The Pleura
The pleural cavity is a closed space (like the inside
of a balloon) within which the lung has grown. As the lung grows into the space,
it picks up a layer of pleura (outside of balloon) and this is called the
visceral pleura. The remainder of the pleura is called the parietal pleura.
Pleura is a membrane that is single celled. Normally it produces a small amount
of fluid that fills the gap between the parietal and visceral layers of pleura.
The best way to see the various aspects of the pleura is to examine a cross
section of the thorax and a frontal (coronal) section.
This is a cross section through
the thorax showing the various parts of the parietal pleura. Notice that the
visceral and parietal pleura are continuous at the root of the lung.
This is a frontal or (coronal)
section through the thorax showing the various parts of the parietal pleura.
Notice again that the visceral and parietal pleurae are continuous at the
root of the lung.
Parts of the parietal pleura. (parietal pleura in
blue;
visceral pleura in purple) costal/mediastinal/cervical (cupular)/diaphragmatic
The Surface of the Lungs
The anterior border of the left lung is pushed out by the heart and this
notch is called the cardiac notch. If you follow this notch inferiorly, you
will find a small lingular lobe.
The lungs fill the pleural
cavities and are divided into lobes. The left lung has 2 lobes and the right
lung has 3 lobes. The bulk of the lung surface is against the ribs and is
called the costal surface. Other surfaces include the diaphragmatic and
mediastinal. Each lung also has 3 borders: anterior, posterior and inferior.
The lobes can be seen in the two adjacent figures.
The costal (lateral) surfaces of
the lungs are shown. In both lungs, the superior and inferior lobes are
separated by the oblique fissure. In the right lung, the superior lobe is
further divided into the superior and middle lobes, which are separated by
the horizontal fissure.
Root of the Lung
You might ask why the artery is in blue in the diagram. Blue
usually represents low oxygen blood and the pulmonary arteries contain just
that. It is called artery because it is leaving the heart. In turn, red
usually represents arteries which have high oxygen content. In this case the
pulmonary veins have just picked up oxygen and are therefore oxygen-rich.
Veins also return blood to the heart.
Root of the right lung - bronchi lie posterior /pulmonary
arteries are superior /pulmonary veins are inferior and anterior
Root of the left lung - bronchus lies posterior /pulmonary artery is
superior / pulmonary vein is inferior and anterior
Other Relationships With the Root of the Lung
In cadaveric lung specimens,
grooves are sometimes left on the mediastinal aspect of the lungs and these
are formed by structures near the lung. On the mediastinal surface of the
right lung, you will find these structures:azygos vein and its arch (over the root of the
lung) /phrenic nerve anterior to the root of the lung /vagus nerve posterior to the root of the lung
/esophagus
On the mediastinal surface of
the left lung, you will find these structures: descending aorta /arch of the aorta over the root of the lung
/right common carotid artery /right subclavian artery /phrenic nerve anterior to the root of the lung/vagus nerve posterior to the root of the lung
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