How does vomiting alter the acid-base balance of the blood?
The short answer is that repeated vomiting causes the blood to become more alkaline. The acid-base balance of anything is measured on the pH scale. The scale goes from 0 to 14, and 7 is neutral. Anything below 7 is acidic. Conversely, anything above 7 is basic. Normally, the pH of blood is neutral (or very close to it). Charged hydrogen particles in the blood will cause the blood to be acidic, but that acidity is countered by the alkaline electrolyte bicarbonate. When you vomit, large amounts of hydrogen particles are lost with the stomach acid. All of a sudden there is less acidity in the body, but no change has occurred to the amount of alkaline electrolyte bicarbonate. Essentially, the lost acid no longer balances out the alkalinity of the blood. The blood becomes more basic as a result. Usually the body compensates just fine, but prolonged vomiting could eventually lead to hypokalemia (low potassium levels).
In order to function as it should, human blood requires an appropriate balance of acidic and alkaline compounds, known as the "acid-base balance." While this is normally a function performed by our kidneys and lungs, sometimes this state of balance can become skewed; an example of this is acidosis, when the blood becomes too acidic, or alkalosis, when the blood becomes too basic.
When we vomit, we are expelling contents of our stomachs—including hydrochloric acid (HCl)—from our body. These acidic contents are lost without an equivalent loss of the alkaline bicarbonates. Thus, the remaining liquid contents of the stomach—which are alkaline rather than neutral—are absorbed by blood vessels and carried off to the bloodstream. While this is not a process that happens with minor bouts of vomiting, it will occur with prolonged vomiting.
Blood needs an appropriate acid-base balance to ensure all its components and other body organs work accordingly. Acidosis is a condition where there is a higher level of acidity or low pH levels in the blood. Alkalosis is a condition where the blood has a higher level of alkalinity or registers a high pH on the scale.
Vomiting is normally a protective function of the body that helps in getting rid of harmful substances like toxins. However, vomiting also leads to dehydration and the removal of acidic hydrogen compounds. The acidic hydrogen compounds are balanced by the bicarbonate, which is alkaline and ensures that the blood maintains an almost neutral pH condition. Thus, prolonged vomiting may lead to an increase in alkalinity if the body fails to compensate for the loss of hydrochloric acid.
When you vomit you are expelling gastric contents. The pH of the stomach is highly acidic because of HCL hydrochloric acid. HCL has a pH of about 0.8, remember that the pH scale is from 0-14. When you lose gastric contents, you also lose this very strong acid. Proton pumps in the gastric mucosa work to replace this lost acid but they can't replace it quick enough, especially if you vomit repeatedly. The pH of the stomach becomes more alkaline or basic(because you have lost the HCL). The microvilli of the mucosa is highly vascular(has a good blood supply). Now, the alkaline fluid or chyme is readily absorbed by the blood vessels in the stomach and transported to the bloodstream or cardiovascular system. Vomiting once or twice will not change the pH of the blood but intractable vomiting will.
Vomiting alters the acid-base balance by causing a massive loss of chloride from the stomach as hydrochloric acid (HCl). This causes an increase of bicarbonate in the extracellular fluid (any fluid in the body that is not part of the fluid in the cells). Information from: Thibodeau, Gary A. and Patton, Kevin T., Structure & Function of the Body, 2008, St. Lewis, Mosby Elsevier.