The Respiratory System
last authored: April 2010, David LaPierre
last reviewed:
Introduction
Life is often thought of as synonymous with breathing - as the story goes, God gave Adam the "breath of life". The lungs are the cornerstone of the respiratory system, exchanging gas between the atmosphere and the blood.
Blood pumped from the heart's right ventricle enters the pulmonary arteries. Blood in the pulmonary capillaries, flows past air-filled alveoli and exchanges old carbon dioxide for fresh oxygen. This new blood flows through pulmonary veins and enters the left atrium, to be pumped through the rest of the body.
Upper Airways
Main article: upper airways
Inspired air travels through the nose and pharynx, where it is heated, humidified, and filtered of particles greater than 10 um in diameter.
Air passes through the open larynx and through the trachea, which is 10-12 mm in diameter and held in shape by U-shaped cartilage rings.
There are perhaps 23 levels of bifurcation leading to the left and right lungs. Bronchi are the left and right initial bifurcations, and sequential bifurcations, containing cartilage. There are approximately five generations of large, intasegmental bronchi and about 15 generations of smaller intrasegmental bronchi. These become bronchioloes and end in alveoli, discussed soon.
The Lungs
main article: lung structure
Functions of the lung
- gas exchange
- blood reservoir
- filter against emboli
- metabolic location of enzymes (ie, ACE)
- thermal reservoir
- protecting against heat loss
The lungs are located in the thorax. The right lung has 3 lobes, 55% of total lung, while the left has two lobes. Each weighs x-x. and is x large. They are covered with the thin pleural lining - only a few cells thick. Between the lungs and chest wall is the pleural space, a very small (potential space) which contains fluid to lubricate the lungs.
Lungs are extremely elastic due to the rigid bony thorax and their cellular and connective composite.
Resources and References
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