pH regulation

Blood pH pH = measure of hydrogen ion concentration pH = -log [H + ] Blood pH = pH imbalances are quickly lethal  body needs to compensate H + intake: - food - drink - metabolism (carbohydrate, protein, lipid) - breathing H + output - urine

Figure 19.23

pH regulation Three lines of defense: - Buffers - Respiration - Kidneys Buffer reactions are nearly instantaneous. However, they are limited to the amount of buffer available in the blood Respiration helps buffer the blood by shifting H+ into HCO3-. However, it can be limiting and take several minutes Kidneys are the only organ which can get rid of H+. However, they can take several hours (time enough to be dead!!-  therefore, the presence of the other 2 lines of defense)

pH regulation Three lines of defense: - Buffers - Respiration - Kidneys

First line of defense: Buffers Buffers: - protein buffer - bicarbonate buffer - phosphate buffer Only free H + contributes to pH H + can be shifted from a strong acid to a weaker one. Strong acid  complete dissociation (100) HCl  (100)H + + (100) Cl - Weak acid  (100) H 2 CO 3  (80) H 2 CO 3 + (20) H + + (20) HCO 3 -

pH regulation If strong acid intake: H + + Cl - + ( blood Na + HCO 3 - )  Na + Cl - + H + + HCO 3 - Less H+ is circulating into the blood -  smaller shift toward acidosis If strong base intake: Na + OH - + (blood H 2 CO 3 )  H 2 O + Na + HCO 3 - Less OH- is circulating in the blood  smaller shift toward alkalosis

Second line of defense: breathing Three lines of defense: - Buffers - Respiration - Kidneys

CO 2 + H 2 O  H 2 CO 3  H + + HCO 3 - CO 2 retention: ↑ blood H +  ↓ pH  acidosis CO 2 loss: ↓ blood H +  pH ↑  alkalosis

Figure 17.22

Figure 19.24

Third line of defense: kidneys Three lines of defense: - Buffers - Respiration - Kidneys Kidneys are the only organs able to eliminate H + from the body  slow process

H + can be bound to HCO 3 - for transport to the bladder and eliminated H + can be added to NH 3 to make ammonia (NH 4 + ) and eliminated H + can be eliminated directly by exchange with Na + Urine is usually slightly acid. It’s pH varies with food and drink intakes

Clinical applications: Acidosis: Blood pH<7.35

Figure 19.28