Acid-Base Balance and Mrs. Hira

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Questions and Answers

Which acid is produced as a result of normal biological activities?

Uric acid (correct)

Formic acid

Phosphoric acid

Acetic acid

What is the normal ratio of bicarbonate to carbonic acid in the blood?

20:1 (correct)

30:1

10:1

1:1

Which buffer system is primarily responsible for maintaining the extracellular pH?

Bicarbonate buffer system (correct)

Hemoglobin buffer system

Phosphate buffer system

Protein buffer system

Which mechanism represents the second line of defense against pH shifts?

Renal mechanism Signup and view all the answers

What occurs when a strong acid enters the blood in relation to the bicarbonate buffer system?

Carbonic acid is fixed up by bicarbonate Signup and view all the answers

Which component primarily serves as a buffer in intracellular fluid and blood plasma?

Albumin Signup and view all the answers

What is the consequence of a decreased bicarbonate level in relation to blood pH?

Decreased blood pH leads to acidosis Signup and view all the answers

Which does the Henderson-Hasselbalch equation relate to the bicarbonate buffer system?

pH, bicarbonate concentration, and carbonic acid concentration Signup and view all the answers

What role does hemoglobin play during increased hydrogen ion concentration in the blood?

Hemoglobin acts as a buffer for hydrogen ions. Signup and view all the answers

Which of the following correctly identifies a volatile acid?

Carbonic acid Signup and view all the answers

How does the Henderson-Hasselbalch equation relate to acid-base balance in the body?

It illustrates the relationship between pH, bicarbonate, and carbonic acid concentration. Signup and view all the answers

In which way do the kidneys contribute to acid-base regulation?

By producing ammonia and regulating non-volatile acids. Signup and view all the answers

What typically indicates a normal pH balance in arterial blood gas analysis?

7.35 - 7.45 Signup and view all the answers

Which of the following best describes the anion gap and its significance?

It reflects the balance of cations and anions in the blood. Signup and view all the answers

What are the primary systems involved in the regulation of blood pH?

Buffering system, respiratory mechanisms, and renal mechanisms Signup and view all the answers

What is the significance of bicarbonate in the blood's buffering system?

It neutralizes metabolic acids, maintaining pH. Signup and view all the answers

What characterizes a volatile acid compared to a non-volatile acid in the human body?

Volatile acids can be eliminated by respiration. Signup and view all the answers

Which of the following pairs constitutes a proper buffer system?

CH3COOH and CH3COO- Signup and view all the answers

How does the Henderson-Hasselbalch equation relate pH to the acid-base concentration?

It states that pH equals $pK_a$ when the concentrations of acid and base are equal. Signup and view all the answers

Which statement best describes the role of buffers in pH regulation?

Buffers resist pH changes by preventing complete dissociation of acids or bases. Signup and view all the answers

What is the significance of the anion gap in metabolic acidosis?

It helps differentiate between types of metabolic acidosis. Signup and view all the answers

Given the ABG results of pH = 7.26, PCO2 = 42 mmHg, and HCO3- = 17 mg/dl, which condition does this patient most likely have?

Metabolic acidosis Signup and view all the answers

Which metabolic processes contribute to acid production in the human body?

Oxidation of fats generates acetoacetic acid. Signup and view all the answers

What happens to pH when the concentration of a weak acid in a buffer is increased?

pH will decrease if strong acids are introduced. Signup and view all the answers

Study Notes

Case Study: Mrs. Hira

Mrs. Hira, a 75-year-old diabetic, has a long history of non-compliance with insulin.
She was recently admitted to the hospital.
ABG results:
- pH = 7.26
- PCO2 = 42 mmHg
- HCO3− = 17 mg/dL

Lecture Objectives

List volatile and non-volatile acids
Describe the Henderson-Hasselbalch Equation
Explain the mechanism of buffers in the human body
Discuss normal pH regulation by buffers, respiratory, and renal systems
Explain the anion gap and its biochemical significance
Interpret Arterial Blood Gases (ABGs) values

The Body and pH

Homeostasis of pH is tightly controlled.
Extracellular fluid pH = 7.4
Blood pH = 7.35–7.45
pH < 6.8 or > 8.0 results in death.
Acidosis (acidemia) occurs below 7.35.
Alkalosis (alkalemia) occurs above 7.45.

Acids and Bases (Bronsted-Lowry Theory)

Acids are H⁺ donors.
Bases are H⁺ acceptors.
Strong acids dissociate completely in solution (e.g., HCl, NaOH).
Weak acids dissociate partially in solution (e.g., lactic acid, carbonic acid).

Buffers

Function: Resist pH changes upon strong acid/base addition.
Composition: Always exists as a pair:
- Weak acid + salt of its conjugate base
- Weak base + salt of its conjugate acid

Henderson-Hasselbalch Equation

Used to determine the pH of blood or other buffer solutions.
pH = pKa + log ([conjugate base]/[acid])

How Buffers Resist pH Change

Buffer pH = pKa when [HA] = [A⁻]
Weak acid (HA) and conjugate base (A⁻) react with added acid or base.
- HCl (strong acid) reacts with weak base A⁻
- NaOH (strong base) reacts with weak acid HA

Efficiency of a Buffer

A buffer is most effective when [salt] = [acid].
pH = pKa

Titration Curve for Weak Acids

Shows the relationship between pH and added hydroxide.
The buffering region is a key part of the pH-titration relationship.

