MMED2931 wk 5 an6 l3 p3

Carbon dioxide (CO₂) is transported in three primary ways: - Dissolved in plasma - Bound to hemoglobin - As bicarbonate (HCO₃⁻)

Approximately 7% of carbon dioxide in the blood is transported in dissolved form.
Follows Henry's Law: - States that the quantity of gas dissolved in a liquid is proportional to its partial pressure. - Thus, a higher partial pressure of CO₂ results in more CO₂ being dissolved in the blood.
Comparison with Oxygen: - Carbon dioxide is significantly more soluble in blood than oxygen. - Only about 1.5% of oxygen is transported as dissolved oxygen.

About 23% of carbon dioxide is transported bound to hemoglobin.
Forms carbaminohemoglobin, where CO₂ binds to hemoglobin.
Binding Dynamics: - CO₂ binds to different sites on hemoglobin than oxygen does. - The binding of oxygen decreases hemoglobin's affinity for CO₂. This indicates: - Oxyhemoglobin (hemoglobin bound to oxygen) has a lower affinity for CO₂. - Reduced hemoglobin (hemoglobin that has released oxygen) has a greater affinity for CO₂. - Consequently, hemoglobin is more likely to pick up CO₂ after delivering oxygen to tissues.
Haldane Effect: - Refers to the enhanced uptake of CO₂ by hemoglobin upon the release of oxygen. - This effect facilitates the unloading of oxygen in tissues and enhances the uptake of CO₂.

The majority of CO₂ is transported as bicarbonate ions (HCO₃⁻).
Reaction Process: 1. CO₂ diffuses into red blood cells. 2. In the presence of carbonic anhydrase, CO₂ reacts with water (H₂O) to form - Carbonic Acid (H₂CO₃) 3. Carbonic acid dissociates into hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻).
Bicarbonate Buffer Equation: - The equation is critical for understanding respiratory physiology and acid-base balance. - This will be further discussed in the next lecture focusing on respiratory control.
Cellular Dynamics: - The formation of hydrogen ions (H⁺) is buffered by hemoglobin to prevent cellular acidity. - Excess H⁺ can bind with hemoglobin, helping to manage pH levels within the cells.

After bicarbonate forms in red blood cells: - It builds up and creates a concentration gradient against the intracellular bicarbonate concentration. - Transport Mechanism: Bicarbonate is transported out of the red blood cells in exchange for chloride ions (Cl⁻), via an antiporter mechanism. - This process helps maintain electrical neutrality within the cells as negative charges are removed from the cell.

The cycle of carbon dioxide and its transport: - Red blood cells transport dissolved CO₂, carbonic acid, etc., towards the lungs. - Venous Circulation dynamics: - The dissolved CO₂ diffuses into the lungs down its partial pressure gradient. - Reduction in CO₂ partial pressure in the lungs encourages more CO₂ to be released from the blood into the alveoli. - Reactions in the lungs: - As CO₂ reduces, the bicarbonate reaction shifts right: ext{HCO}_3^- + ext{H}^+ ightleftharpoons ext{H}_2 ext{CO}_3 ightleftharpoons ext{CO}_2 + ext{H}_2 ext{O} - CO₂ diffuses across the membrane into the alveoli to be exhaled.

The transport of carbon dioxide effectively manages acid-base balance within the blood and supports efficient gas exchange in the lungs.
All CO₂ transport mechanisms are vital for maintaining physiological homeostasis.
The understanding of this process is essential for studying respiratory function and its regulation in various medical contexts.