Acid-Base Balance

Buffer Systems in the Human Body

• Buffers: Chemical systems that prevent drastic pH changes in bodily fluids by reducing hydrogen ion concentration fluctuations. Weak acids and weak bases are common buffer substances.
• Acid-Base Balance: Crucial for physiological function; measured by pH scale.
• Buffering Efficiency: The body's buffering systems are highly efficient, with different systems acting at differing speeds.

Types of Buffering Systems

• Plasma proteins: Account for a substantial portion of blood buffering power and intracellular buffering.

  • Mechanism: Amino acids within proteins ionize in response to pH fluctuations. Amino groups accept H+ to increase pH, while carboxyl groups release H+ to decrease pH.
  • Hemoglobin: Vital protein in red blood cells; buffers hydrogen ions released during CO2 conversion into bicarbonate.

• Phosphates: Exist in two forms as weak acid or weak base in the blood.

  • Sodium dihydrogen phosphate (weak acid): Reverts to a weak base upon contact with strong bases.
  • Sodium monohydrogen phosphate (weak base): Reacts with strong acids, accepting hydrogen ions.

• Bicarbonate-Carbonic Acid Buffer: Primary buffer in interstitial fluid.

  • Mechanism: Sodium bicarbonate reacts with strong acids to form carbonic acid and other salt. Carbonic acid reacts with strong bases to form bicarbonate and water.
  • Ratio: Bicarbonate and carbonic acid exist in a 20:1 ratio for normal blood pH.
  • Regulation: CO2 expulsion through lungs regulates carbonic acid levels, while renal functions control bicarbonate levels.

Respiratory Regulation

• CO2 and pH Relationship: CO2 reacts with water to form carbonic acid, impacting blood pH. Elevated CO2 levels (e.g., holding breath) lower pH, while reduced CO2 levels (e.g., hyperventilation) increase pH.

• Hyperventilation: Rapid and deep breathing expels excess CO2, reducing carbonic acid and leading to alkalosis.

• Hypoventilation: Impaired breathing increases carbonic acid and causes acidosis.

• Hypercapnia: Elevated blood CO2 level; caused by issues with respiratory function, or certain drugs.

• Hypocapnia: Low blood CO2 level; commonly resulting from hyperventilation conditions.

• Carbonic Anhydrase: Enzyme catalyzing CO2 hydration to bicarbonate—vital to the reaction.

• Chemoreceptors: Monitor CO2 levels within blood and CSF to adjust respiratory rate. Peripheral sensors in the aorta and carotid arteries, and central sensors in the medulla oblongata, immediately modulate breathing.

• Respiratory Adjustments: Minor changes in breathing can adequately adjust pH; increasing respiratory rate by twofold for minimal duration can raise blood pH by 0.2 units.

Renal Regulation

• Bicarbonate Conservation: The kidneys control blood bicarbonate level, a vital part of metabolic pH regulation.
• Renal Tubule Mechanism:
  • Reabsorption of sodium by antiport mechanism exchange H+ from filtrate.
  • Production of bicarbonate.
  • Formation of carbonic acid leading to bicarbonate that transfers to peritubular capillaries.
  • Secretion of hydrogen ions that may combine with substances and be removed from body.
• Factors affecting Bicarbonate Conservation: Diuretics inhibition of carbonic anhydrase, diarrhea, Addison's disease, renal damage, and uncontrolled diabetes.
• Chloride and Bicarbonate Relationship: Loss of chloride can lead to greater bicarbonate reabsorption to maintain electrolyte balance.
• Hydrogen Ion Interactions: Hydrogen ions and potassium compete for exchange with sodium—the availability of K+ affects the amount of H+ and consequently bicarbonate retention.

Ketoacidosis

• Mechanism: Inadequate glucose availability causes fatty acid breakdown; ketone bodies form, lowering blood pH.
• Symptoms: Deep and rapid breathing, fruity breath (presence of acetone, a ketone). Other symptoms include dry skin/mouth, flushed face, nausea, vomiting, and stomach pain.

Blood pH

• Normal Range: 7.35-7.45
• Acidosis: Blood pH below 7.35. (Symptoms include cognitive impairment, tingling, muscle twitching/spasms, nausea and vomiting). Caused by metabolic or respiratory disorders.
• Alkalosis: Blood pH above 7.45. (Symptoms include cognitive impairment, tingling, muscle twitching/spasms, nausea and vomiting). Caused by metabolic or respiratory disorders.
• Impact of Extreme pH Changes: Extreme pH fluctuations can damage proteins, disrupting metabolic function, leading to tissue damage, and potentially death.

Explore the critical role of buffer systems in maintaining pH balance within the human body. This quiz covers the types of buffers, their mechanisms, and their efficiency in physiological functions. Understand how proteins and phosphates contribute to acid-base balance.