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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…

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4.2 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,

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4.3 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.

Essential features of…

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4.4 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.


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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…

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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…

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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…

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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…


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