4.3 Lower Respiratory Tract Histology Flashcards
What are the conduction pathways of the respiratory system?
- Nostrils
- Pharynx
- Larynx
- Trachea
- Bronchi
- Terminal Bronchioles
What are the gas exchange surfaces of the respiratory system?
- Respiratory bronchioles
- Alveolar ducts
- Alveoli
What three main functions of the respiratory system do its histological structures correspond with?
- Air conduction
- Air modification
- Gas exchange
What is the inner layer of an airway called?
Mucosa
What is the inner layer of an airway composed of?
[Mucosa]
- Epithelium
- Basement membrane
- Lamina propria (loose connective tissue)
What structures may exist in the lamina propria of the mucosa?
- Glands
- Smooth muscle
What is the layer of the airway beneath the mucosa called?
Submucosa
What type of connective tissue is found in the submucosa of airways? What structures are found in this layer?
- Dense (fibrous)
Structures found include:
- Hyaline cartilage
- Large veins
What is the outer layer of an airway called?
Adventita
What does the adventitia of airways contain?
Connective tissue
Describe respiratory epithelium.
- Psuedostratified columnar epithelium with ciliated cells and goblet cells
What are the glands called that exist in the lamina propria under respiratory epithelium?
Seromucous glands (sero: water, mucous: mucous)
What is the smooth muscle that lines the wall of the trachea called?
Trachealis muscle
What is the role of the trachealis muscle?
To join the ends of the hyaline cartilage rings that encircle the trachea
What does it mean for an airway to be patent?
Open
What are the three kinds of cells in respiratory epithelium (imagine a diagram in your head)
- Ciliated cells
- Goblet cells
- Basal cells (stem cells)
What are the two less common types of cell present in respiratory epithelium?
- Brush sensors with microvilli: chemosensory receptors associated with nerve fibres
- Small granule cell: release hormones and cytokines
What is the name of the loose connective tissue that lies in the mucosal layer under respiratory epithelial cells?
Lamina Propria
What does lamina propria contain (four things) in the lining of airways?
- Defense cells (MLP)
- Elastic fibres
- Mixed serous (s) and mucous (m) glands, forming seromucous glands
- Vessels (e.g., mucosal venules)
Describe the transition between the mucosa and submucosa of airways
Gradual transition from loose to dense CT. No identifiable boundaries.
What are the four functions of respiratory mucosa?
- Serous secretions hydrate coating layer and humidify air
- Heat transfer from mucosal venules warms air
(think: the air needs to be WARM and MOIST) - Mucociliary escalator
- Immune function
How does the respiratory mucosa remove pathogens?
Things that cannot get across the membrane:
- Immunglobulins, antiproteases and lysozymes are added to the viscous film to disarm bacteria
Things that do get across the membrane:
- Defence cells in lamina propria (MLP)
Which part of an airway is responsible for holding the airway open?
Cartilage
Where is cartilage generally considered to be located within an airway?
Submucosa
What is the name given to the connective tissue that surrounds hyaline cartilage? Is it loose or dense,m and regular or irregular?
- Perichondrium (around cartilage)
- Dense, regular connective tissue
What type of connective tissue is present in the adventitia of airways?
Loose
What causes the sponge-like appearance of lung tissue?
Numerous alveoli/air sacs
What is the singular term for alveoli?
Alveolus
What is the name of the walls between alveoli?
Interalveolar septae
What type of cells lines interalveolar septae?
Simple squamous epithelium
Describe the internal composition of interalveolar septae
- Very little smooth muscle
- Many elastic fibres
- Extensive capillary network
What are the different names that can be used to refer to pneumocytes?
Pneumocytes, septal cells, alveolar cells
Name and describe the two types of pneumocytes
Type 1: Squamous for exchange
Type 2: Cuboidal, secretes surfactant
other than type 1 and type 2 pneumocytes, what is the other common type of cell in the lungs? Is it part of the eipthelium itself?
- Alveolar macrophages
- Not part of the epithelium; sits on top instead
Are type 1 or type 2 squamous epithelial cells more common in the lungs?
Type 1
Where is surfactant stored before it is secreted?
Secretory granules in type 2 pneumocytes
What are the roles of secretions from type 2 pneumocytes?
- Decrease alveolar surface tension
- Clear foreign materials
- Modulate alveolar immune responses
Before differentiation, what types of cells are alveolar macrophages? Where do they differentiate?
- Originally monocytes
- Differentiate in lungs
What are the different possible fates of alveolar macrophages?
- Pass up mucociliary escalator
- Remain in situ in septal CT
- Moved in lymph to pulmonary lymph nodes
What are the two sets of vessels that take blood to the lungs?
- Take the blood to be oxygenated
- Deliver oxygen to cells in the lungs
Why is the interalveolar septum also known as the respiratory membrane?
It isn’t:
- The respiratory membrane is the barrier between air and blood
- The interalveolar septum is the wall between alveoli
Recall the structure of the interalveolar septum
- Epithelium (type 1 and 2 pneumocytes)
- Basement membrane (incl. basal and retiular lamina
- Connective tissue (low smooth muscle, high elastic, high capillary network
What does attenuated mean?
Very thin
What are the three layers of the respiratory membrane?
- Epithelium (type 1 septal cells)
- Basement membrane (double-sided basal lamina)
- Endothelium of capillary
Where are the organelles located within type 1 alveolar cells?
Perinuclear (around nucleus). Away from the main exchange site
What type of vesicles assist with gas exchange in the alveoli?
Pinocytotic vesicles
