Respiratory histology

Question 1

What is the upper respiratory tract?

Answer 1

Nasal cavity
Paranasal sinuses
Pharynx

Question 2

What are the functions of the upper respiratory tract?

Answer 2

Warm air
Humidify air
Clear particulates

Question 3

What is the lower respiratory tract?

Answer 3

Larynx
Trachea
Bronchi
lungs

Question 4

What are the functions of the lower respiratory tract?

Answer 4

Clear mucus
Allow elastic recoil
Allow gaseous exchange
Remain patent (open)

Question 5

What is the conducting portion?

Answer 5

Conduit /passageway
Air conditioning system
Nasal cavity to terminal bronchioles

Question 6

What is the respiratory portion?

Answer 6

Involved in respiration
Distal to terminal bronchioles - respiratory bronchioles to alveoli sacs.

Question 7

How is the respiratory system supported?

Answer 7

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.

Question 8

What do all tissues of the conducting portion have?

Answer 8

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.

Question 9

What do the respiratory layers look like?

Answer 9

see picture

Question 10

What is respiratory epithelium?

Answer 10

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

Question 11

What are the cells in the respiratory epithelium?

Answer 11

Goblet cells
Ciliated columnar cells
Basal cells - repair epithelium.

Question 12

What is the mucociliary escalator?

Answer 12

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

Question 13

What happens to the mucociliary escalator in smoking?

Answer 13

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.

Question 14

What is the nasal cavity?

Answer 14

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.

Question 15

What does the nasal cavity look like?

Answer 15

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.

Question 16

What is olfactory epithelium?

Answer 16

Produces and transmits the sense of smell.
It is found over the superior turbinate bone of the nasal cavity.

Question 17

What are the cells in the olfactory epithelium?

Answer 17

Bipolar olfactory neurones.
Supporting columnar cells
Basal cells - which regenerate olfactory bipolar neurones.

Question 18

What is the histology of the olfactory epithelium?

Answer 18

Pseudostratified columnar epithelium.
There are no cilia or goblet cells.
Instead the serous glands produce the mucous.

Question 19

What are the olfactory neurones?

Answer 19

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.

Question 20

What is the histology of the larynx?

Answer 20

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.

Question 21

What does the respiratory portion look like?

Answer 21

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

Question 22

What is the histology of the bronchiole?

Answer 22

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.

Question 23

What are club cells?

Answer 23

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

Question 24

What are the components of the alveoli walls?

Answer 24

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.

Question 25

What is the interstitial component of the alveolar septum?

Answer 25

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.

Question 26

What is pathology of the alveoli walls?

Answer 26

Can have diseases where wall is thickened, or destroyed, or blocks, leading to reduced gas exchange and shortness of breath.

Question 27

What does the alveoli wall look like?

Answer 27

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

Question 28

What are the alveoli cells?

Answer 28

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.

Question 29

What are type II pneumocytes?

Answer 29

Have lamellar bodies - produce lipid, a component of surfactant. Can differentiate into type I.

Question 30

What are alveoli macrophages?

Answer 30

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.

Question 31

Where is the typical respiratory epithelium found?

Answer 31

Nasal cavity Larynx Trachea Bronchi

Question 32

What supporting tissues help to keep the conducting portion patent?

Answer 32

From the trachea to the terminal bronchioles: C-shaped hyaline cartilage. There is some smooth muscle.

Question 33

What supporting tissues help to keep the respiratory portion patent?

Answer 33

Elastic tissue

Question 34

What does the trachea look like?

Answer 34

c-shaped cartilage, linked by smooth muscle. Lined by respiratory epithelia. Contains lots of glands in the submucosa. See picture

Question 35

What does the bronchus look like?

Answer 35

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.

Question 36

How does the histology change from the trachea to the bronchus?

Answer 36

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.

Question 37

How does the histology change from the bronchus to the bronchioles?

Answer 37

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.

Question 38

What are the short term changes of the bronchus if repeatedly exposed to irritants?

Answer 38

More goblet cells, more mucous, reduced clearance, causes a cough. Decreased clearance of pathogens - infections / inflammation.

Question 39

What are the long term changes of the bronchus if repeatedly exposed to irritants?

Answer 39

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.

Question 40

Here is a TEM of the air blood interface at the alveolus. What cell is indicated by A?

Answer 40

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.

Question 41

What is emphysema?

Answer 41

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.

Question 42

What is pneumonia?

Answer 42

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.

Question 43

What is pulmonary fibrosis?

Answer 43

Fibroblasts proliferate within the alveolar walls Deposit more extracellular matrix fibre Thicken septum and barrier for gas exchange. See picture

Question 44

How are the airways protected from pathogens?

Answer 44

Mucociliary escalator, traps pathogens Intraepithelial cells in the respiratory epithelium. Lymphoid tissue Macrophages / dust cells in the alveoli Club cells secrete anti-microbial factors.