and cleaving food does not
break down the long chain molecules and release the
sugars.
This is because we can’t release sugars from carbohydrates
by physically breaking them up.
Chemical breakdown
The chain of sugars is held together by…
chemical bonds
Chemical bonds require a chemical technique if they
are to be broken.
Problem with food size
Problem 2
- The food we start with is often large in size.
Being large, the food tends to be unable to dissolve.
We say it is large and insoluble.
Food solubility
The food needs to be soluble so that it can dissolve in
the blood and thus, be transported around the body.
The smaller the food, the more likely they will dissolve.
So the digestive system has to cope with both these
problems.
Soluble product
Digestion
Blood vessel
The digestive system:
The digestive system, being an organ system, is
made of a group of organs all working together.
Each organ has a particular function and only by
working together will they get the job done.
External digestive system
The only visible parts of the digestive system are the
entry and exit points.
Mouth
Anus
The sound of a rumbling stomach and the fact that
food looks very different when it leaves, compared to
when it enters mean that the body must be doing
something to the food during its journey.
What happens to the food in our bodies?
What happens to the food in our body?
It is digested.
This means it is broken down.
This digestion happens in 2 ways.
As we know all food has a physical shape and is
made of chemicals. These chemicals are held
together by chemical bonds.
Chemical and physical digestion
Our digestive system uses both:
chemical digestion
physical digestion
As we move through the digestive system, we will see one or
both of these methods in action at any one time.
physical
The shape of the food must be
physically changed so that it can
fit through the small diameter of
the digestive system.
chemical
This allows useful chemicals
to be released and dissolve
in the blood. To be broken
down chemically, the bonds
must be broken.
The digestive tract
All food enters our digestive system through the
mouth and waste material leaves through the anus.
The digestive system is really
one long tube with an opening
at each end.
mouth
Stretched out it is a 9m tube!
anus
Our guts
But how does a 9m tube fit into a space,
which is less than a metre long?
It is extremely folded!
In addition, the tube passes through organs on its
route from the mouth to the anus.
Digestive system diagram
Physical digestion
The mouth is where digestion begins. Here we find both
chemical and physical methods of digestion.
We will consider physical digestion first.
If you look in the mirror and smile, you immediately notice
your teeth.
You will also realise that your teeth are different shapes.
You have 4 basic types of teeth; each type is designed
for a different role.
Action in the mouth
Together, these teeth can break up most foods that
we put into our mouths. The mechanical act of
chewing food is part of physical digestion.
Once the teeth have digested the food, it may be small
enough to be swallowed. However, some food can be
sharp and it would be uncomfortable to swallow. The
food also needs chemically breaking down.
Therefore, the mouth produces a substance that solves
both of these problems at the same time.
Saliva
These glands (a special type of tissue)
produce saliva, a sticky liquid.
As mentioned, the saliva has two jobs.
Being a liquid, it softens the food and allows the digested
food to be rolled into a ball just before it is swallowed.
It also contains a chemical known as an enzyme.
Enzyme properties:
What is an enzyme?
Enzymes are chemicals, which act to speed up chemical
reactions. They are produced from glandular tissue,
which is found all over the body.
In order to understand how an enzyme works, you have
to think of it as having a particular shape.
Somewhere on the surface of the enzyme is an
important region known as the active site.
What’s so special about enzymes?
We will use the shape below to represent on particular enzyme.
Active site
enzyme
In order for an enzyme to be able to speed up or
catalyse a reaction, it must attach to the
chemicals that are reacting. It does so using its
active site.
Specificity of enzymes
+
The red areas on these
two reacting chemicals
represents the areas
where the active site of
the enzyme will attach.
The enzyme will attach to
both at the same time.
Enzymes are very specific.
Enzymes can only speed up certain reactions.
If the shape of the reacting chemicals does not match the
shape of the active site, the enzyme will not be able to
work.
The environment matters
Therefore, enzymes are specific to certain reactions.
Enzymes are also very particular about the environment
that they work in.
To understand this, think of how you do homework.
You probably have a certain place to
work, or you work at a certain time,
you may like listening to music whilst
you work or else you can only work if it
is completely silent.
Enzymes and pH
Different enzymes work best in different conditions.
If the condition is wrong, their active site can change
shape. Say one particular enzyme works best in acidic
conditions (pH less than 7). If the pH rises and the
conditions become alkaline, the enzyme changes shape
and stops working. It can no longer fit with the reacting
particles of the chemical reaction.
pH< 7
pH 10
Food groups and enzymes
The bulk of the food that enters the digestive system is
from the three main food groups:
proteins
carbohydrates
fats
Therefore, it is not surprising that the digestive system
has enzyme-producing glands that relate to these
three types of food.
