Thorax, tracheobronchial tree and lungs

Question 1

Describe the structure of the thoracic wall

Answer 1

Twelve thoracic vertebrae
12 ribs
Intercostal muscles (external, internal and innermost)
Sternum (manubrium, body and xiphoid process)

Question 2

What is the neurovascular supply to the thoracic wall?

Answer 2

Blood supply:
Anterior intercostal arteries (arising from internal thoracic and muscolophrenic arteries)
Posterior intercostal arteries (arising from the descending aorta)

Nerve supply:
Intercostal nerves anterior rami of spinal nerves T1 to T11)

Question 3

How does the diaphragm aid with breathing?

Answer 3

Depresses (flattens) on inspiration to decrease intrathoracic pressure and elevates during expiration pushing air out of the lungs

Question 4

What are the functions of the thoracic wall?

Answer 4

1. Breathing - thoracic wall moves anteriorly and laterally to increase volume of the thoracic cavity
2. Protection of vital organs - heart, lungs, major vessels and some abdominal viscera

Question 5

What are the layers of the thoracic wall from the skin inwards?

Answer 5

Skin - Superficial fascia - External intercostal muscles - Internal intercostal muscles - Innermost intercostal muscles - Parietal pleura - Pleural cavity - Visceral pleura - Lungs

Question 6

Name the accessory muscles of respiration and their function

Answer 6

Scalene muscles - elevate rib cage

Sternocleidomastoid - elevate rib cage

Pectoralis - increases diameter of ribcage

Question 7

What structures pass through the hilum of the lung?

Answer 7

2 pulmonary arteries (carrying deoxygenated blood to the lungs)
2 pulmonary veins (carrying oxygenated blood away from the lungs)

Question 8

Where in the tracheobronchial tree are aspirated objects most likely to be located?

Answer 8

In the right main bronchi due to the fact that this bronchi is more wide and vertical making it easier for aspirated objects to reach this location

Question 9

What and where is the costodiaphragmatic recess?

Answer 9

Region in the pleural cavity referring to the space between the inferior aspect of the lungs and the inferior margin of the pleural cavities - the lungs are able to fill this space during forced inspiration

Question 10

What is the neurovascular supply to the diaphragm?

Answer 10

Blood supply:
Superior phrenic arteries (arising from thoracic aorta)
Branches of the internal thoracic arteries
Inferior phrenic arteries (arising from abdominal aorta)

Nerve supply:
Phrenic nerve (C3-5) 
Some intercostal nerves

Question 11

How does the tracheobronchial tree divide as it moves down the lungs?

Answer 11

Trachea 
Main bronchi (primary division)
Lobar bronchi (secondary division)
Segmental bronchi (tertiary division)

Question 12

What is the structure of the diaphragm?

Answer 12

2 muscular domes that converge in a large central tendinous region

Question 13

What nerves innervate the accessory muscles of respiration?

Answer 13

Scalene muscles - anterior rami of C3-C8

Sternocleidomastoid muscles - CN XI (Accessory)

Pectoralis minor - Medial pectoral n. (C8, T1)

Pectoralis major - Clavicular head = lateral pectoral n.
Pectoralis major - Sternal head = medial pectoral n.

Question 14

Where in the intercostal space would you find the neurovascular contents and why is this clinically relevant?

Answer 14

The neurovascular bundle (made up of the artery, vein and nerve supplying the intercostal space) lay in the costal groove - an indention on the inferior aspect of each rib bone.
This is relevant as it must be avoided during invasive procedures by incising the inferior aspect of the intercostal space.

Question 15

Describe the arrangement of the pleural layers (with their points of reflection)

Answer 15

Parietal pleura lines the thorax whilst visceral pleura lines the lungs with a point of reflection at the hilum of each lung. The POTENTIAL space between the pleura is the pleural cavity.
Surface tension holds the 2 closely together.

Question 16

What are the names given to the various aspects of the parietal pleura?

Answer 16

Costal pleura - related to ribs and intercostal spaces
Diaphragmatic pleura - covering diaphragm
Mediastinal pleura - covering mediastinum

Question 17

What innervates the parietal pleura?

Answer 17

Intercostal nerves and phrenic nerve (C3,4,5)

Question 18

What is the mediastinum?

Answer 18

A central region between the lungs bounded by the pleural cavities that contains all the principal tissues and organs of the chest except the lungs (e.g. heart, thyroid)

Question 19

Describe the basic embryological development of the lungs

Answer 19

Respiratory system is an outgrowth (diverticulum) of the gut tube - occurs at approx. 4 weeks
Grows into multiple buds which develop either into mesoderm (blood supply, smooth muscle, cartilage and visceral pleura) or endoderm (linings and glands)
Respiratory epithelia develops at approx. 26 weeks
Lungs are not fully developed until age 7-10

Question 20

How does the trachea develop and how can this go wrong?

Answer 20

The oesophagus and the trachea separate at 4-5 weeks by forming a septum between the two.

If this goes wrong then a blind-ended oesophagus can form or a fistula (in which the oesophagus and the trachea are still attached)

Question 21

What is the triangle of safety and its clinical relevance?

Answer 21

The triangle of safety is a space for chest drains to be inserted and is found in the region between the mid-axillary line, the posterior border of the pectoralis major with the drain being inserted into the inferior aspect of the 4th intercostal space

Question 22

What are the surface markings of the oblique fissures?

Answer 22

Spinous process of T3 posteriorly to the 6th costal cartilage anteriorly

Question 23

What are the surface markings of the horizontal fissure?

Answer 23

Passes from the 4th costal cartilage at the sternum to the 4th rib mid-axillary line.

Question 24

How does respiratory epithelium differ between the trachea and the bronchi (and bronchioles)?

Answer 24

Bronchi/Bronchioles epithelium is less tall and contains less goblet cells; contains more elastin (in Lamina Propria) and fewer submucosal glands
Cartilage support replaced by smooth muscle as you move distally down the tracheobronchial tree

Question 25

How are the ribs classified?

Answer 25

Vertebrosternal = ribs 1-7
Vertebrocostal = ribs 8-10 
Floating = ribs 11-12

Question 26

What are the functions of the external and internal intercostal muscles?

Answer 26

External = inspiration 
Internal = expiration

Question 27

How does division of the lungs differ between right and left?

Answer 27

Right has 3 lobes (superior, middle and inferior divided by oblique and horizontal fissures)
Left has 2 lobes (superior and inferior divided by an oblique fissure)

Question 28

What nerves can potentially be damaged by lung pathology?

Answer 28

Phrenic nerves (pass anterior to hilum)
Vagus nerves (pass posterior to hilum)

Question 29

What is a tension pneumothorax and what consequences does it have?

Answer 29

Progressive build up of air within the pleural space leading to:

Mediastinal shift
Tracheal deviation 
Diaphragmatic depression 
Unilateral hyperinflation 
Increased intercostal space size
Hyper-resonance

Question 30

What are the surface markings of the trachea?

Answer 30

Palpable via sternal notch
Bifurcation = T4/5
Enters lung hilum at T5/6