TBL 10 - Tracheobronchial Tree and Pulmonary Alveoli Flashcards
Where is the epithelium of the trachea and its airways derived from and where does the lung bud (respiratory diverticulum) come from?
Endoderm
Caudal outgrowth from the anterior wall of the distal foregut
Where does the connective tissue, cartilage, and smooth muscle of the airways come from?
Mesenchymal cells of visceral mesoderm
What does the tracheoesophageal septum do?
Divides distal foregut into posterior and anterior portions occupied by the esophagus and trachea, respectively
What is the most common type of tracheoesophageal fistula and why can it be associated with polyhydramnios and pneumonia?
The upper portion of the esophagus ending in a blind bound and the lower segment forming a fistula with the trachea.
TEF results in polyhydramnios where amniotic fluid enters the trachea instead of the stomach and intestines causing pneumonitis and pneumonia
Describe the differentiation process that is associated with angiogenic proliferation of pulmonary capillaries from the segmental pulmonary arteries
lung buds branch, differentiation of lobar and segmental bronchi occurs leading to differentiation at the distal ends of the segmental bronchi
Describe fetal breathing and aspiration of amniotic fluid
Breathing movements before birth are important for for lung developing and conditioning respiratory muscles. At birth, lung fluid is absorbed by blood and lymph and some is expelled through trachea. Some fluid is resorbed from alveolar sacs creating a surfactant on the membrane preventing an air-water interface with high surface tension preventing collapse of the alveoli
What is the purpose of the conducting airways before the alveolar sacs and what allows this to happen?
Moisten, warm, and filter air before the sacs. The respiratory epithelium has an underlying connective tissue with a dense microcirculation and glandular acini to secrete mucus onto the epithelium
What is the connective tissue under the epithelium that lines the lumen called and what is the mucosa?
Lamina propria and it plus the epithelium are called the mucosa
What type of cells make up the respiratory epithelium?
Basal cells and tall columnar cells that are ciliated or filled with mucus forming goblet cells
What nerves stimulate mucus production?
Parasympathetic nerves
What nerves inhibit mucus production?
Sympathetic nerves
What do the motile cilia do?
Move the mucus layer along the apical surface towards the oral cavity for elimination or swallowing
What is the respiratory mucosa characterized by?
Longitudinal folds forms by densely packed longitudinally oriented elastic fibers in the lamina propria. These fibers extends into the walls of the pulmonary alveoli
What do the 16-20 C shaped rings of hyaline cartilage in the trachea and main bronchi do? What muscle is associated with them and what does the muscle do?
Prevent collapse of airways during respiration. The muscle is the tracheal and it contracts during forced expiration like coughing to prevent the rings from flaring open posteriorly
Where do the respiratory epithelium and mucous glands extend into?
Lobar and segmental bronchi
How is hyaline cartilage organized in lobar bronchi? Where does it end?
Discontinuous plates that become smaller as they progress and eventually terminate in the distal ends of the segmental bronchi
How are bronchioles characterized?
Lack cartilage and mucous glands. They have smooth muscle that resides external to the bronchiolar mucosa
Where does the circumferential smooth muscle layer begin and what does it do?
Lobar bronchi and it is involved in bronchoconstriction and bronchodilation
What is the functional relevance of the histological observation that bronchioles lack goblet cells and mucous glands?
The mucus will probably increase surface tension and cause the alveoli to collapse. It can also clog up the system at this point
What is the pathogenesis of asthma?
Heightened response of the trachobronchial tree to numerous stimuli. Mucosal and submucosal edema in the bronchi and bronchioles occurs as does thickening of the basement membrane, hypertrophy of the smooth muscle, and infiltration of leukocytes (eosinophils)
How do elastic fibers in lobar and segmental bronchi, bronchioles, and stroma of the interalveolar septa contribute to normal respiration?
They encircle the smooth muscle helping with recoiling after expansion or constriction
What type of cells line the bronchioles?
Simple columnar epithelium that are often ciliated. There are also Clara cells
What are Clara cells?
Nonciliated columnar cells in the bronchioles. There are secretory cells that discharge material into the airway lumen. They play an antiinflammatory and detoxification role. They also are progenitor cells for the other bronchiolar epithelial cells in response to injury
What forms the lungs parenchyma? And what is the stroma?
The alveoli constitutes 90% of the lung parenchyma, the functional portion of the organ. The storm is everything else, the structures and supporting tissues
What makes up the alveolar epithelium
Type I pneumocytes (simple squamous epithelial cells) make up 95% of surface area. Cuboidal shaped type II pneumocytes make up the rest
What do type II pneumocytes secrete and what is the function of that secretion?
Pulmonary surfactant. It contains complexes of phospholipids, protein, and carbohydrates that are part of the fluid that coats the alveolar surfaces preventing collapse of the alveoli by reducing surface tension
What is the pathological significance of interalveolar pores (of Kohn)?`
Allows air from one alveolus to move to another. Allows spread of infection
Why is progressive surfactant accumulation in the fluid-filled lungs before birth critical for neonatal respiration? When is the mature number of pulmonary alveoli attained?
Prevents development of a high surface tension from an air-water interface which would cause collapse of the lungs during expiration. New alveoli are formed during the first 10 years of life
Why are premature infants susceptible to respiratory distress syndrome (RDS) and how is it treated?
They don’t have enough surfactant leading to partial collapse of the alveoli. Treatment involves artificial surfactant or treating mothers with glucocorticoids that stimulate surfactant production
What is the interalveolar septum
Wall that adjacent alveoli in the alveolar sacs share
Where do pulmonary capillaries reside?
Elastic fiber-rich stroke of the inter alveolar septa
What forms the blood-air barrier and what is the function?
A basement membrane between the epithelium of the capillary and the type I pneumocytes. It allows the pulmonary circulation to be exposed to the filtered air at a very short diffusion distance
What engulfs pathogens in the alveolar lumens and what is their course after engulfing the pathogens?
Macrophages remove debris from alveoli, they move up the bronchial tree, where they are carried by cilia and are eventually swallowed or
expectorated with mucus
What are heart failure cells?
Macrophages that phagocytosed erythrocytes from the bloodstream that escaped (due to heart failure) into the alveolar spaces
