Thorax

Question 1

What is the structure of the thorax

Answer 1

It is egg-shaped, with the narrower end superior towards the neck and the wider end inferior.

the upper and lower parts of the thoracic cage are cut off obliquely so that the superior opening (thoracic inlet) slopes downwards and forwards at approximately 45°, whereas the inferior opening slopes (thoracic outlet) downwards and backwards

A bony and muscular structure:
Bony components:
12 thoracic vertebrae posteriorly
12 pairs of ribs laterally and their costal cartilages
Ribs pass from behind anteriorly, connecting the thoracic part of the vertebral column to the sternum; as the ribs pass anteriorly, they also slope downwards. Consequently, the anterior end of the rib is at a lower level than its posterior part.

Sternum anteriorly

Muscular component:
Intercostal space - space between adjacent ribs; filled by muscles, among which are found the intercostal vessels and nerves

sixth intercostal space is probably the longest, with those above and below gradually decreasing in length

upper spaces are wider than the lower ones, which also tend to be narrower posteriorly

Question 2

What is the function of the thorax

Answer 2

Assists respiration - primary aspect

In inspiration - intrathoracic volume is increased by action and movement of ribs and diaphragm to increase anteroposterior, lateral and vertical dimensions of thorax to cause intrapulmonary pressure to be more -ve - air is sucked in

In expiration - helps passive expiration to increase intrathoracic pressure to expel air

Protection of vital organs, i.e. heart, lungs, mediastinum, liver and kidneys - from external trauma via strong and flexible thorax

Provides muscle attachments - via irregular bony landmarks of thoracic vertebrae, ribs and sternum, also clavicle

Question 3

Describe structure of typical ribs

Answer 3

Ribs 3-9

Large head on posterior end with two facets for articulation with body of own vertebra and that above.

Crest on centre of head separating two facets; costovertebral ligament from crest to insert and blend with IV disc of its own vertebra

Short flattened neck joins head to the shaft

Prominent tubercle marked at the junction on posterior aspect of neck .

small oval articular facet on tubercle posteromedial part for articulation with transverse process of corresponding vertebra; Non-articular and roughened lateral surface

Approximately 3 cm lateral to the tubercle the shaft turns downwards and inwards, giving it a twisted appearance; this is the angle of the rib

Long slender shaft with subcostal groove - continuation of neck laterally

Articulates anteriorly with its corresponding costal cartilage

Question 4

What are the true ribs

Answer 4

Upper 7 ribs (pairs)

Costal cartilages of the upper seven ribs articulate directly with the sternum

Question 5

What are the false ribs

Answer 5

Lower 5 ribs (pairs)

Costal cartilages of lower 5 ribs either indirectly have an attachment to sternum or no attachment (ribs 11-12)

Question 6

What are the floating ribs

Answer 6

Ribs 11 and 12

Ribs 11 and 12 have no anterior connection with other ribs or with the sternum

No articulation with TP of T11-12

Rib tips are palpable

Question 7

What is the structure of the atypical ribs 1

Answer 7

Rib 1 structure:
C - shaped - short and sharply curved

Head has a single facet for articulation with the body of the T1

Shaft has superior and inferior surfaces, and medial and thickened lateral borders.

Shaft is not angled and remains broad throughout its length

Lower surface of shaft has a shallow subcostal groove running longitudinally

Superior surface of shaft has two grooves separated by scalene tubercle

Anterior groove of shaft transmits the subclavian vein, and the posterior groove the subclavian artery and first thoracic nerve; the two vessels being separated by scalenus anterior attaching to the scalene tubercle

Anterior and posterior to these grooves, the shaft is roughened by muscle and ligament attachments

Like other ribs, the tubercle has a facet for articulation with the transverse process

Anteriorly, it articulates with the manubrium by its costal cartilage forming first sternocostal joint - a primary cartilaginous synchondrosis

Question 8

What is the structure of atypical rib 2

Answer 8

Rib II, like rib I, is flat but twice as long. It articulates with the vertebral column in a way typical of most ribs

Question 9

What is the structure of atypical rib 10

Answer 9

shows many of the features of a typical rib, being long with a definite angle

The head of rib X has a single facet for articulation with its own vertebra

Question 10

What is the structure of atypical rib 11 and 12

Answer 10

Ribs XI and XII articulate only with the bodies of their own vertebrae and have no tubercles or necks. Both ribs are short, have little curve, and are pointed anteriorly

Rib 11 - About half the length of the 10th rib

Rib 12 - very short and ‘dagger-like’ in appearance

Question 11

Describe structure and function of costal cartilages

Answer 11

Structure: Hydroelastic properties - relatively mobile thus can flex in all directions equally

Function: Attach anterior aspect of corresponding ribs to sternum

Question 12

Describe the contents of the instercostal spaces

Answer 12

Intercostal spaces - space between adjoining ribs

Contents: neurovascular bundle
○ Intercostal arteries & veins
○ Intercostal nerve
○ These lie in the costal groove along the inferior margin of the superior rib and pass in the plane between the inner two layers of muscles.

Muscles: 3 layers
	○ External Intercostal
	○ Internal Intercostal
	○ Innermost intercostal
	○ 3 layers of muscles fibres run 90 degrees to each other - helps with their respiratory function to change internal diameters of thorax to affect intrathoracic pressure for respiration

Question 13

Describe the structure of the sternum

Answer 13

Consists of:
	• Manubrium
	• Body
	• Xiphoid process
	• Attachment of ribs

Angle of louis - use to orientate to 2nd rib

Question 14

Describe movement of ribs in inspiration

Answer 14

PUMP HANDLE -Movement of the upper ribs (1-5th:6-7th ) about an axis along their necks causes their anterior ends to be raised, and with them, the body of the sternum so the anteroposterior diameter of the thorax is increased

			BUCKET HANDLE -Movement of ribs 6-7th:8-10th results in an outward and upward movement of their anterior ends. This lateral excursion of the ribs and their costal cartilages causes a widening of the infrasternal angle with a consequent increase in the transverse diameter of the thorax. Because the shape of the costotransverse joints of these lower ribs is flat, there is both rotation and gliding of one bone against the other

		Intermediate ribs 6 and 7 show both pump-handle and bucket-handle types of movement. Ribs 11 and 12 are not attached anteriorly and thus have very little influence on increasing the transverse diameter of the thorax.

Increase in vertical diameter - Diaphragm descends

Question 15

Describe movement of ribs in expiration

Answer 15

During expiration, the reverse movements of the ribs and sternum occur, with a decrease in both the anteroposterior and transverse thoracic diameters

Question 16

Describe normal movement of ribs in respiration

Answer 16

Inspiration : expiration ratio = 1:2

Both sides of chest should move in symmetry

Question 17

Describe muscle action in inspiration

Answer 17

Inspiration requires the activity of the diaphragm and external intercostal muscles to increase the diameters of the thoracic cage, which lowers the intra-thoracic pressure, drawing air into the lungs.

Question 18

Describe muscle action in expiration

Answer 18

Expiration is the relaxation of muscles and the elastic recoil of tissues to expel air from the lungs.

Question 19

Describe muscle action in forced expiration

Answer 19

Forced expiration requires the recruitment of muscle activity to enhance the power of air expulsion.