Respiratory histology Flashcards
What is the upper respiratory tract?
Nasal cavity
Paranasal sinuses
Pharynx
What are the functions of the upper respiratory tract?
Warm air
Humidify air
Clear particulates
What is the lower respiratory tract?
Larynx
Trachea
Bronchi
lungs
What are the functions of the lower respiratory tract?
Clear mucus
Allow elastic recoil
Allow gaseous exchange
Remain patent (open)
What is the conducting portion?
Conduit /passageway
Air conditioning system
Nasal cavity to terminal bronchioles
What is the respiratory portion?
Involved in respiration
Distal to terminal bronchioles - respiratory bronchioles to alveoli sacs.
How is the respiratory system supported?
Conducting portion: Cartilage changes into plates in the bronchi to not present in the bronchioles.
Not required in bronchioles as rely on smooth muscles to keep them open.
In the respiratory portion, elastic in the alveolar septum keeps them open.
What do all tissues of the conducting portion have?
Respiratory mucosa - epithelium and lamina propria (thin connective tissue).
Submucosa - vessels and serous and mucous glands to moisten air.
Cartilage and or muscle layer
Adventitia - connective tissue holding the structure together.
The components of these layers change to allow specialisation.
What do the respiratory layers look like?
see picture
What is respiratory epithelium?
Ciliated pseudostratified columnar epithelium, that contains goblet cells.
Goblet cells do not stain well due to the mucous.
There are multiple nuclei present at multiple layers, but it’s not stratified, as each cell is attached to the basement membrane, so is pseudo-stratified.
See picture
What are the cells in the respiratory epithelium?
Goblet cells
Ciliated columnar cells
Basal cells - repair epithelium.
What is the mucociliary escalator?
Made up from goblet cells and ciliated columnar cells, and serous and mucous glands.
Cilia beat to move mucous trapped particulates to the pharynx for swallowing.
See picture
What happens to the mucociliary escalator in smoking?
Smokers have more goblet cells so more mucous secretion. This decreases the movement of mucous.
Leads to chronic coughing and chronic infections, maybe chronic bronchitis.
What is the nasal cavity?
Most Is lined with typical respiratory mucosa.
Adjusts the temperature and humidity of the inspired air, because it is highly vascularised.
It also has a large surface area due to turbinate bones, which humidifies the air.
What does the nasal cavity look like?
There are lots of goblet cells.
There are serous glands in the submucosa, these stain well, compared to mucous glands that don’t stain.
See pictures.
What is olfactory epithelium?
Produces and transmits the sense of smell.
It is found over the superior turbinate bone of the nasal cavity.
What are the cells in the olfactory epithelium?
Bipolar olfactory neurones.
Supporting columnar cells
Basal cells - which regenerate olfactory bipolar neurones.
What is the histology of the olfactory epithelium?
Pseudostratified columnar epithelium.
There are no cilia or goblet cells.
Instead the serous glands produce the mucous.
What are the olfactory neurones?
Bipolar olfactory neurones have olfactory hairs.
These are non-motile cilia, which trap odours and convert eh chemical signals into electrical stimuli.
The stimuli then travel up the action potential synapse at the olfactory tract.
What is the histology of the larynx?
Mostly lined with respiratory epithelium (Pseudostratified ciliated columnar epithelium )
Some areas are stratified, which provides protection as air has quite turbulent flow and can cause abrasion of the mucosa.
Found over the upper epiglottis and true vocal cords.
See picture.
What does the respiratory portion look like?
Alveolus culminates in alveolar sacs, which have individual alveola separated by alveolar septum.
It is the site of gas exchange air blood interface created by alveolar wall.
See picture
What is the histology of the bronchiole?
Simple cuboidal epithelium.
Some ciliated cells, but in respiratory portion decreases.
No goblet cells, as don’t want mucous secretion as would block the alveoli and decrease the efficiency of gas exchange.
Instead have increase in club cells - domed apical surface, which create an appropriate environment for the lower respiratory portion.
What are club cells?
Respiratory bronchioles have bronchiolar exocrine club cells which:
Are non-ciliated.
Produce a component of surfactant - which keeps airways open.
Are stem cells.
Contain enzymes that detoxify noxious (harmful) signals.
Secrete anti-microbial factors and cytokines.
See picture
What are the components of the alveoli walls?
