histology: the respiratory system

this section traces the passage of air from the trachea to the capillaries in the alveolus. the trachea is the largest tube in the respiratory system which is bolstered by 20 or so cartilage rings and smooth muscle. it has a PSCC epithelium with goblet cells and tracheal glands in the submucosa. the trachea then branches into the brochi, which have smatterings of cartilage and are like smaller versions of the trachea. bronchioles (from organ systems: primary for each lung, secondary for each lobe, tertiary for each bronchopulmonary segment) have no cartilage, and epithelium which begins to transition from PSC to simple columnar. terminal bronchioles are the last section of the airway that does not take place in gas exchange, and they have simple columnar epithelium with no goblet cells. next comes the respiratory bronchioles, where gas exchange begins to take place, which have simple cuboidal epithelium and the beginnings of alveoli protruding out from the walls. these transition into alveolar ducts, which are basically smaller respiratory bronchioles with simple squamous epithelium and many alveolar sacs. finally, the air reaches the alveolar sac, which is the end of the passageway.

between the alveolar sacs is the interalveolar septum, where gas exchange with blood actually takes place. this border is lined with type 1 and 2 pneumocytes, involved in gas exchange and surfactant secretion, respectively. thus, in order to reach the blood, gas has to diffuse through: type 1 pneumocyte cell, type 1 pneumocyte basement membrane, endothelial basement membrane, endothelial cell. also between the interalveolar septum are some fibroblasts, alveolar phagocytes, and a scant CT matrix called the zona diffusa.

questions
1. describe the passage of air from the trachea to the alveoli.
2. describe the physical support of the trachea
3. describe the layers of the trachea.

distinguishing characteristics of:
4. bronchi...
5. bronchiole...
6. terminal bronchiole...
7. respiratory bronchiole...
8. alveolar duct...
9. alveolar sac...

10. what are the two alveolar surfaces formed by epithelia?
11. what is inside the interalveolar septa?
12. describe the barrier between blood and air in the alveoli.

answers
1. trachea, bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli.
2. ~20 cartilage rings with smooth muscle (trachealis) spanning the posterior openings.
3. PSCC in mucosa with goblet cells, sometimes diffuse lymphatic tissue. submucosa of CT and tracheal glands. hyaline cartilage layer, then adventitia.

4. fragmented hyaline cartilage, PSCC with goblet cells.
5. smooth muscle but no cartilage, PSCC to simple columnar epithelium with goblet cells.
6. simple columnar, cilia but no goblet cells. clara cells secrete lipoprotein surfactant.
7. beginning of gas exchange; alveoli begin to protrude through walls. simple cuboidal epithelium with no cilia.
8. like a smaller respiratory bronchiole with many alveolar sacs.
9. terminal room of alveoli at ends of ducts, simple squamous epithelium.

10. type 1 pneumocytes which allow for gas exchange and type 2 pneumocytes which secrete surfactant.
11. CT matrix called zona diffusa, fibroblasts, alveolar phagocytes, capillaries. zone fiber phago cap
12. pneumocyte, pneumocyte basement membrane, endothelium basement membrane, endothelium.