Respiratory System

THE PATHWAY IN THE HUMAN RESPIRATORY SYSTEM.

* Air enters the nostrils
* passes through the nasopharynx,
* the oral pharynx
* through the glottis
* into thetrachea
* into the right and left bronchi, which branches and rebranches into
* bronchioles, each of which terminates in a cluster of
* alveoli

Diseases of the LungsPneumonia
Pneumonia is an infection of the alveoli. It can be caused by many kinds of both bacteria (e.g., Streptococcus pneumoniae) and viruses. Tissue fluids accumulate in thealveoli reducing the surface area exposed to air. If enough alveoli are affected, the patient may need supplemental oxygen.
Asthma
In asthma, periodic constriction of the bronchiand bronchioles makes it more difficult to breathe in and, especially, out. Attacks of asthma can be •triggered by airborne irritants such as chemical fumes and cigarette smoke•airborne particles to which the patient is allergic.

Link to discussion of allergic asthma.



Emphysema

In this disorder, the delicate walls of the alveoli break down,reducing the gas-exchange area of the lungs. The condition develops slowly and is seldom a direct cause of death. However, the gradual loss of gas-exchange area forces the heart to pumpever-larger volumes of blood to the lungs in order to satisfy the body's needs. The added strain can lead to heart failure.

The immediate cause of emphysema seems to be therelease of proteolytic enzymes as part of the inflammatory process that follows irritation of the lungs. Most people avoid this kind of damage during infections, etc. by producing anenzyme inhibitor (a serpin) called alpha-1 antitrypsin. Those rare people who inherit two defective genes for alpha-1 antitrypsin are particularly susceptible to developing emphysema.