HLTH1004 W2 L2.4.6

Carbonic Acid-Bicarbonate Buffer System

• Functionality

  • Buffers carbon dioxide released from all body cells during metabolism.

  • Converted carbon dioxide forms carbonic acid, leading to bicarbonate and hydrogen ions.

  • Helps stabilize pH in extracellular space by preventing pH changes from metabolic and fixed acids.

Limitations of the Buffer System

• Dependence on Respiratory System

  • Can only buffer changes in pH related to carbon dioxide if the respiratory system is functioning correctly.

  • Damage to the respiratory control center limits buffer efficacy.

• Bicarbonate Availability

  • Buffering capacity constrained by available bicarbonate ions.

  • Generally not a problem, as kidneys produce a significant reserve of sodium bicarbonate.

Mechanisms of Action

• Buffering Reaction Process

  • Reaction is reversible, adjusting concentrations of sodium ions and bicarbonate based on the presence of various products.

  • Bicarbonate derived from carbonic acid picks up hydrogen ions to maintain pH balance.

  • Carbon dioxide and water produced from this reaction are expelled via the lungs.

• Temporary Solution

  • Buffers provide short-term regulation and do not eliminate all hydrogen ions.

  • Recycling of buffering molecules is essential but limited in supply.

  • Systems require continuous regulation to maintain pH within tight limits (around 7.35-7.45).

Role of Respiratory and Renal Systems in Acid-Base Regulation

• Respiratory Compensation

  • Increase respiratory rate expels more carbon dioxide, aiding in pH stabilization when it falls below normal limits.

  • pH rises when carbon dioxide levels decrease; affects the buffer system dynamics.

• Renal Compensation

  • Kidneys manage bicarbonate secretion/reabsorption and excretion of hydrogen ions.

  • Regulation occurs through changes in kidney permeability, affecting urine concentration of acids and bicarbonate.

  • Metabolic acids produced daily necessitate hydrogen ion excretion to maintain balance.

  • Kidneys assist lungs by eliminating any CO₂ that

    • Enters renal tubules during filtration

    • Diffuses into tubular fluid en route to renal pelvis

Filtering and Elimination of Waste Products

• Urine as a Waste Management System

  • Urine can efficiently eliminate large volumes of waste, including hydrogen ions.

  • Filtration occurs primarily in the glomerulus, involving water retention and extra ions eliminated in urine.

• Kidney Functions Beyond Urine Production

  • Tubule cells assist with ammonia generation to buffer protons.

  • Involvement of kidneys in managing acid-base balance highlights their metabolic functions.

Physiological Impacts of Buffer System Disturbances

• Potential Disorders

  • Disturbances can lead to severe circulatory, respiratory, or renal disorders affecting acid-base equilibrium.

  • Conditions like heart failure or hypertension may hinder buffering capacity and lead to imbalances.

• Impact of Nervous and Renal Systems

  • Disorders of the nervous system may disrupt control over acid-base mechanisms, affecting respiration and kidney functions.

Summary of Important Concepts

• Water's Vital Role

  • Essential for cellular processes, providing a transport medium for gases, nutrients, and waste, including protons.

  • Influences buffering capacity and homeostasis.

• Intracellular vs. Extracellular Fluid Concentrations

  • Different ion and water concentrations within various compartments significantly impact metabolic processes.

  • Blood plays a crucial role in maintaining water balance and facilitating movement between compartments.