Question: Exercise 8.6: The Role Of Carbon Dioxide As You Know, Pulmonary Ventilation Is Necessary For Oxygen To Become Available To Body Cells. It Is Also Necessary For The Waste Product Of Cellular Respiration, Carbon Dioxide (CO), To Be Eliminated From The Blood. If The Expiration Process Of Ventilation Were To Fail, The Accumulation Of Carbon Dioxide In The …

Exercise 8.6: The Role of Carbon Dioxide As you know, pulmonary ventilation is necessary for oxygen to become available to body cells. It is also necessary for the waste product of cellular respiration, carbon dioxide (CO), to be eliminated from the blood. If the expiration process of ventilation were to fail, the accumulation of carbon dioxide in the blood mostly in the form of H.CO, would quickly exceed the blood’s buffering capability resulting in toxic blood acidity. The carbonic acid-bicarbonate buffer system of the blood helps to maintain arterial blood pH at 7A +/-0.05. When carbon dioxide diffuses into the blood from metabolizing cells, most of it enters the red blood cells where it combines with water to form carbonic acid. This reaction can be written as: Reaction A H,O+CO, H.COM The carbonic acid formed in this reaction is short-lived. It quickly dissociates in water to form hydrogen ions and bicarbonate ions, which are the buffer. Reaction B: H,CO, H H + HCO, Often the two reactions are combined, the formula for the formation of bicarbonate ions and hydrogen ions from carbon dioxide and water is: Reaction HọO + CO2 + HCO, + H+ + HCO, Note that the bicarbonate ion (HCO, ) is the buffer and is typically stored in the blood by binding with Na to create sodium bicarbonate, the stable form of this natural buffer. Reaction D: HCO, + Na + NaHCO, When breathing rate changes from normal to very shallow (hypoventilation) or from normal to rapid (hyperventilation), the amount of carbonic acid in the blood will also change. We can follow the chemical reactions above for the carbonic acid-bicarbonate buffer system to see how a change in blood levels of CO affects carbonic acid production and therefore, changes in blood pH. During hypoventilation, the amount of carbon dioxide exhaled has decreased, allowing the amount of CO, to build in the blood. With more Co, available to react with water, more carbonic acid is able to form (Reaction A). The increase in carbonic acid leads to an increase in H+ (hydrogen lons) production (Reaction B), which in turn decreases the pH of the blood. In fact, hypoventilation can result in a clinical emergency known as respiratory acidosis, in which the buffers (ex.HCO,) have failed to bind up the excess H* (Reaction B) and result in a rapid decrease in blood pH. During hyperventilation, the amount of carbon dioxide exhaled has increased, therefore, decreasing the amount of Co, available in the blood. With less CO available to combine with water, the amount of carbonic acid also decreases in the blood. Less carbonic acid results in a decrease in H-production, and therefore an increase in pH. Opposite to what we see in hypoventilation, hyperventilation can result in respiratory alkalosis. If either of these imbalances in pH occur, the body must return the blood pH to normal. The respiratory system assists the body regulation of pH levels in the blood through the control of pulmonary ventilation. For example, during exercise carbon dioxide levels rise due to increased metabolism. Consequently, the chemical equation described above shifts to the right and more hydrogen and bicarbonate ions are produced. The rising levels of hydrogen ions result in a decrease in blood pH. The drop in blood pH triggers chemoreceptors in the aortic arch, carotid bodies and brain to cause an increase in pulmonary ventilation rate. As a result, the heavier breathing removes the Respiratory Sytem 241 more carbon dioxide from the blood through expiration. As the carbon dioxide levels in the blood begin to decrease, the chemical equation shifts to the left and more hydrogen ions and bicarbonate ions form carbonic acid. This process continues until hydrogen ion levels (and pH) in the blood return to normal The Effect of a Buffer on pH The scientific method involves steps to either accept or reject a stated hypothesis (explanation of a phenomena that is able to be tested). Review the information about the scientific method in the Introduction of this lab manual before completing this exercise. Fill out and turn in the scientific method worksheet on the next page for 10 points after the completion of the experiment. During this exercise you will demonstrate the influence of sodium bicarbonate (NaHCO, a buffer) by introducing Co, into water and into a sodium bicarbonate solution. A pH indicator (phenol red) will be used to indicate a pH change. Phenol red changes from red to yellow when the pH becomes acidic (below 7.0). You will be observing and recording pH changes during the experiment. Materials and Set-Up: Obtain 3 clean test tubes. Label the tubes A, B and C with a Sharpie pen. Into tubes A and B, add 2 ml of water. Into tube C add 2 ml of a sodium bicarbonate solution. Add 5 drops of phenol red to all three tubes. Obtain 2 clean straws and a pair of safety glasses or goggles. Procedure: Note: This procedure should be done over a sink in the lab. 1. While leaning over the sink, take a deep breath and exhale gently up to 30 seconds into Tube 8. Stop the moment it turns yellow. Repeat this same procedure for Tube C. 2. Record the colors of Tubes A, B and in the data table below. Rinse and return the test tubes. Dispose of the straws and wrappers in the trash can. Return your safety glasses. Data Table: Tube A Tube B Tube 1. Observation: Explain the carbonic acid bicarbonate buffer system and explain how phenol red changes with pH. 2. Hypothesis: Based on your knowledge explained above, predict which tube(s) should turn yellow. 3. Experiment Include all the steps involved in the experiment and identify the control tube. 4. Results: Include the data you gathered for each tube. 5. Conclusion: Discuss all the results indicating why the results occurred for each tube. Include whether or not it supported your hypothesis. It is ok if the hypothesis is rejected, as long as you give plausible explanation(s) why it was not supported.