Carbon Dioxide Equilibrium and Transport

Vocabulary flashcards covering the chemical equilibrium, transport mechanisms, acid-base regulation, and physiological effects of carbon dioxide in the blood.

Eucapnia

The steady-state physiological condition where alveolar ventilation eliminates $\text{CO}_2$ at exactly the same rate that tissues produce it ($200\,mL/min$), maintaining arterial and alveolar $P\text{CO}_2$ at approximately $40\,mm\,Hg$.

Volatile Acid

An acid, specifically carbonic acid ($\text{H}_2\text{CO}_3$), that exists in equilibrium with a gas ($\text{CO}_2$) that can be eliminated from the body via alveolar ventilation.

$\text{CO}_2$ Hydrolysis Reaction

The reversible chemical equilibrium $\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{HCO}_3^- + \text{H}^+$, which governs the relationship between dissolved carbon dioxide, carbonic acid, and plasma $[\text{H}^+]$. In plasma, the reaction is left-shifted such that dissolved $\text{CO}_2$ is approximately $500$ times greater than $\text{H}_2\text{CO}_3$.

Plasma $\text{CO}_2$ Solubility Factor

The physical constant describing carbon dioxide dissolution in plasma at $37^\circ\text{C}$, where $0.03\,mmol$ of $\text{CO}_2$ dissolves in $1\,\text{L}$ of plasma for each $mm\,Hg$ of $P\text{CO}_2$, yielding $1.2\,mmol/L$ of dissolved $\text{CO}_2$ at a $P_a\text{CO}_2$ of $40\,mm\,Hg$.

Hypoventilation (Respiratory Acid-Base Effects)

A state of decreased alveolar ventilation where $\text{CO}_2$ production temporarily exceeds elimination, resulting in elevated $P_a\text{CO}_2$, a right shift in the hydrolysis reaction, and increased blood levels of carbonic acid ($\text{H}_2\text{CO}_3$) and $[\text{H}^+]$.

Hyperventilation (Respiratory Acid-Base Effects)

A state of increased alveolar ventilation where $\text{CO}_2$ elimination temporarily exceeds production, resulting in decreased $P_a\text{CO}_2$, a left shift in the hydrolysis reaction, and decreased blood levels of carbonic acid ($\text{H}_2\text{CO}_3$) and $[\text{H}^+]$ (increased pH).

Carotid Bodies

Peripheral hypoxic chemoreceptors that sense low oxygen levels (such as at high altitude) and increase ventilatory drive, driving hyperventilation that lowers $P_A\text{CO}_2$, lowers $P_a\text{CO}_2$, and causes respiratory alkalemia.

Carbonic Anhydrase

An intracellular enzyme catalyst located inside erythrocytes (absent in plasma) that accelerates the hydration reaction of $\text{CO}_2$ and $\text{H}_2\text{O}$ into $\text{H}_2\text{CO}_3$ by approximately $13{,}000$ times.

Chloride Shift (Hamburger Phenomenon)

The reciprocal exchange across the erythrocyte membrane where generated intracellular bicarbonate ($\text{HCO}_3^-$) diffuses into the plasma while chloride ions ($\text{Cl}^-$) diffuse from plasma into the red blood cell to maintain electrochemical neutrality.

Plasma Carbamino Compounds

Compounds formed in plasma when dissolved $\text{CO}_2$ binds non-enzymatically to free amino groups of plasma proteins ($\text{CO}_2 + \text{prot-NH}_2 \rightarrow \text{prot-NHCOO}^- + \text{H}^+$), releasing $1\,mmol$ of $\text{H}^+$ for each millimole formed.

Carbaminohemoglobin

The compound formed within erythrocytes when carbon dioxide binds non-enzymatically to the terminal amino groups of hemoglobin protein ($\text{CO}_2 + \text{HbO}_2\text{-NH}_2 \rightarrow \text{Hb-NHCOO}^- + \text{H}^+ + \text{O}_2$).

Haldane Effect

The physiological property where deoxygenation of hemoglobin increases its affinity for carbon dioxide and hydrogen ions ($\text{H}^+$), thereby increasing the blood's overall carrying capacity for $\text{CO}_2$.

Bohr Effect

The physiological process where the binding of carbon dioxide and hydrogen ions ($\text{H}^+$) decreases hemoglobin's affinity for oxygen, shifting the oxygen equilibrium curve to the right ($\text{H}^+ + \text{HbO}_2 \rightleftharpoons \text{HHb} + \text{O}_2$) and facilitating oxygen release to tissues.

Carbon Dioxide Dissociation Curve

The graphical relationship between $P\text{CO}_2$ and blood $\text{CO}_2$ content that is relatively linear compared to the sigmoid oxygen curve, allowing changes in alveolar ventilation to produce direct and efficient adjustments in blood $\text{CO}_2$ content.

Bicarbonate Fraction of $\text{CO}_2$ Transport

The primary mode of carbon dioxide transport in the blood, accounting for approximately $80\%$ of the total $\text{CO}_2$ transported from systemic tissues to the lungs (compared to $8\%$ dissolved and $12\%$ as carbamino compounds).