Lungs and Lung Disease Ch.4 Revision Notes

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Lungs and lung disease
4.1 Structure of the human gas-exchange system
Lungs act as an interface for exchange of gases and how their functions can be affected by both pathogens
and lifestyle.
Energy is released in the form of ATP during respiration.
A large volume of oxygen and carbon dioxide must be exchanged in mammals because:
they are relatively large organisms with a large volume of living cells
they maintain a high body temperature and therefore have high metabolic and respiratory rates
Due to this, mammals have specialised exchange surfaces-lungs.
Mammalian Lungs
The lungs are located inside the body because:
air is not dense enough to support and protect these delicate structures
they would otherwise lose a great deal of water and dry out
The RIB CAGE supports and protects the lungs. The ribs can be moved by the muscles between them.
Main parts of the human gas-exchange system:
Name Structure/Function
Lungs Lobed, made up of series of highly branched tubules (bronchioles) ending in alveoli
(tiny air sacs)
Trachea Flexible airway, supported by rings of cartilage which prevent the trachea collapsing
when pressure inside it falls as we breathe in. Walls made up of muscle, lined with
ciliated epithelium and goblet cells, which produce mucus that traps dirt particles and
bacteria from the air inhaled. The cilia move mucus up to the throat, where is
swallowed into the stomach.
Bronchi Two divisions of the trachea, similar structure to the trachea, and also produce mucus
to trap dirt particles and have cilia. The larger end of a bronchus is supported by
cartilage, however the amount of cartilage is reduced as the bronchi get smaller,
deeper into the lungs.
Bronchioles Series of branching subdivisions of the bronchi. Narrow tubes. Walls are made of
muscle lined with epithelial cells. This muscle allows them to constrict so that they can
control the flow of air into and out of the alveoli.
Alveoli Minute air-sacs at the end of the bronchioles. They contain collagen and elastic fibres,
and they are lined with epithelium. The elasticity allows the alveoli to stretch as they
fill with air when breathing in. They then spring back when breathing out in order to
expel the carbon dioxide-rich air. The alveolar membrane is the gas-exchange surface.

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The mechanism of breathing
The process of moving air in and out of the lungs is called breathing or ventilation, it is essential to maintain
diffusion of gases across the alveolar epithelium.
INSPIRATION occurs when the pressure of the atmosphere is higher than the pressure inside the lungs,
resulting in air being forced into the alveoli.
EXPIRATION occurs when the air pressure inside the lungs is higher than that of the atmosphere, causing the
air to be forced out of the lungs.…read more

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Exchange of gases in the lungs
Site of gas exchange in mammals is the epithelium of the alveoli. Alveoli are tiny air sacs 100-300m in
diameter. To ensure a constant supply of oxygen to the body, a diffusion gradient must be maintained at the
alveolar surface.…read more

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Lung disease- pulmonary tuberculosis
Tuberculosis (TB) is an infectious disease that can affect any part of the body although it is usually found in
the lungs as these are the first site of infection. It kills approximately 2 million people every year, more than
any other infectious disease.
Causes and Symptoms
Caused by one of two species of rod-shaped bacteria- Mycobacterium tuberculosis or
Mycobacterium bovis.
Symptoms include; a persistent cough, tiredness, and loss of appetite that leads to weight loss.…read more

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The suffer coughs up damaged lung tissue containing bacteria, along with blood. Without
treatment the TB spreads to the rest of the body and can be fatal.
Preventing the spread of TB depends upon the public services available. Services depend upon
public, political and economic circumstances of a country, and are a compromise between these and
scientific understanding. A vaccination may seem an obvious preventative measure however a lack of
money, political will and public confidence in the process makes it difficult to implement effectively.…read more

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Effects of fibrosis
Shortness of breath, especially when exercising Due to a considerable volume of the air space
being occupied by fibrous tissue, which means
that less air is taken in with each breath.
Due to the epithelium being thickened, the
diffusion pathway is increased and the diffusion
of oxygen into the lungs is extremely slow.
The loss of elasticity makes ventilating the lungs
very difficult.
Maintaining a diffusion gradient across the
exchange surface is also difficult.…read more

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One or more of the allergens causes white blood cells on the lining of the bronchi and bronchioles to
release histamine, which has the following effects:
Lining of the airways become inflamed
Cells of the epithelial lining secrete more mucus than usual (goblet cells)
Fluid leaves the capillaries and enters the airways
The muscle surrounding the bronchioles contracts and so constricts the airways
There is a greater resistance to the flow of air into and out of the alveoli, making it difficult to
ventilate the…read more

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Shortness of breath Due to difficulty exhaling air because of the
reduced elasticity in the lungs. The lungs cannot
be emptied of much air, meaning it is difficult to
breath in fresh oxygen and so the sufferer feels
breathless. The smaller alveolar area leads to
reduced level of oxygen in the blood and so the
patient tries to increase their oxygen supply by
breathing more rapidly.…read more


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