Remember that the shape of the chemicals within the
different food groups will be different. Therefore the
shape of the enzymes that digest these chemicals will
also be different.
Digestive enzymes:
Carbohydrates are chains of identical sugar molecules.
The enzyme that digests carbohydrates must be able to
break the chemical bonds between the individual sugar
molecules.
sites of enzyme attack
sugar
The product of the chemical breakdown of carbohydrates
is sugar. The sugar is known as glucose.
Enzymes that digests carbohydrates are known as
amylases.
Enzyme driven reaction
The digestion of carbohydrates can be represented
by the following equation.
Carbohydrates
amylase
amylase
Sugars
Proteins and amino acids
As with carbohydrates, proteins are made of chains of
chemicals. However, instead of the chain containing
identical molecules, in protein these molecules are
different.
Protein is made up of chains of amino acids. There
are over 20 different kinds of amino acid.
sites of enzyme attack
amino acids
Imagine a bead necklace made up of over 20
different kinds of bead.
Enzymes for digesting proteins
The enzymes that digest proteins must
be able to break the chemical bonds
between the different amino acids.
Enzymes that digest protein are known
as proteases.
amino
acids
The digestion of proteins can be represented by the
following equation.
protease
Protein
Amino Acids
sites of
enzyme
attack
Fat in our food
Fats are made up of a molecule of glycerol phosphate
attached to three fatty acid molecules.
The enzymes that digest fats must be able to break the
chemical bonds between the glycerol phosphates and the
fatty acids.
Fats are also known as lipids.
fatty
acids
site of
enzyme
attack
glycerol
phosphate
Enzymes for digesting fat
The enzymes that digest fats must be able to break
the chemical bonds between the glycerol phosphates
and the fatty acids.
Fats are also known as lipids.
Enzymes that digest fat (lipid) are known as lipases.
Fat digestion can be represented by the following equation:
lipase
Fat
Fatty Acids + Glycerol Phosphate
Carbohydrase in saliva
Of these three enzymes, the only one that is released
within the mouth is amylase. This is partly because the
conditions within the mouth are suitable for amylase
action.
It works best within an alkaline (pH > 7) environment.
The amylase in saliva in combination with other digestive
amylases added later from the pancreas and the small
intestine complete carbohydrate digestion.
Digestive action of the mouth - summary
Carbohydrates
Fats
Proteins
physical
digestion
chemical
digestion
The food could now
pass down either the
trachea (windpipe) or
the gullet/oesophagus.
chemically and
physically digested
physically
digested
sugars
How it gets down to the stomach
Epiglottis
The flap is known as the epiglottis.
If ever food accidentally got into the trachea, we would
choke and try to cough it back out.
How do we swallow?
Once the ball of food has passed through the top of the
gullet, it is forced downwards by waves of muscular
contraction.
Keeping it down
The swallowing process finishes with a muscle known
as a sphincter relaxing and the food passes into the
stomach.
The sphincter muscle found at the entry
and exits points of the stomach acts
rather like a drawstring on a bag.
It allows the stomach to shut off both
entry and exit points and hold food
inside it.
The basics on the stomach
The stomach is basically a muscular bag, filled with
hydrochloric acid (HCl).
cross section of stomach
food enters from
the oesophagus
muscle tissue
glandular tissue makes:
hydrochloric acid, mucus
and protease enzyme
digested food leaves
liquids mix with the food
Gastric processes:
When the food enters the stomach.
The sphincter contracts behind it.
The food is then subjected to
a coordinated attack.
Firstly the
the hydrochloric acid
…attacks any microbes (bacteria) that may have been
swallowed accidentally when the food was eaten.
Microbes
Food bolus
HCl
Protein digestion
Secondly, the hydrochloric acid provides the perfect
conditions for protease enzyme.
These enzymes begin digesting the proteins in the
swallowed food.
These proteins are broken down to release the amino
acids.
protein
protease
Protease enzymes work best under acidic conditions
(pH < 7).
amino
acids
Mucus and muscles
Thirdly, the muscular tissue of the stomach has the
ability to contract and relax and in doing so, physically
grinds the food inside it.
Mucus is produced to protect the lining of the stomach
from the acid. If the mucus were not present, the
hydrochloric acid would actually digest the tissue that
had made it!
Making gastric juice
presence
of HCl
wall of
stomach is
protected
muscle and
glandular
tissue
layer of
mucus
The hydrochloric acid, mucus, food and enzyme
solution is given the name - gastric juice.
