1 Gas Exchange and Transport - EXSC 330

Comprehensive vocabulary flashcards covering gas concentrations, partial pressures, respiratory gas exchange, blood oxygenation mechanisms, hemoglobin dynamics, the oxyhemoglobin dissociation curve, and carbon dioxide transport.

Partial Pressure

The individual pressure exerted by the molecules of each specific gas within a mixture of gases, calculated as the gas concentration percentage multiplied by the total mixture pressure.

Dalton's Law

The physical law stating that the total pressure of a mixture of gases is equal to the sum of the individual partial pressures exerted by each component gas ($P = P_A + P_B + P_C$).

Ambient Air Partial Pressures (Sea Level)

Under standard atmospheric conditions ($760\,\text{mmHg}$), dry ambient air comprises oxygen at $20.93\%$ ($P\text{O}_2 = 159\,\text{mmHg}$), carbon dioxide at $0.03\%$ ($P\text{CO}_2 = 0.2\,\text{mmHg}$ to $0.23\,\text{mmHg}$), and nitrogen at $79.04\%$ ($P\text{N}_2 = 600\,\text{mmHg}$).

Tracheal Air Humidification

The process by which inspired air becomes saturated with water vapor from mucosal passages at $37^\circ\text{C}$, adding a water vapor pressure of $47\,\text{mmHg}$, lowering dry gas pressure to $713\,\text{mmHg}$, and reducing effective inspired $P\text{O}_2$ to $149\,\text{mmHg}$.

Alveolar Air Composition

The steady gas concentration within pulmonary alveoli altered by continuous carbon dioxide addition from venous blood, consisting of $14.5\%\,\text{O}_2$ ($P\text{O}_2 = 103\,\text{mmHg}$), $5.5\%\,\text{CO}_2$ ($P\text{CO}_2 = 39\,\text{mmHg}$), and $80.0\%\,\text{N}_2$ ($P\text{N}_2 = 571\,\text{mmHg}$).

Henry's Law

The gas law stating that the mass of a gas that dissolves into a liquid at a constant temperature is directly proportional to the partial pressure gradient above the liquid and the solubility coefficient of the gas in that fluid.

Gas Solubility Coefficient

The volume of gas dissolved per $100\,\text{mL}$ ($1\,\text{dL}$) of fluid; carbon dioxide has a high solubility coefficient of $57.03\,\text{mL}$, making it approximately $25\times$ more soluble in liquid than oxygen ($2.26\,\text{mL}$).

Dissolved Gas Quantity Formula

The calculation determining gas volume in solution: $\text{solubility coefficient} \times (\text{gas partial pressure} \div \text{total pressure})$; for arterial whole blood ($P\text{O}_2 = 100\,\text{mmHg}$) at sea level, dissolved oxygen is $2.26\,\text{mL} \times (100\,\text{mmHg} \div 760\,\text{mmHg}) = 0.3\,\text{mL/dL}$.

Pulmonary Respiration Gas Pressure Gradients

The driving forces for external respiration across alveolar-capillary membranes where $P\text{O}_2$ diffuses down a gradient from alveoli ($\approx 100\,\text{mmHg}$) to capillaries ($\approx 40\,\text{mmHg}$), and $P\text{CO}_2$ diffuses from capillaries ($\approx 46\,\text{mmHg}$) to alveoli ($\approx 40\,\text{mmHg}$).

Alveolar Gas–Blood Gas Equilibration Time

The duration required for capillary blood to reach full partial pressure equilibrium with alveolar gas, taking $0.25\,\text{s}$ at rest within a total capillary transit time of $0.75\,\text{s}$, and decreasing to approximately $0.4\,\text{s}$ during maximal exercise.

Dissolved Oxygen in Plasma

The physical state of oxygen accounting for approximately $2\%$ of total blood transport ($0.003\,\text{mL}\,\text{O}_2$ per $\text{mmHg}\,P\text{O}_2$ per $\text{L}$ of blood); it establishes blood and tissue $P\text{O}_2$, regulates breathing, and determines hemoglobin saturation.

Hemoglobin Molecule Structure

A quaternary globular protein composed of four polypeptide subunits (two alpha and two beta chains), each linked to a heme group containing one central iron ($\text{Fe}$) atom capable of reversibly binding a single $\text{O}_2$ molecule.

