Respiratory System: Pulmonary Ventilation and Gas Exchange

Comprehensive vocabulary definitions regarding the anatomy and physiology of pulmonary ventilation, gas transport, and respiratory regulation.

Pulmonary ventilation

The movement of gases between the atmosphere and the alveoli, consisting of inspiration and expiration.

Pulmonary gas exchange

The exchange of respiratory gases between the alveoli and the blood within the pulmonary capillaries.

Tissue gas exchange

The exchange of respiratory gases between the blood in systemic capillaries and the systemic cells of the body.

Eupnea

Rhythmic, quiet breathing that occurs at rest.

Boyle’s Law

The principle stating that at a constant temperature, the pressure of a gas is inversely related to its volume, expressed as $P_1V_1 = P_2V_2$.

Intrapulmonary pressure

The pressure of air within the alveoli, which fluctuates during breathing and eventually equalizes with atmospheric pressure.

Intrapleural pressure

The pressure within the pleural cavity, which is typically about $4\,mm\,Hg$ lower than intrapulmonary pressure to keep the lungs inflated.

Tidal volume

The amount of air inhaled or exhaled per breath during quiet breathing, typically about $0.5\,L$ ($500\,mL$).

Medullary respiratory center

The region of the brainstem containing the Ventral Respiratory Group (VRG) and Dorsal Respiratory Group (DRG) that coordinates breathing.

Pontine respiratory center

Also known as the pneumotaxic center, it facilitates smooth transitions between inspiration and expiration.

Apnea

The absence of breathing, which can occur voluntarily, be drug-induced, or result from neurological disease or trauma.

Central chemoreceptors

Receptors in the medulla that monitor the $pH$ of cerebrospinal fluid (CSF) to regulate ventilation based on $PCO_2$ levels.

Peripheral chemoreceptors

Receptors located in the aortic arch and carotid bodies that respond to changes in blood $PO_2$, $PCO_2$, and $H^+$ levels.

Hypoxic drive

A condition where $PO_2$ levels become the primary stimulus for breathing because chemoreceptors have become less sensitive to $PCO_2$.

Hering-Breuer reflex

An inhalation reflex initiated by baroreceptors to prevent overinflation of the lungs by shutting off inspiration.

Compliance

The ease with which the lungs and chest wall expand, determined by surface tension and elasticity.

Minute ventilation

The total amount of air moved between the atmosphere and alveoli in one minute, calculated as $Tidal\,volume \times Respiration\,rate$.

Anatomic dead space

The space within the conducting zone where no gas exchange occurs, typically measuring about $150\,mL$.

Spirometer

An instrument used to measure respiratory volumes and assess respiratory health.

Residual volume

The amount of air remaining in the lungs even after the most forceful expiration.

Vital capacity

The total amount of air a person can exchange through forced breathing, calculated as $TV + IRV + ERV$.

Dalton’s Law

The law stating that the total pressure in a mixture of gases is equal to the sum of the individual partial pressures.

Henry’s Law

The law stating that the solubility of a gas in a liquid is dependent upon the partial pressure of the gas and its solubility coefficient.

Ventilation-perfusion coupling

The physiological adjustment where bronchioles regulate airflow and arterioles regulate blood flow to maximize gas exchange efficiency.

Chloride shift

The process where bicarbonate ($HCO_3^-$) diffuses out of erythrocytes into the plasma while chloride ($Cl^-$) diffuses in.

Bohr effect

The phenomenon where hydrogen ion ($H^+$) binding to hemoglobin causes a conformational change that decreases its affinity for $O_2$.

Hyperventilation

A breathing rate or depth above the body's demand, leading to low blood $CO_2$ (hypocapnia) and potential respiratory alkalosis.

Hypoventilation

Breathing that is too slow (bradypnea) or too shallow (hypopnea), leading to high blood $CO_2$ (hypercapnia) and respiratory acidosis.

Hyperpnea

The increase in breathing depth to meet increased tissue metabolic needs during exercise while blood gas levels remain relatively constant.