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Clinical Anatomy and
Physiology of the Chest and Lungs
Many health workers have difficulty understanding and interpreting the clinical
signs and symptoms of respiratory diseases. With a clear understanding of the
basic anatomy and physiology of the chest and lungs it is much easier to
understand these signs and symptoms
This chapter will discuss:
c The anatomy of the lower airways and the lungs
c The function of the lungs exchange of oxygen and carbon dioxide
c Different diseases effect different parts of the lungs
c The defence and protection of the lungs
The anatomy of the lower airways and the lungs
The airways are divided into:
c the upper respiratory tract, from the nostrils to the larynx or throat
c the lower respiratory tract, from the throat to the diaphragm.
The upper respiratory tract is covered in the manual on CONDITIONS OF
THE EAR, NOSE AND THROAT.
Below and on the next page are diagrams of the upper respiratory tract
and the lower respiratory tract..
The important structures of the lower respiratory tract include:
The trachea and bronchi
The lower respiratory airway is wide at
the trachea. The trachea divides into two
main bronchi which enter the lungs.
Each bronchus in turn divides several
times into narrower and narrower bronchi.
The trachea and bronchi have
Pharynx
cartilage support.
Smaller bronchi and bronchioles
The larger bronchi divide into smaller
bronchi, which divide further into
the bronchioles. The bronchioles are very
narrow and have a diameter of 1mm
or less. The bronchioles eventually lead
into small sac-like structures
called the alveoli.
Larynx
Oesophagus
Trachea
Upper respirator y tract
Right Lung
Left Lung
Trachea
Upper lobe
Lymph nodes
Bronchus
Middle lobe
Bronchioles
Lower lobe
Pleura
Fissure
Alveolus
Mucous glands
Trachea
Mucous layer
Bronchus
Cross-section
of airway
Bronchiole
Trachea and
bronchus
Diagram of the lower respirator y tract and lungs
The airways consist of three layers including a mucous membrane and a muscle
layer. Mucous glands are present in the lining of the airways. These glands
are present until the very small bronchi. There are no mucous glands
in the bronchioles.
The alveoli
Each bronchiole ends in a group of tiny sac-like structures, each one called an
alveolus. Each lung has about 300 million alveoli. They are very small and cannot
be seen easily with the naked eye. Each alveolus is surrounded by a capillary
blood vessel. Gases, e.g. oxygen and carbon dioxide, move across the alveolar
membrane into the blood vessels and vice versa. A continuous exchange of gases
takes place between the alveoli and the capillary blood vessels that surround them.
Bronchiole
Alveolus
Blood
capillary
Left lung
Gas exchange
The covering of the lungs - the pleura
There is a double-layered covering of the lungs
called the pleura. There is a small amount of
lubricating fluid in between the two layers
of the pleura.
Other structures in the lungs
The lungs also contain blood vessels and lymph
channels. There are also many lymph nodes
which are found mainly at the site where
the main bronchi and large blood vessels enter
the lung. This area is known as the hilum.
Visceral
pleura
Pleural
cavity
Diaphragm
DEFLATED
INFLATED
An enlarged pleural space in
lung collapse (pneumothorax)
Divisions of the lungs
The lungs are divided into lobes. The right lung has three lobes (upper, middle,
lower) and the left lung has two lobes (upper and lower). Membranes called
fissures divide the lungs into lobes.
It is important to know these structures because different respiratory diseases
affect different parts of the airways and lungs
The function of the lungs exchange of oxygen and carbon dioxide
The main function of the lungs is to keep the correct amount of oxygen and
carbon dioxide in the blood. In order to do this we breathe air into the airways
of the lungs. The air then moves all the way down to the sac-like endings of the
airways called the alveoli. In the alveoli, the oxygen from the air moves into
the blood stream which surrounds each tiny alveolus. This vital oxygen is now
available for the body's needs.
Carbon dioxide, which is a waste product from body tissues, is carried in the
blood stream to the lungs. In the lungs, the carbon dioxide is moved across
the alveoli into the airways and then breathed out.
Alveolus
O2
Oxygen moves from
alveolus into blood
CO 2
Carbon dioxide
moves from blood
cell into alveolus
Blood capillary
Gas exchange
The exchange of gases can be increased or decreased by breathing at a faster
or slower rate, or by breathing more deeply.
The body can increase the amount of oxygen and decrease the amount of carbon
dioxide in the blood stream by breathing at a faster rate or more deeply.
The body may have to breathe faster because:
c The body needs more oxygen e.g. during exercise, running or straining.
c The normal supply of oxygen is obstructed. There may be some obstruction
to the flow of air in the airways or there may be an obstruction to the
flow of gases across the alveoli into the blood stream. This may be due
to diseases like asthma, bronchitis or pneumonia.
Whatever the cause, the body will try to increase the amount of oxygen in the
blood stream by breathing at a faster rate or more deeply.
Most of the time the lungs are able to provide enough oxygen for the body's needs.
If, for any reason, there is a severe shortage of oxygen in the blood, this will result
in cyanosis. Cyanosis causes a blue colour of the lips, mouth and tongue.
See Chapter 5 of the BASIC MEDICAL SCIENCES manual for more on cyanosis.
There is carbon dioxide in the blood stream. Carbon dioxide is an acidic waste
product of body metabolism. The level of carbon dioxide in the blood may rise
because there may be an over production of carbon dioxide, e.g. from running
or exercising. In some medical conditions, e.g. diabetes, there may be an
over production of acid (ketones) which will also result in deeper breathing.
