AcidBase Balance and the Anion Gp酸碱平衡及阴离子间隙.docVIP

Acid-Base Balance and the Anion Gap The body strives for electrical neutrality. Cations = Anions One of the cations is very special, H+, and its concentration is monitored and regulated very closely. c. Volatile acid (CO2) and non-volatile acids, lactate, H2PO4-, H2CO3 Blood pH is described by the Henderson-Hasselbalch equation Note the importance of Arterial CO2, indicated as PaCO2, Bicarbonate, HCO3 – Carbonic anhydrase We measure the pH of arterial blood. Arterial blood has been through the lungs and should be at optimal pH. This is not the case for venous blood. 7.35-7.45 Central nervous system control of respirations and therefore PaCO2 The control of bicarbonate, HCO3 –, by the kidneys Retention or Excretion So how does it all work under normal circumstances to keep our pH about 7.4? Normally, CO2 production and loss are matched PaCO2 is maintained at about 40 mmHg PaCO2 is regulated by respiration rate, either slowing down or speeding up respirations, to either blow off or retain CO2. Control comes from the CNS by regulating respiration rate. Production rate of CO2 is not subject to regulation, The kidney regulates plasma [HCO3 – ] (by extension [H+] and pH) by three mechanisms Reabsorption of filtered HCO3 – , this is a recovery operation Formation of titratable acid, H2PO4- distal tubule Excretion of NH4+ distal tubule Get this. The kidney glomerulus passively filters on the order of 4000 mmol of HCO3 –each day. This has to be reabsorbed. To lose it would be a disaster. In order to reabsorb this filtered load of HCO3 –, the tubular cells must therefore secret 4000 mmol of hydrogen ions. This allows the conversion of carbonic acid to CO2 and water, which will passively come back into the proximal tubular cell. The secretion of titratable acid by the kidney, used to actually modify the blood pH, goes on in the distal tubule. 6. Basically, the regulation of arterial pH includes Regulation of PaCO2 by the respiratory system. Regulation of HCO3 – b