User:Trorstad/Kidney

Acid–base balance
Main article: Acid–base homeostasis

The two organ systems that help regulate the body's acid-base balance are the kidneys and lungs. Acid–base homeostasis is the maintenance of pH around a value of 7.4. The lungs are part of respiratory system which helps to maintain acid–base homeostasis by regulating carbon dioxide (CO2) concentration in the blood. The respiratory system is the first line of defense when the body experiences and acid-base problem. It attempts to return the body pH to a value of 7.4 by controlling the respiratory rate. When the body is experiencing acidic conditions, it will increase the respiratory rate which in turn drives off CO2 and decreases the H+ concentration, therefore increasing the pH. In basic conditions, the respiratory rate will slow down so that the body holds onto more CO2 and increases the H+ concentration and decreases the pH.

The kidneys have two cells that help to maintain acid-base homeostasis: intercalated A and B cells. The intercalated A cells are stimulated when the body is experiencing acidic conditions. Under acidic conditions, the high concentration of CO2 in the blood creates a gradient for CO2 to move into the cell and push the reaction HCO3 + H <--> H2CO3 <--> CO2 + H2O to the left. On the luminal side of the cell there is a H+ pump and a H/K exchanger. These pumps move H+ against their gradient and therefore require ATP. These cells will remove H+ from the blood and move it to the filtrate which helps to increase the pH of the blood. On the basal side of the cell there is a HCO3/Cl exchanger and a Cl/K co-transporter (facilitated diffusion). When the reaction is pushed to the left it also increases the HCO3 concentration in the cell and HCO3 is then able to move out into the blood which additionally raises the pH. The intercalated B cell responds very similarly, however, the membrane proteins are flipped from the intercalated A cells: the proton pumps are on the basal side and the HCO3/Cl exchanger and K/Cl co-transporter are on the luminal side. They function the same, but now release protons into the blood to decrease the pH.