The respiratory system takes in air, modifies and filters the air, and then transports the
air to the respiratory part of the lung where oxygen and carbon dioxide can diffuse in
and out of the blood. Traditionally, the respiratory system is divided into a conducting
part and a respiratory part.
To these, the ventilation mechanism is added.
1. Conducting part: nasal cavities, nasal pharynx, oral pharynx, larynx, trachea, bronchi,
bronchiole, and terminal bronchioles.
2. Respiratory part: respiratory bronchioles, alveolar ducts, alveoli.
This is where the
action is: exchange of O
3. Ventilation mechanism consists of thoracic cage, intercostals muscles, diaphragm,
and the elastic and collagen fibers of the lung.
Most of the conducting portion of the respiratory tract is covered with ciliated
pseudostratified columnar epithelium with many goblet cells.
The ciliated columnar cells
are the most abundant.
Each of these cells has a least 300 cilia on its apical surface.
Inside the cell membrane the cilia are attached to a basal body (centrioles).
would expect, the basal body is surrounded by many mitochondria as it takes energy
(ATP) to move the cilia. (Again note the polarity that is characteristic of many epithelial
cells). The goblet cells are the next most frequent cells. They secrete mucus, a
In addition to these cells, there are three other cell types:
short cells that are on the basement membrane but do not extend to the luminal
cells which are columnar cells with extensive microvilli on the apical
surface and sensory nerve endings on their basal surface; and finally,
part of the diffuse neuroendocrine system) that secrete hormones.
cells (stem cells) can differentiate into the other cell types.
1. The vestibule (nares) has keratinized stratified squamous epithelium, sebaceous glands, and
2. In the fossae (nasal cavities), there is gradual loss of keratin and transition to ciliated
pseudostratified columnar with goblet cells. The lateral part of the fossae has three boney
middle and inferior conchae
. The epithelium of the
conchae is specialized as
epithelium. Beneath the epithelium lies the CT, again
referred to as lamina propria.
There are mucous and serous glands in this lamina and