The Thoracic cage and Lungs

Question 1

What are the features of the external intercostal muscles?

Answer 1

11 pairs of muscles that run inferioanteriorly.
Originate at the lower border of the rib and insert in the superior border of the rib below.
Act to elevate the ribs, increasing the vol of the thorax.
Innervated by intercostal nerves (T1-T11)

Question 2

What are the features of the internal intercostal muscles?

Answer 2

Lie deep to external
Run inferioposteriorly from the rib above to the rib below.
The interosseous part reduces the thoracic volume by depressing the ribcage, and the interchondral part elevates the ribs.
Innervated by intercostal nerves (T1-T11).

Question 3

What are the features of the innermost intercostal muscles?

Answer 3

Deepest, positioned at the most lateral part.
The interosseous part reduces the thoracic volume by depressing the ribcage, and the interchondral part elevates the ribs.
Innervated by intercostal nerves (T1-T11).

Question 4

What are the features of the transversus thoracis?

Answer 4

Runs from the inferior surface of the sternum and attaches onto the costal cartilages of ribs 2-6.
Acts to weakly depress the ribs.
Innervated by intercostal nerves (T2-6).

Question 5

What are the features of the subcostals?

Answer 5

Thin slips of muscle which run from the internal surface of one rib to the second and third ribs below. Share the action of the internal intercostals and are innervated by the intercostal nerves.

Question 6

What are the intercostal nerves?

Answer 6

Part of the somatic nervous system, supply the intercostal muscles and the skin.
Arise from thoracic spinal nerves T1-11 and run deep to the internal intercostal muscles in a groove just below the rib.

Question 7

What happens during inspiration?

Answer 7

The diaphragm contracts, flattening itself and lifting the thoracic cavity. The external intercostals contract causing elevation of the ribs and sternum. This leads to an increased volume in the thoracic cavity, and a decreased pressure. The pressure outside the lungs is higher and so air rushes in from an area of high pressure to low pressure.

Question 8

What happens during passive expiration?

Answer 8

The diaphragm and external intercostal muscles relax, returning them to their original position. The elastic recoil of the lungs returns them to their original volume. The reduced volume of air, gives increased pressure within the lungs. The increased pressure within the lungs is greater than outside the lungs which means that air rushes out of the lungs from an area of high pressure to low pressure.

Question 9

What happens during forced breathing?

Answer 9

Forced breathing, also known as hyperpnea, is a mode of breathing that can occur during exercise or actions that require the active manipulation of breathing. During forced breathing, inspiration and expiration both occur due to muscle contractions of the diaphragm and intercostal muscles, other accessory muscles including the scalenes and the obliques.

Question 10

What are the pleurae?

Answer 10

The pleurae refer to the serous membranes that line the lungs and thoracic cavity. There are two pleurae, one present on each lung. Each pleura can be divided into two parts:
Visceral pleura – covers the lungs.
Parietal pleura – covers the internal surface of the thoracic cavity

Question 11

What is the pleural cavity?

Answer 11

The potential space between the viscera and parietal pleura.
It contains serous fluid for lubrication, but also provides a pleural seal that holds the outer surface of the lungs against the inner surface of the thoracic wall. This ensure that when the thoracic cavity expands or reduces, the lungs will move with it due to the surface tension of the pleural fluid.

Question 12

What are the major differences between the visceral and parietal pleura?

Answer 12

The Visceral pleura covers the outer surface of the lungs and extends into the interlobar fissures. Only sensitive to stretch and receives autonomic innervation via the pulmonary plexus (derived from the sympathetic trunk and vagus nerve).

The Parietal pleura is thicker and can be subdivided according to the part of the body to which it is in contact with. For instance, it is made up of the mediastinal, cervical, costal and diaphragmatic pleura. Sensitive to pressure, pain and temperature and is innervated by the phrenic and intercostal nerves (T1-12).

Question 13

What are the recesses present in the pleural cavity?

