Anatomy III: Blood and the Cardiovascular and Respiratory Systems

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Anatomy III: Blood and the Cardiovascular and Respiratory Systems

Dr. José Luis Monroy Antón

6 CMLesson 11 Pleura. Vessels, nerves and lymphatics of the pleural cavity

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Thoracic cavity

Remember that the thoracic cavity is divided into three compartments

• Right pulmonary cavity: right lung surrounded by pleurae
• Left pulmonary cavity: left lung surrounded by pleurae
• Mediastinum: the central space between them

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What is pleura?

• Each pulmonary cavity is independently lined by a membrane that also reflects onto the external surface of the lungs occupying the cavities
• If you push your fist into a balloon:
  • Your fist represent the hilum of the lung
  • The inner part of the elastic wall is the visceral pleura
  • The external wall of the balloon is the parietal pleura
  • The air cavity is the pleural cavity, that contains a thin film of fluid

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Origin of the pleura

Remember that at the embryonic period, the lung buds grow into the pericardioperitoneal canals, so:

• The invaginated epithelium of the lung buds forms the visceral pleura
• The epithelium that covers the pericardioperitoneal canals forms the parietal pleura.

Pharynx Trachea Parietal pleura Lung bud Visceral pleura Pericardioperitoneal canal Visceral peritoneum

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Pleural cavity fluid and expansion

The pleural cavity contains a capillary layer of serous pleural fluid

• It lubricates the pleural surfaces
• It allows the layers of pleura to slide smoothly over each other
• It provides the cohesion that keeps the lung surface in contact with the thoracic wall, thanks to the surface tension
• It makes the lung expand and fill with air when the thorax expands

Pleural cavity Collapsed lung - Visceral pleura Parietal pleura Thoracic wall lined with endothoracic fascia Visceral pleura Parietal pleura Endothoracic fascia Fascial membranes Phrenico- pleural fascia (part of endothoracic fascia)

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Visceral pleura characteristics

Visceral pleura:

• It covers the lung and adheres to all its surfaces
  • It covers also the surface within the fissures
• Normally we cannot dissect the visceral pleura in the cadaver from the surface of the lung
• It provides the lung with a smooth slippery surface, enabling it to move freely on the parietal pleura
• At the hilum, the visceral and parietal pleura are continuous

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Parietal pleura characteristics

Parietal pleura:

• It lines the pulmonary cavities, so it is adhered to:
  • Thoracic wall
  • Mediastinum
  • Diaphragm
• It is thicker than the visceral pleura
• It is easy to separate it from the surface that it covers, at the cadaver and in living people

Cervical pleura Trachea Cervical pleura Bronchial tree (representing root of lung) * Costal part Costal pleura Pleural cavity Costal surface of left lung covered with visceral pleura Visceral pleura Cardiac notch * Mediastinal part Lingula * Diaphragmatic part Costodiaphragmatic recesses

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Parts of the parietal pleura

The parietal pleura consists in four parts:

• Costal
• Mediastinal
• Diaphragmatic
• Cervical

Visceral pleura Parietal pleura Costal pleura Diaphragmatic pleura Mediastinal pleura Cervical pleura Endothoracic fascia Fascial membranes Hilum of lung (site of entry of root of lung) Suprapleural membrane Cervical pleura Mediastinal part Costal part Diaphragmatic part Endothoracic fascia Mediastinum Visceral pleura Diaphragm

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Costal part of parietal pleura

• It covers the internal surfaces of the thoracic wall, so it is very close to the endothoracic fascia
• The endothoracic fascia separates the costal parietal pleura from the structures of the thoracic wall, such as sternum, ribs, intercostal muscle, etc
• The endothoracic fascia is very thin and consists of loose connective tissue. It is very easy to separate the fascia from the thoracic wall in cadaver and in living people
  • Very useful, because this allows the surgeon to access to extra-pleural structures without opening the pleural cavity

Costal part Endothoracic fascia

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Mediastinal part of parietal pleura

• It covers the medial aspects of the mediastinum
• It continues superiorly as cervical pleura into the root of the neck
• It continues anteriorly and posteriorly with the costal pleura
• It continues inferiorly with the diaphragmatic pleura
• Over the hilum, the pleura is a continuous antero- posterior sheet from the sternum to the vertebrae
• At the hilum, it reflects laterally to become continuous with the visceral pleura

57 Mediastinal part

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Diaphragmatic part of parietal pleura

It covers the superior surface of the diaphragm on both sides of the mediastinum with two exceptions:

• The costal attachments of the diaphragm
• The part covered by the pericardium at the central tendon