The stomach’s digestive action - summary
sugar
protein fat
carbohydrate
physical
digestion
chemical
digestion
muscular tissue
of stomach
protease enzyme and
hydrochloric acid
sugars
carbohydrates
fats
amino
acids
proteins
and after the stomach…
By this stage many large insoluble molecules are slowly
being digested to produce the small soluble molecules that
can easily be absorbed into the blood system.
Small soluble molecules
Glucose
Amino Acids
Glycerol phosphate
It is also clear that the fat has yet to be chemically digested.
This happens in the next section of the digestive system.
The small intestine:
The name of this organ is deceiving. Although it is called
small, it can stretch up to 6 metres in length. In order to fit
into the body, it is heavily folded.
When the gastric juices leave
the stomach, they pass into
the small intestine.
X-ray of the small intestine
Dealing with the acid
A nasty problem!
The gastric juices are very acidic. There could be a
danger of the lining of the small intestine being digested.
Luckily two substances are produced to stop this
happening. The first is mucus and we have seen how
this works. The second is bile.
Bile is made in the liver. It is a yellow/green liquid that
is naturally alkaline (pH > 7).
Why neutralise?
This means that when bile and the gastric juices meet,
the result is neutralisation of the acid.
pH >7
+
pH <7
Neutralisation
This is essential for lipase (the enzyme that
digests fat) to function properly.
The active site of the lipase enzymes is only
effective in conditions above pH 7.
How is the fat digested?
Let’s consider the process of fat digestion.
This section of the digestive system exemplifies the true
idea of an organ system as a group of organs working
together for a common function.
The influential organs in the digestion of fat are the:
gall bladder
liver
small intestine
pancreas
Each organ plays its part in turning fat into fatty acids
and glycerol phosphates.
A whole lot of bile
liver produces bile
fat within the
gastric juice
bile is released from the gall
bladder and passes down
through the bile duct
The bile and the fat meet within the small intestine.
The bile emulsifies the fat. This basically means the fat
is physically broken into smaller pieces.
emulsification by bile
Notice that the fat has not been chemically digested,
only physically. The result is a greater surface area
over which the enzyme, lipase, can attack the fat.
Influx of enzymes
The pancreas and the small intestine now release
enzymes.
Both organs produce all three enzyme types:
pancreas
amylases
proteases
lipases
small intestine
Lipid digestion:
If we just consider fat, the lipase begins to break its
chemical bonds:
lipase
glycerol
phosphate
fat
fatty
acids
Digestion in small intestine - summary
sugar
carbohydrates
fat
amino acids
protein
physical digestion
chemical digestion
bile emulsifies the fat
muscular action of the
small intestine
lipase enzyme
protease enzyme
carbohydrase enzyme
sugar
amino acids
fatty acids
glycerol
phosphate
Digestive processes - summary
The three processes of chemical digestion can be
summarized as follows.
Large insoluble
food
Enzyme
Small soluble food
Carbohydrates
amylase
sugars
Proteins
protease
amino acids
Fats
lipase
glycerol phosphates
and fatty acids
Design of the small intestine
There is a further advantage for the small intestine in
being a narrow tube.
With the enzymes being produced in the lining of the
tube, it is essential that the food be forced to mix with
them to ensure that there is efficient digestion before the
food passes through the organ.
If the tube is tight, the food is forced against the sides of
the tube and thus, mixes directly with the enzymes.
enzymes come into contact with food.
What about the waste?
Now that the large insoluble molecules have been
digested down into the small soluble molecules, the body
must separate them from the waste food that has not
been digested.
No food is 100% useful and so there will
always be some waste that needs excreting.
In order to understand how the body carries out this
selection procedure, we need to take a closer look at
the lining of the small intestine.
Inside the small intestine
At first glance, the small intestine appears to
have a flat surface.
However, if we consider what it has to do, we will
understand why this idea cannot be correct.
Absorption:
The small intestine is the site of absorption of useful
molecules of digested food.
These molecules must pass across the lining of the small
intestine and enter the blood stream.
Their destinations are the cells of the body.
Our body cells constantly need these chemicals and
therefore the absorption process must be very efficient
to keep up with the high demand.
Surface area and absorption
If absorption were to occur across a flat lining, then not
enough molecules would pass across the lining in the
desired time.
The only way to improve this situation would be to create
a larger surface area over which absorption could occur.
That is exactly what is present in the small intestine.
Its lining is in fact a highly folded lining, which creates an
enormous surface area in a small space.
