Comprehensive Respiratory Physiology: Gas Transport, Mechanics, and Exchange

Vocabulary practice flashcards covering respiratory physiology, including gas transport in the blood, pulmonary mechanics, acid-base balance, and alveolar-capillary gas exchange.

Henry's law

A physical gas law stating that the volume of gas dissolved in a liquid is directly proportional to its partial pressure and solubility coefficient: $V_{gas} = \alpha \times \frac{P_{gas}}{P_{atm}}$.

Hemoglobin structure

A tetrameric hemoprotein consisting of globin (four polypeptide chains: two alpha and two beta) and four iron-containing heme groups, wherein divalent iron ($Fe^{2+}$) reversibly binds $O_2$.

Oxygen-carrying capacity of hemoglobin

The maximum volume of $O_2$ bound per gram of hemoglobin; theoretically $1.39\,ml/g$, but $1.34\,ml/g$ in vivo after taking into account non-functional forms such as methemoglobin.

$$P_{50}$$

The partial pressure of oxygen at which hemoglobin is $50\%$ saturated; its normal reference value in adult males is $27\,mmHg$.

Oxyhemoglobin dissociation curve (Barcroft curve)

A sigmoid-shaped curve depicting the non-linear relationship between $PO_2$ and hemoglobin oxygen saturation ($SO_2$); it displays a plateau between $60\,mmHg$ and $100\,mmHg$ that serves as a safety margin for arterial oxygenation.

Bohr effect

The rightward displacement of the oxyhemoglobin dissociation curve caused by increased $PCO_2$ and $[H^+]$ ions (decreased pH), which lowers hemoglobin's affinity for $O_2$ and enhances oxygen unloading into tissues.

Haldane effect

The effect of oxygenation on carbon dioxide carriage, whereby deoxygenated hemoglobin has a higher affinity for $CO_2$ and $H^+$ ions, enabling venous blood to carry more $CO_2$ than oxygenated blood.

Carbaminohemoglobin

The chemical complex formed when $CO_2$ binds reversibly to the globin amino groups of hemoglobin ($\text{Hb-NH}_2 + CO_2 \rightleftharpoons \text{Hb-NH-COOH}$), representing approximately $30\%$ of blood $CO_2$ transport.

Chloride shift (Hamburger phenomenon)

The process at the tissue level where bicarbonate ($HCO_3^-$) produced inside erythrocytes diffuses out into the plasma in exchange for chloride ions ($Cl^-$) entering the erythrocyte to maintain electrical neutrality.

Henderson-Hasselbalch equation (blood pH)

The chemical equilibrium equation used to calculate arterial blood pH from bicarbonate and carbon dioxide levels: $pH = 6.1 + \log\left(\frac{[HCO_3^-]}{0.03 \times PCO_2}\right)$.

Aerobic cellular respiration

The oxygen-dependent intracellular catabolic process producing cellular energy, represented by the chemical equation $C_6H_{12}O_6 + 6 O_2 \rightarrow 6 CO_2 + 6 H_2O + \text{Energy (heat + ATP)}$.

Endocrine and metabolic functions of the lungs

Non-respiratory pulmonary endothelial processes, which include converting angiotensin I into angiotensin II via ACE, clearing circulating serotonin and norepinephrine, releasing prostaglandins and histamine, and maintaining a local fibrinolytic system.

Conducting zone

The non-alveolated section of the respiratory tree encompassing generations $0$ through $16$ (from the trachea to terminal bronchioles) that conducts inspired and expired air without gas exchange.

Respiratory zone

The fully alveolated distal segment of the airway tree spanning generations $20$ through $23$ (alveolar ducts and alveolar sacs) that serves as the main site of gas exchange.

Alveolar-capillary barrier

A specialized membrane measuring approximately $0.3 - 0.5\,\mu m$ in thickness through which respiratory gases diffuse, composed of surfactant film, alveolar epithelium, interstitial space, and capillary endothelium.

Pleural pressure ($P_{pl}$)

The hydrostatic pressure in the potential space between the parietal and visceral pleurae, which is subatmospheric at rest ($\approx 756\,mmHg$ absolute, or $-4\,mmHg$ relative to atmospheric pressure).

Transpulmonary pressure ($P_{tp}$)

The distending transmural pressure holding the lungs open against their elastic recoil, calculated as the difference between alveolar pressure and pleural pressure: $P_{tp} = P_{alv} - P_{pl}$ ($+4\,mmHg$ at rest).

Respiratory muscles

The skeletal muscles driving airflow: normal quiet inspiration uses the diaphragm and external intercostals; forced inspiration engages neck accessories (scalenes, sternocleidomastoid); forced expiration recruits internal intercostals and abdominal muscles.

