8.1 Thoracic anatomy

Question 1

Structure of thoracic cage

Answer 1

Comprised of the sternum, thoracic vertebrae, ribs and costal cartilages.

Question 2

Roles of thoracic cage: in relation to movements of respiration and protection of thoracic contents.

Answer 2

1) acting as a dynamic generator of change in intrathoracic pressure to drive ventilation, particularly when diaphragmatic action alone is not sufficient.
2) protection of the thoracic viscera

Question 3

How is the thoracic wall structured to assist in ventilation?

Answer 3

The structure of the thoracic wall is both rigid due to its bony components and yet mobile courtesy of various points of articulation between these bones.

Question 4

Surface markings on the chest of the apex beat and borders of the heart

Answer 4

Apex beat: 5th left intercostal space close to MCL.
Heart borders: 3rd right costal cartilage (1cm lateral to sternum), 6th right costal cartilage (1cm lateral to sternum), 2nd left intercostal space (1cm lateral to sternum)

Question 5

Surface markings of lung apices

Answer 5

Lung apices: 2cm above medial 1/3rd clavicle, 6th rib in the mid-clavicular line (MCV), the 8th rib in the mid-axillary line (MAL) and the 10th rib in the para-vertebral line (PVL).

Question 6

Surface markings of the diaphragm

Answer 6

• left and right dome associated with the corresponding lung above.
• muscular part is attached to the xiphoid process of the sternum, the eleventh and twelfth ribs, lower costal cartilages and the first to third lumbar vertebrae (L1-3).
• its vertebral attachments are via muscular slips called crura, the right arising from L1-3 and the left from L1-2 vertebral bodies.
• peripheral edge of the muscular part of the diaphragm forms the costophrenic angle with the thoracic wall.

Question 7

How does the chest expand on inspiration?

Answer 7

During inspiration, movement of the ribs upwards and outwards increases the lateral and anteroposterior diameters of the thorax, while flattening of the diaphragm due to its contraction increases the vertical dimension of the thoracic cage.

Question 8

Why carry out percussion of the chest wall?

Answer 8

• determine whether the underlying tissues are filled with air, fluid, or solid material.
• detect dullness due to heart and liver, or resonance of gas-filled cavities i.e. lung fields and gas in stomach.

Question 9

What is auscultation?

Answer 9

Listening to sounds

Question 10

Auscultation of heart sounds

Answer 10

• aortic semilunar valve: medial 2nd right intercostal space
• tricuspid valve: medial 4th/5th left intercostal space just lateral to sternum
• pulmonary semilunar valve: medial 2nd left intercostal space
• mitral valve: 5th left intercostal space close to MCL

Question 11

Auscultation of breath sounds

Answer 11

Can hear breath sounds over lung fields -the pleural apices and bases of lungs- and over the trachea.

Question 12

Role of intercostal muscles and diaphragm in shallow breathing.

Answer 12

The drawing of minimal breath into the lungs; uses the intercostal muscles rather than the diaphragm.

Question 13

What is pneumothorax?

Answer 13

Collection of air within the pleural cavity surrounding a lung resulting in the lung collapsing.

Question 14

Diaphragm innervation

Answer 14

Phrenic nerves (origins C3,4,5).

Question 15

Internal intercostal muscles

Answer 15

The internal intercostals are thickest close to the sternum, their fibres running at right angles to those of the external intercostals and becoming membranous at the angles of the ribs. Forced expiration is thought to be dependent primarily upon contraction of the internal intercostal muscles, which depress the ribs. Diaphragm relaxes (can be pushed superiorly by accessory abdominal muscles), reducing thoracic volume.

Question 16

What are flail segments?

Answer 16

Flail chest= a segment of the thoracic wall separates from the rest of bony thoracic cage.
Separated from the rest of the thoracic wall, this ‘free’ portion moves paradoxically during breathing. Flail segment moves inwards on pressure fall (expiration) etc.

Question 17

Tension pneumothorax

Answer 17

Progressive increase in air within the pleural cavity with each breath, the air being unable to escape upon expiration – this leads to rapid deterioration in respiratory function. Venous return to the heart is impaired as the expanding pleural cavity places pressure on the heart and great vessels.

Question 18

Causes of pneumothorax

Answer 18

Trauma or interventional procedures may damage the parietal pleura, resulting in ingress of air into this potential space, or lung abnormalities (subpleural blebs and bullae), may rupture, damaging the visceral pleura, permitting air within the lung to enter the pleural cavity.

Question 19

Rib fractures consequences

Answer 19

Can lead to pneumothorax or flail chest.

Question 20

Segmental intercostal nerves & vessels.

Answer 20

Intercostal spaces contain the intercostal muscles, nerves, arteries, veins and associated lymphatic vessels and nodes.

Question 21

External intercostal muscles

Answer 21

Fibres of the external intercostal muscles run forwards and downwards from the tubercles of the ribs, becoming membranous close to the sternum.
They are most active during inspiration, pulling the ribs upwards and outwards.