Oxygen-Carrying Capacity of Hemoglobin

The maximal oxygen amount bound to hemoglobin, where each gram of hemoglobin binds $1.34\,\text{mL}\,\text{O}_2$, yielding normal carrying contents of approximately $15\,\text{g\,Hb/dL}$ in men ($\approx 20\,\text{mL}\,\text{O}_2\text{/dL}$) and $14\,\text{g\,Hb/dL}$ in women.

Iron-Deficiency Anemia

A condition in which a deficit in iron impairs hemoglobin synthesis and red blood cell oxygen-carrying capacity, reducing aerobic capacity and causing marked elevations in peak exercise heart rates.

Secondary Polycythemia

A physiological adaptation to sustained low $P\text{O}_2$ exposure at high altitudes, characterized by stimulated erythropoiesis that elevates red blood cell count, hematocrit, and blood oxygen volume percent.

Cooperative Binding

The allosteric binding property of hemoglobin wherein the binding of an $\text{O}_2$ molecule to one iron atom alters molecular conformation, progressively facilitating the attachment of subsequent oxygen molecules to the remaining heme sites.

Oxygen Transport Cascade

The progressive downward pressure gradient of oxygen partial pressure as it travels from ambient air ($159\,\text{mmHg}$) to alveoli ($103\,\text{mmHg}$), arterial blood ($98\,\text{mmHg}$), mean capillaries ($40\,\text{mmHg}$), and active muscle mitochondria ($2\text{--}3\,\text{mmHg}$).

Oxyhemoglobin Dissociation Curve

An S-shaped sigmoid curve displaying the relationship between plasma $P\text{O}_2$ and percentage hemoglobin saturation, featuring an upper plateau buffer above $60\,\text{mmHg}$ and a steep slope promoting rapid tissue unloading below $60\,\text{mmHg}$.

Arteriovenous Oxygen Difference (a-v̄O2 difference)

The numerical difference between arterial and mixed-venous oxygen contents representing peripheral oxygen extraction; resting values average $4\text{--}5\,\text{mL}\,\text{O}_2$ per $100\,\text{mL}$ blood, increasing to $15\text{--}18\,\text{mL}\,\text{O}_2$ during intense exercise.

The Bohr Effect

A downward and rightward shift of the oxyhemoglobin dissociation curve triggered by elevations in temperature, hydrogen ion concentration (reduced pH), $P\text{CO}_2$, or $2,3\text{-DPG}$, which decreases hemoglobin's affinity for oxygen to enhance unloading.

2,3-Diphosphoglycerate (2,3-DPG)

A metabolic byproduct of anaerobic glycolysis in mature erythrocytes that binds loosely to hemoglobin, lowering its oxygen affinity to facilitate greater tissue oxygen unloading during exercise, altitude acclimatization, and chronic training.

Myoglobin (Mb)

An iron-containing globular protein within cardiac and skeletal muscle fibers that contains a single heme group; it reversibly stores oxygen and rapidly shuttles it to mitochondria at low cellular $P\text{O}_2$ ($< 5\,\text{mmHg}$) without being affected by the Bohr effect.

Plasma Bicarbonate

The primary method of blood carbon dioxide transport ($60\text{--}80\%$ of total $\text{CO}_2$), formed when $\text{CO}_2$ hydrates into carbonic acid and dissociates into hydrogen ions and bicarbonate ($\text{HCO}_3^-$).

Carbonic Anhydrase

An enzyme concentrated in red blood cells that rapidly catalyzes the reversible reaction uniting carbon dioxide with water to form carbonic acid: $\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3$.

Chloride Shift

An ionic exchange mechanism maintaining electrical neutrality across erythrocyte membranes, in which bicarbonate ions ($\text{HCO}_3^-$) diffuse out into plasma and chloride ions ($\text{Cl}^-$) move into red blood cells at systemic tissues, reversing at the lungs.

Carbaminohemoglobin (HbCO2)

A chemical complex representing approximately $20\%$ of blood carbon dioxide transport, formed when $\text{CO}_2$ binds directly to terminal amino acid groups on the globin chains of hemoglobin.

The Haldane Effect

The physiological principle stating that oxygenation of hemoglobin in pulmonary capillaries promotes the unloading and release of carbon dioxide from carbaminohemoglobin and blood buffers into the alveoli.