The Respiratory System: Anatomy, Physiology, and Pathology

Vocabulary flashcards covering the anatomical structures, mechanics of ventilation, gas exchange physiology, chemical control mechanisms, and pathological conditions of the respiratory system.

Nasopharynx

The superior region of the pharynx located behind the nasal cavity that permits airflow and protects against inhaled pathogens.

Oropharynx

The middle division of the pharynx situated behind the oral cavity that accommodates air passage and guards against inhaled and ingested pathogens.

Laryngopharynx

The inferior portion of the pharynx extending from the oropharynx to the oesophagus that routes inspired air toward the larynx and ingested materials toward the oesophagus.

Epiglottis

A flexible structure composed of elastic fibrocartilage that covers the entrance of the larynx during deglutition to prevent food from entering the trachea.

Trachea

A tubular conduit located anterior to the oesophagus supported by $16\text{–}20$ C-shaped hyaline cartilage rings and lined with ciliated columnar epithelium to sweep mucus upwards.

Primary Bronchi

The initial branches arising from the bifurcation of the trachea; the right primary bronchus is wider and more vertically oriented than the narrower left primary bronchus.

Pleura

A double-layered serous sac enclosing each lung, composed of an inner visceral layer adherent to the lung surface, an outer parietal layer lining the thoracic cavity, and an intervening pleural cavity.

Alveoli

Microscopic cup-shaped pouches lined with simple squamous epithelium and anchored by elastic tissue that serve as the terminal units for pulmonary gas exchange.

Respiratory Membrane

A thin, permeable, and moist barrier formed by the alveolar epithelium, basement membranes, and capillary endothelium across which $O_2$ and $CO_2$ diffuse.

Boyle's Law

The physical law stating that gas pressure is inversely proportional to container volume, dictating that expansion of the thoracic cavity lowers intrapulmonary pressure below atmospheric pressure during inspiration.

External Respiration

The exchange of respiratory gases between the alveolar air spaces and the blood circulating within pulmonary capillaries across the respiratory membrane.

Internal Respiration

The diffusion of gases between systemic capillaries and surrounding body tissue cells governed by differences in local partial pressures of $O_2$ and $CO_2$.

Carbonic Anhydrase

An erythrocyte enzyme that catalyzes the hydration of $CO_2$ into carbonic acid ($H_2CO_3$), which rapidly dissociates into hydrogen ions ($H^+$) and bicarbonate ions ($HCO_3^-$).

Central Chemoreceptors

Sensory cells located near the medulla oblongata bathed in cerebrospinal fluid (CSF) that stimulate ventilation when detecting increased $CO_2$ tension or elevated $H^+$ concentration.

Peripheral Chemoreceptors

Sensory receptors located within the aortic arch and carotid bodies that monitor arterial blood and signal the respiratory centre to heighten ventilation when blood $CO_2$ or acidity increases.

Hering-Breuer Reflex

A protective neural mechanism mediated by pulmonary stretch receptors (baroreceptors) that prevents alveolar overinflation during sustained inspiration.

Haldane Effect

The physiological phenomenon wherein high partial pressures of $CO_2$ promote $CO_2$ binding to haemoglobin, consequently lowering the molecule's binding affinity for $O_2$.

Lung Compliance

A measure of the stretchability of pulmonary tissue, determining the mechanical effort required to expand the lungs and inflate the alveoli.

Lung Elasticity

The mechanical recoil capacity of lung tissue that permits it to passively regain its original resting dimensions following inspiratory expansion.

Asthma

A chronic inflammatory airway condition triggered by environmental stimuli that elicits smooth-muscle bronchoconstriction, mucosal inflammation, and hypersecretion of mucus, causing reduced ventilation.

Chronic Bronchitis

A component of chronic obstructive pulmonary disease (COPD) characterized by prolonged airway inflammation, persistent mucus hypersecretion, and airway lumen narrowing resulting in a productive cough.

Emphysema

A component of COPD marked by progressive destruction of alveolar walls, loss of pulmonary elastic recoil, and permanent enlargement and air trapping in distal air spaces.

Pneumonia

An inflammatory infection of the lung parenchyma characterized by alveolar exudation of fluid, pus, and inflammatory cells, resulting in diminished gas diffusion and hypoxaemia.

Pulmonary Oedema

An abnormal extravasation of fluid into the alveolar spaces and interstitium—commonly secondary to left ventricular failure—that severely impairs oxygen diffusion and causes pink frothy sputum.

Pulmonary Embolism

A life-threatening vascular obstruction wherein a thrombus occludes the pulmonary arterial circulation, creating an acute ventilation-perfusion ($V/Q$) mismatch while alveolar ventilation remains preserved.