Lecture 28 Flashcards
Layers from bronchus to alveoli
Intrapulmonary bronchus
Bronchiole
Terminal bronchiole
Respiratory bronchiole
Alveoli
Intrapulmonary bronchus
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.
Bronchiole/terminal bronchiole
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
Respiratory bronchiole
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
Club cells (aka Clara cells)
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
Alveoli vs club cell substances
Alveoli has surfactant
Club cellls have surfactant-like substances
Alveoli
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
Pores of kohn
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
Alveolar duct
Is a hallway with the alveoli budding off on either side, like a room on either side of the hallway
Alveolar sac
Is collections of many alveoli that form a larger room. Collection of many rooms forming a larger room
Type I pneumocytes
Simple squamous epithelial cells that make up the majority of the alveolar wall
Type II pneumocytes
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.
Endothelial cells
Thin cells that compose the walls of the capillaries that are found between adjacent alveoli
Alveolar macrophages
Larger cells found in the lumen or walls of alveoli; can often see ingested content in cytoplasm. May see granular cytoplasm
Function of lamellar bodies that are in epidermis of skin
Forms water barrier
Alveolar macrophages (dust cells)
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
Lung of smoker
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
Alveolar septum
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
