The Respiratory System
Describe the structure and function of the pleural cavity.
The pleural cavity is a fluid-filled space between the parietal and
membranes of the thoracic cavity. These membranes, the pleurae, create pleural fluid that
lubricates the contact between opposing surfaces of the lungs and thoracic cavity wall. This fluid
prevents friction during inspiration and expiration. The surface tension of the fluid also keeps the
lungs expanded against the thoracic walls, preventing collapse of the lung.
Describe the effects of smoking on (a) alveolar structure, (b) cilia
and alveolar macrophages,
and (c) the bronchial epithelium.
Components of tobacco smoke lead to destruction of alveolar walls.
The resulting loss
of surface area for gas exchange is a condition known as emphysema. Smoking also slows the
activity of cilia and macrophages of the respiratory mucosa. This leads to accumulation of
mucus, irritants, and carcinogens. The carcinogens lead to cancer growth in the bronchial
epithelium and mucosal glands.
Describe the histological changes that occur in the walls of
bronchial tree, beginning with the
trachea proceeding to the alveoli.
1) The supportive cartilaginous rings of the trachea are replaced
with irregular plates
in the primary bronchi and eliminated altogether in the bronchioles. (2) The respiratory
epithelium transitions from pseudostratified ciliated columnar cells to simple cuboidal cells in
the bronchioles and simple squamous cells in the alveoli. (3) Goblet cells are present in the
bronchi but absent elsewhere. (4) A layer of smooth muscle appears in the walls of the bronchi
and is present throughout the tree to the respiratory bronchioles.
Describe all the anatomical changes to the larynx that account for
the deeper voice of men
compared to women.
The thyroid cartilage of males grows larger than in females, and its
prominence protrudes further anteriorly. The vocal ligaments, which stretch from the arytenoid
cartilage to the thyroid cartilage, are therefore longer in males. Longer cords vibrate more slowly
than do shorter cords, resulting in a deeper voice.
Explain the difference in muscles used for active inspiration and expiration.
Active inspiration involves the diaphragm and external intercostal
Additionally, the scalenes, sternocleidomastoid, and pectoralis minor may also be involved.
Active expiration involves relaxation of the diaphragm and contraction of the internal
intercostals, oblique and transverse abdominis muscles, and, in certain circumstances, the