22 Questions
What is the main goal of the regulation of the bicarbonate/carbonic acid system?
Maintain a ratio of 20 Bicarbonate: 1 Carbonic Acid
Which organ is responsible for regulating the metabolic component (HCO-3) in the bicarbonate/carbonic acid system?
Kidneys
What is the duration of respiratory compensation?
24 hours
What is the effect of H2CO3 reduction on kidney function?
Kidneys decrease HCO-3 to maintain pH 7.4
What is the term for a decrease in HCO-3 levels in the blood?
Metabolic acidosis
How many types of acid-base disturbances are there?
4
What is the primary function of buffer systems in the body?
To maintain a constant pH by neutralizing effects of hydrogen ions
What is the measure of the concentration of hydrogen ions in an aqueous solution?
pH
How many moles of H+ are yielded by reactions in the body per day?
15-20 mol
What is the term for the state of internal balance to maintain physical and chemical conditions by living systems?
Homeostasis
What is the term for a molecule or ion capable of donating a proton (H+)?
Acid
What is the primary role of the kidney in regulating acid-base balance?
To reabsorb bicarbonate from the urine
What is the term for a disturbance in which the body has too much acid?
Acidosis
What is the term for a disturbance in which the body has too much base?
Alkalosis
What is the ratio of HCO3- to H2CO3 in normal arterial blood?
20:1
How do the kidneys respond to a decrease in HCO3- levels in the blood?
Reabsorb and synthesize HCO3-
What is the pH of the renal tubular fluid when the Na+ – H+ exchange system stops?
4.5
What is the main mechanism by which the lungs regulate H2CO3 levels?
Ventilation
What happens to H2CO3 levels in the blood during hyperventilation?
H2CO3 levels decrease
What is the role of the kidneys in regulating the metabolic component of the acid-base balance?
Excrete and reabsorb HCO3-
What is the effect of an increase in H+ concentration on the respiratory center?
It increases the rate of ventilation
What is the pK of the buffer at 37°C?
6.1
Study Notes
Respiratory Compensation
- Respiratory compensation is fast and reaches maximal capacity in 24 hours
- Changes in ventilation affect the denominator (respiratory) component of the H-H equation
Combined Regulation of the HCO-3 / H2CO3 Buffer System
- The ultimate aim of regulation is to maintain a ratio of 20 Bicarbonate : 1 Carbonic Acid
- At this ratio, arterial blood pH = 7.40 ± 0.05
- Kidneys regulate the metabolic component (HCO-3)
- Lungs regulate the respiratory component (H2CO3)
- Regulation also includes compensation for excess or deficiency of the other
Disturbances in Acid-Base Balance
- There are four types of acid-base disturbances:
- Metabolic acidosis
- Metabolic alkalosis
- Respiratory acidosis
- Respiratory alkalosis
Metabolic Acidosis
- Happens due to:
- Build-up of acid in blood
- Excess HCO3- loss by excretion via kidney or diarrhea
- Results in:
- Low HCO3- in blood
- Disruption of HCO3-/ H2CO3 ratio
- The body tries to maintain the HCO3-/ H2CO3 ratio of 20:1 to keep the pH 7.40
Kidney Regulation of Bicarbonate
- Kidneys regulate the metabolic (HCO3-) component
- Depending on the acid-base status, kidneys may:
- Excrete HCO3- in urine
- Reabsorb HCO3- partially or completely
- Synthesize HCO3- by renal tubules
- Changes introduced by the kidneys affect the numerator of the H-H equation
- HCO3- synthesis, excretion, or reabsorption involves the Na - H+ exchange mechanism by the kidney tubules
Lung Regulation of H2CO3
- Lungs regulate the respiratory (H2CO3) component
- Regulation is mainly by ventilation, i.e., Hypoventilation or Hyperventilation
- In hypoventilation:
- CO2 is retained
- pCO2 in alveolar spaces ↑
- H2CO3 in the blood ↑
- In hyperventilation:
- CO2 is exhaled "blown off"
- pCO2 in alveolar space ↓
- H2CO3 in the blood ↓
Terminology
- Homeostasis is the state of internal balance to maintain physical and chemical conditions by living systems
- Acid is a molecule or ion capable of donating a proton (H+)
- Base is a substance that dissociates in aqueous solution to form hydroxide ions OH−
- Buffers are substances that maintain a constant pH by neutralizing the effects of hydrogen ions
- pH is a measure of how acidic/basic water is or a measure of the concentration of hydrogen ions in an aqueous solution
- pK is the pH value at which a chemical species will accept or donate a proton
This quiz covers the regulation of the bicarbonate/carbonic acid buffer system, including the ultimate aim of maintaining a specific ratio to maintain arterial blood pH.
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