11 Thoracic Wall and Lung

THE THORAX

Thoracic Wall and Lung

Learning Objectives

By the end of the course students will be able to:

1. Describe the bony elements of the thorax, including the sternum, ribs and costal cartilages
2. Identify the contents of a typical intercostal space, including muscles, nerves, and vessels.
3. Describe the process of respiration and the movements the thoracic cage makes when the intercostal muscles and diaphragm are stimulated
4. Describe the structure and surface projections of the pleural cavity. Identify its recesses.
5. Distinguish between parietal and visceral pleura and between parietal and visceral pericardium. Identify the various divisions of the parietal pleura.
6. Identify and describe the location of the lungs in the thoracic cavity
7. Identify the pulmonary arteries, veins and bronchi in the hilum of the lungs
8. Define a bronchopulmonary segment and its general organization
9. Describe the lymphatic drainage of the lungs and pleurae and the nodes involved

Reference: Moore, Clinically Oriented Anatomy, chapter 1.

Particularly relevant Blue Boxes in Moore 

●Dislocation and Separation of Ribs, p. 85

●Intercostal nerve Block, p. 97

●Pulmonary Collapse, p. 120

●Pneumothorax, Thoracentesis, p. 121

●Insertion of a Chest Tube, p. 121

●Auscultation of Lungs, p. 123

●Bronchoscopy, p. 123

To access the Netter Presenter Database click here

Grant’s Dissector, 15th Edition, pp 63 – 73

To access Gray’s Photographic Dissector section on the Thoracic Wall and Lung click here

To access the Primal Pictures software click here 

Check out the Primal Pictures model of the Thorax and the Lungs

 
THE THORAX

THE THORACIC CAGE (Netter 183; Moore 74-81)

The thoracic cage is a bony and cartilaginous structure which surrounds the thoracic (chest) cavity. It supports the pectoral (shoulder) girdle and upper limbs and provides attachment points for many muscles of the neck, back, chest and shoulders.One of the primary functions of the thorax is respiration. The ribs and the diaphragm move so that the thoracic cavity increases and decreases in size during the inspiratory and expiratory phases of respiration. It also aids in returning venous blood back to the heart because of the negative pressure produced with respiratory movements.

Secondarily, it serves to protect the organs located within its cavity plus some organs of the abdominal cavity.

The main thoracic organs which you will examine in your dissection of the thorax are the:

• lungs
• heart

The other structures are:

• aorta and its branches
• superior and inferior vena cavae
• trachea and primary bronchi
• sympathetic trunks and their associations
• azygos and hemiazygos venous systems

The bony thorax:

• is flattened antero-posteriorly in the adult.
• is covered by upper limb muscles (Netter 185, 186.

The thoracic spinal nerves supply the thoracic region as well as the anterior abdominal wall (Netter 188, 253).

Ribs and Thoracic Vertebrae

The ribs enclose and protect some of the abdominal viscera (Netter 194).

The first rib is atypical. It is short, flat and more sharply curved than any of the others. It has upper and lower surfaces, with outer and inner borders, and on its head there is one articular facet only.

The upper surface has two grooves for the subclavian artery and subclavian vein, separated by the scalene tubercle for the attachment of the scalene anterior muscle.

This rib has very little movement during respiration and serves as a base attachment for the intercostal muscles and the ribs below. In other words, during respiration, the muscles in the first intercostal space contract, drawing up on the rib below, which in turn allows its muscles to pull up on the rib below it and so forth, until all ribs have moved through a small distance. The combined movements increase the transverse and anteroposterior diameters of the thoracic cavity.

The 12 thoracic vertebrae (Netter 154) have the following landmarks:

• The body or centrum is flattened, on the left side, from T6 down due to the impression of the descending aorta.
• The pedicle
• The transverse processes
• The spinous processes
• The articular processes (synovial joints)
• The laminae, which are removed during a laminectomy to gain access to the spinal cord.
• The vertebral foramen forms the vertebral canal with the vertebral foramina from other vertebrae.
• The intervertebral foramina formed by vertebral notches are the exit points for the spinal nerves.

