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Questions and Answers
What occurs when there is denaturation of proteins?
What occurs when there is denaturation of proteins?
What pH range indicates a state of alkalosis in a person?
What pH range indicates a state of alkalosis in a person?
Which of the following is a source of H+ loss in the body?
Which of the following is a source of H+ loss in the body?
Which statement correctly defines an acid?
Which statement correctly defines an acid?
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How is the body primarily generating H+ during metabolism?
How is the body primarily generating H+ during metabolism?
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Which statement accurately describes the role of buffering in the body?
Which statement accurately describes the role of buffering in the body?
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What are the major buffering systems in the body?
What are the major buffering systems in the body?
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What is one characteristic of proteins that makes them effective buffers?
What is one characteristic of proteins that makes them effective buffers?
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Which of the following is true about zwitterions?
Which of the following is true about zwitterions?
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During acid loading in the body, a good buffer must be able to:
During acid loading in the body, a good buffer must be able to:
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Which of the following statements correctly describes the acid dissociation constant (Ka)?
Which of the following statements correctly describes the acid dissociation constant (Ka)?
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What is the relationship between pKa and acid strength?
What is the relationship between pKa and acid strength?
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What does a reversible reaction in chemical equilibrium imply?
What does a reversible reaction in chemical equilibrium imply?
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Which of the following correctly represents the general equation for the dissociation of a weak acid in water?
Which of the following correctly represents the general equation for the dissociation of a weak acid in water?
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How does an increase in hydrogen ion concentration [H+] affect the pH of a solution?
How does an increase in hydrogen ion concentration [H+] affect the pH of a solution?
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Which statement accurately describes the role of proteins in buffering?
Which statement accurately describes the role of proteins in buffering?
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What is a zwitterion?
What is a zwitterion?
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What is the main function of the Henderson-Hasselbalch equation?
What is the main function of the Henderson-Hasselbalch equation?
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Study Notes
Lecture 9: Acids and Bases
- The lecture covers acids and bases, focusing on the importance of a stable physiological pH range.
- The CO2/bicarbonate buffer system is the most important buffering system in the extracellular fluid (ECF).
- A conceptual difference exists between pH and pKa.
- Choosing suitable chemical buffers is discussed, along with the Henderson-Hasselbalch equation's significance in homeostasis control of ECF pH.
- Different types of acid-base imbalances and their compensatory responses are covered.
Learning Outcomes
- Students learn the normal physiological range of ECF pH.
- Students understand why humans are called acid generators.
- Various sources of acids in the body are summarized.
- Three methods to balance acid-base are named.
- The Henderson-Hasselbalch equation is reproduced, and the normal ratio of HCO3: H2CO3 is indicated.
- The equilibrium equation between CO2, carbonic acid, and bicarbonate/hydrogen ion is presented.
- Students learn how to choose an appropriate buffer based on three criteria.
- A table summarizing four acid-base imbalance types (changes in pH, bicarbonate ion, and partial pressure of carbon dioxide) is discussed.
Pre-class Micro-module 8
- The micro-module focused on whether the body produces more acids or bases.
- Definitions of acids and bases, along with examples, were provided.
Scenario
- A male subject's blood sample (analyzed for bicarbonate, oxygen, and carbon dioxide) was discussed.
- The blood bicarbonate (HCO3⁻) reacts with H+ ions.
- The outcomes associated with this are discussed, like dietary intake affecting blood pH.
- Three bodily methods to regulate blood pH and their effects are described.
pH
- pH is a measure of hydrogen ion concentration.
- It is defined as the negative logarithm to base 10 of free hydrogen ion concentration.
- pH decreases as acidity increases.
- pH = – log10 [H+].
- The lower-case letter "p" refers to the power, and "H" refers to the hydrogen ion (proton).
- Log10 scale. A change of one integer value in pH changes the concentration by a factor of 10.
- The pH scale ranges from 0 to 14.
- A pH of 7 is neutral.
- Values below 7 are acidic, and above 7 are alkaline.
- Common examples of different pH values are listed for demonstration.
Importance of a Stable Physiological pH
- Normal pH of plasma arterial blood is 7.35-7.45 (slightly alkaline).
- pH affects protein functions and biochemical reactions, so it's tightly regulated.
- Acid-base imbalance complications include conformational change in protein structure, balance changes of potassium, neuron and muscle excitability changes, cardiac arrhythmia, and vasodilation of arterioles.
Consequence of Abnormal pH
- Acids and bases disrupt bonding.
- This causes denaturation, a loss of protein structure and amino acid sequence, leading to a loss of function.
Disorder of Acid-Base Balance
- Acidosis is a condition with blood pH below 7.35.
- Alkalosis is a condition with blood pH above 7.45.
- Symptoms of acidosis and alkalosis for the central nervous, respiratory, heart, muscular, and digestive systems are mentioned.
Our Body Is an Acid Generator
- Most H+ ions are produced via daily metabolism (approximately 1 mmol/kg body weight/day).
- Sources of H+ gain include proteins, fats, and metabolism (lactic acid, keto acids).
- Sources of loss include the kidneys (primarily as H2PO4- and NH4+) and the lungs (CO2).
Definitions of Acids and Bases
- Acid: A substance that releases free H+ in solution.
- Base: A substance that accepts free H+ in solution.
Dissociation of a Weak Acid
- A weak acid dissociation is a reversible reaction.
- In chemical equilibrium, the ratio of reactants to products is constant.
- The general equation for a weak acid dissociation in water is HA ⇌ H+ + A-.
Acid Dissociation Constant (Ka)
- Ka is an equilibrium constant measuring the extent to which an acid dissociates in aqueous solution.
