Oxyhemoglobin Dissociation Curve and Acid-Base Regulation Notes

Exam Preparation and Deadlines

Deadline for submissions:
- All assignments must be completed by Sunday night at 11:59 PM.
- Most students are on track, with only a few pending tasks.
- Ensured students complete Chapter 5 before moving to upcoming topics.

Next exam now covers the remainder of Chapter 5.
Exam date pushed back by one week to allow adequate preparation.
- Last chapters are typically short; thus, expect early class dismissals on those nights.

Importance of the oxyhemoglobin dissociation curve in understanding hemoglobin saturation.
Default Curve Characteristics:
- X-axis: Partial pressure of oxygen (PaO2).
- Y-axis: Hemoglobin saturation (%).
Understand variable attraction of hemoglobin to oxygen in different body conditions.
Key Observations:
- Hemoglobin's affinity for oxygen changes, especially between the lungs and tissue.
- In lungs: High attraction for oxygen (loads onto hemoglobin).
- In tissues: Hemoglobin must release oxygen (unloads) for metabolic activity.

PaO2 of 60 mmHg correlates to 90% saturation.
At 20 mmHg, saturation decreases significantly (approx 30%).
The curve’s flat portion from 60 to 100 is termed the safety zone.
- Allows for tolerable drops in oxygen without critical loss of saturation (still ~90% saturation at PaO2 = 60).
Shift Dynamics:
- Right Shift:
- Indicates hemoglobin's decreased affinity for oxygen (easier unloading).
- Conditions favoring this: Exercise, Increase in temperature, Increase in carbon dioxide (CO2), decreased pH (more acidic).
- Left Shift:
- Indicates hemoglobin's increased affinity for oxygen (holds onto it).
- Conditions favoring this: Lower temperature, Increase in pH (more basic), and presence of fetal hemoglobin.

Increased temperature
Increased CO2 concentration (hypercapnia)
Decrease in pH (acidosis)
Elevated levels of 2,3-bisphosphoglycerate (2,3-BPG) especially in pregnancy.

Transport Mechanisms of CO2:
- Bicarbonate ion, dissolved in plasma, and bound to hemoglobin in red blood cells.
- CO2 transport mechanisms affect blood acidity and pH.
Physiological responses during exercise include increased respiratory and metabolic rates leading to shifted curves.

Definition: Blood that passes from the right to left side of the heart without gas exchange occurring in the alveoli.
Types of Shutting:
- Absolute Shunt:
- Anatomical shunt (e.g., congenital heart defects, septal defects).
- Capillary shunt (e.g., due to alveolar collapse or edema).
- Relative Shunt: Perfusion exceeds ventilation, leading to areas of the lung not being properly ventilated.

Definitions:
- Hypoxemia: Low PaO2 levels in arterial blood.
- Hypoxia: Low O2 availability at the tissues.
Four Categories of Hypoxia:
- Hypoxic Hypoxia: Low oxygen tension in the blood.
- Anemic Hypoxia: Inadequate hemoglobin or impaired transport capacity.
- Circulatory Hypoxia: Inadequate blood flow to tissues.
- Histotoxic Hypoxia: Tissues are unable to utilize oxygen (e.g., cyanide poisoning).

Chemical Buffer System: Immediate response to resist pH changes (e.g., carbonic acid-bicarbonate buffer system, phosphate buffer system, protein buffer system).
Respiratory System: Adjusts pH through changes in respiration rate and depth (hyperventilation leads to decreased CO2, while hypoventilation increases CO2).
Renal System: Excretes or reabsorbs acids and bases to maintain pH balance.

Respiratory and renal compensations reflect the body's attempt to restore normal pH in acid-base disturbances
Metabolic Acidosis: Examples include lactic acidosis, diabetic ketoacidosis, or renal failure.
Metabolic Alkalosis: Caused by excessive loss of acid or gains in bicarbonate, through vomiting, diuretics, etc.
- Renal compensation for alkalosis involves excretion of bicarbonate to lower pH.

Understanding and interpreting the oxyhemoglobin dissociation curve and nomogram values is essential.
Review shifts in the dissociation curve related to physiological conditions.
Prepare for upcoming quizzes on curve characteristics and reading nomograms.