L2 Respiratory Pressures and Surfactant (PDF)

Respiratory pressures and Surfactant Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae Rules before lectures COLLEGE OF MEDICINE Review Questions List the function of the respiratory system? Muscles of inspiration are ……………..…………… Muscles of quiet expiration are ………………. Mu...

Respiratory pressures and Surfactant Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae Rules before lectures COLLEGE OF MEDICINE Review Questions List the function of the respiratory system? Muscles of inspiration are ……………..…………… Muscles of quiet expiration are ………………. Muscles of deep expiration are ………………. Define terms, Intra-alveolar, Intra-pleural, and Trans-pulmonary pressure List the function of intrapleural pressure. Describe surfactant and list its function. Lung Pressures Lung pressures are intra-alveolar , intrapleural and transpulmonary pressures. 1- intra-alveolar (Intrapulmonary Pressure ): Intra-alveolar pressure(pressure in the alveoli). (-1to +1) mmHg (0 mmHg =atmospheric pressure = 760 mmHg) -1 mmHg during inspiration, +1 mmHg during expiration. 2- Intrapleural Pressure: Pressure in the intrapleural space= (-6 to -2.5) mmHg Average -4 mmHg * Pressure is negative (suction pressure). Why the intrapleural pressure is negative? This negativity is due to the continuous tendency of the lung to recoil against the continuous tendency of the chest to expand. Intrapleural pressure (IPP) At the end of expiration = -2.5 mmHg. During inspiration = -6 mmHg. Deep inspiration = -12 mmHg. In Valsalva maneuver (Forced expiration against closed glottis) , IPP= +50 mmHg, while the intra-alveolar pressure = +100mmHg. +ve IPP can occurs in ??????? +IPP occurs in Valsalva Maneuver, cough and Pneumothorax Lung Pressures 3- Transpulmonary Pressure (TPP): Pressure difference across the wall of the lung. Intra-alveolar pressure – intrapleural pressure Always positive. Average = + 4 mmHg Importance of intrapleural pressure 1. 2. 3. 4. Helps lung inflation during inspiration Prevents lung collapse Decreases the work of breathing Helps venous and lymphatic drainage Surfactant Alveolar wall has two types of cells. 1. Type I pneumocyte: 95 % of the alveolar cell. Important in gas exchange. 2. Type II pneumocyte: 5% of the alveolar cell. It secretes surfactant. Surfactant is a mixture of Phospholipids (Dipalmatoyl- phospatidyle-choline, DPPC) and Ca++. What is Surface Tension??  Force exerted by fluid in alveoli to resist distension.  Lungs secrete and absorb fluid, leaving a very thin film of fluid  This film of fluid causes surface tension Function of surfactant 1. Decrease surface tension of the fluid lining the alveoli → maintains lung expansion by Formation of monomolecular layer at the interface between the fluid lining the alveoli and the air → decrease surface tension. Reduces attractive forces of hydrogen bonding by becoming interspersed between H2O molecules. 2. Prevents pulmonary edema by decreasing the filtration forces. Function of surfactant La Place law 3. Prevents collapse of alveoli during expiration. During expiration the radius of the alveoli decreases and alveoli tend to collapse according to la place law. if T (tension) is not reduced as r is reduced, the tension overcomes the distending pressure (P) → collapse of the alveoli. Concentration of surfactant increases in the alveoli during expiration→ decreases the surface tension → maintain distending pressure and NO collapse of the alveoli 4. Decrease work of breathing. Deficiency of surfactant  Hyaline disease or Respiratory distress syndrome: Newborn fail to secrete adequate amount of surfactant → difficulty of lung expansion. Our case in the video is ……………………………. Summary Define terms, Intra-alveolar, Intra-pleural, and Trans-pulmonary pressure List the function of intrapleural pressure. Describe surfactant and list its function.