Lecture 28

Question 1

Layers from bronchus to alveoli

Answer 1

Intrapulmonary bronchus

Bronchiole

Terminal bronchiole

Respiratory bronchiole

Alveoli

Question 2

Intrapulmonary bronchus

Answer 2

Surrounded by lacy alveoli. Composed of…

Hyaline cartilage in submucosa

• shaped like a plate/cap
• does not reach full way around the bronchus
• submucosa also has submucosal glands that have serous mucus secretions

Smooth muscle

Lamina propria

Basement membrane

Respiratory epithelium
- pseudostratified columnar with cilia and goblet cells

Lumen

Also has elastic fiber throughout, but these are not stained by H and E.

Question 3

Bronchiole/terminal bronchiole

Answer 3

Bronchioles are larger and contain more smooth muscle surrounding them. Terminal bronchioles are smaller with less smooth muscle.

Bronchiole: simple columnar epithelium with cilia

Terminal bronchiole: simple cuboidal epithelium with cilia

Cilia moves particles. Does not have hyaline cartilage nor submucosal glands. Smooth muscle controls diameter of lumen by contracting or relaxing

Question 4

Respiratory bronchiole

Answer 4

Some smooth muscle present. There are budding alveoli interrupting bronchiole walls.

Epithelium transitions from simple cuboidal epithelium with cilia (terminal bronchiole) to simple squamous epithelium

Question 5

Club cells (aka Clara cells)

Answer 5

Large non-ciliated cells that protrude into the lumen of bronchioles. Produces surfactant-like substances, and release them into the lumen and lining of bronchioles; this reduces surface tension of bronchioles and prevents walls of bronchioles from sticking together. Apical surface of club cell has secretory vesicles released into lumen.

Bronchioles do not have hyaline cartilage to keep lumen open

Question 6

Alveoli vs club cell substances

Answer 6

Alveoli has surfactant

Club cellls have surfactant-like substances

Question 7

Alveoli

Answer 7

Rich vasculature, capillary network

Function: Gas exchange with surrounding capillary network

200 million alveoli in adults

Has elastic fibers in wall to allow the walls to
expand and relax during breathing

Question 8

Pores of kohn

Answer 8

The spaces within walls of alveoli that allow
equilibrating air pressure b/w adjacent alveoli. Too much air pressure means it could burst. Pores of kohn prevent this by allowing air equilibrium

Question 9

Alveolar duct

Answer 9

Is a hallway with the alveoli budding off on either side, like a room on either side of the hallway

Question 10

Alveolar sac

Answer 10

Is collections of many alveoli that form a larger room. Collection of many rooms forming a larger room

Question 11

Type I pneumocytes

Answer 11

Simple squamous epithelial cells that make up the majority of the alveolar wall

Question 12

Type II pneumocytes

Answer 12

Cuboidal cells that sit in the corners of the alveolar walls and bulge into the lumen

Compared to type I pneumocytes, type II pneumocytes have a paler cytoplasm and sometimes granules

Has lamellar bodies that contain lipid-protein
complex, and they produce surfactant substance when they are released onto surface of alveolus. In SEM, the dark lines in the lamellar bodies are lamellae

Surfactant reduces surface tension of walls of alveoli to prevent
walls from sticking and allow them to be open. Surfactant lines entire surface of alveolus.

Question 13

Endothelial cells

Answer 13

Thin cells that compose the walls of the capillaries that are found between adjacent alveoli

Question 14

Alveolar macrophages

Answer 14

Larger cells found in the lumen or walls of alveoli; can often see ingested content in cytoplasm. May see granular cytoplasm

Question 15

Function of lamellar bodies that are in epidermis of skin

Answer 15

Forms water barrier

Question 16

Alveolar macrophages (dust cells)

Answer 16

Larger cells, can often see ingested material in cytoplasm. Darker brownish colored granular appearance of cytoplasm b/c it phagocytosed particles.

Function: Phagocytose particles and antigens that have been inhaled and trapped in surfactant or mucus

When alveolar macrophages have phagocytosed the material, they are brought out of respiratory tract via cilia and up to the pharynx, where they are either coughed out of body OR swallowed down esophagus and
destroyed by stomach acid

Question 17

Lung of smoker

Answer 17

If you look at lung of smoker or ppl in polluted area or firefighters, they have many alveolar macrophages with abundant dark coloured staining in cytoplasm

Question 18

Alveolar septum

Answer 18

The wall between 2 alveoli. Location of the air-blood barrier

Pneumocytes and endothelial cells are both epithelial cells, so they both have basement membranes.

Gases pass through these 3 layers during gas exchange and they make up the air-blood barrier:
• Type I pneumocyte (lines air space)
• Basement membrane of type I pneumocyte and endothelial cell
• Endothelial cell