Thoracic Wall, Pleura and Lungs Flashcards
(42 cards)
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Right Lung
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Left Lung
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Muscles of Respiration: Inspiration
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Accessory:
- sternocleidomastoid (elevates sternum)
- anterior scalenes
- middle scalenes
- posterior scalenes (elevate and fix upper ribs)
Principal:
- external intercostals (elevate ribs, thus increasing thoracic capacity)
- interchondral part of internal intercostals (also elevates ribs)
- diaphragm ( domes descend, increasing vertical dimension of thoracic cavity; also elevates lower ribs)
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Muscles of Respiration: Expiration
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Quiet Breathing:
•expiration results from passive recoil of lungs and rib cage
Active Breathing:
- internal intercostals (except interchondral part)
- abdominals (depress lower ribs, compress abdominal contents, thus pushing up diaphragm)
- rectus abdominus
- external oblique
- internal oblique
- transverse abdominals
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Thorax
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Aka (chest) is located between the neck and abdomen and is the superior part of the trunk. It is distinguished from the abdomen by the presence of the rib cage, a resilient, expandable, skeletal frame
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Superior Thoracic Aperture
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- Where the trachea and esophagus enter the thorax from the neck.
- Great arteries and veins of the head, neck and upper extremeties.
- Vagus and phrenic nerves, too!
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Inferior Thoracic Aperture
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More irregular and is bounded by the costal arch, the eleventh and twelfth ribs and the twelfth thoracic vertebrae. Through this opening, abdominal cavity contents protrude high up into the thorax.
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Diaphragm as a Divider
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Abdominal and thoracic organs (viscera) are separated by a musculotendenous sheet, the diaphragm. Structures above the diaphragm are in the thoracic cavity while those inferior to the diaphragm are in the abdominalcavity.
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Thoracic Cavity
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The thoracic cavity contains the heart and lungs, important organs of respiration and circulation. The cavity is divided into paired (right and left) pleural cavities and lungs and the mediastinum
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Skeleton - Ribs
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- The thoracic wall is supported by components of the axial skeleton which include thoracic vertebrae, ribs, sternum and costal cartilage.
- There are twelve vertebrae that are distinguished from the others by their costal facets (articular surfaces for the ribs). In general, thoracic vertebrae have a superior and inferior costal facet on the vertebral body and a transverse facet on the transverse process. The arrangement is such that for T7 vertebrae, the 7th rib would articulate with the superior facet of the vertebral body and the transverse process of T7 and with the inferior facet ofT6
- Twelve pairs of ribs are found that angle from posterior-superior to anterior-inferior position. Important aspects of the rib consist of a head, neck, tubercle, angle and costal groove. The head contains the two facets for articulation with the vertebral bodies while the tubercle contains the facet for the transverse process articulation. The costal groove is the location of the neurovascular bundles that accompany the ribs.
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Skeleton - Sternum
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The sternum is the anterior attachment point of the ribs and consists of three parts, manubrium, body and xiphoid process.
- The clavicle and first rib connect to the manubrium. The second rib attaches to the sternum at the junction of the manubrium and the body (sternal angle). The last rib to make a direct connection to the sternum is the 7th rib.
- Because of the direct connection with the sternum, the first seven ribs are called true ribs. The next three ribs attach to the sternum by cartilage attachments to the ribs just superior to them. These are termed false ribs. The last two ribs are not attached to the sternum at all and are called floating ribs.
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Muscles - External Intercostals
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The external intercostal muscles course from superolateral to inferomedial (modeling the position your hands would take if placed in vest pockets). Anteriorly, the muscle fibers diminish and are replaced by the external intercostal membrane. The external intercostal muscles serve to elevate the ribs, thereby increasing thoracic volume, during forced inspiration.
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Muscles - Internal Intercostals and Innermost Intercostals
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The internal and innermost intercostal muscles course from superomedial to inferolateral. The internal intercostal muscle fibers are replaced by the internal intercostal membrane posteriorly. The innermost intercostal muscles are only found on the lateral portion of the ribs and are separated from the internal intercostal muscles by the intercostal neurovascular bundle. The internal intercostal muscles generally play a role in expiration by depressing the ribs. The cross-hatched arrangement of the intercostal muscles adds strength to the intercostal space.
