What are the functions of the conducting airways?
Where can respiratory epithelium be found and what lies underneath it?
The functions of the conducting airways are moistening, warming, and filtering inspired air before it reaches the alveolar sacs.
Respiratory epithelium is the epithelium of the trachea and bronchi.
Underneath it there is connective tissue that contains a dense microcirculation and glandular acini that secrete mucus onto the apical surface of the epithelium.
Connective tissue beneath epithelium that lines a lumen is called A.
A plus the epithelium is generally referred to as B.
Connective tissue beneat epithelium that lines a lumen is called Lamina Propria.
Lamina Propria plus the epithelium is generally referred to as the Mucosa.
What cells can be found within respiratory epithelium?
Within respiratory epithelium you can find basal cells and tall columnar cells which are either ciliated or filled with mucus to become goblet cells (shaped like a goblet).
Where do the ducts of the glands in the lamina propria open onto and what is the purpose of the mucus that is usually secreted in respiratory epithelium?
Ducts of the glands in the lamina propria open onto a luminal surface.
In respiratory epithelium, these ducts secrete mucus onto the apical surface of the respiratory epithelium which creates a sticky layer that entraps inspired particulate matter.
What do motile cilia of respiratory epithelium do and what is the role of parasympathetic/sympathetic fibers in this action?
Motile cilia of respiratory epithelium move the mucus layer along the apical surface toward the oral cavity for elimination or swallowing.
Parasympathetic fibers of the pulmonary plexuses stimulate mucus production.
Sympathetic fibers of the pulmonary plexuses inhibit mucus production.
What is characteristic about respiratory mucosa?
The respiratory mucosa is characterized by longitudinal folds formed by dense collections of longitudinally oriented elastic fibers in the lamina propria.
What structures within the trachea prevent collapse of the airways during respiration?
The trachea and main bronchi contain 16-20 C-shaped rings of hyaline cartilage that prevent collapse of the airways during respiration.
What is the function of the trachealis muscle?
The trachealis muscle prevents the cartilaginous rings of the trachea from flaring posteriorly during forced expiration, coughing, or sneezing.
How far down do the respiratory epithelium and mucous glands extend in the respiratory track? What type of cartilage can be found in these regions?
The respiratory epithelium and mucous glands extend into the lobar and segmental bronchi.
Hyaline cartilage can be found in these regions organized as discontinuous plates that become progressively smaller and terminate in the distal ends of the segmental bronchi.
What is unique about bronchioles and where does the circumferential layer of smooth muscle reside?
Bronchioles lack cartilage and mucous glands.
The circumferential layer of smooth muscle resides external to the bronchiolar mucosa.
What is the functional relevane of the histological observation that bronchioles lack goblet cells and mucous glands?
What is the pathogenesis of asthma?
Asthma is characterized by the heightened response of the tracheobronchial tree to numerous stimuli. Dyspnea, coughing, respiratory distress, and wheezing result from bronchospasm, bronchial wall edema, and hypersecretion of mucous glands.
Pathologic features include:
- mucosal and submucosal edema in bronchi and bronchioles
- thickening of the basement membrane
- hypertrophy of smooth muscle
- profuse infiltration of leukocytes, mainly eosinophils
- highly viscous intraluminal mucous plugs that adhere to the bronchial walls and narrow the airway
- hypercontraction of smooth muscle increases resistance to airflow
How do elastic fibers in lobar and segmental bronchi, bronchioles, and stroma of the interalveolar septa contribute to normal respiration?
Elastic fibers are embedded smooth muscle cells arranged in crisscrossing bands that completely encircle the lumen of intrapulmonary bronchi.
Parasympathetic vagal stimulation causes contraction, sympathetic stimulation causes relaxation.
What replaces goblet cells of the respiratory epithelium in bronchioles?
What is the function of these new cells (brace yourself)?
Clara cells replace goblet cells in bronchiole respiratory epithelium.
The functions of Clara Cells:
- secrete anti-inflammatory material
- play a role in detoxification
- secrete surfactant-like protective material that coats the brongiolar epithelial surface
- secrete proteolytic enzymes that break down mucus
- secretes a leukocyte protease inhibitor that helps maintain the integrity of bronchiolar epithelium
- involved in transport of water and electrolytes
- act as progenitor (stem) cells for normal reneqal of nonciliated and ciliated bronchiolar epithelial cells, particularly in response to injury.