The 12 pairs of ribs (Netter 183, 184) are characterized by the following:

• rib + cartilage = costa
• Ribs 1-7 are classified as vertebrosternal (true ribs)
• Ribs 8-10 are classified as vertebrochondral (false ribs).
• Ribs 11 and 12 are classified as vertebral (floating).

The different parts of the ribs have the following articulations:

• The head articulates with the sides of bodies of 2 vertebrae (at the same and superior levels (Netter 184), except for rib 1, 11, and 12. It is attached to the intervertebral disc by an intraarticular ligament, but not ribs 1, 11, and 12.
• The neck
• The articulating tubercle attaches to the transverse process of vertebra at the same level (rib 6 is attached to T6); this is a synovial joint called the costotransverse joint.

Costotransverse joints (Netter 184)

●The superior joints (ribs1-7) permit mostly rotation of the rib and the inferior ones  (ribs 8-10) permit mostly gliding movement for the articulated rib.

●Attachments are by medial (neck) and lateral (tubercle) costotransverse ligaments. The superior costotransverse ligament descends from the superior transverse process to the crest of inferior rib.

The rib has the following landmarks (Netter 184):

• The crest for attachments of the superior costotransverse ligaments.
• The angle
• The body
• The costal groove

The costovertebral articulation is formed by the joint of the head and the joint of the tubercle of the rib (Netter 184).

The sternocostal articulation: the joint cavity is divided into 2 by an intraarticular ligament and closed ventrally by ligaments radiating from the perichondrium to the sternum .

Interchondral joints exist between the costal cartilages of ribs 7, 8, and 9 The sternum contains red bone marrow and is thus used for sternal punctures in diagnosing blood diseases.

The Manubrium (Netter 184)

• has the jugular (suprasternal) notch.
• articulates with the clavicle at the sternoclavicular joint (the only bony attachment point of the upper limb to the trunk), rib 1 and half of rib 2.
• forms the attachment points for the pectoralis major, sternocleidomastoid, sternohyoid and sternothyroid muscles.

The sternal angle (of Louis) or manubriosternal joint is a cartilaginous joint and is at about the same level as: (Netter 184)

• the 2nd rib and T4/T5 vertebral body
• the carina of trachea.
• the aorta crossing from right to left (the beginning of the ascending aorta).
• the horizontal plane which separates the superior mediastinum from the inferior.

The second intercostal space is used for listening to aortic (right) and pulmonary (left) valves .

The body of the sternum articulates with half of the head of rib 2 and the heads of ribs 3-7.

• contains red bone marrow.
• forms the attachment site for the pectoralis major anteriorly (Netter 185).

The Xiphoid Process (Netter 183, 184)

is at the level of the 6th thoracic dermatome on the anterior surface of the body.

The thoracic inlet is located superiorly and is the site of entrance of the viscera and vessels from the head, neck and upper limb into the thorax The thoracic outlet is closed by the diaphragm, pierced by the inferior vena cava (T8), aorta (T12) and esophagus (T10), and innervated by the phrenic nerves (C3, 4, 5; )

Clinical Considerations:

Flail Chest is a loss of stability of the thoracic cage that occus when a segment of the anterior or lateral thoracic wall moves freely because of multiple rib fractures, allowing the loose segment to move inward on inspiration and outward on expiration. Flail chest is an extremely painful injury and impairs ventilation thereby affecting oxygenation of the blood and causing respiratory failure.(Click here to view an image and video of flail chest – from NEJM series of Clinical Videos)

Rib fractures: Fracture of the first rib may injure the brachial plexus and subclavian vessels. The middle ribs are most commonly fractured and usually result from direct blows or crushing injuries. The broken ribs may cause pneumothorax and lung or spleen injury. Fractures of the lower ribs may tear the diaphragm, resulting in a diaphragmatic hernia.

