Chapter 22: The Respiratory System

Comprehensive vocabulary flashcards covering anatomical structures, histology, neural pathways, respiratory mechanics, gas laws, transport kinetics, and clinical pathologies of the respiratory system.

Conducting zone

Passages of the respiratory system that serve only for airflow, extending from nostrils through major bronchioles, with no gas exchange occurring.

Respiratory zone

Regions of the respiratory system that participate directly in gas exchange, consisting of the pulmonary alveoli and nearby microscopic structures.

Ala nasi

The flared lateral portion at the lower end of the nose, shaped by alar cartilages and dense connective tissue.

Nasal septum

Vertical dividing wall of bone and hyaline cartilage that partitions the nasal cavity into right and left fossae; formed by the vomer inferiorly, perpendicular plate of the ethmoid superiorly, and septal cartilage anteriorly.

Vibrissae (guard hairs)

Stiff hairs located inside the nasal vestibule that physically block debris and insects from entering the nasal cavity.

Meatus

A narrow air passage beneath each nasal concha (superior, middle, and inferior) that creates air turbulence to cleanse, warm, and moisten incoming air.

Swell body (erectile tissue)

An extensive venous plexus in the epithelium of the inferior concha that swells with blood on one side every $30$ to $60\,\text{minutes}$, shifting airflow to allow the opposite side to recover from drying.

Nasopharynx

The uppermost region of the pharynx situated posterior to the nasal apertures and superior to the soft palate; lined by ciliated pseudostratified columnar epithelium and housing the pharyngeal tonsil.

Oropharynx

The intermediate region of the pharynx located between the soft palate and the epiglottis; passes air, food, and drink and is lined by stratified squamous epithelium.

Laryngopharynx

The lowermost region of the pharynx extending from the epiglottis to the cricoid cartilage, where the esophagus begins; lined by stratified squamous epithelium.

Epiglottis

A superior cartilaginous flap of the larynx that tilts downward during swallowing to close the airway and route food and drink into the esophagus.

Thyroid cartilage

The largest, shield-shaped cartilage of the larynx that features the anterior laryngeal prominence (Adam's apple), which enlarges under the influence of testosterone.

Cricoid cartilage

The ring-like cartilage located at the inferior base of the larynx that connects the larynx directly to the trachea.

Glottis

The collective structure comprising the vocal cords (vocal folds) and the opening between them.

Vocal cords (vocal folds)

Inferior laryngeal folds containing vocal ligaments covered with stratified squamous epithelium that vibrate when air passes between them to generate sound.

Trachealis

Smooth muscle bridging the posterior gap in the C-shaped hyaline cartilage rings of the trachea, contracting or relaxing to regulate airflow and accommodating esophageal expansion.

Carina

An internal median ridge on the lowermost tracheal cartilage that marks the tracheal bifurcation into the right and left main bronchi.

Mucociliary escalator

A primary defense mechanism where mucus produced by goblet cells traps inhaled particles and motile cilia beat continuously upward to propel the mucus to the pharynx for swallowing.

Bronchopulmonary segment

A functionally independent, compartmentalized unit of lung tissue ventilated by a single segmental (tertiary) bronchus ($10$ in the right lung, $8$ in the left lung).

Squamous (type 1) alveolar cells

Thin, broad epithelial cells covering approximately $95\%$ of the alveolar surface area, designed to facilitate rapid gas diffusion between blood and air.

Great (type 2) alveolar cells

Round to cuboidal cells covering approximately $5\%$ of the alveolar surface that repair damaged alveolar epithelium and secrete pulmonary surfactant.

Pulmonary surfactant

A mixture of phospholipids and proteins secreted by great alveolar cells that disrupts hydrogen bonding of water, reducing alveolar surface tension and preventing collapse during expiration.

Alveolar macrophages (dust cells)

The most numerous cells in the lungs; wandering phagocytes that clean the alveoli by engulfing dust particles and debris before migrating up the mucociliary escalator.

