Physiology of Pleura PDF

Physiology of pleura Dr. Shereen Samir  ILOs 1- What is pleura? 2- What is the difference between parietal and visceral pleura? 3-intrapleural fluid and intrapleural pressure 4- What is the importance of intrapleural pressure and its value? ...

Physiology of pleura Dr. Shereen Samir  ILOs 1- What is pleura? 2- What is the difference between parietal and visceral pleura? 3-intrapleural fluid and intrapleural pressure 4- What is the importance of intrapleural pressure and its value?  pleura It is a double-walled sac of serous membrane enclosing the lung. It is formed of two layers: ❑ part of the pleura that lines the thoracic cavity is called "parietal pleura". ❑ Part that cover firmly the outer surface of the lung is "visceral pleura". 1. The parietal layer : is highly sensitive to pain, irritation and inflammation. The sensitivity of 2. The visceral pleura: the pleura is generally insensitive to pain, irritation and inflammation. Only sensitive to stretch  pleural cavity or pleural sac“: ❑The narrow cavity between the two layers of pleura. ❑is lined by a single layer of cells called the mesothelium. ❑This cavity (sac) is filled with "pleural fluid", which is serous fluid secreted by pleura.  Pleural fluid ❑ Def: Fluid in the pleural space. ❑ Normal value: 5 to 10 mL of clear fluid. ❑ Composition : Similar in composition to plasma but lower in protein (< 1.5 g/dl) Contains macrophages (75%), lymphocytes, neutrophils  Pleural fluid ❑ Function: lubricates the apposing surfaces of the visceral and parietal pleura during respiratory movements. This reduces friction between the two layers during respiratory movements. So, it causes lung to slide on the chest wall. Dynamics of pleural fluid Formation : by 1-interstitial tissue of the lung 2-pleural capillaries 3- intrathoracic lymphatics 4- intrathoracic blood vessels  Dynamics of Intrapleural fluid Absorption: main absorption occurs through parietal lymphatics that communicate with the pleural space by means of stoma (pores) normal rate of formation =0.01 mL/kg/h normal rate of absorption =0.01 mL/kg/h ❑ The capacity for lymphatic clearance is 28 times the normal rate of pleural fluid formation. Intrapleural pressure ❑ It is the -ve pressure in the pleural cavity (sac). ❑Causes of negative intrapleural pressure: 1.Lack of air in the pleural cavity. 2.Continuous tendency of the lung to recoil (elasticity) against tendency of chest wall to expand.  ❑ The elastic properties (elastic recoil) of the lungs are due to: ❖ The elastic tissue in the bronchial wall and the interstitial tissues of the lungs. ❖ The surface tension of the fluid lining the alveolar walls. ❑Normal values of I.P.P. (usually a negative pressure): ▪ - 3 mmHg at the end of normal expiration. ▪ - 6 mmHg at the end of normal inspiration. ▪ -30 mmHg in forced inspiration with closed glottis (Muller's experiment). ▪ +40 mmHg in forced expiration with closed glottis (Valsalva's maneuver).  Significance of the negativity of I.P.P. Responsible for the negativity of intra-thorathic pressure (overcomes lung elastic recoil) which helps: 1. expansion of the lung during inspiration and prevents its collapse during expiration. 2. Venous return to the heart 3. Lymphatic drainage  Pneumothorax ❖Def : abnormal collection of air in the pleural space. ❖Symptoms: 1-sudden onset of sharp chest pain. 2- shortness of breath. ❖Causes 1-spontaneous 2-traumatic  Pleural Effusion Collection of large volume of fluid in the pleural space (oedema of the pleural cavity) when the rate of pleural fluid formation exceeds the rate of its absorption.  Pleural Effusion Pathologically, pleural effusion could be: Transudate (low protein content): as a result of ↑capillary pressure or ↓plasma proteins e.g. cardiac failure, hypoproteinaemia (liver cirrhosis) Exudate (high protein content): as result of ↑capillary permeability e.g. pneumonia, inflammation THANK YOU