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Diaphragm
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- The diaphragm is a dome-shaped musculotendinous sheet separating the thoracic and abdominal cavities. Its origin is the perimeter of the body wall, specifically the inferior margin of the thoracic cage and the upper lumbar vertebrae. The fibers extend superiorly and converge upon an aponeurosis called the central tendon.
- The diaphragm’s superior (thoracic) surface is convex, while it’s inferior (abdominal) surface is concave.
- The right dome of the diaphragm is usually more pronounced than the left due to the presence of the liver.
- There are three openings in the diaphragm for the passage of the inferior vena cava, aorta and esophagus but only the IVC is adherent to its margins and thus is affected during respiration (it widens during inspiration facilitating blood flow).
- The diaphragm is the chief muscle of inspiration.
- Motor innervation to the diaphragm is provided by the phrenic nerves; afferent innervation is provided by the phrenic nerves (central) and intercostals nerves (periphery).
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Nerves
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- The nerves in the intercostal space are ventral rami of thoracic spinal nerves.
- The first eleven nerves are termed intercostal nerves while the last (T12) has a special name, subcostal.
- These nerves carry somatic efferents for the intercostal muscles, postganglionic sympathetics (for vascular smooth muscle, sweat glands and arrector pili muscles), and cutaneous afferents.
- The nerves course between the internal intercostal muscle and the innermost intercostal muscle.
- Laterally and anteriorly, the nerve sends off cutaneous branches.
- All nerves course predominantly on the inferior border of the ribs in the costal groove.
- The upper 6 intercostal nerves are confined to the thorax. However as the lower six nerves (“thoracoabdominal nerves”) reach the costal margin they continue on in an inferior direction into the abdominal wall.
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Arteries of the Thoracic Wall
* posteriorly: thoracic aorta --\> posterior intercostal arteries
* anteriorly: internal thoracic ("internal mammary") arteries --\> anterior intercostal arteries
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Thoracic Aorta
Posteriorly, the thoracic aorta gives off segmental arteries that travel in the intercostal spaces. These are called posterior intercostal arteries. Posteriorly, they accompany the intercostal nerves, between the internal intercostal and innermost intercostal muscles on the inferior border of the ribs. They also provide a lateral cutaneous branch.
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Internal Thoracic
* Anteriorly, the blood is supplied by the internal thoracic (“internal mammary”) arteries. These arteries arise from the right and left subclavian arteries, posterior to the clavicles and descend on the anterior thoracic wall, lateral to the sternum. Segmental branches from the internal thoracic artery course in the intercostal spaces and are termed anterior intercostal arteries. Anterior cutaneous branches perforate through the muscles just lateral to the sternum.
* There are substantial anastomoses between the anterior and posterior intercostal arteries. This can provide alternate routes for circulation when there is an there is an obstruction of the aorta.
* At the costal margin, the course of the arteries is different from the intercostal nerves. At the costal margin the internal thoracic artery bifurcates into two terminal branches. One branch continues directly inferiorly into the rectus muscle of the abdomen (superior epigastric artery). The other branch, the musculophrenic artery, continues along the costal margin. As the six inferior posterior intercostal arteries reach the costal margin, they anastomose with the musculophrenic artery.
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Veins of the Thoracic Wall
The venous return from the thoracic wall follows the same pattern as the arterial supply. The internal thoracic vein and its branches collect blood from the anterior thorax and upper abdomen and return it to the subclavian veins. The segmental intercostal veins are also found inferior to the ribs and accompany the posterior intercostal arteries. The arrangement of the neurovascular bundle in the costal groove of the rib is vein, artery and nerve, from superior to inferior. The posterior intercostal veins drain into a collection system in the posterior thoracic wall called the azygos system of veins.