- A large Ka indicates a strong acid.
- A small Ka indicates a weak acid.
Summary: pH and pKa
- pH measures the acidity of a solution. A lower pH means it's more acidic, and a higher pH means it's more alkaline.
- pKa measures the strength of an acid, relating to its ability to donate H+. A lower pKa value means a stronger acid.
Buffering of Hydrogen Ions
- A buffer is a substance that can reversibly bind H+ ions.
- Buffering keeps H+ ions "locked up".
- The lungs and kidneys regulate ultimate homeostasis.
Criteria for a Good Chemical Buffer
- Minimal pH change.
- Ability to accept H+ during acid loading.
- Ability to donate H+ during acid removal.
Chemical Buffers
- The major extracellular buffer system is the CO2/HCO3⁻ system.
- CO2 + H2O ⇌ H2CO3 ⇌ HCO3⁻ + H+.
- Major intracellular buffers include proteins and phosphates.
Protein Buffer
- Proteins are composed of amino acids.
- Some amino acids contain weak acid (carboxyl) and weak base (amino) groups.
- Proteins function as zwitterions/dipolar ions with cationic and anionic charges.
- Hemoglobin acts as an intracellular buffer in red blood cells.
Phosphate Buffer
- Phosphate buffers are very similar to bicarbonate in action, important only in the urine and intracellular fluid, which contain high concentrations of phosphates.
CO2/Bicarbonate Buffer System
- The most significant extracellular buffer.
- CO2 + H2O ⇌ H2CO3 ⇌ HCO3⁻ + H⁺.
- Carbonic anhydrase speeds up the process.
- Increased CO2 raises H+ (kidney compensates).
- Increased H+ pushes the reaction backward, increasing CO2 (exhaled by lungs).
Bodily Ways to Balance Acid Base
- Three ways: chemical buffers (seconds), respiratory system (minutes), and renal system (hours).
- Chemical buffers provide immediate defense against pH changes, combining with or releasing H+.
- Respiratory system adjusts CO2 levels, affecting pH within minutes.
- Renal system regulates H+ and bicarbonate excretion/retention over hours.
Henderson-Hasselbalch (H-H) Equation
- The equation relates pH to pKa, bicarbonate concentration, and CO2 partial pressure.
- pH = pKa + log10 ([HCO3⁻]/[H2CO3]).
Modified Henderson-Hasselbalch Equation
- The modified equation: pH = 6.1 + log10 ([HCO3⁻]/0.03 x PCO2).
Partial Pressure of Gas Molecules
- Partial pressure (P) is the pressure exerted by one gas in a mixture of gases.
- The total pressure (Ptotal) is the sum of all the partial pressures of the gases in the mixture.
Arterial Blood Gas (ABG) Analysis
- ABG tests measure PaO2 and PaCO2 to assess oxygenation and ventilation statuses, respectively.
- The example shows a normal range for parameters.
Homeostatic Regulation of CO2 and HCO3⁻
- Respiratory and renal systems collaborate to maintain blood pH balance around 7.35-7.45.
- The ratio of HCO3- to H2CO3 is crucial (approximately 20:1).
Important Terms (Plasma H+)
- Acidemia (increase in [H+] or decrease in pH) versus alkalemia (decrease in [H+] or increase in pH).
- Acidosis (processes that raise [H+]), and alkalosis (processes that lower [H+])
Types of Acid-Base Imbalance
- The human body experiences four main types of acid-base disorders, with abnormal changes in either PCO2 or HCO3⁻ leading to respiratory or metabolic acidosis/alkalosis, respectively.
- A disturbance triggers a counter-balance or compensation mechanism to normalize the balance.
Types of Acid-Base Imbalances (Table)
- A table summarizing the changes in pH, [HCO3⁻], and PCO₂ for metabolic and respiratory acidosis/alkalosis.
Respiratory Acidosis
- Respiratory acidosis occurs with hypoventilation (reduced alveolar ventilation relative to CO2 production).
- CO2 builds up, leading to an increase in H2CO3, followed by a decrease in pH.
- Renal compensation involves reabsorbing more HCO3⁻, increasing HCO3 buffering capacity.
Respiratory Alkalosis
- Respiratory alkalosis occurs due to hyperventilation (increased alveolar ventilation relative to CO2 production).
- CO2 is "blown off" leading to a decrease in H2CO3, resulting in an increase in pH.
- Renal compensatory mechanisms include excreting more HCO3⁻ to lower the HCO3 buffering capacity.
Metabolic Acidosis
- Metabolic acidosis happens when there's an acid load (e.g., lactic acid from anaerobic respiration).
- This leads to decreased plasma [HCO3⁻], lowering the pH.
- Respiratory compensation involves an increase in ventilation rate to eliminate CO₂ and reduce the acid load.
Metabolic Alkalosis
- Metabolic alkalosis arises from loss of acid (e.g., vomiting), resulting in increased plasma [HCO3⁻], and an increase in pH.
- Respiratory compensation involves decreased ventilation rate to retain CO2 in order to neutralize the increased HCO3 load.
Post-class Micro-modules: Case Studies
- These are case study scenarios related to acid-base balance for practice purposes.
Required Reading
- Basic Concepts in Biomedical Sciences I, Chapter 5, pages 99-120.
The End of This Lecture
- The lecture concludes.
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Description
This quiz covers the critical aspects of acids and bases, particularly focusing on the physiological pH balance within the human body. Key concepts include the CO2/bicarbonate buffer system, acid-base imbalances, and the application of the Henderson-Hasselbalch equation in maintaining homeostasis. Students will enhance their understanding of the significance of pH in physiological processes.
