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AS Biology: Biology and Disease
The Lungs and Lung Disease
The lungs act as an interface with the environment for gas exchange. The function of the lungs may be affected by
pathogens and factors related to lifestyle.
The respiratory surface in the lungs is large enough to collect enough oxygen to supply all of the body’s tissues for
the process of respiration and to remove the carbon dioxide before it builds up to toxic levels.
The volume of oxygen that has to be absorbed and the volume of carbon dioxide that has to be removed are large
in mammals because:
The structure of the respiratory system:
Label the diagram with the following parts: ribs, sternum, nasal cavity, diaphragm, lung, internal intercostal muscles,
external intercostal muscles, heart, epiglottis, trachea, larynx, bronchus, bronchioles.
When we breathe in, air passes into the trachea. C-shaped rings
of cartilage (around 20) maintain the shape of the trachea. Why?
Look at the diagram. What is the function of the cells lining the
trachea and how are they adapted?
The trachea forks into two bronchi, one leading to each lung.
Within the lung, each bronchus branches repeatedly into finer
and finer tubes called bronchioles.
At their tips, the tiniest bronchioles end as a cluster of air sacs
called alveoli. The lungs have a very large surface area because of
these alveoli. There are around 300 million in each lung, and laid
flat would cover around 70m2. This is 35 times the surface area of
the skin!
AS Biology: Biology and Disease
Features of the alveolar epithelium
The thin epithelium of the millions of alveoli in the lungs serves as the respiratory surface. Air enters the
alveoli and the oxygen it contains diffuses across the thin moist walls and into the network of capillaries
that surround each alveolus. At the same time, carbon dioxide from the blood diffuses out into the alveoli
and is breathed out.
Use the diagrams to identify three adaptations of the alveoli for efficient gas exchange:
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1. List in the correct sequence all the structures that air passes through on its journey from the gas exchange
surface of the lungs to the nose.
2. What is the function of the cartilage found as incomplete rings around the trachea?
3. What is the function of the epiglottis?
4. Explain how the cells lining the trachea and bronchus protect the alveoli from damage.
5. Why is it important for mammalian respiratory systems to have such a large surface area?
6. What factors affect the rate of diffusion? Describe how the lungs are adapted to rapid diffusion of gases.
7. The capillaries in the lungs are so tiny that red blood cells slow down and become compressed against the
walls as they pass through. This aids diffusion in two ways. What are these two ways?
8. How is a large concentration gradient maintained between the air in the alveolus and the blood?
9. Describe three differences between inhaled and exhaled air.
AS Biology: Biology and Disease
Ventilation of the lungs
Ventilation is………
The parts of the respiratory system involved in ventilation are:
Air is passed in and out of the lungs by contraction of the intercostals and diaphragm muscles, which alter the
volume of the thoracic cavity. Ventilation ensures there is always a good supply of ‘fresh’ air inside the lungs which
maintains a large concentration gradient between air and blood. Because the flow of air flows through the lungs in
both directions we say that the ventilation is TIDAL.
Air entering the lungs=
Air exiting the lungs =
INSPIRATION
The external intercostal muscles ___________
The ________ intercostals muscles relax
This cause the ribcage to
At the same time the ____________ contracts.
Both actions increase the volume of the ________
The pressure in the thorax and therefore the lungs is now___________
than atmospheric pressure.
______ enters the lungs, inflating the alveoli, until the air pressure in the
lungs
EXPIRATION
Inspiration is always an active process.
When the body is at rest, expiration is a passive process, but during exercise expiration becomes a much more
active process. The internal intercostals muscles contract and the muscles in the abdominal wall contract forcing the
diaphragm upwards. This decreases the volume of the thorax and therefore the volume of air expelled with each
breath increases.
AS Biology: Biology and Disease
PULMONARY VENTILATION
It is sometimes useful to know how much air is taken in and out of the lungs in a given time. To do this we use a
measure called pulmonary ventilation. Pulmonary ventilation is the total volume of air that is moved into the
lungs during one minute. Two factors affect the pulmonary ventilation. These are:
1)
2)
To calculate pulmonary ventilation this formula is used.
TIDAL VOLUME:
VITAL CAPACITY:
RESIDUAL VOLUME:
VENTILATION RATE:
Effect of exercise on ventilation rate and depth of breathing:
1.
2.
3.
4.
5.
During which time period is the man at rest?
What is the man’s pulmonary ventilation during this time?
At what point does the man a) begin to exercise b) stop exercising?
What effect does exercise have on a) his ventilation rate b) depth of breathing?
Calculate the percentage increase for the maximum volume inspired during exercise compared with the
resting tidal volume.
6. Why is this change necessary during exercise?
7. At which point does the man contract his abdominal muscles causing the diaphragm to be forced upwards?
Will his internal intercostals muscles be relaxed or contracted at this time?
8. What is this man’s a) vital capacity b) residual volume c) total lung capacity?