2. Pleura and Lung

Pericardiophrenic Vessels

A long slender branch of the internal thoracic artery. It accompanies the phrenic nerve, between the pleura and pericardium, to the diaphragm, to which it is distributed. It anastomoses with the musculophrenic and superior phrenic arteries. On their course through the thoracic cavity, the pericardiacophrenic arteries are located within and supply the fibrous pericardium. Along with the musculophrenic arteries, they also provide arterial supply to the diaphragm.

Subparts of the Parietal Pleura

Cervical - the dome-shaped layer of parietal pleura lining the cervical extension of the pleural cavity Costal - pleura related to the ribs and intercostal spaces i s termed Mediastinal - pleura covering the mediastinum Diaphragmatic - pleura covering the diaphragm.

Pleural Fluid

Clear plasma filtrate. Contains small solutes like sodium, chloride, bicarbonate, glucose and albumin. Compared to plasma it has around the same concentration of glucose but a higher concentration of albumin and bicarbonate (which makes it a bit alkali). There is around 8-10 ml of pleural fluid in the pleural cavity. Pleural fluid creates a partial vacuum betweeen the two pleural surfaces. This is called mechanical coupling.

Structure of Lung

Each lung has a half-cone shape, with a base, apex, two surfaces, and three borders: • The base sits on the diaphragm. • The apex projects above rib I and into the root of the neck. • The two surfaces-the costal surface lies immediately adjacent to the ribs and intercostal spaces of the thoracic wall. The mediastinal surface lies against the mediastinum anteriorly and the vertebral column posteriorly and contains the comma-shaped hilum of the lung, through which structures enter and leave. • The three borders-the inferior border of the lung is sharp and separates the base from the costal surface. The anterior and posterior borders separate the costal surface from the medial surface.

Lingular of the Left Lung

From the anterior border of the lower part of the superior lobe a tongue-like extension projects over the heart bulge.

Medial View of Right Lung

Impressions: Cardiac, Diaphragmatic, Thymic Grooves: Superior Vena Cava (SVC), Azygus vein, Esophagus

Medial View of Left Lung

Impressions: Cardiac, Diphragmatic Grooves: Aorta, Esophagus

Right Pulmonary Artery

Is longer than the left and passes horizontally across the mediastinum. It passes: • anteriorly and slightly inferiorly to the tracheal bifurcation and anteriorly to the right main bronchus • posteriorly to the ascending aorta, superior vena cava, and upper right pulmonary vein. The right pulmonary artery enters the root of the lung and gives off a large branch to the superior lobe of the lung. The main vessel continues through the hilum of the lung, gives off a second (recurrent) branch to the superior lobe, and then divides to supply the middle and inferior lobes.

Left Pulmonary Artery

Is shorter than the right and lies anterior to the descending aorta and posterior to thesuperior pulmonary vein. It passes through the root and hilum and branches within the lung.

Lung Parenchyma

Is the portion of the lung involved in gas transfer: the alveoli, alveolar ducts and respiratory bronchioles.

Midline Lung and Pleura Extension

Lungs: 10th rib Pleura: 12th rib

Midclavicular Lung and Pleura Extension

Lungs: 6th rib Pleura: 8th rib

Midaxillary Lung and Pleura Extension

Lungs: 8th rib Pleura: 10th rib

Pulmonary Veins

On each side a superior pulmonary vein and an inferior pulmonary vein carry oxygenated blood from the lungs back to the heart. The veins begin at the hilum of the lung, pass through the root of the lung, and immediately drain into the left atrium.

Lymphatic Drainage

Superficial, or subpleural, and deep lymphatics of the lung drain into lymph nodes called tracheobronchial nodes around the roots of lobar and main bronchi and along the sides of the trachea. As a group, these lymph nodes extend from within the lung, through the hilum and root, and into the posterior mediastinum. Efferent vessels from these nodes pass superiorly along the trachea to unite with similar vessels from parasternal nodes and brachiocephalic nodes, which are anterior to brachiocephalic veins in the superior mediastinum, to form the right and left bronchomediastinal trunks. These trunks drain directly into deep veins at the base of the neck, or may drain into the right lymphatic trunk or thoracic duct.

