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RESPIRATION SYSTEM
IN HUMAN
GASEOUS EXCHANGE – RESPIRATORY SYSTEM
HUMAN RESPIRATION SYSTEM
A. Respiration organs.
B. Breathing mechanism.
C. Internal respiration.
GASEOUS EXCHANGE IN HUMAN
A. Respiration organs.
B. Breathing mechanism.
C. Internal respiration.
GASEOUS EXCHANGE OCCURS IN THE RESPIRATORY SYSTEM
The most important are the two lungs. Each lung is filled
with many tiny air spaces called air sacs or alveoli. It is here
that the oxygen diffuses into the blood. Because they are so
full of spaces, lungs feel very light and spongy to touch. The
lungs are supplied with air through the windpipe or trachea.
AIR IS TAKEN DOWN INTO THE LUNGS
1. The NOSE and MOUTH
Air can enter the body through either the nose or mouth. The nose
and the mouth are separated by the palate, so you can breathe
through your nose even when you are eating.
Is is better to breathe through your nose, because the structure of the
nose allows the air to become warm, moist, and filtered before it gets
to the lungs. Inside the nose are some thin bones called turbinal
bones which are covered with a thin layer of cells. Some of these cells
make a liquid containing water and mucus which evaporates into the
air in the nose and moistens it.
Other cells have very tiny hair-like projections called cilia. The cilia
are always moving, and bacteria or particles of dust get trapped in
them and in the mucus. Cilia are found all along the trachea and
bronchi, too. They waft the mucus, containing bacteria & dust, up to
the back of the throat, so that it doesn’t not block up the lungs.
2. The TRACHEA
The air then passes into the windpipe or trachea. At the top of the
trachea, is a piece of cartilage called epiglottis. This closes the
trachea and stops food going down the trachea when you swallow.
This is a reflex action, which happens automatically when a bolus
of food touches the soft palate.
The air then passes into the windpipe or trachea. At the top of the
trachea, is a piece of cartilage called epiglottis. This closes the
trachea and stops food going down the trachea when you swallow.
This is a reflex action, which happens automatically when a bolus
of food touches the soft palate.
Just below the epiglottis is the voice box or larynx. This contains
the vocal cords. The vocal cords can be tightened by muscles so
that they make sounds when air passes over them. The trachea
has rings of cartilage around it, which keep it open.
3. The BRONCHI
The trachea goes down through the neck and into the thorax. The
thorax is the upper part of your body from the neck down to the
bottom of the ribs and diaphragm. In the thorax, the trachea
divides into two. The two branches are called the right and the left
bronchi. One bronchus goes to each lung and then branches out
into many smaller tubes called bronchioles.
4. The ALVEOLI
At the end of each
bronchiole are tiny air
sacs or alveoli. This is
where gaseous
exchange takes place.
ALVEOLAR WALLS FROM THE RESPIRATORY SURFACE
The walls of the alveoli are respiratory surface. Tiny blood vessels,
called capillaries, are closely wrapped around the outside of the
alveoli. Oxygen diffuses across the walls of the alveoli into the blood.
Carbon dioxide diffuses the other way.
The walls of the alveoli have several features which make them an
efficient gaseous exchange surface.
They are very Thin
Alveolar walls are only one cell thick. The
capillary walls also only one cell thick. An
oxygen molecule only has to diffuse across
this small thickness to get into the blood.
They have an excellent transport system
Blood is constantly pumped to the lung along the pulmonary artery.
This branches into thousands of capillaries, which take blood to all
parts of the lungs. Carbon dioxide in the blood can diffuse out into
the air spaces in the alveoli, and oxygen can diffuse into the blood.
The blood is then taken back to the heart in the pulmonary vein,
ready to be pumped to the rest of the body.
They have a large surface area
They have a good supply of O2
In fact, the surface area is
enormous! The total
surface area of all the
alveoli in your lungs is over
100 m2.
Your breathing movements
keep your lung well
supplied with Oxygen.
THE RIBS & DIAPHRAGM MOVE DURING BREATHING
To make air move in and out of the lungs, you must keep changing
the volume of your thorax. First, you make it large so that air is
sucked in. then, you make it smaller again so that air is squeezed
out. This is called breathing or ventilation.
There are 2 sets of muscles which help you to breathe. One set is
in between the ribs. This set is called intercostal muscles made up
of the external and internal intercostal muscles. The other set is in
the diaphragm. The diaphragm is a large sheet of muscle and
elastic tissue which stretches across your body, underneath the
lung and hearth.
BREATHING IN IS CALLED INSPIRATION
When breathing in, the muscles of the diaphragm contract. This
pulls the diaphragm downwards, which increases the volume in the
thorax. At the same time, the external intercostal muscles contact.
This pulls the ribs cage upwards and outwards. Together, these
movements increase the volume of the thorax.
As the volume of the thorax increases, the pressure inside it falls
below atmospheric pressure. Extra space has been made and
something must come in to fill it up. Air therefore rushes in along
the trachea and bronchi into the lungs.
BREATHING OUT IS CALLED EXPIRATION
When breathing out, the muscles of the diaphragm relax. The
diaphragm springs back up onto its domed space because it is
made of elastic tissue. This decreases the volume in the thorax.
The external intercostal muscles also relax. The rib cage drops
down again into its normal position. This also decreases the
volume of the thorax.
As the volume of the thorax decreases, the pressure inside it
increases. Air is squeezed out through the trachea into the nose
and mouth, and on out of the body.
INTERNAL INTERCOSTAL MUSCLES CAN FORCE AIR OUT
Usually, you breathe out by relaxing the external intercostal
muscles and the muscles of the diaphragm. Sometimes, you
breathe out more forcefully – when coughing, for example. Then
the internal intercostal muscles contract strongly, making the rib
cage drop down even further. The muscles of the abdomen walls
also contract, helping to squeeze extra air out of the thorax.
EXERCISE CAN CREATE AN OXYGEN DEBT
All the cells in your body need oxygen for respiration
and all of this oxygen is supplied by the lungs. The
oxygen is carried by the blood to every part of the body.
Sometimes, cells may need a lot of oxygen
very quickly. Imagine, you are running in a
race. The muscles in your legs are using up a
lot of energy. To produce this energy, the
mitochondria in the muscles will be combining
oxygen with glucose as fast as they can, to
provide the energy for the muscles.
A lot of oxygen is needed to work as hard as this.
You breathe deeper and faster to get more oxygen
into your blood. Your heart beats faster to get the
oxygen to the leg muscles as quickly as possible.
Eventually a limit is reached. The heart and lungs
cannot supply oxygen to the muscles any faster.
But more energy is still needed for the race.
How can that extra energy be found?
Extra energy can be produced by anaerobic respiration. Some
glucose is broken down without combining it with oxygen :
Glucose
lactic acid + energy
It doesn’t release very much energy, but a little extra might make all
the difference.
When you stop running, you will have quite a lot of lactic acid in
your muscles and your blood. This lactic acid must be broken
down by combining it with oxygen. So, even though you do not
need the energy anymore, you go on breathing hard. You are taking
in extra oxygen to break down the lactic acid.
While your are running, you built up an oxygen debt. You
‘borrowed’ some extra energy without ‘paying’ for it with oxygen.
Now, as the lactic acid is combined with oxygen, you are paying off
the debt. Not until all the lactic acid has been used up, does your
breathing rate and rate of heart beat return to normal?