Respiratory membrane

A thin barrier approximately $0.5\,\mu\text{m}$ thick across which gas exchange occurs, composed of squamous alveolar cells, capillary endothelial cells, and their shared basement membrane.

Diaphragm

The prime mover of respiration, accounting for two-thirds of resting airflow; contraction flattens it to enlarge the thoracic cavity for inspiration, while relaxation allows it to bulge upward during expiration.

Visceral pleura

The inner layer of the serous membrane that adheres directly to the external surface of the lung and extends into its fissures.

Parietal pleura

The outer serous membrane layer that lines the inner surface of the thoracic cage, mediastinum, and superior surface of the diaphragm.

Ventral respiratory group (VRG)

A respiratory nucleus located in the medulla oblongata containing inspiratory and expiratory reverberating circuits that serves as the primary generator of the respiratory rhythm ($12\,\text{breaths/min}$).

Dorsal respiratory group (DRG)

An integrating center in the medulla oblongata that receives sensory inputs from chemoreceptors, stretch receptors, and higher brain centers to modify respiratory rate and depth.

Pontine respiratory group (PRG)

A respiratory center in the pons that modifies outputs from the VRG and DRG to adapt breathing rhythms to circumstances such as sleep, exercise, vocalization, and emotional states.

Central chemoreceptors

Brainstem neurons situated near the surface of the medulla oblongata that monitor the $\text{pH}$ of cerebrospinal fluid, which reflects systemic arterial $P_{\text{CO}_2}$.

Peripheral chemoreceptors

Sensory structures located in the carotid and aortic bodies that respond to arterial levels of $P_{\text{O}_2}$, $P_{\text{CO}_2}$, and $\text{pH}$, transmitting signals via the glossopharyngeal and vagus nerves.

Inflation (Hering–Breuer) reflex

A protective somatic reflex triggered by pulmonary stretch receptors during excessive lung inflation that inhibits inspiratory neurons to prevent overexpansion.

Boyle's law

A physical gas law stating that at a constant temperature, the pressure of a given quantity of gas is inversely proportional to its volume ($P \propto \frac{1}{V}$).

Charles's law

A physical gas law stating that the volume of a given quantity of gas is directly proportional to its absolute temperature ($V \propto T$), contributing to lung inflation as cool inspired air warms to $37^\circ\text{C}$.

Intrapleural pressure

The subatmospheric pressure existing in the potential space between the visceral and parietal pleurae, normally averaging about $-5\,\text{cm}\,\text{H}_2\text{O}$ at rest and dropping to $-8\,\text{cm}\,\text{H}_2\text{O}$ during inspiration.

Pneumothorax

The presence of atmospheric air in the pleural cavity resulting from a thoracic wall puncture or lung lesion, eliminating negative intrapleural pressure and causing lung collapse.

Atelectasis

The complete or partial collapse of a lung or lobe, often caused by pneumothorax or airway obstruction followed by gas absorption by capillary blood.

Pulmonary compliance

The ease with which the lungs and thoracic wall expand; quantitatively defined as the change in lung volume relative to a given change in pressure ($\frac{\Delta V}{\Delta P}$).

Anatomical dead space

The volume of inspired air (approximately $150\,\text{mL}$) that remains in the conducting zone passages where no alveolar gas exchange occurs.

Alveolar ventilation rate (AVR)

The volume of air that ventilates the alveoli per minute and is available for gas exchange; calculated as $(\text{tidal volume} - \text{dead space}) \times \text{respiratory rate}$, averaging $4{,}200\,\text{mL/min}$.

Tidal volume (TV)

The volume of air inhaled and exhaled in a single cycle during relaxed, quiet breathing, normally around $500\,\text{mL}$.

Inspiratory reserve volume (IRV)

The volume of air in excess of tidal volume that can be inhaled with maximum voluntary effort, normally around $3{,}000\,\text{mL}$.