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Lymphatics of the Thoracic Wall
Lymphatic drainage of the chest wall is important for understanding the spread of breast cancer. In general, lymphatic drainage parallels the arterial supply route but flows in the opposite direction. The lymphatic vessels and nodes of the breast are predominantly situated along the lateral thoracic artery (a branch of the axillary artery). This means that metastasis of breast cancer will occur predominantly towards the axilla and subclavicular regions. Lymphatics also accompany the cutaneous blood is supplied via the posterior and anterior intercostals. Spread can take place along these vessels, reaching the thoracic wall.
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Pleura
As stated above, within the thoracic cavity are two pleural cavities. These are cavities into which the lungs grow. The cavities are separate. This allows for collapse of one lung, while maintaining function in the other. They are basically sacs lined by serous membranes, with the lung growing into these sacs. The lung surface is also covered by these serous membranes. The purpose of these membranes is for lubrication to facilitate movement of the lungs. Inflammation of these membranes can lead to pleurisy and formation of adhesion plaques. This causes extreme pain during breathing. The cavities are normally a “potential space”, meaning that under normal conditions they only contain a few milliliters of serous fluid. However, in certain instances of damage (pneumothorax, hemothorax) the cavities can become a real space, filled with air or fluids. As you learned in histology, these serous membranes are made up of mesothelial cells. These are the cells that are transformed and lead to lung cancer caused by inhalation of asbestos
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Parietal Pleura
The serous membrane covering the body wall is called parietal pleura. It is derived from somatic mesoderm and as such any sensation from the parietal pleura will be perceived similarly to any other somatic sensation. For example, pain from parietal pleura will be perceived as a sharp pain that can be easily localized. The parietal pleura can be divided based on the structures it is covering. These include costal (ribs), cervical, mediastinal (mediastinum) and diaphragmatic (diaphragm).
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Visceral Pleura
The serous membrane covering the lung is called visceral pleura. This pleura is intimately associated with the outside of the lung and covers each individual lobe. It is derived from splanchnic mesoderm. Pain sensation from visceral pleura would be perceived as dull and diffuse.
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Pleural Reflections and Pleural Recesses
At certain locations in the pleural cavities, the parietal and visceral pleura are continuous. This occurs at the hilus or root of the lung where the airways, blood vessels and nerves are entering and leaving. Also, because of the manner in which the lung grows into the pleural cavities, there is a reflection inferior to the hilus. This is called the pulmonary ligament. In addition, the pleural cavity has several recesses. These are necessary to provide room for lung expansion during inhalation. They include costodiaphragmatic and costomediastinal recesses.
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Lobes
* right has three
* left has two
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Surfaces and Borders
There are several surfaces and borders that describe the external anatomy of the lung. These include the apex (the most superior part of the lung), costal, medial and diaphragmatic surfaces (that facing ribs, mediastinum and diaphragm, respectively), inferior border (between diaphragmatic surface and other surfaces) and anterior margin. On the left lung, the anterior margin has some special features. These include a cardiac notch, an indentation resulting from deviation of the heart’s apex to the left, and the lingula, a tongue-like projection just below the cardiac notch.
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Lobes and Fissures
The lobes are created by fissures. Both lungs have an oblique fissure. It originates, posteriorly at the level of the 4th thoracic vertebrae, passing inferiorly. During expiration the anterior location of this fissure is at the point of attachment of the 6th rib to the sternum. This fissure divides the lungs (both left and right) into superior (upper) and inferior (lower) lobes. In addition, on the right lung a second fissure, the horizontal fissure, is seen that originates from the oblique fissure, passing anteriorly following the course of the 4th rib. This creates a third lobe of the right lung, the middle lobe.
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Bronchial Tree
•trunk = trachea --\> right and left mainstem broonchi --\> lobar bronchi ---\> segemntal bronchi (tertiary bronchus) ---\> keep big=furcating (28-30 times) broncioles --\> blind sacs (alveoli)
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Trachea
The trunk of this tree is the trachea. It begins at the larynx and is supported by c-shaped cartilage rings. At about the level of the sternal angle (manubiosternal joint), the trachea bifurcates into right and left main stem bronchi.
