Lab report- bio 273L

Lab report- bio 273L - Experiment # 5 RESPIRATORY...

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Experiment # 5 RESPIRATORY PHYSIOLOGY
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Introduction: The purpose of this lab was to measure the chest dimensions during the respiratory cycle, to perform Valsalva’s manoeuvre, to study the effects of changes in the partial pressure of CO 2 and O 2 and pH on the breathing movements. This lab also examined the neural input to respiration and determined a subject’s respiratory volumes and capacities. At the beginning of the lab experiment, there was a demonstration to show the Law of LaPlace using balloons. Two balloons of different sizes were blown up and connected together by using a tube. The Law of LaPlace states that the pressure (P) inside a bubble formed by a fluid film is a function of two factors: the surface tension of the fluid (T) and the radius of the bubble (r), which is all expressed in the equation: P=2T/r Generally, the fluid lining the alveoli walls creates surface tension. If the surface tension was the same in both small and large alveoli, the small alveoli would have higher inwardly directed pressure than the larger one, and would have an increased resistance to stretch, and therefore, this would mean that more work would be needed to expand the smaller alveoli. (Silverthorn, 2010) Surfactant is a substance that lowers the surface tension of the alveoli. It is more concentrated in smaller alveoli, making their surface tension less than that in larger alveoli. Lower surface tension helps equalize the pressure among alveoli of different sizes and makes it easier to inflate the smaller alveoli. With lower surface tension, the work needed to expand the alveoli with each breath is greatly reduced. Surfactant also prevents the collapse of alveoli during expiration when their volume is small, and it also increases the compliance of the lungs and therefore decreases the work of breathing. (Sukker, 2000)
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The changes in the antero-posterior and lateral diameters of the ribcage during both normal and forced exhalation and inhalation were measured using callipers. The ribs and intercostal muscles are arranged in the body in such a way that the movement of the ribs causes alterations in the dimensions of the chest. At rest, the ribcage decreases in diameter as the lungs are emptied, the diaphragm is relaxed, and the external intercostals return to their original lengths. During inspiration, the diaphragm contracts and thoracic volume increases. During expiration, the diaphragm relaxes and the thoracic volume decreases. (Silverthorn, 2010) The breathing cycle is continuously adjusted in order to accommodate the changing needs of the body. The level of CO 2 in the arteries is monitored and it forms H 2 CO 3 when it combines with water. The H 2 CO 3 dissociates to produce H + and HCO 3 - and if the rate of CO 2 production exceeds its rate of elimination, then the equilibrium shifts to the forward reaction, and more H + are produced. (Bio 273L Lab Manual, 2010) Central chemoreceptors are located near the ventral surface of the medulla oblongata and are stimulated to reflexly increase heart rate. Peripheral
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This note was uploaded on 02/01/2011 for the course BIOL 273 taught by Professor Norman during the Spring '08 term at Waterloo.

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Lab report- bio 273L - Experiment # 5 RESPIRATORY...

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