Expiratory reserve volume (ERV)

The volume of air in excess of tidal volume that can be forcibly exhaled with maximum voluntary effort, normally around $1{,}200\,\text{mL}$.

Residual volume (RV)

The volume of air remaining in the lungs after a maximal voluntary expiration (typically $1{,}300\,\text{mL}$) that prevents alveolar collapse and permits continuous gas exchange.

Vital capacity (VC)

The maximum volume of air that can be exhaled following a maximum inhalation; calculated as $VC = \text{ERV} + \text{TV} + \text{IRV}$ (typically $4{,}700\,\text{mL}$).

Dalton's law

A gas law stating that total atmospheric pressure is equal to the sum of the partial pressures contributed independently by each individual gas in a gas mixture.

Henry's law

A physical law stating that at an air–water interface, at a given temperature, the amount of gas dissolved in a liquid is proportional to its solubility and its partial pressure in the air.

Ventilation–perfusion coupling

The physiologic autoregulation process matching alveolar airflow (ventilation) with pulmonary capillary blood flow (perfusion) through local vasoconstriction, vasodilation, bronchoconstriction, and bronchodilation.

Oxyhemoglobin ($\text{HbO}_2$)

Hemoglobin with one or more oxygen molecules bound to the ferrous ($\text{Fe}^{2+}$) atoms in its heme moieties.

Deoxyhemoglobin (HHb)

Hemoglobin with no oxygen bound to its heme iron groups, which binds hydrogen ions and carbon dioxide with higher affinity than oxyhemoglobin.

Oxyhemoglobin dissociation curve

An S-shaped graphical representation illustrating the non-linear relationship between ambient partial pressure of oxygen ($P_{\text{O}_2}$) and the percentage saturation of hemoglobin.

Carbaminohemoglobin ($\text{HbCO}_2$)

A transport molecule formed when carbon dioxide chemically binds to amino groups of hemoglobin globin chains without directly competing with oxygen binding sites.

Carboxyhemoglobin (HbCO)

A compound formed when carbon monoxide ($\text{CO}$) competitively binds to the iron atom of hemoglobin $210$ times more tightly than oxygen, preventing oxygen transport.

Chloride shift

An antiport mechanism in red blood cells that transports bicarbonate ($\text{HCO}_3^-$) out of the cell into the plasma in exchange for chloride ($\text{Cl}^-$) to maintain electrical neutrality during systemic capillary transit.

Utilization coefficient

The fraction of oxygen in arterial blood released to tissues during capillary passage, typically amounting to about $22\%$ under resting conditions.

Venous reserve

The residual volume of oxygen remaining bound to hemoglobin in blood after passing through systemic capillaries, which sustains life for several minutes during respiratory arrest.

Bohr effect

The physiologic phenomenon where lower $\text{pH}$ and elevated $P_{\text{CO}_2}$ in active tissues weaken the affinity of hemoglobin for oxygen, thereby promoting oxygen unloading.

Haldane effect

The principle stating that deoxygenation of blood increases its capacity to carry carbon dioxide, whereas oxygenation promotes carbon dioxide release.

Hypoxemic hypoxia

A state of low arterial $P_{\text{O}_2}$ usually resulting from inadequate pulmonary gas exchange, high altitude, drowning, or degenerative lung conditions.

Cor pulmonale

Hypertrophy and potential right ventricular failure caused by chronic obstruction and elevated vascular resistance within the pulmonary circulation.

Squamous-cell carcinoma (of the lung)

The most common form of lung cancer, initiating when ciliated pseudostratified epithelium transforms into stratified squamous tissue and develops invasive keratinous lesions.

Small-cell (oat-cell) carcinoma

The least common and most aggressive form of lung cancer, originating in the main bronchi with oat grain-like cell clusters that rapidly invade the mediastinum and metastasize.