Pleural Cavities and Pleura

• Pleural cavities exist on either side of the mediastinum.
• Pleural cavities extend superiorly above the 1st rib into the root of the neck and inferiorly to the level above the costal margin.
• Pleural cavities are completely lined by the pleura.
• Pleural cavities contain the lungs and structures in the roots of the lung.

Pleura

• The pleura consists of two serous sacs/membranes, that enclose the lungs.
• The pleura features two continuous layers, the parietal pleura and visceral pleura spaced with a small amount of serous fluid.
• Serous fluid in the pleura reduces friction during respiratory movements.

Parietal Pleura

• The parietal pleura lines (adheres to) the thoracic wall and the lateral surface of the mediastinum.
• Parietal pleura are composed of:
  • Costal sections
  • Mediastinal sections featuring pleural cuffs that surround structures entering and leaving the lung (root)
  • Diaphragmatic sections
  • Cervical sections (cupula) covering the apex of the lung, and which are part of the suprapleural membrane.

Visceral Pleura

• The visceral pleura lies on the surfaces of the lungs, following their contours, and extends into interlobar fissures.
• The visceral pleura is described as "shiny surface of lung", and is continuous with the parietal pleura.
• At the hilum of each lung, the parietal pleura folds back onto itself, becoming the visceral pleura.
• The pulmonary ligament is a loose extension of the pleural cuff below the lung root, allowing movement during respiration.

Potential Pleural Recesses

• The costodiaphragmatic recess is located between inferior margins of lungs and pleura.
• In the costodiaphragmatic recess, the costal pleura meets diaphragmatic pleura, surrounding upward convexity of diaphragm.
• The costomediastinal recess is posterior to the sternum.
• In the costomediastinal recess the costal pleura is in contact with mediastinal pleura.

Surface Anatomy: Reflections of Lungs and Pleura

• Superiorly, the lung and both layers of pleura are in close contact, their reflection lines are the same.
• Inferiorly, reflection lines differ due to pulmonary recesses.
• Sternal lines differ between right and left sides due to the heart deviating to the left.

Sternal Reflections

• On the right, sternal reflections run inferior towards the xiphoid process (but not right up to it)
• On the left, the sternal reflection is lateral to the sternum

Inferior/Posterior Reflections

• Lungs/visceral pleura lines at the 6th rib, midaxillary line at 8th rib, and process 10
• Parietal pleura crosses the midaxillary line at the 10th rib, and process 12

Reflection Lines

• Inferior border of the lines of lungs occurs at the 8th rib.
• Midavillary pleura lines, crosses the midaxillary line and the 10th rib.

Lungs - General Features

• Lungs feature a blunt apex that projects upward (above 1st rib/clavicle) into root of neck.
• Lungs consist of an anterior border, which is thin and overlaps the heart (cardiac notch indents left lung), a posterior border that is thick, rounded, and located on sides of vertebral column, and an inferior border that is sharp and separates base from costal surface.
• The lung's base (or diaphragmatic surface) is concave, resting inferiorly on diaphragm.
• The lung's costal surface is convex, featuring anterior, lateral and posterior ribs with intercostal muscles.
• The lung's mediastinal surface relates to middle mediastinum (heart/pericardium), containing the hilum of lung and molded to structures.

Right Lung

• The right lung is wider and shorter than the left lung.
• The right lung has three lobes (superior, middle, inferior) and two fissures are divided by oblique and horizontal fissures.

Left Lung

• The left lung is smaller, longer and is two lobes / one fissure (Superior & inferior lobes divided by oblique fissure).
• Anterior border is notched to accommodate heart.
• The inferior end of cardiac notch = tongue shaped process, called lingula, which is part of the anterior border of superior lobe of left lung.

Surface Anatomy - Fissures

• The Oblique fissure is indicated by a curved line from T4 spinous process to the 6th rib costochondral junction, which follows a curve of 6th rib.
• The Horizontal fissure is only in in the right lung as a horizontal line.
• The horizontal fissure runs from the midsternal line at 4th costal cartilage to oblique fissure (midaxillary line), following curve of 4th rib.

Roots of the Lungs

• The hilum is the central part on medial surface and forms the root.
• The lung's root connects lungs to structures in mediastinum, is covered by pleural sleeve, and contains structures that enter / exit at hilum, like pulmonary artery (most superior).
• Other structure at hilum of lung:
  • Superior and inferior pulmonary veins (most anterior, inferior)
  • Main / primary bronchus (middle, posterior)
  • Bronchial vessels
  • Pulmonary nerve plexus
  • Lymph nodes/vessels

Right Lung – Medial Impressions

• Heart
• Inferior vena cava
• Superior vena cava
• Azygos vein (arch)
• Trachea
• Oesophagus
• Superior lobe (right subclavian vessels)

Left Lung – Medial Impressions:

• Heart
• Aortic arch
• Thoracic aorta
• Esophagus
• Left subclavian vessels

Bronchial Tree - Trachea

• The trachea extends from C6 / lower border of cricoid cartilage to T4/T5, contains horseshoe-shaped (C-shaped) hyaline cartilaginous rings (incomplete posteriorly).
• On the posterior portion of the trachea, the rings are completed by involuntary smooth muscle.
• The trachea bifurcates into left and right primary bronchi at T4/T5 directly behind sternal angle at a ridge called “carina”.