Bare area of pericardium Sternal reflection of right pleura Costomediastinal recess Internal thoracic vessels Sternal reflection of left pleura Transversus thoracis muscle Fat pad External oblique Left phrenic nerve Diaphragmatic part of parietal pleura Right phrenic nerve Pericardial sac fused with central tendon Inferior vena cava Esophagus Central tendon Central tendon of diaphragm Thoracic duct Azygos vein Aorta Splanchnic nerve Diaphragmatic part of parietal pleura Sympathetic trunk Costodiaphragmatic recess Latissimus dorsi m. Costal part of parietal pleura Serratus posterior inferior m. Superior view

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Phrenicopleural fascia

Phrenicopleural fascia: a thin elastic layer of endothoracic fascia that connects the diaphragmatic pleura with the muscular fibers of the diaphragm

Bare area of pericardium Sternal reflection of right pleura Costomediastinal recess Internal thoracic vessels Sternal reflection of left pleura Transversus thoracis muscle Fat pad External oblique Left phrenic nerve Diaphragmatic part of parietal pleura Right phrenic nerve Pericardial sac fused with central tendon Inferior vena cava Esophagus Central tendon Central tendon of diaphragm Thoracic duct Azygos vein Aorta Splanchnic nerve Diaphragmatic part of parietal pleura Sympathetic trunk Costodiaphragmatic recess Latissimus dorsi m. Costal part of parietal pleura Serratus posterior inferior m. Superior view

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Cervical pleura

• It covers the apex of the lung, which extends through the superior thoracic aperture into the neck
• Shape of a dome superior to the first rib
• It is a superior continuation of the costal and mediastinal parts of the parietal pleura
• Suprapleural membrane: fibrous extension of the endothoracic fascia that strengthen the cervical pleura:
  • From the internal border of the first rib to the C7 transverse process

Trachea Cervical pleura Costal part Suprapleural membrane Cervical pleura

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Pleural reflection lines

• Pleural reflections: lines along which the parietal pleura changes its direction when passing from one wall to the other
• At the picture are shown by a red line. They are not symmetrical due to the extension of the heart in the left pulmonary cavity
• So we have three lines:
  • Sternal
  • Costal
  • Vertebral

D.M.

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Sternal lines of pleural reflection

• Where the costal pleura is continuous with the mediastinal pleura anteriorly
• They begin at the apex and run inferomedially, passing posterior to the sternoclavicular joints
• Between the levels of 2-4 costal cartilages, both lines right and left descend in contact
• Pleural sacs may even slightly overlap each other

DING

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Right and left sternal lines

• Right sternal line: it descends to the posterior surface of the xiphoid (6th costal cartilage) and turns laterally
• Left sternal line: It descends only to the 4th cartilage, then it passes to the left margin of the sternum and descends to the 6th costal cartilage: this creates a notch called the bare area of the heart, useful for pericardiocentesis

DING

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Costal lines of pleural reflection

Continuations of the sternal lines when the costal pleura continues inferiorly with the diaphragmatic pleura

• Right costal line: runs laterally from the midline
• Left costal line: the line begins at the midclavicular line

DIM

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Costal lines path

• Both lines will go laterally, later posteriorly and then medially
• They pass obliquely through the 10th rib at the midaxillary line
• At the 12th rib they become continuous with the vertebral lines

DIM

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Vertebral lines of pleural reflection

• Round lines, not sharpen
• Located where the costal pleura is continuous with the mediastinal pleura, at the posterior aspect
• They follow a parallel path in the vertebral column, from T1 to T12, where they become continuous with the costal lines
• In the picture, only the most inferior portion of the line is shown

1

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Costodiaphragmatic and costomediastinal recesses

• Even during deep inspiration, the lungs don't fill the pulmonary cavity
• Costodiaphragmatic recesses: potential space that surrounds the convexity of the diaphragm inside the thoracic wall
• Costomediastinal recesses: smaller pleural recesses posterior to the sternum, at the join of the costal pleura with the mediastinal pleura
  • The left recess is larger due to the left cardiac notch

Costodiaphragmatic recesses Bare area of pericardium Costomediastinal recess Sternal reflection of left pleura Fat pad Left phrenic nerve Pericardial sac fused with central tendon

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Pleuritis

• The slide of both layers of pleura does not produce any sound in normal state
• However, during inflammation of the pleura the surfaces are rough
• The friction sound is audible with the stethoscope
• A chronic inflammation may cause a pleural adhesion between both layers
• The main symptom is the pain at moderate exercise

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Vessels of the pleura

Visceral pleura vessels

• Arterial supply: bronchial arteries
• Venous drainage: pulmonary veins

Parietal pleura vessels

• It is supplied by the same arteries that supply the thoracic wall and drained by the same veins:
  • Posterior intercostal arteries
  • Subcostal arteries
  • Anterior intercostal arteries
  • Superior and lateral thoracic arteries
  • Intercostal and subcostal veins