Have a look inside a human’s intestines
The small intestine
Maximising the surface area
The result of this folding means that the surface area
of the lining of the small intestine is enormous!
Direction of Food
Epithelium
of small
intestine
This increases the number of places where small
soluble food molecules can pass across and move
into the blood.
Digestive products in the blood
Remember that the small intestine lining is made up of thousands
of villi.
A
Here is a summary of the process of absorption.
B
S
sugars
O
R
amino acids
P
fatty acids
and glycerol
phosphates
T
I
O
Any indigestible food will leave the small
intestine without having been absorbed.
N
B
L
O
O
D
The large intestine
Let us now move on to the next organ in the system, the
large intestine or colon.
As the food enters this organ, all that is left is waste
material and water. The body will want to leave the waste
material within the digestive system but the water is
valuable.
Water regulation
This water will need to be retained by the body in order to
prevent dehydration.
Remember that all the liquids you drink provide the largest
source of water for the body.
The blood reabsorbs the excess water that is mixed with
the waste food.
Again, if something is going to be absorbed, it
must have somewhere to go.
Getting back excess water
The blood reabsorbs the excess water that is mixed with
the waste food.
LARGE
INTESTINE
B
L
O
O
D
Expelling the waste
Waste material then passes
into a storage organ called
the rectum.
This waste material mainly
consists of indigestible food.
It makes up the bulk of the
faeces (solid excrement) that
will be excreted.
rectum
In order for the waste material to be removed, another
sphincter muscle must relax. This opens the anus and
the faeces can pass out of the system.
Important body tissues in digestion
We have now finished our journey through the digestive
system. We have seen the chemical and physical
digestion of large & insoluble into small & soluble food.
It is important to remember that the digestive system
relies heavily on the presence of two important types of
body tissue.
1. Glandular tissue
This is responsible for the
production of the digestive
enzymes.
2. Muscular tissue
Through constant contraction
and relaxation, the food is kept
moving through the system,
from the mouth to the anus.
Chew it over
Chew it all over
Find the best words to fill the gaps
“Digestion involves __________
types of process. These are
two
firstly ____________
mechanical digestion and secondly _________
chemical
digestion. Chemical digestion is __________
out by
carried
enzymes
___________
which are chemical produced from
___________
tissue. Specific enzymes break down
glandular
specific
__________
types of food. For example carbohydrase
____________
enzyme breaks down ___________
carbohydrates . Mechanical digestion
involves teeth and the tongue but mostly _________
muscle
contraction e.g. the squeezing of the muscular lining of the
________.”
stomach
enzymes
muscle
carbohydrates
chemical
mechanical
glandular
specific
two
carried
stomach
carbohydrase
Digestion equations
Use the words below to create 3 equations to show what
happens when we digest:
1. Carbohydrates
2. Fats
fats
carbohydrates
double sugar
3. Protein.
lipase
single sugar
3 fatty acids
glycerol phosphate
maltose
amino acids
glucose
protein
protease
carbohydrase
True or false?
Do you know your guts?
Down the hatch! Part 1
Questions
*
*
What type of acid is found in the stomach? (12)
The ___________ (10) links the stomach to the
pharynx.
The __________ (7) juices are found within the
stomach.
What happens to the water in the large intestine?
(10)
Where does the process of digestion actually begin?
(5)
This organ stores waste material before it is
discharged from the body? (6)
The _________ (6) moves the food around in the
mouth, preparing it for its journey.
Down the hatch! Part 2
*
*
*
*
___________ (5) transports the dissolved nutrients
around the body.
The first section of the digestive system is known as
the l________. (5)
The chemicals that help to break down food are
collectively called __________. (7)
We eat or ________ food. (6)
This is the name for the soft fleshy part of the throat
that stops food going down the trachea.
E___________. (10)
At the rear of the mouth, this region receives the
bolus of food from the tongue. (7)
The main part of the small intestine is known as the
D____________. (8)
Down the hatch! Part 3
*
*
*
These provide the mechanical breakdown of food in
the mouth? (5)
This organ can be SMALL or LARGE? (9)
The collective name for the useful chemicals that are
absorbed across the lining of the small intestine? (9)
The product of the previous question? (5)
The name for the muscular bag that contains acid?
(7)
Food is __________ (7) down in the digestive
system using both chemical and mechanical
methods.
Down the hatch! Final Part
You will notice that 9 of the questions have a small green
asterisk beside them.
Take the first letter of each of the answers to these
questions. Put these letters in the box below.
Now rearrange them to
find the mystery word!
20 questions
Digestion wordsearch
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