Bronchial Tree - Main (Primary) Bronchi

• The main bronchi are complete cartilaginous rings with each bronchus that enters hilum of lung.
• The Right (main / principal) bronchus is shorter, wider, more vertical and easier for foreign bodies to move into.
• The right bronchus divides into 3 secondary (lobar) bronchi (Right superior lobe bronchus = eparterial bronchus), which arises just outside lung hilum (root) and lies just above pulmonary artery.
• The Left (main / principal) bronchus is longer, narrower (more horizontal), and passes inferior to aortic arch/anterior to thoracic aorta.
• The left bronchus divides into 2 secondary bronchi.

Bronchial Tree - Bronchi

• Secondary bronchi branch in lungs into ten tertiary (segmental) bronchi, which terminate at a bronchopulmonary segment of the lung.
• Bronchi contain cartilage but NOT the bronchioles.
• Bronchioli are smaller branches, of only smooth muscle.
• Types of bronchioli:
  • Terminal
  • Respiratory
  • Alveolar ducts
  • Alveoli (gas exchange)

Pulmonary Circulation

• Pulmonary arteries carry deoxygenated blood from heart to lungs, the blood is not used by lungs to supply tissues, but to be oxygenated in lungs.
• Pulmonary veins carry oxygenated blood from lungs to heart, two from each lung.

Blood Supply / Venous Drainage

• Bronchial Arteries: One right bronchial artery (usually 3rd posterior intercostal artery); two left bronchial arteries (directly from thoracic aorta), supply Bronchi, Pulmonary tissues, and Visceral pleura.
• Bronchial veins drain into: Azygos vein, Hemi-Azygos vein.
• Parietal pleura supplied by arteries that supply the thoracic wall.

Nerve Supply

• Pulmonary nerve plexus is anterior and posterior to bifurcation of trachea / roots of lungs.
• The sympathetic trunk form branches (Broncho-dilators, Vaso-constrictors).
• Parasympathetic fibres from vagus nerve (CN X) (Broncho-constrictors, Vaso-dilators).
• Visceral pleura is sensitive to stretch.
• Sensitive to pain, temperature, touch and pressure
• 1st intercostal nerve supplies cervical pleura
• Phrenic nerve - Medial (central) regions of diaphragmatic pleura & mediastinal pleura.
• Lower intercostal nerves - Periphery of diaphragmatic regions
• Intercostal nerves - Costal / lateral regions.

Lymphatic Drainage

• Superficial lymph plexuses drain into Bronchopulmonary (hilar) lymph plexuses then the Tracheobronchial (carinal) nodes, and connections to parasternal and brachiocephalic nodes, the Bronchomediastinal lymph trunks, and lastly Right lymphatic duct / thoracic duct.

Mechanics of Respiration

• Quiet inspiration involves the diaphragm contracting inferiorly (“flattened"), increasing vertical diameter (volume) of thoracic cavity.
• During quiet inspiration, external intercostal muscles raise the ribs, increasing antero-posterior diameter and transverse diameter.
• Quiet inspiration decreases the pressure of air in the alveoli below the atmospheric pressure (negative pressure), causing air to be pulled/sucked in, which equalizes the pressure.

Muscles involved in quiet inspiration

• Diaphram
• External intercostal muscles
• Forced inspiration achieves maximum increase in thoracic cavity by contraction.
• Anterior and middle scalene raise the 1st rib, sternocleidomastoid raise sternum, serratus posterior superior, pectoralis minor raise ribs.
• If the upper limb is fixed, the sternal origin of pectoris major assists in elevating sternum and ribs.

Mechanics of Respiration – Quiet Expiration

• Quiet expiration is a passive process accomplished by elastic recoil of lungs and relaxation of intercostal muscles and diaphragm.
• During quiet expiration, internal & innermost intercostal muscles move ribs inferiorly, decreasing volume of thorax (and lung and alveoli) and increasing pressure of air in the alveoli, pushing air out to equalise the pressure.

Mechanics of Respiration – Forced Expiration

• Forced expiration is an active process accomplished by contraction of muscles.
• During forced expiration, anterior abdominal wall musculature force diaphragm upward and increase abdominal pressure, including quadratus lumborum (pulling 12th rib down) and serratus posterior inferior (pulling down lower ribs).