Transcript Digestion - Part Two

Topic 9.7
Digestion - Part Two
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Contents
Digestion – Part Two
Mouth to gullet
Gastric processes
The small intestine
Lipid digestion
Absorption
Summary
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Digestive action of the mouth – reminder
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
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Mouth to the gullet:
The semi-digested food has been formed into a ball by
the tongue and is now swallowed.
The ball firstly moves to the pharynx, the region at the
back of the mouth where there is a junction between
two pipes.
It needs to pass down through the gullet. To ensure
that it does not fall into the trachea and thus block our
breathing, a small flap moves to cover the tube.
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Protecting the windpipe
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How it gets down the gullet
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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.
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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.
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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 gullet
muscle tissue
glandular tissue makes:
hydrochloric acid, mucus
and protease enzyme
digested food leaves
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liquids mix with the food
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Contents
Digestion – Part Two
Mouth to gullet
Gastric processes
The small intestine
Lipid digestion
Absorption
Summary
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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
HCl
Food bolus
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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
amino
acids
protease
Protease enzymes work best under acidic conditions
(pH < 7).
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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!
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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.
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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
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fats
amino
acids
proteins
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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.
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Contents
Digestion – Part Two
Mouth to gullet
Gastric processes
The small intestine
Lipid digestion
Absorption
Summary
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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
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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).
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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.
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Parts of the small intestine
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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.
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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.
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Influx of enzymes
The pancreas and the small intestine now release
enzymes.
Both organs produce all three enzyme types:
pancreas
carbohydrases
proteases
lipases
small intestine
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Contents
Digestion – Part Two
Mouth to gullet
Gastric processes
The small intestine
Lipid digestion
Absorption
Summary
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Lipid digestion:
If we just consider fat, the lipase begins to break its
chemical bonds:
lipase
glycerol
phosphate
fat
fatty
acids
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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
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fatty acids
glycerol
phosphate
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Digestive processes - summary
The three processes of chemical digestion can be
summarized as follows.
Large insoluble
food
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Enzyme
Small soluble food
Carbohydrates
carbohydrase
sugars
Proteins
protease
amino acids
Fats
lipase
glycerol phosphates
and fatty acids
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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.
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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.
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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.
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Contents
Digestion – Part Two
Mouth to gullet
Gastric processes
The small intestine
Lipid digestion
Absorption
Summary
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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.
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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.
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Have a look inside a human’s intestines
The small intestine
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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.
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Where is the blood?
The blood is found in minute small vessels known as
capillaries. The capillaries are found protruding into the villi.
The blood approaches the villus, picks up the absorbed food
molecules and then leaves.
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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
B
L
O
O
D
I
O
Any indigestible food will leave the small
intestine without having been absorbed.
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N
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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.
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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.
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Getting back excess water
The blood reabsorbs the excess water that is mixed with
the waste food.
LARGE
INTESTINE
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B
L
O
O
D
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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.
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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.
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Chew it over
Chew it all over
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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
chemical
mechanical
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carbohydrates
glandular
specific
two
carried
stomach
carbohydrase
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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
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3. Protein.
lipase
single sugar
3 fatty acids
glycerol phosphate
maltose
amino acids
glucose
protein
protease
carbohydrase
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True or false?
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Do you know your guts?
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Down the hatch! Part 1
Questions
*
*
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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.
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Down the hatch! Part 2
*
*
*
*
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___________ (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)
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Down the hatch! Part 3
*
*
*
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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.
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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!
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Contents
Digestion – Part Two
Mouth to gullet
Gastric processes
The small intestine
Lipid digestion
Absorption
Summary
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20 questions
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Digestion wordsearch
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