lecture_notes_29_(ta)_2 - Lecture 29 Respiratory Physiology...

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Lecture 29: Respiratory Physiology II Reading: ch 13, section: intro, mechanics, pgs 464-472; 475-484 (pgs 473-480; 483-492, if using 5 rd edition) ( QUESTIONS : WHAT STRUCTURES ARE COMMON TO BOTH THE RESPIRATORY AND DIGESTIVE SYSTEMS ) ( WHEN AVEOLAR PRESSURE IS GREATER THAT ATMOSPHERIC PRESSURE , WHERE DOES AIR GO ? ) Elastic recoil - this is the ( PASSIVE ) force that restores the lungs to their preinspiratory volume after the inspiratory muscles relax at the end of inspiration. It is similar to the force that restores the shape of a balloon when the air within it is released. It is determined by two factors: ( 1 ) elastic properties of pulmonary tissue - pulmonary tissue contains large quantities of elastin fibers. They are arranged in a meshwork that provides the tissue with a high degree of elasticity. ( RESPONSIBLE IN PART FOR DECREASED INTERPLURAL SAC PRESSURE. W HAT’S THE OTHER FACTOR RESPONSIBLE (BESIDES FLUID COHESION) ? ) ( 2 ) alveolar surface tension - this is the force exerted at the interface between a liquid and a gas that tends to minimize the surface area at the interface. It results from the preferential attraction of water molecules for each other. In the alveoli, surface tension acts to resist any increases in alveolar surface area and thereby oppose alveolar expansion during inspiration. Similarly, surface tension acts to minimize alveolar surface area and thereby reduce the size of the alveoli. This force is so strong that it must be counteracted in order to prevent alveolar collapse. This is achieved by the production of a pulmonary surfactant ( THIS EQUALIZES SURFACE TENSION ACROSS ALL ALVEOLI ) that is synthesized by the type II cells and released into the alveoli (Figure 13-16 . ( PREMATURE BABIES DON T HAVE ENOUGH TIPE II CELLS AND THUS ARE IN DANGER OF HAVING THEIR LUNGS COLLAPSE ) Law of LaPlace - Magnitude of inward-directed pressure (P) in a bubble = 2 x surface tension (T)
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This note was uploaded on 05/02/2008 for the course NPB 101 taught by Professor Fuller,charles/goldberg,jack during the Winter '08 term at UC Davis.

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lecture_notes_29_(ta)_2 - Lecture 29 Respiratory Physiology...

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