Surface epithelia
Capillaries - squamous epithelial cell lining the capillaries - endothelium.
Supportive tissue - connective tissue, very thin, just basement membrane, that is shared by the alveolar cell and the endothelial cell. This means there is a very thin diffusion barrier.
What is the interstitial component of the alveolar septum?
This has connective tissue, ECM fibres, reticular fibres, collagen fibres, elastin fibres.
Elastin allows expansion and recoil of alveoli.
Fibroblasts produce the ECM fibres.
There may be macrophages present.
What is pathology of the alveoli walls?
Can have diseases where wall is thickened, or destroyed, or blocks, leading to reduced gas exchange and shortness of breath.
What does the alveoli wall look like?
E = endothelial cell
RBC
P1/I = type 1 pneumocyte
P2/II = type 2 pneumocyte
PC/C = pulmonary capillary
PV = pulmonary vein
M/DC = macrophage / dust cell
What are the alveoli cells?
Pneumocytes:
Type 1 - squamous cells with large cytoplasm that cover most of the alveoli. But nuclei are rarely seen.
Type II, are more numerous but cuboidal so cover less area. More nuclei is seen.
What are type II pneumocytes?
Have lamellar bodies - produce lipid, a component of surfactant.
Can differentiate into type I.
What are alveoli macrophages?
Also called dust cells.
Macrophages and leukocytes migrate from capillaries within the alveoli.
Digest dust and pathogens in lower airways.
Increase in this indicates industrial lung disease.
Where is the typical respiratory epithelium found?
Nasal cavity
Larynx
Trachea
Bronchi
What supporting tissues help to keep the conducting portion patent?
From the trachea to the terminal bronchioles:
C-shaped hyaline cartilage.
There is some smooth muscle.
What supporting tissues help to keep the respiratory portion patent?
Elastic tissue
What does the trachea look like?
c-shaped cartilage, linked by smooth muscle.
Lined by respiratory epithelia.
Contains lots of glands in the submucosa.
See picture
What does the bronchus look like?
It has alveoli on the sides.
There is cartilage, but it does not surround the whole structure, so can be distinguished from the trachea.
There is a ring of smooth muscle for constriction and dilation.
There are also glands.
See picture.
How does the histology change from the trachea to the bronchus?
Cartilage plates rather than C-shaped rings.
Fewer glands in submucosa.
The lamina propria and sub mucosa are separated with a layer of smooth muscle.
Fewer goblet cells.
How does the histology change from the bronchus to the bronchioles?
No cartilage
No glands
More elastin present
Respiratory epithelium changes to cuboidal with club cells.
No goblet cells.
The smooth muscle is not neatly arranged.
What are the short term changes of the bronchus if repeatedly exposed to irritants?
More goblet cells, more mucous, reduced clearance, causes a cough.
Decreased clearance of pathogens - infections / inflammation.
What are the long term changes of the bronchus if repeatedly exposed to irritants?
Thickening of the bronchus wall - the epithelium and the underlying tissue.
Chronic inflammation / exposure to irritants.
Immune infiltrate
Increase in size and number of mucosal glands / smooth muscle cells.
Increase or change in respiratory epithelial cells.
Here is a TEM of the air blood interface at the alveolus. What cell is indicated by A?
See picture.
A is a type 1 pneumocyte, the kidney bean shape shows a red blood cell, which shows the whole structure is a capillary.
This means C is an endothelial cell, so A which is on the opposite side must be a pneumocyte - the squamous cell that backs onto the capillary.
D and E are filled with air.
What is emphysema?
Destruction of the walls of the alveolar ducts, sacs and alveoli.
Reduction in surface area for gas exchange
Loss of elasticity in bronchioles - risk of collapsing.
See pictures.
What is pneumonia?
Infection of lung tissue.
There are lots of immune cells, bacteria and fluid present in the lung.
This prevents air into the alveoli, and reduces gas exchange.
Can be fata is MRSA-resistant.
see pictures.
What is pulmonary fibrosis?
Fibroblasts proliferate within the alveolar walls
Deposit more extracellular matrix fibre
Thicken septum and barrier for gas exchange.
See picture
How are the airways protected from pathogens?
Mucociliary escalator, traps pathogens
Intraepithelial cells in the respiratory epithelium.
Lymphoid tissue
Macrophages / dust cells in the alveoli
Club cells secrete anti-microbial factors.