Acids Produced in 24 Hours

Metabolic reactions produce acids (e.g., lactic acid, pyruvic acid, acetoacetic acid, beta-hydroxybutyrate).
Cellular respiration converts carbon dioxide to carbonic acid.
Uric acid, oxaloacetic acid, and succinic acid are naturally produced.

pH Change and Enzymes

Slight pH changes can be life-threatening, as enzymes function optimally only within narrow pH ranges.
Acid-base balance affects electrolytes (Na⁺, K⁺, Cl⁻) and hormones.

Mechanisms of pH Regulation

First line: Chemical buffer systems (bicarbonate, phosphate, protein).
Second line: Physiological buffers: respiratory (CO2 excretion) and renal (H⁺ excretion).

Buffers in Body Fluids

Bicarbonate: Major extracellular buffer (H₂CO₃/NaHCO₃).
Phosphate: Major intracellular buffer (NaH₂PO₄/Na₂HPO₄).
Proteins: Intracellular and extracellular buffers (including hemoglobin).

Bicarbonate Buffer System

Major extracellular buffering system.
Strong acid is fixed by bicarbonate ion converting to carbonic acid.
Accounts for 65% of buffering in plasma.
H⁺ + HCO₃⁻ <=> H₂CO₃
OH⁻ + H₂CO₃ <=> HCO₃⁻+ H₂O

Normal Ratio in Blood

HCO₃⁻ to H₂CO₃ ratio is normally 20:1.
Allows blood pH to be 7.40.
pH falls (acidosis) when bicarbonate decreases relative to carbonic acid.
pH rises (alkalosis) when bicarbonate increases relative to carbonic acid.

Phosphate Buffer System

Important intracellular buffer system.
Strong acid is fixed by alkaline phosphate converting to acid phosphate.
HCI + Na₂HPO₄ <=> NaH₂PO₄ + NaCl
NaOH + NaH₂PO₄ <=> Na₂HPO₄ +H₂O

Protein Buffer System

Most abundant buffer in intracellular fluid and blood plasma.
Albumin is a key protein buffer.
Amino acids in proteins can accept or donate H⁺.
pKa = 7.4

Hemoglobin Buffer System

Deoxygenated hemoglobin is a better proton acceptor than oxygenated hemoglobin.
Carbonic anhydrase in red blood cells converts CO₂ to carbonic acid.
CO₂ + H₂O <=> H₂CO₃ <=> H⁺ + HCO₃⁻
Bicarbonate diffuses out of red blood cells.
Deoxygenated hemoglobin accepts protons (H⁺ + Hb <=> H⁺Hb)

Carbon Dioxide Transport and Hemoglobin Buffering

CO₂ transport in the blood and hemoglobin buffering are explained through a diagram.

Hemoglobin Buffer System—Continued

Carbonic acid dissociates releasing bicarbonate ions into plasma in exchange for chloride ions (chloride shift).
Hydrogen ions are buffered by hemoglobin molecules.
This helps prevent major pH changes when plasma PCO₂ rises or falls.
Most of hemoglobin's buffering action is due to the imidazole group of histidine.

Buffer Systems

Buffers occur in intracellular (ICF) and extracellular fluid (ECF) compartments.
ICF includes phosphate buffer, hemoglobin buffer, and amino acid buffers.
ECF includes protein buffers, and carbonic acid-bicarbonate buffers.

Maintenance of Blood pH

Blood buffers (bicarbonate, phosphate, and protein).
Respiratory mechanism (using bicarbonate).
Renal mechanism (using bicarbonate, phosphate, and ammonia).

Rates of Correction

Buffers function almost instantly.
Respiratory mechanisms take several minutes to hours.
Renal mechanisms take several hours to days.

When Chemical Buffers Alone Cannot Prevent Changes in Blood pH

Respiratory and renal systems act as a secondary defense against changes

Respiratory Mechanisms

Lungs regulate volatile acids (e.g., carbonic acid).

Renal Mechanisms

Kidneys regulate non-volatile acids (e.g., lactic acids, keto acids).

Arterial Blood Gas (ABG) Analysis

Essential for diagnosing and managing patients' oxygenation, ventilation, and acid-base balance.
Drawn from arteries (radial, brachial, femoral).
ABG reports:
- pH (H⁺ ion concentration)
- PaCO₂ (dissolved CO₂ in blood)
- HCO₃⁻ (metabolic effectiveness)
- PaO₂ (O₂ content of blood)
- SaO₂ (% of hemoglobin saturated)

Acid-Base Disorders

Acid-base disorders are classified as metabolic or respiratory acidosis/alkalosis. -Metabolic acidosis: decreased bicarbonate -Respiratory acidosis: increased carbonic acid -Metabolic alkalosis: increased bicarbonate -Respiratory alkalosis: decreased carbonic acid

Anion Gap

Biochemical tool for assessing acid-base problems, especially metabolic acidosis.
Difference between measured cations (Na⁺ and K⁺) and measured anions (Cl⁻ and HCO₃⁻).
In healthy individuals, the anion gap is typically around 15 mEq/L (range 8-18 mEq/L).
Increased anion gap is associated with metabolic acidosis. Different types of metabolic acidosis could be associated with increased anion gap which includes renal failure, diabetic ketoacidosis, and lactic acidosis. A normal anion gap metabolic acidosis could be due to diarrhea or hyperchloremic acidosis. A low anion gap acidosis could be due to multiple myeloma.

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Description

This quiz explores the acid-base balance in the human body, focusing on the case study of Mrs. Hira. You will learn about volatile and non-volatile acids, the Henderson-Hasselbalch equation, and how buffers regulate pH. Additionally, the quiz will cover the interpretation of arterial blood gas (ABG) results and their clinical significance.