Pleura and the lungs

Question 1

Mediastinum

Answer 1

The region between the right and left pleura which contains many structures:

• Oesophagus
• Trachea
• Heart
• Nerves
• Blood vessels

Question 2

Thoracic cavity

Answer 2

Essentially the ‘chest’ region that contains:

• The right and left pleural cavity.
• The mediastinum and its structures.

Question 3

Embryonic development of the pleura and the lungs.

Answer 3

Starts to occur during weeks 4-6, originating from the endodermal layer.

The primitive trachea branches out to form lung buds.

Lung buds push out into the pericardioperitoneal canal and rapidly divide.

As the lung buds push out, it takes its lining with it, eventually forming the visceral pleura.

The parietal is separated from the visceral pleura through the pleural cavity which develops from the pericardioperitoneal cavity.

Question 4

Visceral pleura

Answer 4

The deeper pleura that adheres to the lungs, difficult to separate from the lung.

Connects with the parietal pleura at the hilum (lung root).

Question 5

Parietal pleura

Answer 5

The more superficial pleura that lines the internal thoracic wall. It is separated from the visceral pleura through the pleura cavity.

This pleura is divided into 4 parts, according to its location:
- Cervical pleura (near the root of the neck).

• Diaphragmatic pleura (on top of the diaphragm).
• Costal pleura ( facing the ribs).
• Mediastinal (facing the mediastinum).

Question 6

Pleural cavity

Answer 6

The space that separates the visceral pleura from the parietal pleural.

Contains serous fluid that allows surface tension between both pleura. The fluid is mainly composed of water which allow H-bond formation.

This allows the lung to always expand as the visceral pleura is always attached to the parietal pleura.

When the distance between the two pleura increases due to invasion of excess material (pleural effusion/ pneumothorax), this disrupts the cohesion and can cause lung to collapse

Pleural effusions:

• Haemothorax (blood)
• Chylothorax (chyle)
• Pyothorax (pus)

Question 7

Recess (pleural cavity)

Answer 7

Excess pleural cavity present around the lung in certain regions.

Costomediastinal (anteriorly, near the cardiac notch)
Costodiaphragmatic (posteriorly)

Fluid can be sampled from these areas for diagnostic tests.

Question 8

Innervation of the parietal pleura

Answer 8

Cervical pleura: 1st intercostal nerve.

Costal pleura: Intercostal nerves.

Mediastinal pleura: Phrenic nerve.

Diaphragmatic pleura: Phrenic nerve and lower intercostal nerves.

Question 9

Innervation of the visceral pleura.

Answer 9

Autonomic pulmonary plexus: branches of the vagus nerve and sympathetic trunk.

There are no sensory neurones at the visceral pleura. Therefore it is not possible to feel pain from the visceral pleura. All pain is from the parietal pleura.

Question 10

Surfaces of the lung

Answer 10

Costal- facing the ribs

Mediastinal- facing the mediastinum.

Diaphragmatic (base)- facing the diaphragm.

Question 11

Borders of the lung

Answer 11

Anterior, inferior and posterior border.

Question 12

The right lung

Answer 12

Larger, heavier, shorter and wider lung containing:

3 lobes, separated by 2 fissures:
Superior
Middle
Inferior

Fissures- oblique and horizontal.
Contains 10 bronchopulmonary segments.

Question 13

The left lung

Answer 13

Smaller lung.

Contains 2 lobes separated by one fissure- the oblique fissure.
Superior and inferior lobes.

Cardiac notch- space for where the heart sits.

Contains lingula, ‘tongue’-like structure.

Question 14

Hilum

Answer 14

Root of the lung that contains the structures that enters and exits the lungs.

Contains:
- Main bronchus, posteriorly.

• Pulmonary arteries, superiorly.
• Pulmonary veins, inferiorly.
• Pulmonary nerve plexus entry.
• Lymphatic vessels and nodes.
• Bronchial veins and arteries.

Question 15

Trachea

Answer 15

Main airway that starts from the larynx (at C6) and bifurcates at T4/5 (sternal angle).

Contains:
- C-shape hyaline cartilage that allows its flexibility and resistance to tension.

• Trachealis muscle, posteriorly which allows constriction of the airway.
• Carina- the point at which it bifurcates into the bronchi.
• Ciliated epithelium and mucous membranes.

Question 16

Primary bronchus

Answer 16

Main bronchus that passes through the hilum into the lung.

Two main bronchi which each supply a lung.

The right main bronchus is wider, shorter and more vertical. This has clinical significance- foreign objects are more likely to enter right lung.

All contains cartilage

Question 17

Secondary bronchi. (Lobar bronchi)

Answer 17

Branches of the main bronchi that supply each lobe of the lung.

Right lung contain 3 secondary bronchi as it has 3 lobes.
Left lung has 2 secondary bronchi as it has 2 lobes.

Question 18

Tertiary bronchi. (segmental bronchi)

Answer 18

Branches of the secondary bronchi that supplies a bronchopulmonary segment.

Question 19

Bronchopulmonary segment.

Answer 19

A region in the lung supplied by a specific tertiary bronchus and a single branch of the pulmonary artery.

There are 10 in the right lung and 8-10 in the left lung.

Each segment functions independently so can be surgically resected in case of pathology, (i.e cancer, infection).

Question 20

Lymphatic drainage of the lung.

Answer 20

Tracheal node- next to the trachea

(superior and inferior) Tracheobronchial nodes: next to the junction between the trachea and bronchus.

Bronchopulmonary nodes: Next to the junction between the lung and bronchus.

All the nodes drain into the right lymphatic duct and thoracic duct which into the right and left venous angle.

Question 21

Innervation of the lung.

Answer 21

Under autonomic nervous control:

Sympathetic nerves- Originated from the sympathetic trunk.
Actions- causes bronchial musculature to dilate and pulmonary vasculature to constrict (as more blood supply is directed to skeletal muscles).

Parasympathetic nerves: Vagus nerves, from C10.
Actions- causes bronchial musculature constriction and pulmonary vasculature dilation.

Question 22

Bronchioles

Answer 22

Branches from the tertiary bronchi that contain no cartilage. Supplies many parts in a bronchopulmonary segment.

The terminal bronchiole: The last bronchiole without alveolar out pockets. Gives rise to many generations of respiratory bronchioles.

Respiratory bronchioles: Contain out pockets of alveoli.

Question 23

Alveoli

Answer 23

‘Air sac’ surrounded by capillaries where gaseous exchange takes place.

Alveolar ducts are lined by alveoli and lead to alveolar sacs.

Two cell types that form alveoli:

• Type 1 pneumocytes, 95% of cells.
• Type 2 pneumocytes, 5% of cells. Productes lung surfracant.

Question 24

Bronchial circulation

Answer 24

Bronchial arteries supply the lung and visceral pleura.

Question 25

Left bronchial arteries

Answer 25

Branches from the abdominal, descending aorta

Question 26

Right bronchial arteries

Answer 26

Branches from the intercostal arteries

Question 27

Bronchial veins

Answer 27

Left veins drain into the Azygos vein Right veins drain into the left superior intercostal veins or the accessory hemiazygos veins.