1.1. THE HUMAN RESPIRATORY SYSTEM
 Is a network of organs and tissues that help us breathe. The primary
function of this system is to introduce oxygen into the body and expel
carbon dioxide from the body.
 Aside from the lungs, there are also muscles and a vast network of blood
vessels that facilitate the process of respiration.
To demonstrate how the human respiratory system works, first take a deep breath
in.
As a person does that, air
enters the body through the
nostrils present in the nose.
The air then goes into the
nasal passage which is lined
with fine hair (cilia) and
mucus. Mucus is secreted by
the glands inside the nasal
passage. When the air passes
through, the dust particles
and other impurities are
trapped by the cilia and
mucus so that clean air enters the lungs.
Figure 1:diagram of the human respiratory system
The pharynx is the part of
the throat between the mouth
and the windpipe. So, air enters from the nose into in pharynx and the goes into the
trachea (windpipe). Now air passes through the trachea, it does not collapse even
when there is no air because it is supported by rings of soft bones called cartilage.
The upper end of the trachea has a voice box called the larynx. The trachea runs
down the neck and divides into two smaller tubes called ‘bronchi’ at its lower end
and these are connected with the lungs.
The singular of bronchi is bronchus and they divide in the lungs to form a large
number of smaller tunes called ‘bronchioles.’ They have tiny pouch like air sacs at
the end called ‘alveoli’ (singular – alveolus). This is where oxygen enters the
blood and the carbon dioxide is expelled.
1.2. GAS EXCHANGE
 Inside the lungs, oxygen passes from the air into the blood and carbon
dioxide passes out of the blood into the air. This is called gas exchange.
The diagram shows how the process of gas exchange takes places.
The blood inside the
capillary has come from
the heart. Before that, it
came from the organs of
the body. The cells in
these organs used up
oxygen and produced
carbon dioxide as a
waste product. This
means that the blood
now contains little
amounts of oxygen and
a lot more carbon
dioxide.
As air enters, the alveoli or air sacs of the lungs get filled. This air contains
oxygen. The alveoli are surrounded by blood capillaries due to which oxygen
diffuses out of the alveoli into the blood. The oxygen is carried by a red pigment
called haemoglobin present in blood. As the blood passes through the tissues of
the body, the oxygen
Figure 2:The diagram of an air sac in the lungs
then diffuses into the
cells due to its higher concentration in blood. This oxygen combines with the
digested food or glucose present in the cells to release energy. Carbon dioxide is
produced as a waste product.
The carbon dioxide then diffuses into the blood due to its higher concentrations in
body tissues. Blood carries carbon dioxide back to the lungs where it diffuses in to
the alveoli and then expelled from the body.
1.2. BREATHING
 When we breathe, air moves into and out of our body. There are two
movements involved in the process of breathing:
1. Inspiration (also known as inhalation) – This is breathing air into the body.
When we inspire:

The intercostals muscles found between the ribs contract.

This raises the ribs upwards and outward expanding the ribcage

diaphragm contracts and flattens, pulling downwards.

The lung volume increases and the air pressure inside the lungs
decreases.

Air is then pushed into the lungs.
2. Expiration (also known as exhalation) – This is breathing air out of our
body.
When we expire:





The intercostal muscles relax.
This lowers the ribs downwards and inwards.
The diaphragm relaxes, moving back upwards.
The lung volume decreases and the air pressure inside the lungs
increases.
Air is then forced out of the lungs.
NOTE: Breathing and Respiration are not the same thing. Respiration is the
process in which food is broken down in the cells with the help of oxygen to
produce energy while Breathing is purely exchange of gases (carbon dioxide
and oxygen). Breathing is a part of respiration
1.4. RESPIRATION
 Living cells need energy to stay alive. They get their energy from nutrients,
especially glucose.
 Inside the cell, glucose takes part in a chemical reaction called respiration.
Respiration is a chemical reaction that happens in all living cells, including
plant cells and animal cells. It is the way that energy is released from
glucose so that all other chemical processes for life can happen
 In this chemical reaction, glucose combines with oxygen to produce carbon
dioxide, water and energy. The oxygen that combines with glucose in this
reaction comes from the air. So this is sometimes known as aerobic
respiration. ‘aerobic’ just means ‘with air.’
Aerobic respiration is the release of energy from glucose by reacting it with
oxygen inside living cells. It takes place in the mitochondria of the cell.
 There is also anaerobic respiration, which happens without the presence
of oxygen.
You need to know both the word and symbol equation for aerobic respiration.
 Aerobic respiration occurs in plants as well as animals. Oxygen enters plant
cells through the stomata. Plants produce their food via photosynthesis and
release energy from it through the process of respiration.
What is the energy used for?
The energy produced during respiration is used in many different ways, some
examples of what it is used for are:

Working your muscles

Growth and repair of cells

Building larger molecules from smaller ones i.e. proteins from amino acids

Allowing chemical reactions to take place

Keeping your body temperature constant

Sending messages along nerves
***IT IS ADVISABLE TO USE THE NOTES AND TEXT BOOK
HAND IN HAND. DON’T JUST RELY ON ONE OF THEM***