By breathing faster or deeper the body will usually be able to correct the level
of carbon dioxide. The faster we breathe, the more carbon dioxide is moved
from the blood into the airways and then breathed out of the body.
The normal respiratory rate is 12 - 20 breaths per minute in adults.
A faster breathing rate is called tachypnoea (tachy = fast, pnoea = breathing)
A fast breathing rate (tachypnoea) is an important sign of respiratory disease.
A fast breathing rate can cause dehydration
There is always some moisture (water) in the air that is breathed out.
Therefore a fast breathing rate will result in water being lost from the body.
If the breathing rate is increased for long periods of time it can result in
dehydration. For this reason, it is very important to give plenty of fluids, orally
or intravenously, to patients with respiratory disease or who have fast breathing
rates for other reasons. This is especially important in young infants and children.
Give plenty of fluids to patients
with respiratory disease.
In some diseases where the acid level in the blood rises, e.g. diabetes or
aspirin poisoning, the body will increase its breathing rate to help get rid
of the excess acid.
The heart rate increases when the breathing rate increases. A faster breathing
rate increases the amount of gases exchanged. The heart rate will increase the
flow of blood through the lungs.
When there is a normal breathing rate (12 - 20 breaths per minute), the amount
of oxygen and carbon dioxide in the blood stream is at the correct level for the
body's needs. Most respiratory diseases cause the breathing rate to increase.
Since an increased breathing rate (tachypnoea) can cause dehydration, it is
important to give fluids to patients with respiratory disease.
Different diseases effect different parts of the lungs
Different respiratory diseases effect different parts of the lungs and produce specific
signs and symptoms. Diseases involving the lower respiratory tract include:
c Infection of the bronchi is called bronchitis. In bronchitis the lining of the
bronchi becomes inflamed, the mucous layer becomes thick and much excess
mucus is produced.
c Infection of the bronchioles is called bronchiolitis.
c Infection of the alveoli is called pneumonia. Pneumonia usually affects one or
more lobes (lobar pneumonia).
c Tuberculosis is a chronic infection which usually affects the hilar lymph nodes
and the alveoli.
c Asthma is not a lung infection but an allergic condition. In asthma, the muscle
layer of the smaller bronchi and bronchioles goes into spasm and causes the
airways to narrow.
c Lung cancers usually develop in the bronchi.
c Pleurisy and asbestos dust affect the pleura.
The defence and protection of the lungs
The lung is exposed to many harmful agents which are present in the air that
is breathed. For this reason, it has a very well developed defence system.
The lungs are mainly protected by:
c Mucous secretion
Mucus is secreted by the bronchial mucous glands. The mucus forms a moist
protective layer which lines the bronchi and bronchioles and also contains
antibodies against infection. The mucus traps foreign bodies such as dust, dirt,
bacteria and air pollution and so prevents them entering and establishing
themselves in the airways.
c Dehydration will dry out the mucus. When the mucus is dry and hard, it is
more difficult for the lungs to protect themselves against infection and foreign
bodies. Patients with respiratory disease must keep well-hydrated to prevent
their mucus drying out and becoming hard and thick.
c Fine hairs or cilia
The cilia are fine hair-like structures which line the airways. This carpet-like
layer moves systematically and pushes the mucus out of the airway. The mucus
which is moved out the airway contains foreign bodies. In this way the cilia
cleanse the lungs. Tobacco smoke and dehydration prevent the cilia from
functioning properly.
c The cough reflex
Any irritant e.g. excessive mucus, dust, dirt or other foreign body, may
stimulate the nerve endings in the airway and cause the person to cough
out the irritant.
c White blood cells in the alveoli - macrophages
These cells lie in the alveoli and destroy dust particles and bacteria.
Some important aspects of the anatomy and physiology of the lungs and lower
respiratory tract have been discussed. The next chapter will focus on how to
examine and interview a person with respiratory disease.
Summar y: Clinical anatomy
and physiology of the chest and lungs
c The airways are divided into the upper and lower respiratory tract.
The lower airways begin at the trachea and divide into two main bronchi
which enter the lungs. In the lungs, the bronchi divide into smaller bronchi
called bronchioles and finally reach the tiny air sacs called alveoli.
c The airways generally have three layers, including a mucous membrane (with
mucous glands) and a muscle layer.
c The main function of the lungs is to maintain the correct amount of oxygen
and carbon dioxide in the blood stream.
c Oxygen in the alveoli of the lungs moves into the blood stream and carbon
dioxide in the blood stream enters the lungs and is then breathed out.
Most of the exchange of gases takes place across the alveoli.
c By increasing or decreasing the breathing rate or by breathing more deeply,
the body is able to increase or decrease the exchange of gases.
c The normal respiratory rate is 12 - 20 breaths per minute. A faster breathing
rate is called tachypnoea. Tachypnoea is an important sign of
respiratory disease.
c Breathing at a faster rate increases the amount of oxygen and decreases
the amount of carbon dioxide in the blood stream. The breathing rate increases
during exercise or as a result of respiratory diseases like asthma, bronchitis,
pneumonia or severe diabetes.
c If the breathing rate is increased for a long period of time, dehydration can
occur. So it is important to give fluids to patients with respiratory disease
or tachypnoea from other causes.
c Different respiratory diseases affect different parts of the airways and lungs.
c Mucous secretion, the cilia, the cough reflex and white blood cells
(macrophages) all help to protect and defend the lungs against harmful agents
in the air, e.g., dust, dirt, bacteria, smoke etc.