Thoracic Cavity PDF

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Summary

Respiratory anatomy - thoracic cavity overview....

Description

Resp. Anatomy - Thoracic Cavity Thorax Functions: Protect internal organs. Acts as a closed vessel within which the pressure changes necessary to fill and empty the lung occur. Mechanical movements of the thoracic structures change the intrathoracic volume. When the volume of a closed vessel increases, pressure within falls. Superior aperture open and continuous with neck. Inferior aperture closed by diaphragm - contains a number of diaphragmatic apertures through which important structures pass between the thorax and abdomen. Cavity divided into three compartments: 1)Left and 2)Right pleural cavities - Lined by pleura (closed sacs of serous membrane) and entirely independent of each other. (allows one to function if the other pleural cavity has been pierced) This also allows for isolation of an infection. 3)Mediastinum - covered in cardiovascular nodes. Clinical relevance: Inflammation or disease can cause pleurisy. Inflamed pleural layers rub against each other each time lungs expand. Causes sharp pain. Roughness of pleural surfaces produces a pleural friction rub audible on auscultation. Left parietal pleura deviates away from the body of the sternum in the region of the 5th intercostal space (pleural notch). Corresponding cardiac notch in left lung. Clinical relevance: Bare area of pericardium exposed by notches can be pierced with a needle and the pericardial cavity drained of fluids (pericardiocentesis) without entering pleural cavity/ damaging the lungs. Parts of the pleurae: 1) Parietal: Outer pleura Squamous mesothelial cells. Divided into regions based on the structures it comes into contact with. Costal pleura, diaphragmatic pleura, mediastinal pleura and cervical pleura/cupola. Pulmonary ligament is a sleeve of pleura that hangs down from the pleura surrounding the root of the lung. Separated from thoracic wall by loose CT layer (endothoracic fascia). Secrete pleural fluid. Extend 2-3 cm above the medial ⅓ of the clavicle (cupola).

Clinical relevance:

The cupola of the lung extends into the root of the neck. Penetrating wounds to the neck or poor technique in attempting to access the subclavian vein may tear the cervical pleura allowing air into the pleural cavity (pneumothorax), causing the lung to collapse. 2) Visceral: Low cuboidal mesothelial cells. Inner pleura. Tightly adhered to lung surface/ continuous with lung CT. (Function of mesothelium is to provide a slippery, non-adhesive and protective surface. Lines serous cavities and internal organs.) Visceral and parietal pleura are separated by a pleural cavity (potential space) containing only a thin layer of serous fluid allowing them to slide across each other easily. Pleural recesses: (areas where pleura reflect from one surface to another - don’t usually contain lung) Costomediastinal recess occurs anteriorly between the costal and mediastinal parts of the parietal pleura and is larger on the left side due to the cardiac notch. Costodiaphragmatic recess occurs between costal and diaphragmatic parts of the parietal pleura. Fluids can collect in these spaces (pleural effusion) eg. serous fluid (hydrothorax), blood (hemothorax), chyle (chylothorax) - drains from small intestine into lymphatic fluid during digestion - and pus (empyema). Clinical relevance: Fluid may have to be removed via hypodermic needle (thoracocentesis) or by insertion of a chest tube. Pleural Fluid: Insufficient - ‘friction rub’ Overproduction or under resorption - pleural effusion. Accumulation of fluid in pleural space which can seriously compromise lung function. Two types: Transudative: Caused by systemic factors eg. congestive heart failure. Exudative: Caused by local factors eg. inflammation. Once capacity for fluid to accumulate in the recesses is exceeded, lung function begins to be compromised. Visible by x-ray and CT, etc. Place where fluid accumulates will depend somewhat on the position of the patient. Pleural extent and margins: Begin behind sternoclavicular joints. Reach midline at sternal angle. Descend in midline to 4th costal cartilage. Right side: Meets sternal margin at 7th costal cartilage. Mid clavicular at rib 8. Mid axillary at rib 10. Dorsal midline at T12. Left side: 2-2.5 cm lateral to sternum until 6th costal cartilage. Pleural space (between visceral and parietal pleura) is at most a couple of mm. The potential space can increase in size due to accumulation of air, blood, pus, etc. But an increase in the pleural space requires a decrease in the size of the lung-NB consequences.

Note: lungs stay outside pleural space....