Tidal volume

By the end of this chapter you should be able to :
1. Describe the structure of the human gas exchange system, including the microscopic
structure of the walls of the trachea, bronchioles and alveoli with their associated blood vessels
2. Describe the distribution of cartilage, ciliated epithelium, goblet cells and smooth muscle in the
trachea, bronchi and bronchioles
3. Describe the functions of cartilage, cilia, goblet cells, smooth muscle and elastic fibres in the
gas exchange system;
4. Describe the process of gas exchange between air in the alveoli and the blood;
5. Explain the terms tidal volume and vital capacity;
6. Describe the effects of tar and carcinogens in tobacco smoke on the gas exchange system;
7. Describe the signs and symptoms of emphysema, chronic bronchitis and lung
8. Describe the effects of nicotine and carbon monoxide on the cardiovascular system
with reference to atherosclerosis, coronary heart disease and strokes;
9. Evaluate the epidemiological and experimental evidence linking cigarette smoking to
disease and early death;
10. Discuss the problems of cardiovascular disease and the ways in which smoking may
affect the risk of developing cardiovascular disease;
11. Use the knowledge gained in this section in new situations or to solve related
Features of gas exchange surface:
1. Large surface area
this increased surface area allows the diffusion of increased volumes of oxygen,
required by larger animals and those with high levels of activity.
2. Moist.
Oxygen and carbon dioxide can only diffuse across membranes permeable to
water. Therefore all gas exchange surfaces are moist.
3. Thin membrane.
Gas exchange surfaces are thin so that diffusion is efficient. The thinner the
membrane, the faster the rate of diffusion.
4. Permeable.
Only membrane that are permeable to water and therefore gases can be used;
waterproof surfaces are not permeable to gases.
5. Transport system.
Transport system ensures a partial pressure gradient exists, in mammals,
between the air and the blood in the alveoli.
6. A respiratory pigment.
Haemoglobin increases the uptake of oxygen.
7. Ventilation mechanisms.
In humans, ventilation is called breathing.
The gaseous exchange system links the circulatory system with the atmosphere. It is
adapted to :
1. Clean and warm the air that enters during breathing
2. Maximise the surface area for diffusion of oxygen and carbondioxide between the blood
and atmosphere
3. Minimise the distance for this diffusion
4. Maintain adequate gradients for this diffusion
Structure Involved :
The structure involved are the breathing system
consisting the trachea, bronchi, branchioles and alveoli
The trachea or windpipe connects the larynx with two
bronchi that lead into the lungs
The trachea kept hollow by U-shape cartilages for easy
passage of air. The innermost layer is lined by
pseudostratified epithelium, which has cilia and mucus
secreting cells. Mucus is produced by the goblet cells of
the ciliated epithelium.
Each bronchus has the same structure as the trachea and
branches to form a ‘tree’ of bronchioles, which also has
ciliated, mucus secreting epithelium but no cartilage
Each bronchiole ends with an alveolar sac, which is
surrounded by network of capillaries
Both alveoli and capillaries have thin simple squamous
epithelia to facilitate diffusion of gases across them with
least resistance. Thus, the air in the alveoli and the blood
is hardly 1 µm away
Structure Involved : cont …
The walls of the alveoli have elastic fibres that stretch during breathing and recoil during expiration to
help force out the air. This helps to maintain the pressure potential between the gases inside the
alveoli and those within the blood.
The total surface area of the alveoli in human is around 100 square meters, the size of a tennis court.
The total volume of air that can get into the alveoli of a young man averages 4,6 liters and another 1,5
liters found in the trachea, bronchus and bronchioles where no gaseous exchange occurs.
Phagocytotic white blood cells known as macrophage patrol the surfaces of the alveoli and entire air
passages to rid them of fine dust particles and bacteria especially during infection.
17% O2
4% CO2
Blood flows out
21% O2
0,04% CO2
Red blood cell
The process of gaseous exchange in
the alveolus
Blood flows in
Thin endothelium
Lung Volumes and Capacities
1. At rest we need to ventilate our lungs with
about 6,0 dm3 of air per minute.
2. Tidal volume (0,5 dm3) is the volume of air
that is breathed in and out by man at rest. The
volume is about 500 cm3.
3. Inspiratory reserve volume (3,1 dm3) is the
extra volume of air taken in voluntarily after the
normal inhalation.
4. Expiratory reserve volume (1,2 dm3) is the
volume of air that can be further breathed our
after the normal exhalation.
5. Vital capacity (4,8 dm3) is the volume of air
breathed our after a forced inspiration followed
by a forced expiration. This about 4,800 cm3 for
normal people but athletes have higher vital
capacity through training.
6. Residual volume (1,2 dm3) is the volume of air
still left in the lung after a maximal forced
expiration. This residual volume includes the air
left in the trachea, bronchi and bronchioles,
which cannot be contracted to expel the air.
7. Total lung capacity (6 dm3) is the maximum
volume of air in the lung after forced inhalation.
This is same as the vital capacity plus the
residual volume.
Ventilation Rate :
this is the total volume of air moved into the
lungs in one minute. Ventilation rate
(expressed as dm3/min) is calculated as :
tidal volume x breathing rate
CO2 and O2 Distribution
CO2 and O2 Transportation
Haemoglobin Dissociation Curve
Breath Rate and Heart Rate Control
1. There are over 4000 different chemicals in cigarette, many of which are toxic.
2. Three main components of cigarette smoke pose a threat to human health, damaging in
particular either the gaseous exchange or cardiovascular system.
3. Tar, settles on the lining of the airways in the lungs  cancer
4. Carbon monoxide, combines with Hb  carboxyhaemoglobin, 250 times more readily
than it does with oxygen
5. Nicotine is the drug in tobacco
1. Chronic bronchitis  high infection
2. Ephysema : alveolar burst:  high infection  smaller quantities of elastin
3. Chronic obstructive pulmonary disease : refers to the overall condition, which is a
progressively disabling disease.
- rare in non-smoker
- 90% of people deaths from chronic obstructive disease are attributed to smoking
- 98% of people with emphysema are smoker
- 20% of smokers suffer from emphysema
- deaths from pneumonia and influenza are twice as high among smokers.
4. Lung cancer  tar  carcinogen  cancer
- smokers are 18 times more likely to develop lung cancer than non-smokers
- 1/3 of all cancer deaths are a direct result of cigarette smoking
- 25% of smokers die of lung cancer
1. Atherosclerosis : accumulation of fatty material in artery wall
- this build-up of atheroma, which contain cholesterol, fibers, dead muscle cell and
platelets, is termed atherosclerosis
- cholesterol is insoluble in water and so transported in the blood plasma in tiny
balls of lipid and protein called Lipoproteins :
a. LDL (Low Density Lipoprotein)  bad
b. HDL (High Density Lipoprotein)  good
2. Coronary Heart Disease : Atherosclerosis at the coronary artery. There are 3 form :
a. Angina pectoris  severe chest pain
b. Heart attack / myocardial infraction, large branch of coronary is obstructed by a
blood clot
c. Heart Failure due to blockage of a main coronary artery
3. Stroke
- stroke occurs when an artery in the brain burst so that blood leaks into brain tissue
or the artery is blocked by plaques
- the brain tissue is starved of oxygen and dies
- a stroke may be fatal or cause mild or severe disability
- as a result of a stroke, some people are unable to control part of their body;
others may lose their ability to speak or some or their memory