every single second there are trillions of biochemical reactions going on inside our bodies these reactions are mediated by enzymes and for those enzymes to function properly the pH of our body fluids need to be within a tightly regulated range this pH depends on the ratio of concentration of bases mainly bicarbonate or hco3 minus and acids mainly carbon dioxide or CO2 and it's calculated by a fairly lengthy equation called the henderson-hasselbach equation where pH equals 6.1 plus the log of the concentration of bicarbonate divided by .03 times the partial pressure of carbon dioxide now if we focus on the pH of our arterial blood we can design a diagram or acid-base map with a concentration of bicarbonate on the x-axis and the partial pressure of carbon dioxide or pco2 on the y-axis using the henderson-hasselbach equation we can plot a line called the isohydric line that starts at the origin the term isohydric means that along these points they all share the same or ISO concentration of hydrogenated ions hydric so isohydric for example let's say the bicarbonate concentration is 24 Milli equivalents per liter and the partial pressure of carbon dioxide is 40 millimeters of mercury according to the henderson-hasselbach equation that would give us a pH of 7.4 now we'd have the same pH of 7.4 if there's a bicarbonate concentration of 36 Milli equivalents per liter and a partial pressure of carbon dioxide of 60 millimeters of mercury or with a bicarbonate concentration of 12 ml equivalents per liter and a partial pressure of carbon dioxide of 20 millimeters of mercury in fact we can draw out two more isohydric lines this time for a pH of 7.35 and another for a pH of 7.45 a normal physiologic pH is between 7.35 and 7.45 so you can see that there are a lot of combinations of bicarbonate concentrations in partial pressure of carbon dioxide that are between these two lines that would result in a normal pH now because it's so important for the body to stay between these lines it's designed several mechanisms to maintain homeostasis or balance one mechanism involves the lungs specifically the rate and depth of breathing which controls the amount of carbon dioxide that's breathed out the other mechanism involves the kidneys which can carefully control the amount of bicarbonate that's excreted now sometimes these regulatory processes get Disturbed specifically if there's a decrease in the ratio of bicarbonate concentration to partial pressure of carbon dioxide the pH drops below 7.35 and we shift to the upper left part of the acid-base map where there's acidosis on the other hand when the ratio increases the pH rises above 7.45 and we move to the lower right part of the acid-base map where there's alkalosis acidosis and alkalosis can be classified according to their root cause as being either respiratory or metabolic respiratory pH disorders result from some problem with the respiratory system and it results in a partial pressure of carbon dioxide value that's too low or too high for example when breathing too shallow due to diseases like pneumonia carbon dioxide can't get eliminated efficiently and as a result it accumulates in the blood the partial pressure of carbon dioxide therefore usually Rises and so the pH decreases and this causes a respiratory acidosis on our acid-base map this could be represented by any point within a shaded region of pH values much lower than 7.35 and a partial pressure of carbon dioxide above 45 millimeters of mercury that's only acute though meaning that it goes on for a limited period of time typically just a few days that's because the kidneys recognize that the pH has decreased and they try to compensate for the imbalance by retaining more bicarbonate which usually ends up Rising above 26 Milli equivalents per liter this brings the pH as close to the normal line of 7.35 as possible but it does take a few days for the kidneys to do this so it's considered The Chronic phase of the condition on the flip side if a person is breathing faster than normal there's excessive carbon dioxide loss so partial pressure of carbon dioxide decreases and the pH Rises on the map this shifts us into the area of respiratory alkalosis where the pH is a lot higher than 7.45 and the partial pressure of carbon dioxide has dropped below 35 millimeters of mercury once again there's an acute phase but over several days The Chronic phase kicks off and the kidneys start to excrete more bicarbonate which decreases below 22 Milli equivalents per liter and pulls the pH closer to the normal range again now in metabolic pH disorders the main problem is that there's an abnormality in the bicarbonate concentration for example metabolic acidosis might result from diarrhea or a renal disease where there's a severe bicarbonate loss that causes the bicarbonate concentration to dip below 22 Milli equivalents per liter which ends up decreasing the pH as a compensation the respiratory system immediately tries to blow off carbon dioxide by taking deeper and more frequent breaths and this decreases the partial pressure of carbon dioxide this compensation starts happening within minutes rather than taking days and the result is that the partial pressure of carbon dioxide usually Falls so even though the overall pH still Falls that helps prevent the pH from getting really low back to our Map There's a single area of metabolic acidosis with ph values lower than 7.35 bicarbonate concentrations below 22 Milli equivalents per liter and partial pressure of carbon dioxide below 35 millimeters of mercury on the other hand metabolic alkalosis can result from an inability to excrete excess bicarbonate in the urine and this leads to an increase in the bicarbonate concentration and therefore a rise in the pH again there's an immediate respiratory compensation this time with slow shallow breathing which allows partial pressure of carbon dioxide to rise above 45 millimeters of mercury and prevents the pH from getting really high so on the map we can mark the single area of metabolic alkalosis characterized by pH higher than 7.45 bicarbonate concentration above 26 Milli equivalents per liter and a partial pressure of carbon dioxide above 45 millimeters of mercury in other words in metabolic abnormalities there are no acute and chronic phases since respiratory compensation starts right away if there's a single respiratory or metabolic problem which Falls somewhere within one of these shaded regions the result is this simple acid-base disorder sometimes though there can be more than one acid-base disturbance at the same time for example there could be a problem causing an acidosis and another problem causing an alkalosis and in this case the two would partially neutralize each other alternatively there might be two problems that both result in an acidosis or they both result in an alkalosis and those cases would result in a more severe pH disturbance because they'd compound each other and there'd be no compensation all these are called mixed acid-base disorders and fall somewhere in between the shaded areas of the map alright as a quick recap an acid-base map shows the relationship between pH bicarbonate concentration and partial pressure of carbon dioxide in respiratory and metabolic acidosis or alkalosis and how these values are adjusted when there's a renal or respiratory compensation in a nutshell respiratory acidosis in the acute phase is characterized by high partial pressure of carbon dioxide without any change in bicarbonate concentration so there's a very low ph in The Chronic phase due to renal compensation bicarbonate concentration gets high too so pH is relatively higher but still lower than normal similarly respiratory alkalosis in the acute phase is characterized by low partial pressure of carbon dioxide and a very high pH in The Chronic phase as a result of renal compensation bicarbonate concentration gets low as well so again the pH is still high but it's not as high as it was before in contrast in metabolic acidosis you get low bicarbonate concentration but instant respiratory compensation so partial pressure of carbon dioxide goes down as well and as a result the pH is low but not as low as it would be without compensation with metabolic alkalosis you have high bicarbonate concentration with an instant compensatory increase in partial pressure of carbon dioxide and this leads to a high pH but not as high as it would be without compensation