BSC 215 Lecture Notes - Lecture 48: External Intercostal Muscles, Intercostal Muscle, Bronchus
11 Jun 2018
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Lungs
The lungs are a pair of cone‐shaped bodies that occupy the thorax. The mediastinum,
the cavity containing the heart, separates the two lungs. The left and right lungs are
divided by fissures into two and three lobes, respectively. Each lobe of the lung is
further divided into bronchopulmonary segments (each with a tertiary bronchus), which
are further divided into lobules (each with a terminal bronchiole). Blood vessels,
lymphatic vessels, and nerves penetrate each lobe.
Each lung has the following superficial features:
• The apex and base identify the top and bottom of the lung, respectively.
• The costal surface of each lung borders the ribs (front and back).
• On the medial (mediastinal) surface, where each lung faces the other lung, the
bronchi, blood vessels, and lymphatic vessels enter the lung at the hilus.
The pleura is a double‐layered membrane consisting of an inner pulmonary (visceral)
pleura, which surrounds each lung, and an outer parietal pleura, which lines the thoracic
cavity. The narrow space between the two membranes, the pleural cavity, is filled with
pleural fluid, a lubricant secreted by the pleura.
Mechanics of Breathing
Boyle's Law describes the relationship between the pressure (P) and the volume (V) of
a gas. The law states that if the volume increases, then the pressure must decrease (or
vice versa). This relationship is often written algebraically as PV = constant, or P 1V 1 =
P 2V 2. Both equations state that the product of the pressure and volume remains the
same. (Boyle's Law applies only when the temperature does not change.)
Breathing occurs when the contraction or relaxation of muscles around the lungs
changes the total volume of air within the air passages (bronchi, bronchioles) inside the
lungs. When the volume of the lungs changes, the pressure of the air in the lungs
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Document Summary
The lungs are a pair of cone shaped bodies that occupy the thorax. The mediastinum, the cavity containing the heart, separates the two lungs. The left and right lungs are divided by fissures into two and three lobes, respectively. Each lobe of the lung is further divided into bronchopulmonary segments (each with a tertiary bronchus), which are further divided into lobules (each with a terminal bronchiole). Blood vessels, lymphatic vessels, and nerves penetrate each lobe. The pleura is a double layered membrane consisting of an inner pulmonary (visceral) pleura, which surrounds each lung, and an outer parietal pleura, which lines the thoracic cavity. The narrow space between the two membranes, the pleural cavity, is filled with pleural fluid, a lubricant secreted by the pleura. Boyle"s law describes the relationship between the pressure (p) and the volume (v) of a gas. The law states that if the volume increases, then the pressure must decrease (or vice versa).