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Right and Left Mainstem Bronchi
* The right main stem bronchus is wider, shorter and more vertical than the left. This is important when considering the possible location of foreign objects that are aspirated into the lungs; they are more likely to be found in the right lung due to this difference in morphology. The main stem bronchi are also supported by cartilage.
* At the point where the airways enter the lung, they again divide into lobar bronchi and then into segmental bronchi (tertiary bronchus). The area of the lung supplied by a segmental bronchus is a bronchopulmonary segment. The areas of the lung supplied by particular segmental bronchi are very well defined. They are supplied independently by a segmental bronchus and a tertiary branch of the pulmonary artery, separated from adjacent segments by connective tissue septae and, thus, are surgically resectable.
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Blood Vessels
* The total output of the right heart is sent to the lungs. The pulmonary trunk originates at the pulmonary valve. Blood is pumped from the right ventricle into the trunk that quickly bifurcates into right and left pulmonary arteries. The arteries become associated with the airways as they enter the lung and remain associated with the airways throughout the lung. Because the blood carried by these arteries has just returned from the rest of the body, it is low oxygen, high carbon dioxide content. The pulmonary arterial system delivers this blood to the alveoli where the blood is reoxygenated, releasing carbon dioxide during expiration.
* Reoxygenated blood is then taken up by the pulmonary venous system to be returned to the left atrium of the heart. Unlike the arteries, the pulmonary veins do not follow the airways.
* The ability to identify the airways and blood vessels as they enter and leave the lung at the hilus is important. The arrangement is different between right and left lungs. However, using the following rule should allow you to always correctly identify the structures. The most anterior and inferior structures at the hilus of the lung are the pulmonary veins. The airways are easily distinguished because of the presence of cartilage. The remaining structures must be the pulmonary arteries.
* Because the pulmonary arteries that accompany the airways are low in oxygen, a second arterial system is present in the lung to supply oxygenated blood to the airways. These are the bronchial arteries. The bronchial arteries originate from the descending aorta, usually close to the midline. They also accompany the airways into the lung.
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Lymphatics
* From the lungs, lymphatic drainage follows the airways and proceeds in a retrograde fashion compared to the arterial blood flow.
* There are numerous intra- and extrapulmonary nodes along the airways and the trachea. The lymph flows between these nodes in vessels that cannot usually be identified at the gross anatomy level. They drain upwards towards the neck, eventually draining fluid back into the venous system. This occurs by the right lymph duct into the right subclavian vein and by the thoracic duct into the left subclavian vein.
* The right lung and the left lower lobe drain into the right lymph duct while the left upper lobe drains into the thoracic duct. Spread of lung cancers can occur through the lymphatic system.
* Cancer cells from the lung disseminated into the lymphatics can reach the general circulation. Bronchogenic carcinoma is the most common type and is responsible for about 30% of the malignancies. Cigarette smoking and urban living are major causative factors. Lung cancers predominantly metastasize to the pleura, hilum of the lung, mediastinum, skull and brain. Supraclavicular lymph nodes are often enlarged and hard when there is carcinoma of the bronchus. Because their enlargement alerts the examiner of the possibility of thoracic or abdominal malignant disease, these nodes are commonly referred to as sentinel lymph nodes.
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Nerve Supply
* Innervation of the lungs and visceral pleura are via autonomics through the pulmonary plexus. Both visceral efferents and afferents reach the lungs through this plexus that is found between the aortic arch and the tracheal bifurcation.
* Nerve fibers follow the branching of the airways. Visceral efferents from the sympathetic system cause – bronchodilation, vasoconstriction and decreased mucus secretion. The postganglionic sympathetic fibers that contribute to the plexus have their cell bodies in the sympathetic chain, from the superior cervical ganglion to the T5 sympathetic ganglion.
* The parasympathetic efferents (from vagus nerve) oppose the sympathetic innervation, causing – bronchoconstriction, vasodilation and increased mucus secretion. Visceral afferents are present although the course of these fibers and their function are unknown.
