Acid Base Balance: The Basics

What is acidosis?

• Too much acid in body fluids

• pH falls below normal range (7.35 to 7.45)

• Kidneys and lungs cannot maintain health acid-base balance

What is alkalosis?

• Body fluids contain an excess of base

• pH rise above normal range (7.35 to 7.45)

Why do we have net “acid load” in the body?

• Due to metabolic processes and dietary intake

• Important to maintain pH balance

• Cellular metabolism produces waste that is neutralised by acids such as sulfuric acid. Incomplete glucose or fat metabolism produces lactic and ketoacids

• Food requires break down as well by metabolism

What is an intracellular buffer?

• ~57% of total body buffering capacity

• Increasing ECF hydrogen or bicarbonate moving across cell membranes slowly

• Can take hours for full effect

• Special case: RBCs, hydrogen or bicarbonate move quickly, and Hb crucial role in buffering

• Maintains cellular homeostasis

• ICF

What is a protein buffer?

• Different amino acids with ionisable groups can accept or donate hydorgen ions

• Most important of intracellular buffers along with phosphates

• Important role in plasma

• Located in ICF and blood plasma

• Maintains pH for enzyme function, cell survival and homeostasis

What is a phosphate buffer?

• Most important intracellularly and can act to buffer acids in urine

• Dihydrogen phosphate ion acts as a weak acid which buffers a strong base

• Monohydrogen phosphate acts a weak base by buffering hydrogen released by a strong acid

• Sodium salts of dihydrogen phosphate and monohydrogen phosphate

• ICF and renal tubules

• Prevents drastic pH shifts that would damage cells, disrupt enzyme activity and impair metabolic processes

What is the role of the lungs and its importance in '“opening” buffering?

• Lungs regulate blood pH by continuously exhaling carbon dioxide

• Prevent acid buildup

• Provide open buffer system by allowing a by product (carbon dioxide) to continually escape the reaction via exhalation

• Relies on diffusion across gradients and is passive

• Respiratory centre in medulla stimulates increase in breathing when plasma carbon dioxide rises

What is the global control of the kidneys via excretion of hydrogen ions?

• Hydrogen ions removed from blood by tubular sebretion. Hydrogen ions exit the peritubular capillaries and enter nephon in distal tubule and collecting duck. Kidneys oppose the process by acidosis and remove non-volatile acids

• Bicarbonate ions are reabsorbed by the nephron and enter peritubular capillaries

• Reabsorption of bicarbonate ions into blood opposes acidosis. Bicarbonate ions bind with hydrogen ions, removing source of acidity.

• Tubular secretion and reabsorption work together to control pH.

Explain the bicarbonate buffering system with reference to the Henderson-Hasselbalch equation.

• Body maintains a perfectly 20:1ratio to keep blood at a pH of 7.4

• If one component changes the other system compensates to restore this balance

• Metabolic Acidosis: Bicarbonate levels drop. To compensate, lungs increase breathing to blow oof carbon dioxide to lower the denominator.

• Respiratory Acidosis: Carbon dioxide levels rise due to hypoventilation. In response, kidneys retain and reabsorb bicarbonate, raisng the numerator.