Why is it that when we hold our breath we soon feel an urge to breathe?
The laws of nature demand that for our cells to live and work properly they must have enough energy. This is obtained through cellular respiration, where the energy locked within the glucose molecule is released with the help of oxygen and about twenty other specific molecules. The chemicals produced in this reaction are carbon dioxide and water.
When you hold your breath, within a few seconds, the oxygen level in your blood begins to drop and the carbon dioxide level begins to rise. This takes place because your cells are constantly using up oxygen and producing carbon dioxide through cellular respiration. Everyone knows that without enough oxygen we can't live very long. But most people don't know that having too much carbon dioxide in your blood is toxic to your brain cells and causes death.
Just like the sensor in the fuel tank and the fuel gauge on the dashboard of your car alerts you to how much fuel your car has, so too, sensors in the main arteries leading to, and within, your brain detect the changes in the blood levels of oxygen and carbon dioxide and this information is sent to the respiratory center in the base of your brain (medulla). The respiratory center seems to know what the normal levels of oxygen and carbon dioxide should be in your blood. So, when your blood level of oxygen drops and carbon dioxide rises, because you’re holding your breath, it sends out messages telling you to breathe in and out to bring these levels back to normal.
Experience tells us that the longer we ignore the urge to breathe, the more intense it becomes, as the blood level of oxygen drops, and the carbon dioxide level rises, further. The respiratory center, having already given us fair warning, now becomes ever more demanding in trying to prevent our death from a lack of oxygen and having too much carbon dioxide.
When we agree (or are finally forced) to take a breath, this is accomplished by messages from the respiratory center traveling down the spinal cord and into the motor nerves which signal the muscles of respiration to contract. This activity increases the volume of your chest cavity and air is literally sucked into your lungs, where it travels along the airways to the alveoli. The alveoli are grape-like sacs surrounded by hundreds of microscopic blood vessels (capillaries) and it is here where the exchange of gases takes place. Oxygen enters the blood from the inhaled air and carbon dioxide leaves the blood and goes into the air to be exhaled by the elastic recoil of the lung tissue. These actions cause the oxygen and carbon dioxide levels in your blood to return to normal. The sensors in the main arteries leading to, and within, your brain detect and relay this new information to the respiratory center and in response it turns off the urge for you to breathe (at least for the next few seconds).
Three Questions for Mr. Darwin
1) Where did the information come from to tell my body how to make all the parts of my respiratory system so I can breathe in enough oxygen and send out enough carbon dioxide?
2) From where did the information come to not only tell my body how to make the sensors for oxygen and carbon dioxide but also place them exactly where they’re needed and how do they know what they’re supposed to do?
3) How does my respiratory center know, not only what the level of oxygen and carbon dioxide should be in my blood, but also what to do about it when these levels aren’t right?
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Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.
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