Describe the structure of the bronchi.
- Begin at bifurcation of trachea
- Branch ~8 times in each lung
- Branches of pulmonary arteries and veins run in CT of adventitia
- respiratory epithelium similar to trachea, gradual decrease in goblet cells
- Increase in elastic fibers in l. propria
- Smooth muscle appears at mucosa/submucosa interface
- Submucosal glands gradually decrease
- Hyaline cartilage becomes small, discontinuous plates in the adventitia
Describe the structure of the roof of the nasal cavity.
- Olfactory (psuedostratified) epithelium containing basal cells and bipolar sensory neurons with sensory cilia embedded in odorant containing serous secretions
- Bipolar sensory neurons are supported by non-neuronal sustentacular cells
- Lamina propria contains Bowman's glands (serous, simple, nonalveolar)
Describe the structure of the bronchioles.
- continuous with the bronchi
- Branch ~6 more times to reach terminal bronchioles- end of conductive portion of respiratory system (~500um in diameter)
- Simple columnar/cuboidal epithelium- contains ciliated cells and Clara cells, but no goblet cells
- Elastic CT and smooth muscle both prominent
- No submucosal glands
- no cartilage in adventitia
How do secretions change from the bronchi to the bronchioles?
In the bronchioles, seromucous secretions are decreased to keep airways clear and lubricating secretions are increased to decrease surface tension and keep airways open.
What is a Clara cell?
- secretory cell in the bronchiole epithelium
- Polarized machinery for lipoprotein synthesis and apical secretion- secretions are lubricating and anti-inflammatory
- Prominent SER containing detoxification enzymes
What are the two components of the respiratory portion of the respiratory system?
- Respiratory Bronchioles
- Alveoli Proper
What are respiratory bronchioles?
- Short stretches of bronchiolar epithelium
- Interspersed with scattered alveoli
What is the general structure (not layers) of the alveoli proper?
- cluster around alveolar ducts at the end of respiratory bronchioles
- site of gas exchange with adjacent alveolar capillaries
- continuous alveolar capillaries are the terminal ends of branches of the pulmonary arteries
Describe the structure of the layers of the alveoli proper.
- Epl: mixture of squamous (Type I) and cuboidal (Type II) pneumocytes
- Mucosa/submucosa: little/no smooth muscle, elastic fibers prominent for recoil, some reticular CT between alveoli (interalveolar septae)
- Adventitia: very sparse
- Pores: connecting pores between adjacent alveoli to facilitate air pressure equalization
What are dust cells?
Alveolar macrophages which are able to migrate across respiratory epithelium/pneumocytes, removing debris (particulate matter)
What does gas exchange occur across?
- 1) simple squamous alveolar epithelium (Type I) with tight junctions
- 2) Fused basal laminae from the basement membrane of pneumocytes and endothelial cells
- 3) continuous capillary endothelial cells with tight junctions
Describe the structure/function of Type II pneumocytes.
- Secrete surfactant= phospholipoprotein in secretory vessels = Lamellar bodies
- Secreted apically on the lumenal side of alveoli, decreasing surface tension
What is emphysema?
- Extreme destruction of the interalveolar septae (reticular CT) due to chronic inflammation- attacked by dust cells
- Alveolar tisssue loses its compartmentalized appearance, and large gaps are observed.
How does cystic fibrosis affect the respiratory system?
- Poorly trafficked CFTR mutants disrupt Cl secretion and H2O balance leading to a thickening of the mucous secretions that are deposited over the respiratory epithelium and within ducts of submucosal glands
- Cilia cannot beat effectively to clear debris
- Overtime, microorganisms are trapped in the mucous and recruit dust cells. Eventually chronic inflammation occurs in the l. propria leadinng to fibrosis.
- Fibrosis= accumulation of collagen I fibers and loss of elastic fibers that impedes airflow deeper into the bronchioles and alveoli