Download Regions of the Respiratory Tract Airfl ow through the respiratory

Regions of the Respiratory Tract
Airfl ow through the respiratory system can be broken down
into three interconnected regions: the upper airway ; the conducting
airway ; and the alveolar airway
Th e upper airway consists of the entry systems, the nose/nasal cavity
and mouth that lead into the pharynx. Th e larynx extends from the lower
part of the pharynx to complete the upper airway.
upper airway provides two functions in airfl ow—
(1) fi ltering out large particulates to prevent them from reaching the
conducting and alveolar airways and (2) serving to warm and humidify
air as it enters the body.
Th e conducting airway begins at the trachea and branches Th ese
branches are made up of bronchi, bronchioles, and terminal
bronchioles.,
. Th e fi rst 16 generations of passages form the conducting zone of the
airways that has many functions
1- transports gas from and to the upper airway
2- Epithelial cells in the conducting airway can secrete a variety of
molecules that aid in lung defense. Secretory immunoglobulins
(IgA), collectins (including surfactant protein (SP) -A and SP-D),
defensins and other peptides and proteases, reactive oxygen species, and
reactive nitrogen species are all generated by airway epithelial cells. Th
ese secretions can act directly as antimicrobials to help keep the airway
free of infection.
3- Airway epithelial cells also secrete a variety of chemokines and
cytokines that recruit traditional immune cells and other immune eff ector
cells to site of infections
4-Th e walls of the bronchi and bronchioles are innervated by the
autonomic nervous system. Th e β 2 receptors mediate bronchodilation.
Th ey also increase bronchial secretions (eg, mucus), while α 1 adrenergic
receptors inhibit secretions.
Alveolar Airway
Th e last seven generations form the respiratory zones where gas
exchange occurs . It made up of transitional and respiratory bronchioles,
alveolar ducts, and alveoli .
Th e alveoli are lined by two types of epithelial cells.
1- Type I cells are fl at cells with large cytoplasmic extensions and are
the primary lining cells of the alveoli, covering approximately 95% of the
alveolar epithelial surface area.
2- Type II cells
(granular pneumocytes) are thicker and contain numerous lamellar
inclusion bodies. Although these cells make up only 5% of the surface
area, they represent approximately 60% of the surface.CAL BOX 34–1
. Type II cells are important in alveolar repair as well as other cellular
physiology. One prime function of the type II cell is the production of
surfactant
3- Th e alveoli also contain other specialized cells, including pulmonary
alveolar macrophages (PAMs, or AMs), lymphocytes, plasma cells,
neuroendocrine cells, and mast cells. PAMs are an important component
of the pulmonary defense system.
Role of Surfactant in Alveolar Surface Tension
Surfactant is film of lipoprotein lining the alveoli that lowers surface
tension of water and prevent alveolar closure
.. If the surface tension is not kept low when the alveoli become smaller
during expiration, they collapse.
Surfactant is important at birth.. After birth, the infant makes several
strong inspiratory movements and the lungs expand. Surfactant keeps
them from collapsing again. Surfactant defi ciency is an important cause
of infant respiratory distress syndrome (IRDS)
Respiratory Muscles
1-Movement of the diaphragm accounts for 75% of the change in
intrathoracic volume during quiet inspiration. Attached around the bottom
of the thoracic cage, this muscle moves downward when it contracts
-2 . Th e other important inspiratory muscles are the external
intercostal muscles, which run obliquely upward and
forward from rib to rib. so that when the external intercostals contract
they elevate the lower ribs. Th is pushes the sternum outward and
increases the anteroposterior diameter of the chest.
3-A decrease in intrathoracic volume and forced expiration result when
the expiratory muscles contract. Th e internal intercostals have this
action because they pull the rib cage downward when they contract