Thoracic outlet syndrome is compression of neurovascular structures in the thoracic outlet causing a combination of pain, numbness, tingling or weakness and fatiigue in the upper limb caused by pressure on the brachial plexus (lower trunk – C8 and T1 nerve roots) by a cervical rib. A cervical rib may also compress the subclavian artery in the thoracic outlet, resulting in ischemic muscle pain in the upper limb. Compressions on the neurovascular bundle may also occur as a result of bulking up of the anterior and middle scalene muscles.

Muscles of the Thoracic Wall (Netter 185 186, 187; Moore 86-90)

The muscles of the thorax consist of the intercostals and diaphragm. The intercostal muscles are arranged as three layers (external layer, internal layer and an incomplete innermost layer) between the ribs. The diaphragm closes the thoracic outlet and separates the thoracic cavity from the abdominal cavity. The three layers of the intercostal muscles are:

• The external intercostal muscles: they project inferiorly in a posterior to anterior direction. They are replaced in the front by the external intercostal membrane. They are most active in INSPIRATION
• The internal intercostal muscles: they project superiorly in a posterior to anterior direction (perpendicular to fibers of external intercostals). They are replaced in the back by the internal intercostal membrane. They are most active in EXPIRATION.

The innermost intercostal muscles: they  include the transversus thoracis. The transversus thoracis arises from the back of the sternum and the xiphoid process and inserts onto costochondral junctions from ribs 3-6. Innermost intercostal muscles can bridge more than one intercostal

Transversus Thoracis muscles  – from inside the posterior surface of the sternum and travel   superiorly and laterally to 2^nd – 6^th ribs

Levator Costarum muscles – from the transverse process of thoracic vertebrae to insert on tubercle of rib below posteriorly

MUSCLES OF RESPIRATION

Respiration is the process of exchanging O₂ with CO₂. In order to get the oxygen into the lungs, all of the the ribs and intercostal muscles act together to increase the volume of the thoracic cavity (Netter 193). The ribs and diaphragm move in such a way that three dimensions of the thoracic cavity are increased: During inspiration, the lateral dimensions of the thoracic cavity are increased by the 7-10th ribs moving laterally (the bucket-handle movement). The anteroposterior dimension is increased by the sternum being pushed forward by the true ribs (1- 6 – pump-handle movement). The superoinferior dimension is increased by the diaphragm contracting and becoming lower. During restful breathing, the diaphragm probably does most of the work, although small movement in all directions probably occur. During increased need for oxygen (exercise, pathology), the lateral and anterioposterior movements will be increased. When the thoracic muscles can no longer do the job, other muscles, called accessory muscles of respiration, attaching to the thorax will be called into action (pectoralis major and minor, sternocleidomastoid, scalenes, etc.) During quiet expiration, the intercostal muscles and the diaphragm relax and the elastic fibers of the lung and the costal cartilages recoil to their original state before inspiration. The automatic nature of the respiratory cycle is controlled in the respiratory centers of the brain stem. Forced expiration requires contraction of the anterior abdoominal muscles and the costal part of the internal intercostals.

Clinical Considerations

Normal balance between costal and diaphragmatic ventilation depends on body type, posture, age, sex, activity, atate of health and even clothing. Except in the following circumstances, ventilation tends to be an unequal mix of costal and diaphragmatic contributions.

1. Diaphragmatic ventilation. Young children and elderly persons with reduced thoracic compliance tend to breath diaphragmatically. ALso, horn and wind instruments players and vocalists develop greater control over diaphragmatic and abdominal musculature.

2. Costal ventilation. Obese people and women in advanced pregnancy cannot effectively contract the diaphragm and therefore fvor abdominal musculature

Intercostal spaces

Intercostal vein, artery and nerve form a neurovascular bundle lying between internal intercostals and innermost intercostals (Netter 188).

Intercostal nerves are mixed nerves containing both motor and sensory fibers.

• Posterior (dorsal) rami innervate back muscles between the angle of the ribs and the spinous processes of the vertebrae, with cutaneous branches innervating the overlying skin.
• Anterior (ventral) rami innervate intercostal musculature, periosteum of the ribs and skin of the thorax (dermatome).
• T7, 8, 9 , 10 and 11 innervate the abdominal wall (Netter 253).
• T12 (the subcostal nerve) and L1 innervate the region above the pubis.

