The Lungs And Their Subdivisions

Each primary bronchus enters the medial border of a lung through a pulmonary (PUL-moh-neh-ree) hilum (HIGH-lum). This is a ''trifle'' (hil) little slit in the ''lung'' (pulmon), through which major air tubes, blood vessels, and nerves enter and leave the organ.

Organ 1

Organ 1

The lungs, themselves, are two cone-shaped, spongy, pinkish-colored organs located within the thoracic cavity, and flanking the heart on either side. The right lung contains three lobes (major sections), while the left lung has only two lobes. These lobes are separated from each other by thin sheets of connective tissue. [Study suggestion: Recall that, in most people, about 2/3 of the heart lies to the left of the body midline. Does this give you any ideas about possible explanations for the differences in the number of lobes between the lungs?]

Basically, every structure in the respiratory system lying beyond the right and left primary bronchi is a part of the lungs and their lobes. Each lobe of the lung, in turn, is subdivided by many lobules (LAHB-yools) or ''little lobes,'' separated by sheets of connective tissue. Each lobule is shaped like a hexagon, and is the smallest subdivision of the lung that is still visible to the naked eye.

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