acid base balance

• What is the primary factor that determines acid-base balance in the body?

  Hydrogen ion concentration ([H+])
• How is hydrogen ion concentration expressed in a manageable way?

  As potential hydrogen (pH)
• What are the two main ways in which acid-base balance is regulated?

  • Balance between intake or production of H+ and net removal from the body
  • The kidneys play a key role in regulating H+ removal

  
• What is required for precise control of extracellular fluid [H+]?

  Multiple acid-base buffering mechanisms
• How do [H+] levels influence enzyme systems?

  They impact virtually all cellular and bodily functions
• What is the sodium concentration in extracellular fluid?

  142 mEq/L
• How does the sodium concentration compare to that of hydrogen ions?

  Sodium concentration is about 3.5 million times greater than that of H+
• What is the normal variation in [H+] compared to [Na+]?

  One millionth of that of [Na+]
• What is the normal pH range for plasma and muscle?

  7.35-7.45
• What are the components of a buffer pair in body fluids?

  • A weak acid
  • The conjugate base of that acid

  
• What is a weak acid?

  An acid that demonstrates only a moderate tendency to dissociate
• What is a conjugate base?

  What remains after the acid loses its proton (H+)
• What does the equation HA ⇌ H+ + A- represent?

  The relationship between a weak acid and its conjugate base
• What happens when [H+] starts to increase in a buffered solution?

  Some of the dissolved A- associates with free H+ to form HA
• What is the net effect of the association reaction in a buffered solution?

  It removes some additional H+ from the solution
• What occurs during the reverse dissociation reaction in a buffered solution?

  Dissolved HA dissociates in response to declining [H+], releasing H+
• What governs the relative rates of association and dissociation reactions in a buffer system?

  • The law of mass action
  • Rate is proportional to the product of the concentrations of the reactants
• What happens when a strong acid like HCl is added to a buffered solution?

  HCl rapidly dissociates, increasing [H+] in the solution
• How does the addition of HCl affect the association reaction in a buffered solution?

  The resultant rise in [H+] increases the product of [H+] x [A-], raising the rate of the association reaction
• What happens when a new equilibrium is reached in a buffered solution after adding HCl?

  [H+] is higher than before the addition of HCl, but lower than it would have been without the buffer
• What is the role of buffers in the body?

  • Buffers resist changes in pH
  • They cannot prevent changes entirely

  
• What are the three primary systems that regulate [H+] in body fluids?

  1. Chemical acid-base buffer systems
  2. The respiratory centre
  3. The kidneys

  
• What is the function of the chemical acid-base buffer systems?

  They immediately combine with an acid or a base to prevent excessive [H+] changes
• What does the respiratory centre regulate in terms of acid-base balance?

  Removal of CO2 and carbonic acid (H2CO3) from the extracellular fluid
• How do the kidneys contribute to acid-base balance?

  They can excrete either acid or alkaline urine to readjust extracellular fluid [H+] toward normal
• What is the bicarbonate buffer system responsible for?

  • About 86% of total buffering capacity in the extracellular compartment
  • Protein and hemoglobin account for the rest

  
• What are the two main components of the bicarbonate buffer system?

  A weak acid (H2CO3) and a bicarbonate salt (e.g., sodium bicarbonate)

  
• What happens during metabolic acidosis in relation to the bicarbonate buffer system?

  Increased [H+] is buffered by HCO3-, forming more H2CO3

  
• What occurs during metabolic alkalosis in relation to the bicarbonate buffer system?

  Reduced H2CO3 formation causes CO2 to combine with H2O

  
• What are the four main types of acid-base imbalance?

  1. Respiratory acidosis
  2. Respiratory alkalosis
  3. Metabolic acidosis
  4. Metabolic alkalosis
• What does it indicate if blood pH falls below 7.35?

  Acidosis, which can lead to depressed CNS activity
• What does it indicate if blood pH rises above 7.45?

  Alkalosis, which can lead to over-excitability of CNS and peripheral nerves
• What is the anion gap and how is it calculated?

  Anion gap = [L+] + [Na+] – [Cl-] – [HCO3-]
• What is the normal range for the anion gap?

  10 – 20 mm/l
• How does increased ventilation affect [H+] levels?

  • It eliminates CO2 from extracellular fluid
  • Reduces [H+] by mass action
• What happens when ventilation decreases in relation to CO2 levels?

  CO2 levels increase, ultimately followed by elevated [H+]
• What is the role of pulmonary expiration in acid-base balance?

  It balances metabolic formation of CO2

  
• How does increased [H+] concentration affect alveolar ventilation?

  It stimulates alveolar ventilation

  
• What happens to CO2 after it is formed in the body?

  • It diffuses into interstitial fluids and blood
  • It is transported to the lungs where it diffuses into the alveoli
  • Pulmonary ventilation transfers CO2 to the atmosphere
• What is the concentration of dissolved CO2 in extracellular fluid?

  About 1.2 mol/L