Answer 13

The pleural cavity is not completely filled by the lungs. This gives rise to recesses – where the opposing surfaces of the parietal pleura touch, allowing for a place for fluid to collect.
There are two recesses present in each pleural cavity:
Costodiaphragmatic – located between the costal pleurae and the diaphragmatic pleura.
Costomediastinal – located between the costal pleurae and the mediastinal pleurae, behind the sternum.

Question 14

What is pneumothorax?

Answer 14

A pneumothorax (commonly referred to a collapsed lung) occurs when air or gas is present within the pleural space. This removes the surface tension of the serous fluid present in the space, reducing lung extension. Symptoms include chest pain, shortness of breath and asymmetrical chest expansion. Can occur spontaneously or as a result of direct blunt trauma.

Question 15

What are the physical features of the lung?

Label a diagram

Answer 15

Each lung consists of an apex (superior end), base (inferior), lobes separated by fissures, costal, mediastinal and diaphragmatic surfaces and anterior, inferior and posterior borders.

The right lung has 3 lobes: superior, middle and inferior separated by horizontal and oblique fissures. The left lung has superior and inferior lobes separated by an oblique fissure.

Question 16

What is the cardiac notch?

Answer 16

On the left lung, the anterior border is marked by a deep notch, created by the apex of the heart.

Question 17

What is the blood supply and draining system of the lungs?

Answer 17

The lungs are supplied with deoxygenated blood through the pulmonary arteries, but once the blood has received oxygen it leaves via the pulmonary veins.
The bronchial arteries branch from the descending aorta and supply the bronchi, lung roots, visceral pleura and supporting lung tissues. The right bronchial vein drains into the azygos vein, whilst the left drains into the accessory hemiazygos vein.

Question 18

How are the lungs innervated?

Answer 18

Nerve supply for the lungs comes from the pulmonary plexus.
Parasympathetic fibres come from the vagus (stimulate secretion from the bronchial glands, contraction of bronchial smooth muscle, and vasodilation of the pulmonary vessels)
Sympathetic fibres come from the sympathetic trunks (stimulate relaxation of bronchial smooth muscle, and vasoconstriction of the pulmonary vessels)
Visceral afferent conduct pain impulses to the sensory ganglion of the vagus nerve.

Question 19

What is the hilum of the lung?

Answer 19

The lung root is a collection of structures that suspends the lung from the mediastinum (only connection to mediastinum). Each root contains a main bronchus, pulmonary artery, two pulmonary veins, bronchial artery, lymphatic vessels, branches of the vagus and sympathetic nerves.

Question 20

Where is inhaled material likely to be found?

Answer 20

The right main bronchus is more vertical than the left and hence, inhaled material is more likely to pass into it.

Question 21

How is the bronchial tree divided?

Answer 21

The bronchial tree begins with the trachea, which divides into the left and right bronchus. Each bronchus enters the root of the lung, passing through the hilum. Inside the lungs, they divide to form the lobar bronchi – one supplying each lobe.
Each lobar bronchus then further divides into several tertiary segmental bronchi.
The segmental bronchi give rise to many conducting bronchioles, which eventually lead into terminal bronchioles. Each terminal bronchiole gives off respiratory bronchioles, which feature thin walled outpocketings that extend from their lumens. These outpockets are the alveoli, lined with type I and II pneumocytes – the site of gaseous exchange.

Question 22

What is a bronchopulmonary segment?

Answer 22

The area of lung ventilated by a tertiary division (segmental bronchi) of the bronchial tree. Each segment has its own bronchus and pulmonary artery branch. Pulmonary veins are intersegmental. There are 10 segments for the right lung and 9 for the left lung.
Conditions such as lung abscess may be localised to these segments and patients can be positioned accordingly to facilitate postural drainage. Secretions collected in anterior segments drain better if the patient is in the supine position, and posterior ones in the prone position.

Question 23

What are the features of the diaphragm?

Answer 23

Diaphragm is a double-domed sheet of skeletal muscle that separates the thoracic cavity from the abdominal cavity and undergoes contraction and relaxation to alter the volume of the thorax, thereby causing inspiration and expiration.
It is attached to the lumbar vertebrae and arcuate ligaments, costal cartilages 7-10, ribs 10-12, xiphoid process of the sternum. The right dome is slightly higher than the left due to the presence of the liver.

