Histology of the Respiratory System

Question 1

Describe the mucous and serous membrane in/on the lungs

Answer 1

The respiratory system contains a mucous membrane containing mucus secreting cells to varying degrees and a serous membrane lining the pleural sacs which envelope each lung. The lung appears shiny due to it being covered by moist pleura.

Question 2

What is the difference between the respiratory and conducting portions of the respiratory tract?

Answer 2

Conducting portion moves air and includes tubes all the way down to the bronchioles whilst the respiratory portion contians alveoli and includes respiratory bronchioles.

Question 3

What are the different structures of the respiratory tract - which are conducting and which are respiratory portions?

Answer 3

Component of the repiratory tract: nasal cavity, pharynx, larynx, trachea, primary bronchi, secondary brinchi, brochioles, terminal bronchioles, repiratory brinchioles, alevolar ducts and alveoli. (the last 3 are the repiratory portion. Everywhere down to the primary bronchi is extrapulmonary and the remainder are intrapulmonary.

Question 4

Describe the cell types of the different portions of the respiratory tract

Answer 4

Nasal cavity to the largest bronchioles are all lined with a pseudostratified ciliated epithelium with goblet cells sereting mucus. Bronchioles to terminal bronchioles are simple columnar epithelium with cilia, Clara cells but no goblet cells. The repsiratory bronhcioles and alveolar ducts are lined with simple cuboidal epitheloum with clara cells and very few cilia. Finaly the alveoli have type 1 and 2 pneumocytes which are squamous cells.

Question 5

Describe the histology of the non olfactory region of the nasal cavity?

Answer 5

Nasal cavities: Non-olfactory regions contain venous sinuses in their lamina propria. The venous plexuses swell every 2-30 minutes alternating air flow from side to side preventing overdrying. Patency maintained by surrounding cartilage or bone.

Question 6

Describe the olfactory regions of the nasal cavity

Answer 6

The Olfactory region has particular thick pseudostratified epthelium located in the posterior superior regions of each nasal fossa. There are no goblet cells and it contains microvilli. Oflactory cells are bipolar neurones have dentries that extend to the surface forming a swelling. From this swelling non motile cilia extend and increase the surface area to respond to odours. The lamina propria blends with the sub mucosa. Bowman’s/oflactory glands secrete serous liquids to the surface for odours to dissolve in.

Question 7

Describe the histology and function of the vocal cords, ventricles and ventricular folds?

Answer 7

The ventricular folds and the vocal cords are lined with pseudostrafied epithelium containsing mucous glands and numerous lymph nodules. The ventricles and the ventricular folds contribute to the resonance of the voice. The vocal cords contain a vocal ligament of elastic fibres and a vocalis muscle. The vocal cords close to build up pressure when coughing.

Question 8

Describe the histolgoy of the tracheal wall

Answer 8

1. Mucosa (epithelia, lamina Propria and muscularis mucosa) – ciliated Pseudostratified (sometimes called respiratory epithelium) Secretions from here and the submucosal glands contains: mucins, water, lysozyme, antiproteases and lymphocytes contribute immunoglobulins. 250 cilia per cell beating at 12Hz, mucus blanket about 5um thick, lamina Propria has many immune cells and a layer of elastic fibres.
2. Submucosa containing mucus glands
3. Muscularis externa
4. Horse ring shaped ring of cartilage that can be transformed to bone with age, opposite this ring shaped cartilage on the other side of the trachea is a Fibroelastic membrane containing the trachealis muscle – this constricts the trachea expelling air more quickly.
5. Adventitia

Question 9

Describe the histology of the bronchus

Answer 9

1. Mucosa – ciliated Pseudostratified (no lamina Propria)
2. Submucosa containing mucus glands
3. Irregular Crescent shaped ring(s) of cartilage that can be transformed to bone with age

Question 10

Describe the histology of the bronchioles

Answer 10

1. Epithelia – simple columnar merging towards simple cuboidal
2. Smooth muscle
3. Surrounding alveoli keep it open

Question 11

Describe the histology of the Alveoli

Answer 11

1. Very thin simple squamous cells (type 1 alveolar cells) allowing efficient gas exchange
2. Simple cuboidal cells (type 2) which release surfactants preventing the alveoli collapsing in on themselves.
3. Many macrophages (which get washed out of images taken by microscopes).

Question 12

Which blood supply provides the lung’s with nutrients?

Answer 12

The bronchial arteries feed the bronchioles with nutrient and oxygen not the pulnonary veins.

Question 13

Why does asthma make it hard to expel air?

Answer 13

In asthma allergens cause bronchoconstriction making it very hard to expel air form the airways because during expiration the bronchial walls are no longer maintained open by the surrounding alveoli.

Question 14

What are clara cells

Answer 14

Clara cells are modified goblet cells. These secrete a surfactant lipoprotein preventing the walls sticking together during expiration as well as the abundant clara cell protein (CC16).

Question 15

What do alveoli open into?

Answer 15

Alveoli open into a respiratory bronchiole, an alveolar duct, and alveoli sac or another alveolus. Their walls have abundant capillaries and are supported by a basketwork of elastic and reticular fibres.