It is early on a Saturday morning and the swim club is warming up for their regi

Question

It is early on a Saturday morning and the swim club is warming up for their regional meet. Savannah and Hannah are almost finished with their set and discussing their races. “I’m really excited to swim the 50 Free!” says Hannah. “I am going to try for a personal best and maybe get a BB time”. “I don’t see how you can swim that whole race without taking a breath. I would be dying” replies Savannah. The meet has begun and Hannah is behind the blocks preparing for the 5o Free. Savannah is at the opposite end of the lane ready to cheer her on. She is watching Hannah and notices her taking big deep breaths and breathing very rapidly. “I hope she is okay” Savannah whispers to herself as the beep signals the start of the race. She watches in amazement as Hannah plows through the water her legs pumping so fast they create a wake behind her and never once turning her head to take a breath. The race ends as quickly as it started. Savannah cheers as the board shows Hannah’s time for the race. “She did it… 31.65 sec!. 4. Before Hannah started her race she voluntarily changed her breathing rate and depth. a. (5pts) Describe what would happen to her blood CO2 levels and thus stimulus to breathe as a result of this change. *Hint: Recall the relationship between breathing rate, blood CO2 levels, and chemoreceptors. b. (5pts) Explain why changing her breathing before the race could improve her 50 free race time.

Explanation / Answer

Answer for a and b);

A) voluntary control of respiration bypasses the medullary respiratory neurons.

Excess CO2 or lack of O2 ( due to fast inspiratory and expiratory attempts)

Stimulates carotid and aortic bodies,impulses travels through vagus nerve from aortic bodies and glossopharyngeal nerve from carotid bodies ,sends impulses to the respiratory area,which cause increase in rate and depth of respiration.

This will

We know that rise in arterial pCO2 or fall in arterial pO2 or pH stimulates medullary chemoreceptors to increase rate and depth of respiration.

Mechanism;

Co2 penetrates the brain and gets hydrated to form carbonic acid which dissociated into H+ and HCO-3. Increase in H+ concentration decreases the pH.

So,Here the effect is due to penetration of CO2 in brain and decrease in pH.

Effect of the stimulation;

It increased rate and depth of respiration,regulates respiration from minute to minute and provides late drive to increase in rresponse to increase iin arterial pCO2and contributes to increase in pulmonary ventilation upto 80%.

Therefore,

Inhalation of CO2 upto 4%will cause 2 times increase in pulmonary ventilation( increased pCO2 to 15mmHg)

Inhalation of CO2 between 4 to 7% will cause increase in pulmo ary ventilation linearly to increase in concentration of CO2 in inspired air.

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