Boyle-Mariotte law

The physical law stating that at constant temperature and mass, the pressure of a gas is inversely proportional to its volume ($P_1 V_1 = P_2 V_2$), explaining how thoracic volume expansion lowers alveolar pressure below atmospheric pressure.

Pulmonary compliance ($C$)

A measure of the distensibility of the lungs or chest wall, defined mathematically as the change in volume per unit change in transmural distending pressure: $C = \frac{\Delta V}{\Delta P} = \frac{1}{E}$.

Pneumothorax

The abnormal entry of atmospheric air into the pleural space resulting in equalization of intrapleural pressure with atmospheric pressure ($P_{pl} = P_{atm}$), causing lung collapse and outward expansion of the thoracic wall.

Laplace's law (alveoli)

The physical principle relating the distending collapse pressure ($P$) inside an alveolus to its surface tension ($T$) and radius ($r$): $P = \frac{2T}{r}$.

Pulmonary surfactant

A complex mixture of phospholipids and proteins synthesized by type II alveolar cells that reduces alveolar surface tension, prevents small alveoli from collapsing, and enhances lung compliance.

Poiseuille's law

The equation determining laminar flow resistance ($R$) through an airway tube based on fluid viscosity ($\eta$), tube length ($L$), and tube radius ($r$): $R = \frac{8\eta L}{\pi r^4}$.

Reynolds number ($Re$)

A dimensionless quantity determining the transition between laminar and turbulent flow regimes: $Re = \frac{\rho \cdot v \cdot d}{\eta}$, where $\rho$ is density, $v$ is mean velocity, $d$ is diameter, and $\eta$ is viscosity.

Respiratory volumes and capacities

Standard spirometric subdivisions of lung air, including tidal volume ($500\,mL$), inspiratory reserve volume ($3000\,mL$), expiratory reserve volume ($1200\,mL$), residual volume ($1200\,mL$), and total lung capacity ($5900\,mL$).

Tiffeneau index

The diagnostic ratio of forced expiratory volume in one second to vital capacity ($FEV_1 / VC$), with a normal value of $75\% - 80\%$ in healthy individuals.

Physiological dead space

The combined volume of inspired gas that does not take part in gas exchange, calculated as the sum of anatomical dead space (conducting airways) and alveolar dead space (ventilated but unperfused alveoli).

Dalton's law

The law stating that the total pressure of a gas mixture equals the sum of the partial pressures of its component gases: $P_{gas} = F_{gas} \times P_{tot}$.

Water vapor pressure ($P_{H_2O}$)

The partial pressure exerted by water vapor ($47\,mmHg$ at $37^\circ C$) in humidified inspired air, reducing the effective dry partial pressures of other respiratory gases: $P_{gas} = (P_{atm} - P_{H_2O}) \times F_{gas}$.

Fick's law of diffusion

The law dictating that the rate of gas diffusion across the alveolar-capillary barrier is proportional to surface area ($S$), the diffusion constant ($K$), and the partial pressure difference ($P_1 - P_2$), and inversely proportional to barrier thickness ($e$): $\dot{V}_{gas} = \frac{K \cdot S \cdot (P_1 - P_2)}{e}$.

Lung diffusing capacity ($D_L$)

A composite functional parameter reflecting the conductance of the alveolar-capillary membrane, expressed in $ml\,min^{-1}\,mmHg^{-1}$ and measured clinically using carbon monoxide: $D_L = \frac{\dot{V}_{gas}}{P_1 - P_2}$.

Anatomical right-to-left shunt

The normal physiological bypass where deoxygenated blood from the bronchial and coronary (Thebesian) veins empties directly into the pulmonary veins and left heart, producing a normal alveolar-arterial $PO_2$ difference ($P_A O_2 \approx 105\,mmHg$ vs. $PaO_2 \approx 100\,mmHg$).

Ventilation-perfusion ratio ($\dot{V}_A / \dot{Q}$)

The regional match between alveolar ventilation and pulmonary capillary blood flow, which averages $\approx 1.0$ overall, but is high at the apex ($\dot{V}_A > \dot{Q}$) and low at the base ($\dot{V}_A < \dot{Q}$) in an upright lung due to gravity.

Extreme ventilation-perfusion mismatch

Pathological states where complete bronchial obstruction creates a true shunt with $\dot{V}/\dot{Q} = 0$ (perfused but unventilated), and vascular obstruction creates alveolar dead space with $\dot{V}/\dot{Q} \rightarrow \infty$ (ventilated but unperfused).