What type of epithelium lines the airways and much of the nasopharynx?
pseudostratified ciliated columnar epithelium
What cells make up the respiratory epithelium?
- pseudostratified ciliated columnar epithelial cells
- secratory cells (infoldings of epithelium)
- goblet cells and mucin glands producing mucous
- sensory cells
- receptors to detect irritants, mechanical disturbances
- initiate cough reflex, sense of irritation
What are the proportions of cell types in the respiratory epithelium?
- pseudostratified ciliated columnar cells - 30%
- move mucous
- goblet cells - 30%
- secrete mucous
- basal (stem) cells - 30%
- in base, renew epithelium
- brush cells with microvili - 3%
- sensory?
- serous cells - 3%
- secretory but unknown product
- small granule cells
- endocrine, sensory
What are the layers of the trachea?
- mucosa lining the surface
- submucosa (intermediate)
- adventitia (contains cartilage where present)
What comprises the tracheal mucosa?
respiratory epithelium and lamina propria
What comprises the tracheal submucosa?
connective tissue and glands (serous and mucous)
What comprises the tracheal adventitia?
cartilage, outer layer of connective tissue binding trachea into neck
What structural changes occur at the intrapulmonary bronchi?
- walls thinner than trachea
- cartilage ring now individual plates, less organized
- smooth muscle now runs in a ring around the mucosa
- lies between mucosa lamina propria and submucosa
- glands still present
- presence of lymph nodules
What is the differential between bronchus and bronchiole?
loss of cartilage
What is the structure of bronchioles?
- 1-2mm in diameter
- ~10-15th dichotomous branch
- respiratory epithelium gradually loses goblet cells and then ciliated columnar cells, then gains clara cells
- smooth muscle still present
- radial connective tissue keeps airways open against negative pressure and surface tension of the mucous
What are clara cells?
- columnar and cuboidal cells with short microvilli (no cilia)
- release surfactant to break the surface tension and resist collapse
- surfactant is a glycoprotein
- may also make neutralizing toxins
- increasing presence deeper into bronchioles
What is the structure of the terminal bronchioles?
- no goblet cells
- clara cells
- cuboidal epithelium with some cilia
- 1-2 layers of smooth muscle (still dynamic)
- give rise to the respiratory bronchioles where gas exchange takes place
- breaks in the terminal bronchial wall (R)
What is the structure of the respiratory bronchioles?
- branching off terminal bronchioles (T)
- first respiratory structures
- gives rise to the alveolar ducts (D, chains of alveoli)
- alveoli appear (A)
- thin walled pouches off respiratory bronchioles
- epithelium of the respiratory bronchioles is cuboidal
- becomes squamous where it forms alveoli
What is the structure of alveoli?
- thin walls called interalveolar septa
- 200 microns across
- lined by mainly simple squamlous epithelium
- wall contains pulmonary capillaries
- individual alveoli are connected by pores, allowing passage of air
- ~300 million of them, 140m2 surface for gas exchange
What is the structure of the interalveolar septum?
- contains reticular fibres and elastin (connective tissues) arranged radially to pull the alveoli open against the negative pressure
- maintain positive pressure
- work with surfactant
What is the structure of the pulmonary capillaries?
- form a dense anastamosing network around alveoli
- very thin layer of epithelium - can see individual RBCs through the alveolar wall
- exchange occurs on the epithelial surface of the alveoli (pneumocytes)
What are pneumocytes?
- cells that make up the exchange surface of the alveolar epithelium
What are type I pneumocytes?
- simple squamous epithelium
- form wall between the air and the blood
- majority of alveolar and tf gas exchange surface (95%)
- stop fluid from leaking out of the pulmonary capillaries into the alveolar space
- prevent pulmonary congestion that causes SOB
- ‘water-proofed’ with tight junctions and thick basal lamina
What are type II pneumocytes?
- more numerous than type I but only 5% alveolar area
- cuboidal epithelium with short microvilli and lamellar bodies
- lamellar bodies are secratory vesicles with wavy lined structure
- produce surfactant to combat surface tension
- tucked between where two septa meet (not on surface)
- act as stem cells to produce type I and type II pneumocytes
What is the structure of the alveolar blood-gas barrier?
- exchange occurs between type I pneumocytes and endothelial cells of the capillary
- they share a fused basal lamina between them
- can be thickened in various pathology and disease
- normally ~0.1-1.5 microns wide
What is the fate of an alveolar macrophage?
- some that phagocytose debris crawl up to cilia to be swept into the stomach
- others migrate into the alveolar wall and reside there permanently
What cell type is pleura?
- mesothelium (simple squamous epithelium)
- supported by basal lamina and fibrous connective tissue
- connective tissue contains blood vessels and lymphatics
- some lymphatics drain into pleural space (conduit for bugs and cancer)
- microvilli on surface of mesothelium epithelium trap hyaluronic acid to lubricate the pleural space