Question 24

What are the openings of the diaphragm?

Answer 24

Caval hiatus at T8: allows inferior vena cava and terminal branches of the right phrenic nerve to pass through.
Oesophageal hiatus at T10: allows oesophagus, right and left vagus nerves and branches of left gastric vein/artery to pass through.
Aortic hiatus at T12: allows aorta, thoracic duct and azygous vein to pass through.

Question 25

What is the action of the diaphragm?

Answer 25

During inspiration it contracts and flattens, increasing the volume of air in the thorax, causing air to be drawn in. During expiration it relaxes to return to its original shape, decreasing the volume of air in the thorax, causing air to leave.
Contraction of the diaphragm also causes blood to be drawn in from the inferior vena cava to the right atrium as intra-thoracic pressure is decreased and intra-abdominal pressure is increased.

Question 26

How is the diaphragm innervated?

Answer 26

Receives motor innervation from the phrenic nerve (left phrenic nerve supplies the left hemidiaphragm, right phrenic nerve supplies the right hemidiaphragm). Each phrenic nerve is formed in the neck within the cervical plexus, and contains fibres from spinal roots C3-C5.

Question 27

What is the blood supply of the diaphragm?

Answer 27

The majority of the arterial supply to the diaphragm is delivered via the inferior phrenic arteries, which arise directly from the abdominal aorta. The remaining supply is from the superior phrenic, pericardiacophrenic, and musculophrenic arteries. The draining veins follow the aforementioned arteries.

Question 28

What happens in diaphragmatic paralysis?

Answer 28

Trauma, compression, myopathies or neuropathies can cause a lesion to the phrenic nerve which can lead to diaphragmatic paralysis. This creates paradoxical movement - The affected side of the diaphragm moves upwards during inspiration, and downwards during expiration. Unilateral diaphragm paralysis is usually asymptomatic but If both sides are paralysed, the patient may experience poor exercise tolerance, orthopnoea (shortness of breath) and fatigue.

Question 29

What is a V/Q scan?

Answer 29

For ventilation (V) scans, a radioactive gas is breathed by the patient and a gamma camera is used to measure the position of the radioactivity within the alveoli.
For perfusion (Q) scans, radioactive technetium is attached to albumin and injected into the bloodstream. The location of the radioactivity in the lung is measured using a gamma camera.
V/Q scans can be used to diagnose diseases which cause an isolated blockage of the pulmonary artery without affecting the bronchi.

Question 30

Where is the internal mammary artery located?

Answer 30

Internal mammary artery (or internal thoracic artery) originates from the subclavian artery and runs vertically down behind the costal cartilages on the inside of the thoracic wall and onto supply the abdominal wall and diaphragm, eventually joins the external iliac artery. Not prone to atherosclerosis.

Question 31

What is intercostal recession?

Answer 31

Patients with extreme breathlessness may need to use many accessory muscles to generate much lower pressure within the thorax during inspiration and higher pressures during expiration. In some patients the pressures needed to support breathing overcome the intercostal muscles and we can observe ‘intercostal recession’, the intercostal spaces suck in during inspiration. It’s an important sign of advance respiratory distress.

Question 32

Which arteries are commonly involved in a heart bypass surgery?

Answer 32

One way to treat narrowing of the coronary arteries of the heart is to use another blood vessel to bypass the blockage. The left internal mammary artery (IMA) runs very close to the left anterior descending (LAD) coronary artery, grafting of the IMA to the LAD is common.

Question 33

What is an electrocardiograph?

Answer 33

Electrocardiograph measures electrical activity in the heart. A change in a patient’s ECG is a really valuable test. It is essential that six chest electrodes are placed identically for every ECG.

Question 34

What are the surface markings of the lowest extent of the lungs?

Answer 34

Beginning at the midclavicular line, with the lowest part of the lung lies at the tip of the 6th rib, at the mid-axillary line at the 8th rib and posteriorly the 10th rib.