Intercostal Nerves (Netter 188; Moore 93-96)

Each of the 12 pairs of thoracic nerves is numbered after the vertebra just cranial to the intervertebral foramen through which each nerve passes. For example, nerve T4 emerges below vertebra T4.

Each spinal nerve divides into a dorsal primary ramus and a ventral promary ramus.  The dorsal primary rami innervate the posterior aspect of the associated dermatome and myotome, – the true muscles of the Back and the skin of the back, a few inches lateral to the midline.

The ventral primary rami continues ventrally as the intercostal nerve in company with the intercostal artery and vein. The intercostal nerve supplies the parietal pleurae, the intercostal muscles and skin, through two branches: the lateral cutaneous (perforating) branch penetrates the internal and external intercostal muscles at approximately the midaxillary line. It subsequently bifurcates into anterior and posterior branches of the lateral cutaneous nerve to supply the skin in a dermatomal fashion. The anterior cutaneous (perforatng) branch penetrates the internal intercostal muscles and the external intercostal membrane just lateral to the sternum. It bifurcates into medial and lateral branches of the anterior cutaneous nerve to supply the skin in the anterior chest.

Clinical Considerations:

Landmarks. Nerve T4 supplies the dermatome that contains the nipple; T10 supplies the dermatome containing the umbilicus.

Intercostal nerve block is accomplished by injecting an anesthetic immediately beneath the inferior edge of a rib, posteriorly. If a needle or catheter is inserted into the pleural space, for example, to perform a thoracentesis, it should be placed just above the inferior rib in the intercostal space (rather than just below the rib above the intercistal space) to avoid the main neurovascular bundle which travels in a groove in the inferior edge of the rib above the intercostal space.

Intercostal arteries and veins (Netter 188; Moore 93-96)

The thoracic wall is supplied by three sources of blood supply:

The thoracic cavity contains:

• right and left pleural cavities (Netter 195)
• right and left lungs.
• the mass of the mediastinum in the middle (Netter 206).

The mediastinum contains (Netter 208, 209, 227, 228):

• the heart
• the pericardium and associated great vessels.
• the trachea and the structures traversing the thorax such as the esophagus, the vagus nerves, the phrenic nerves and the thoracic duct.

PLEURAL REFLECTIONS    (Netter 193, 194; Moore 131)

The pleura form a continuous “balloon-like” encasement for the pleural cavities, each of which is empty except for a small amount of pleural effusion to provide moisture to allow the pleural layers to move freely over each other. The pleura which is directly applied to the lung tissue and the root of the lung is called “VISCERAL” pleura. The remainder, which is not in direct contact with lung tissue is called “PARIETAL” pleura. The parietal pleura is subdivided (depending on the region/structure adjacent to it as follows:

●mediastinal     ● costal    ●diaphragmatic ●cervical (or cupola)

The visceral pleura

• is a layer of simple squamous epithelium over surface of lung.
• is not innervated by general sensory nerves and thus is insensitive to somatic (temperature, touch, pressure) pain
• provides a moistened and lubricated surface for lung movement.

Adhesions with the parietal pleura may result from infections, inflammatory reactions and lung immobility.

The parietal pleura (Netter 193, 194)

• is attached to the costal, diaphragmatic and mediastinal surfaces by the endothoracic fascia.
• projects into the root of the neck as the cupula. This area is vulnerable to wounds and needles and its perforation will result in equalization of external and pleural pressures, i.e. a pneumothorax. The pressure in the pleural cavity is slightly below atmospheric pressure but is erroneously  referred to as “negative pressure”.
• is innervated by free sensory nerve endings of the intercostal and phrenic nerves. Pain may be referred to dermatomes served by specific thoracic intercostal and phrenic nerves. For example, irritation of the diaphragm and mediastinal pleura by the phrenic nerve may result in referred pain to the shoulder because the phrenic nerve,and the supraclavicular nerves (which supply the shoulder with general sensation)  have contributions from the same levels, C3, C4.) Severe pain caused possibly by adhesions is called pleurisy.