Costodiaphragmatic Pleural Recess

The costodiaphragmatic recess, also called the costophrenic recess or phrenicocostal sinus, is a potential space in the pleural cavity, at the posterior-most tips of the cavity, located at the junction of the costal pleura and diaphragmatic pleura (in the costophrenic angle). It measures approximately 5 cm vertically and extends from the eighth to the tenth rib along the mid-axillary line. The lungs expand into this recess during forced inspiration; however, the recess never fills completely. During expiration, it contains no lung tissue, only pleural fluid.

Costomediastinal Pleural Recess

The costomediastinal recess is a potential space at the border of the mediastinal pleura and the costal pleura. It assists lung expansion during deep inspiration, although its role is not as significant as the costodiaphragmatic recess, which has a greater volume. The lung expands into the costomediastinal recess even during shallow inspiration. The costomediastinal recess is most obvious in the cardiac notch of the left lung.

Innervation of the Pleura

The parietal pleura is innervated by the intercostal nerves, with the mediastinal and diaphragmatic pleura also innervated by the phrenic nerve. Visceral pleura is innervated by the vagus nerve and sympathetic fibres. It is insensitive to pain stimuli.

Main, Secondary and Tertiary Bronchi

The first bronchi to branch from the trachea are the right main bronchus and the left main bronchus. These are the widest and enter the lungs at each hilum, where they branch into narrower secondary bronchi known as lobar bronchi, and these branch into narrower tertiary bronchi known as segmental bronchi. The right main bronchus is wider and takes a more vertical course through the root and hilum than the left main bronchus. Therefore, inhaled foreign bodies tend to lodge more frequently on the right side than on the left.

The Left Lung

The left Inng is smaller than the right lung and has two lobes separated by an oblique fissure. The oblique fissure of the left lung is slightly more oblique than the corresponding fissure of the right lung.

Pleural Recesses

The lungs do not completely fill the anterior or posterior inferior regions of the pleural cavities. This results in recesses in which two layers of parietal pleura become opposed. Expansion of the lungs into these spaces usually occurs only during forced inspiration; the recesses also provide potential spaces in which fluids can collect and from which fluids can be aspirated.

Pleura

The pleura is divided into two major types, based on location: • Parietal Pleura - Pleura associated with the walls of a pleural cavity • Visceral Pleura - Pleura that reflects from the medial wall and onto the surface of the lung. Adheres to and covers the lung.

Pulmonary Arteries

The right and left pulmonary arteries originate from the pulmonary trunk and carry deoxygenated blood to the lungs from the right ventricle of the heart. The bifurcation of the pulmonary trunk occurs to the left of the midline just inferior to vertebral level TIV /V, and anteroinferiorly to the left of the bifurcation of the trachea.

The Right Lung

The right lung has three lobes and two fissures. • The oblique fissure separates the inferior lobe (lower lobe) from the superior lobe and the middle lobe of the right lung. • The horizontal fissure separates the superior lobe (upper lobe) from the middle lobe.

Bronchioles

The terminal bronchiole is the most distal segment of the conducting zone. It branches off the lesser bronchioles. Each of the terminal bronchioles divides to form respiratory bronchioles which contain a small number of alveoli.

Pleural cavity

The thin fluid-filled space between the two pulmonary pleurae (known as visceral and parietal) of each lung. The pleural cavity can be viewed as a potential space because the two pleurae adhere to each other (through the thin film of serous liquid) under all normal conditions.

Trachea

The trachea is a flexible tube that extends from vertebral level CVI in the lower neck to vertebral level TIV /V in the mediastinum where it bifurcates into a right and a left main bronchus. The trachea is held open by shaped transverse cartilage rings embedded in its wall the open part of the C facing posteriorly. The lowest tracheal ring has a hook-shaped structure, the carina, that projects backwards in the midline between the origins of the two main bronchi. The posterior wall of the trachea is composed mainly of smooth muscle.

Lungs

The two lungs are organs of respiration and lie on either side of the mediastinum surrounded by the right and left pleural cavities . Air enters and leaves the lungs via main bronchi, which are branches of the trachea. The right lung is normally a little larger than the left lung because the middle mediastinum, containing the heart, bulges more to the left than to the right.

Lung Innervation

Visceral efferents from: • the vagus nerves constrict the bronchioles • the sympathetic system dilates the bronchioles.

Hilum

Within each root and located in the hilum are: • a pulmonary artery • two pulmonary veins • a main bronchus • bronchial vessels • nerves • lymphatics .