- State the Henderson-Hasselbalch equation for the carbon dioxide-bicarbonate buffer system.
- State the major sources for the input of fixed acids and bases into the body, including metabolic processes and activities of the gastrointestinal tract.
- Describe how the input of fixed acids and bases affects body levels of bicarbonate.
- Explain why body levels of carbon dioxide are usually not altered by the input of fixed acids and bases.
- Explain why some low-pH fluids alkalinize the blood after they are metabolized.
- Describe the reabsorption of filtered bicarbonate by the proximal tubule.
- Describe how bicarbonate is excreted in response to an alkaline load.
- Describe how excretion of acid and generation of new bicarbonate are linked.
- Describe how the titration of filtered bases is a means of excreting acid.
- Describe how the conversion of glutamine to ammonium and subsequent excretion of ammonium accomplishes the goal of excreting acid.
- Describe how the kidneys handle ammonium that has been secreted in the proximal tubule.
- State how total acid excretion is related to titratable acidity and ammonium excretion.
- Define the 4 categories of primary acid-base disturbance and the meaning of compensation.
- Describe the renal response to respiratory acid-base disorders.
- Identify the primary types of renal tubular acidosis (RTA).
A key task of the body is to regulate acid-base balance. Perturbations in acid-base balance are among the most important problems confronting clinicians in a hospital setting. The kidneys are major players in the excretion of acids and bases and in the maintenance of acid-base balance. As explained below, the kidneys work in partnership with the respiratory system to keep plasma acid-base status within normal limits.
It is essential for the body to control the concentration of free protons (hydrogen ions) in the ECF. Although most substances regulated by renal processes exist at plasma levels in the millimolar range or greater, the normal hydrogen ion concentration is a seemingly miniscule 40 nanomolar (1 nanomole is 1 millionth of a millimole). Even though very small, this level is crucial for body function. Proteins contain titratable groups that reversibly bind hydrogen ions. As sites on membrane proteins protonate and deprotonate in response to changes in extracellular pH, the resulting alteration of local charge density affects the shape, and therefore the behavior of those proteins. The plasma levels of hydrogen ions are constantly being altered by a number of processes, including (1) metabolism of ingested food, (2) secretions of the gastrointestinal (GI) tract, (3) de novo generation of acids and bases from metabolism of stored fat and glycogen, and (4) changes in the production of carbon dioxide.
The essence of the physiological response to these changes comes down to 2 processes: (1) matching the excretion of acid-base equivalents to their input, that is, maintaining balance, and (2) regulating the ratio of weak acids to their conjugate bases in buffer systems. Buffer systems limit changes in pH to a small range. The 2 processes of excreting acids and bases, and regulating ...