Thorax

• Thoracic cavity


  The cavity of the thorax filled laterally by the lungs, each lying in its pleural cavity. The space between the pleural cavities is the mediastinum.

  
• Mediastinum


  • Central movable partition that separates the two lung and pleural cavities, extending superiorly to the thoracic inlet, inferiorly to the diaphragm, anteriorly to the sternum and posteriorly to the vertebral column

  
• The mediastinum is a very mobile area, with a minimum of loose connective tissue between the mobile structures, so the space between them can be readily distended by inflammatory fluid, neoplasm, etc, from the neck
• Division of mediastinum


  1. Superior mediastinum (continuous with neck above and inferior mediastinum below)

  2. Inferior mediastinum (middle mediastinum containing pericardium and heart, anterior mediastinum between pericardium and sternum, posterior mediastinum between pericardium and vertebral column)
• Pleura


  Membrane of fibrous tissue that surrounds each lung and lines the thoracic cavity

  
• Parietal pleura


  • Lines the thoracic wall, covers the thoracic surface of the diaphragm and extends into the root of the neck to line the undersurface of the suprapleural membrane

  
• Visceral pleura


  • Reflects from the medial surface and completely covers and adheres to the outer surfaces of the lungs and extends into the depths of the interlobar fissures

  
• The two pleural layers become continuous with one another by means of a cuff of pleura that surrounds the structures entering and leaving the lung at the hilum of each lung

  
• The pleural cavities are completely separated from each other by the mediastinum, so abnormal events in one pleural cavity do not affect the other cavity

  
• Pleural effusion


  Excess fluid that accumulates within the pleural space, compromising the underlying lung which may collapse
• Pleural fluid


  Clear fluid found in the pleural space (5-10 ml), normally produced daily and absorbed by capillaries
• Nerve supply of pleura


  • Parietal pleura is sensitive to pain, temperature, touch, and pressure, supplied segmentally by the intercostal nerves. Diaphragmatic and mediastinal pleura is supplied by the phrenic nerve. Visceral pleura is insensitive to common sensations, receiving an autonomic nerve supply from the pulmonary plexus.
• Trachea


  Mobile cartilaginous and membranous tube, beginning in the neck as a continuation of the larynx and ending below by dividing into the right and left principal bronchi at the level of the sternal angle

  
• Tracheal rings


  • About 15-20 U-shaped rings of hyaline cartilage embedded in the tracheal wall, with smooth muscle (trachealis muscle) and elastic fibers to restore normal position during movement
• Blood supply of trachea


  Upper two-thirds supplied by inferior thyroid arteries, lower third supplied by bronchial arteries. Sensory nerve supply from vagi and recurrent laryngeal nerves.

  
• Bronchi


  The trachea bifurcates into the right and left principal bronchi, which become smaller with irregular plates of cartilage replacing the U-shaped bars found in the trachea

  
• Bronchioles


  • Smallest bronchi that divide and give rise to terminal bronchioles, which then divide into respiratory bronchioles leading to alveolar ducts and sacs

  
• Principal bronchi


  • Right principal bronchus is wider, shorter and more vertical than the left, leading to more foreign bodies entering the right side. The left principal bronchus is narrower, longer and more horizontal.

  
• Lungs


  • Soft, spongy and very elastic, pink or grey in colour, with a blunt apex projecting into the neck. The root of the lung is where the bronchus and pulmonary vessels enter/leave, forming the hilum.

  
• Right lung


  • Slightly larger than the left lung, divided by oblique and horizontal fissures into upper, middle and lower lobes

  
• Left lung


  • Smaller than the right lung, divided by an oblique fissure into upper and lower lobes. The anterior border is thin and overlaps the heart, forming the cardiac notch.

  
• Bronchopulmonary segment


  The smallest anatomically, functionally, and surgically independent units of the lungs that can be isolated and removed without affecting adjacent regions

  
• Bronchopulmonary segment


  • Each segmental bronchus is accompanied by a branch of the pulmonary artery, its own lymphatic vessels and autonomic nerve supply

  
• Blood supply of lungs and bronchi


  The bronchial tree, lung, and visceral pleura receive blood supply from the bronchial arteries, branches of the descending aorta. The parietal pleura is supplied by the internal thoracic artery.

  
• Nerve supply of lungs


  Structures of the lung and visceral pleura are supplied by the pulmonary plexus, formed from branches of the sympathetic trunk and receiving parasympathetic fibers from the vagus nerve.