Visceral and parietal pleurae are continuous at the root of the lungs, where pulmonary artery and vein, and bronchus penetrate the lung The pulmonary ligament found inferior to the root of the lungs is a segment of reflected pleura which forms a sleeve.

The parietal pleura:

• on the costal surface, is continuous with the mediastinal pleura anterior to the vertebral column (vertebral reflection).
• is continuous with the mediastinal pleura posterior to the sternum (sternal reflection).
• and is continuous with the diaphragmatic pleura near the thoracic wall (costal
• reflection).

The parietal pleurae (Netter 193, 194)

• touch at the level of ribs 2-4.
• are separated between ribs 4-6 due to the heart indentation.

The base of the parietal pleurae is found:

• at the level of the 8th costal cartilage in the midclavicular line .
• at the level of the 10th costal cartilage in the midaxillary line.
• at the level of rib 12 dorsally.

The pleural cavity contains pleural fluid which 1. acts as a lubricant to allow the lungs to move within the chest cavity and 2. provides for the surface adhesion between the parietal pleurae and the visceral pleurae and lung to remain in contact during respiraion.

Pulmonary Vasculature – (Moore 116- 118)

2 PULMONARY ARTERIES (Netter 203)

• are derived from the bifurcated pulmonary trunk.
• lie anterior to the bronchi as they enter the hilus.

The right pulmonary artery:

• is crossed over by the azygos vein whereas the left one is crossed over by the arch of the aorta at T5 (Netter  224-225).
• divides into lobar branches
• and then tertiary branches which have a close relationship with the tertiary bronchi in the bronchopulmonary segments (Netter 197).
• bring deoxygenated blood which will be oxygenated at the level of the terminal alveolar ducts and the bronchial sacs. Oxygenated blood is returned to the heart by pulmonary veins.

4 PULMONARY VEINS (Netter 203)

• 2 lower pulmonary veins from the veins of the inferior lobe of each lung, return to the left atrium of the heart.
• The upper right pulmonary vein comes from the superior and middle lobe of the right lung.
• The upper left pulmonary vein comes from the superior lobe of the left lung.
• The pulmonary veins also drain oxygenated blood supplied to the lungs by the bronchial arteries.

BRONCHIAL ARTERIES (Netter 204) arise from the descending aorta or 3rd intercostal branch and supply oxygenated blood to the lung tissue. They carry oxygen-rich blood unlike the pulmonary arteries.

Lymphatics (Netter 205; Moore 117, Fig. 139)

• are extensive and follow the vascular tree.
• Drain the pulmonary tree, pulmonary vessels and connective-tissue septa
• Run along the bronchiole and bronchi toward the hilus, where they drain to the pulmonary and then bronchopulmonary nodes (hilar) nodes, which in turn drain to the inferior (carinal) and superior tracheobronchial nodes. The tracheal (paratracheal) nodes, bronchomediastinal nodes and trunks and eventually to the thoracic duct on the left side and right lymphatic duct on the right
• An exception to this general rule is that the left lower lobe lymphatics may cross over to the right side and thus affect the right lung if there is a tumor in the left lower lobe.

Autonomic Nerves (Netter 206; Moore 118, Fig. 1.40)

• The bronchopulmonary plexus supplies both parasympathetic and sympathetic nerves to the bronchial and vascular trees.
• Parasympathetic fibers are supplied by the Vagus nerve (Cranial Nerve X)  and secretomotor to glands in the bronchial mucosa and to visceral motor to smooth muscle in the walls of the bronchi..
• Sympathetic fibers are postganglionic fibers and vasomotor to arterial system.

Remember:

Parasympathetic innervation (from Vagus Nerve, Cranial Nerve X)

            ● Contracts smooth muscle in airways

            ● Promotes secretion from mucosal glands

Sympathetic innervation

            ● Relaxes smooth muscle in airways

            ● Decreases secretion from mucosal glands

            ● Constricts blood vessels in lungs

Thoracic Wall and Lung Quiz click here