In this article I will plot the journey of a single oxygen molecule floating around in the atmosphere that is suddenly sucked into the nose of a carbon based unit. A wild ride ensues when our oxygen molecule hitches a ride on a red blood cell and travels through the body to deliver much needed oxygen to a single cell.
The impulse to breath begins with a cluster of neurons in the Respiratory Center of the brain located in the Medulla Oblongata. where rising levels of CO² causes the pH of the CSF to decrease (becoming acidic) and triggers inhalation.
I can’t handle all this pressure…
In the peripheral nervous system (PNS), acetylcholine (ACh) binds to receptor sites on individual fibers of the diaphragm. When enough of these chemical signals are received by your muscle fibers, an action potential is created causing your entire diaphragm to contract. As a result, the diaphragm contracts and moves downward, and the intercostal muscles pull the rib cage outward. This causes the air pressure within the alveoli to be lower (negative pressure) than the atmospheric pressure (760mmHg).
The chest cavity expands air is sucked into the nose and enters the upper airway. The oxygen molecule gets filtered, humidified, and warmed as it passes through the Nasopharynx and Conchae by being thrashed around. Next the molecule will pass the Oropharynx of the mouth into the Laryngopharynx, passing the Epiglottis and Glottis into the Trachea of the lower airway.
Did you remember the map?
From the Trachea the oxygen molecule has to make a decision to go left or right. It decides to go right and travels into the Right Main Stem Bronchus and then into the Bronchi and even smaller Bronchioles and finally into the grape like Alveoli.
The oxygen molecule in the Alveolus is passed to the Pulmonary Capillaries through the Respiratory Membrane. Through the process of a Concentration Gradient, the concentration of PCO² (45mmgH) is higher than the PO²(40mmgH) within Pulmonary Capillaries. The oxygen molecule attaches to Hemoglobin (one of four oxygen molecules to attach to one of 280 million Hemoglobins in a Red Blood Cell (RBC)).
The oxygen molecule rides its host RBC through the Pulmonary Venules, the Superior Pulmonary Vein, and the Left Atrium, through the Bicuspid or Mitral Valve, and into the Left Ventricle.
Hitting the Super Highway
The oxygen molecule and its host is then pumped through the Aortic Semi Lunar Valve into the Ascending Aorta and sent to the Aortic Arch. On this particular journey the RBC is sent into the Left Common Carotid, into the Superficial Temporal Artery, and Into the Capillary Beds where …
You have reached your destination. Please do not forget your luggage.
The Partial Pressure of Oxygen (PO²) within the brain cell is 40mmgH and the Partial Pressure of Carbon Dioxide (PCO²) is 45mmgH. Conversely, the Red Blood Cell’s Partial Pressure of Oxygen (PO²) is 100mmgH and the Partial Pressure of Carbon Dioxide (PCO²) is 40mmgH. The Concentration Gradient causes the oxygen molecule to hop off into the brain cell. Meanwhile carbon dioxide is picked up by the the Red Blood Cell.
The Jet Lag Cure
The mitochondrion takes up the oxygen molecule and uses it to convert glucose into CO², H²O, and adenosine triphosphate (ATP). Before glucose can be converted to ATP, it has to be broken down into two pyruvate molecules. This process is known as glycolysis. From here, pyruvate is converted into acetyl coenzyme A (acetyl CoA) and enters the process known as Krebs cycle where ATP production occurs. CO² and extra H²O are waste byproducts of the process and are eliminated by the body. ATP is the energy or fuel used by the cells. Without ATP, neurons very quickly lose their ability to fire and the brain starts shutting down.
The Return Trip…
Now that the Concentration Gradient has moved the oxygen molecule into the cellular tissue, a carbon dioxide molecule has been picked up and heads through the Internal Cerebral Vein, Great Cerebral Vein of Galen, Straight Sinus, and Superior Sagittal Sinus (Dural Sinuses) into the Confluence of the Sinuses and drains into the Right Internal Jugular Vein. From here it goes into the Right Brachiocephalic Vein, into the Superior Vena Cava, into the Right Atrium, through the Tricuspid Valve, into the Right Ventricle, through the Pulmonary Semi Lunar Valve, into the Left Pulmonary Artery, into the Pulmonary Arterioles, and into the Pulmonary Capillaries where the process of Concentration Gradient occurs again.
During relaxation, the acetylcholine molecules bound to receptor sites will break down and vacate the receptor sites they occupied on the diaphragm. The muscles relax and air (as well as carbon dioxide) is pushed out of the lungs through the nose following the same path used by the oxygen molecule causing exhalation.
I hope that was an educational as well as entertaining journey. Until next time get addicted and become an EMSJunkie!