Respiratory System Physiology: Gas Exchange, Transport, and Regulation

A set of essential vocabulary flashcards reviewing pulmonary ventilation, external and internal respiration, gas laws, hemoglobin saturation dynamics, gas transport mechanisms, and neural/chemical respiratory control.

Pulmonary ventilation

The mechanical process of moving air into and out of the lungs (breathing) carried out by the respiratory system.

External respiration

The exchange of $O_2$ and $CO_2$ across the respiratory membrane between the air in the alveoli of the lungs and the blood in the pulmonary capillaries.

Transport of respiratory gases

The movement of $O_2$ and $CO_2$ through the bloodstream between the lungs and systemic body tissues, mediated by the cardiovascular system.

Internal respiration

The exchange of $O_2$ and $CO_2$ between systemic capillary blood and the surrounding tissue cells, mediated by the cardiovascular system.

Dalton's Law

A gas law stating that the total pressure exerted by a mixture of gases equals the sum of the partial pressures exerted by each individual gas, where each gas exerts a pressure directly proportional to its percentage in the mixture.

Henry's Law

A gas law stating that at a constant temperature, the amount of a gas that dissolves in a liquid is directly proportional to its partial pressure and its solubility coefficient ($\text{Concentration} = \text{Pressure} \times \text{Solubility coefficient}$).

Respiratory membrane

The air-blood barrier across which pulmonary gas exchange occurs, composed of the alveolar epithelium (Type I cells), pulmonary capillary endothelium, and their fused basement membranes.

Ventilation

The amount or flow of gas reaching the alveoli in the lungs.

Perfusion

The blood flow reaching the pulmonary capillaries that surround the alveoli.

Ventilation-perfusion coupling

An autoregulatory mechanism matching alveolar airflow to pulmonary capillary blood flow, wherein low alveolar $P_{\text{O}_2}$ causes arteriole constriction and high alveolar $P_{\text{O}_2}$ causes arteriole dilation.

Oxyhemoglobin

The bright red form of hemoglobin produced when oxygen molecules bind to the iron atoms of the heme groups ($\text{HbO}_2$).

Deoxyhemoglobin

The dark red form of hemoglobin resulting from the dissociation and release of oxygen molecules ($\text{HHb}$).

Carbaminohemoglobin

Hemoglobin bound to carbon dioxide on its globin polypeptide chains, responsible for carrying roughly $20\%$ to $23\%$ of $CO_2$ in the blood.

Carbonic anhydrase

An enzyme present inside red blood cells that rapidly and reversibly catalyzes the hydration of carbon dioxide into carbonic acid: $\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3$.

Chloride shift

The exchange of bicarbonate ($\text{HCO}_3^-$) and chloride ($\text{Cl}^-$) ions across red blood cell membranes via transport proteins to maintain electrical neutrality during gas transport.

Haldane effect

The phenomenon in which the oxygenation of hemoglobin alters its affinity for carbon dioxide: lower $P_{\text{O}_2}$ increases hemoglobin's affinity for $CO_2$, while higher $P_{\text{O}_2}$ decreases it.

Bohr effect

The weakening of the hemoglobin-oxygen bond caused by decreased pH (acidosis) and elevated $P_{\text{CO}_2}$, altering hemoglobin's structure and enhancing oxygen unloading to metabolically active tissues.

2,3-bisphosphoglycerate (BPG)

A glycolytic intermediate produced in red blood cells in response to hormones (thyroxine, hGH, epinephrine, norepinephrine, testosterone) and high altitude that binds hemoglobin and enhances oxygen unloading.

Fetal hemoglobin (Hb-F)

A form of hemoglobin present in the fetus that possesses a higher oxygen affinity than adult hemoglobin (Hb-A), facilitating the transfer of oxygen from maternal blood into fetal circulation.

Hering-Breuer reflex

An inflation reflex where pulmonary stretch receptors (mechanoreceptors) in visceral pleura and airways are stimulated by lung over-inflation, triggering inhibitory impulses that prevent overexpansion.

Hypercapnia

An abnormally elevated level of carbon dioxide ($CO_2$) in the blood, serving as the most powerful chemical stimulus for the respiratory centers to increase ventilation.

Hypocapnia

An abnormally low concentration of carbon dioxide ($CO_2$) in the blood, typically resulting from hyperventilation.

Acute mountain sickness (AMS)

A clinical syndrome caused by rapid ascent to elevations above $8000\text{ feet}$, characterized by headaches, shortness of breath, nausea, and dizziness, and capable of progressing to lethal cerebral or pulmonary edema.

Carbon monoxide poisoning

A toxic condition caused by carbon monoxide ($CO$) binding to heme with greater affinity than oxygen, thereby blocking $O_2$ binding to hemoglobin and leading to hypoxia, tissue damage, and death.