lecture respiratory 2025-03-08T16:04:45.792Z

Overview of Oxygen Transport

• Transport Methods

  • Oxygen is transported in two main ways in the bloodstream:

    • 1. Dissolved in Plasma: Only about 1.5% of oxygen is dissolved in plasma, which is a very insignificant amount.

    • 2. Bound to Hemoglobin: The majority of oxygen (about 98.5%) is transported by binding to hemoglobin in red blood cells.

Hemoglobin and Oxygen Binding

• Shape Change of Hemoglobin: Hemoglobin undergoes a shape change as it binds oxygen, increasing its affinity for oxygen.

  • Binding Sequence:

    • Begins with one oxygen bound, increases affinity with two, becomes more catalytic at three, reaches maximum affinity with four.

• Effect of Oxygen Concentration:

  • High concentration of oxygen reduces the change in affinity for oxygen, while low concentration increases it.

• Saturation Curve:

  • The relationship between oxygen saturation and partial pressure of oxygen is sigmoid (S-shaped), indicating sensitivity at low oxygen levels and less sensitivity at high levels.

  • This means that low oxygen environments (like tissues) can significantly affect hemoglobin saturation and oxygen release.

Factors Influencing Hemoglobin Saturation

• Partial Pressure of Oxygen (pO2):

  • The primary driving force for hemoglobin binding/unloading of oxygen.

    • High pO2 = High saturation, low pO2 = Low saturation.

• Temperature:

  • Higher temperatures decrease affinity, whereas lower temperatures increase it (shifts curve left).

  • High body temperature leads to easier unloading of oxygen.

• pH and CO2 Levels:

  • Higher CO2 (increased acidity) reduces affinity for oxygen; lower CO2 increases affinity.

  • Increased hydrogen ions (more acidic) lead to decreased affinity for oxygen.

Transport of Carbon Dioxide

• Transport Methods:

  • Carbon dioxide travels in three ways:

    • 1. Dissolved in Plasma: About 7-10%.

    • 2. Bound to Hemoglobin: About 20-23% forms carbaminohemoglobin.

    • 3. As Bicarbonate Ions: Approximately 70% of CO2 is converted to bicarbonate ions in blood.

• Conversion Mechanism:

  • CO2 + H2O ⇌ H2CO3 (carbonic acid) ⇌ HCO3- (bicarbonate) + H+ (hydrogen ions).

  • Reaction facilitated by the enzyme carbonic anhydrase.

• Driving Force of CO2 Release: CO2 exits the bloodstream into lungs due to higher partial pressure of CO2 in the blood compared to the alveoli.

Blood pH Regulation

• Buffer System:

  • The bicarbonate buffer system helps stabilize blood pH by allowing CO2 to convert to bicarbonate and vice-versa, accepting and releasing hydrogen ions.

• Breathing Impact on pH:

  • Hypoventilation (slow, shallow breathing): Increases CO2, decreases pH (more acidic).

  • Hyperventilation (rapid breathing): Decreases CO2, increases pH (more basic).

Control of Breathing

• Neural Mechanisms:

  • The medulla oblongata regulates breathing, particularly the ventral respiratory group (VRG), which sets rhythm.

• Chemoreceptors:

  • Central chemoreceptors: Located in the brain, sensitive to CO2 and pH.

  • Peripheral chemoreceptors: Located in the carotid and aortic bodies, sensitive to changes in O2, CO2, and pH.

• Influence of Factors:

  • Changes in CO2, O2, and pH will affect breathing rate and depth.

• Emotional and Cortical Control: Breathing can be modified by emotional states (hypothalamus) and consciously controlled (cortical).

Pathologies Related to Breathing

• Chronic Obstructive Pulmonary Disease (COPD):

  • Characterized by emphysema and bronchitis, leading to obstructive airway diseases that reduce ability to forcefully exhale air.