tirsdag den 24. maj 2011

A little about: Lung Ventilation

Our lung ventilation is controlled by a feed-forward mechanism. As soon as you start to work there is an increase of breathing. The brain sends message that this must be increased. For easy work increases lung ventilation, it means that we get more air in, but neither pCO2 and PO2 increases. This is because, among other things, to our hemoglobin in red blood cells, as previously mentioned an upper limit for the binding of oxygen molecules to oxygen molecules per 4. hemoglobin molecule. If there already is a 100% saturation of blood, he can not rise. Instead of an increased ventilation caused by pCO2 and PO2 increased ventilation due to receptors in the muscles and the command from the brain increases sensitivity of the respiratory center. By hard work changed the partial pressure a bit. A center in the medulla oblongata (the extended spinal cord) are affected by changes in pCO2 and PO2, this center is most sensitive to changes of pCO2. In the brain, cerebrospinal fluid is flowing, this will never in our blood, because the brain's blood vessels form a semi-permeable barrier, the so-called blood-brain barrier. Carbon dioxide can diffuse through this barrier, and are formed carbonic acid and therefore also bicarbonate and free H +. In cerebrospinal fluid, there is no special buffering effect, then H +-concentration can quickly cause changes in pH. They now obtained hydrogen ions affect the central chemo receptors in the respiratory center. When H + concentration increased the pH falls and ventilation increased. There are also peripheral chemo receptors in the neck artery. Flowing constantly a lot of blood over those. They react to an increase in pCO2 and a decrease in pH in the blood by increasing ventilation, they react too little to PO2. There may also be hard work, a production of lactate (acid residue obtained by lactic acid formation in an acid-base reaction). Here functioning respiratory mechanism almost backward: the pH is reduced, making the pCO2 increases. The change will stimulate a significant increase in ventilation, leading to a reduced alveolar pCO2 and PO2, which is constant