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PinkMonkey Online Study Guide-Biology

alveoli, the combined area of which is about 100 square meters, i.e., about a hundred times the area of skin on the human body. Thus a vast surface is exposed for exchange of gases in the lungs.

A transverse section of a lung shows a number of bunches of grape-like structures called alveoli lined by flat epithelial cells showing connective tissues and blood capillaries in between. It also shows a section of terminal bronchioles lined by smooth muscle fibers. Respiratory bronchioles and blood capillaries may also be visible.

Figure 17.5 Transverse Section of lung


Mechanism of breathing

The mechanism of breathing in man involves two events: inspiration or breathing in of fresh air and expiration or breathing out of foul air,. Humans breathe about 16 to 18 times per minute.

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Table of Contents

17.0 - Introduction
17.1 - Gaseous Exchange and Transport

Chapter 18





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