Respiratory System Glossary

Active breathing – Breathing that requires muscular effort during both inspirationThe process of inhaling, driven by diaphragm and external intercostal contraction. and expirationThe process of exhaling, which can be passive (relaxation of respiratory muscles) or active (involvi, as during exercise.

Air flow – The movementA fundamental property of life involving motion of the body or its parts. of air into and out of the lungs, driven by pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. gradients.

Alveolar pores – Small openings between adjacent alveoliMicroscopic air sacs in the lungs where gas exchange occurs between air and blood. that allow air pressure to equalize and provide collateral ventilation.

Alveolar surface tension – The cohesive force of waterThe universal solvent essential for life. moleculesGroups of atoms bonded together. lining the alveoli that tends to collapse the air sacs.

Alveolar macrophages – Immune cellsThe basic structural and functional units of life. in the alveoli that engulf and destroy pathogens and debris.

Alveoli – Tiny air sacs in the lungs where gas exchange occurs between air and blood.

Asthma – A chronic inflammatory disorder causing airway constriction, wheezing, and difficulty breathing.

Bicarbonate – An ion (HCO₃⁻) that transports most carbon dioxide in the blood.

Boyle’s law – Gas law stating that pressure and volume are inversely related when temperature is constant (P₁V₁ = P₂V₂).

Bronchi – Large airways that branch from the trachea into the lungs.

Bronchioles – Small airways that branch from bronchiThe large airways that branch from the trachea into the lungs, dividing into smaller bronchioles. and lead to alveolar ducts.

Bronchitis – Inflammation of the bronchi causing coughing and mucus production.

Bronchopulmonary segmentsThe subdivisions of lung lobes, supplied by tertiary bronchi. – Functionally independent divisions of lung lobes, each supplied by a tertiary bronchus.

Carbonic acidA substance that releases hydrogen ions (H⁺) in solution. – Weak acid (H₂CO₃) formed when carbon dioxide dissolves in blood plasmaThe liquid component of blood..

Cardiac notch – Indentation on the left lung where the heart is positioned.

Charles’s Law – Gas law stating that volume and temperature are directly related when pressure is constant (V₁/T₁ = V₂/T₂).

Cilia – Tiny hair-like projections on respiratory epithelial cells that sweep mucus and debris upward.

Compliance – The ease with which the lungs can expand; a measure of lung distensibility.

Conchae – Scroll-shaped bones in the nasal cavityThe internal space behind the nose that filters, warms, and humidifies incoming air. that increase surface area and turbulenceIrregular, chaotic blood flow that increases resistance and can contribute to clot formation. for warming and humidifying air.

Dalton’s Law – Gas law stating that total pressure of a gas mixture equals the sum of partial pressures of individual gases.

Deoxyhemoglobin – Hemoglobin that has released its oxygen to tissues.

Elastic cartilageA flexible connective tissue found in joints, the ear, nose, and rib cage. Cartilage can be of three – Flexible cartilage found in the epiglottisA flap of cartilage that covers the trachea during swallowing to prevent food from entering the airw and external ear.

Emphysema – Chronic obstructive disease characterized by destruction of alveolar walls and loss of lung elasticity.

Epiglottis – Flap of elastic cartilageA flexible cartilage type found in the ear and epiglottis. that covers the larynxThe voice box; contains vocal cords and connects the pharynx to the trachea. during swallowing to prevent food from entering the airways.

Expiration – The process of breathing out or exhalation.

Expiratory reserve volume – The additional volume of air that can be forcefully exhaled after a normal exhalation (approximately 1200 mL).

External intercostals – Muscles between the ribsCurved bones forming the rib cage; articulate with thoracic vertebrae and most with the sternum. that elevate the rib cage during inspiration.

External respirationThe process of gas exchange, including ventilation, external and internal respiration. – Gas exchange between the lungs and blood (O₂ loading and CO₂ unloading in pulmonary capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues.).

Forced vital capacity – The maximum volume of air that can be forcefully exhaled after a maximum inhalation.

Functional residual capacity – The volume of air remaining in the lungs after a normal expiration (approximately 2400 mL).

Henry’s Law – Gas law stating that the amount of gas dissolved in a liquid is proportional to its partial pressureThe pressure exerted by a single gas in a mixture; drives diffusion in respiration..

Hyaline cartilage – Smooth, glassy cartilage that reinforces the trachea and larger bronchi.

Inspiration – The process of breathing in or inhalation.

Inspiratory reserve volume – The additional volume of air that can be forcefully inhaled beyond a normal breath (approximately 3000 mL).

Inspiratory capacity – The maximum volume of air that can be inhaled after a normal expiration (approximately 3600 mL).

Internal respiration – Gas exchange between blood and body tissues (O₂ unloading and CO₂ loading in systemic capillaries).

Intrapleural pressure – The pressure in the pleural cavity between the parietal and visceral pleurae (normally negative/subatmospheric).

Intrapulmonary pressure – The pressure inside the alveoli (equal to atmospheric pressure at rest).

Larynx – The voice box; a cartilaginous structure connecting the pharynxThe muscular passageway connecting the mouth to the esophagus and larynx. to the trachea that contains the vocal cords.

Lobes – Major divisions of the lungs (three in the right lung, two in the left lung).

Lower respiratory tract – Structures below the larynx including the trachea, bronchi, bronchiolesSmall airways branching from the bronchi that lead to alveoli; lack cartilage and control airflow wi, and alveoli.

Meatuses – Air passages beneath each nasalTwo small rectangular bones forming the bridge of the nose. concha.

Mucociliary escalator – The coordinated movement of ciliaHair-like projections on the surface of some cells that move fluids or particles. that propels mucus and trapped particles upward toward the pharynx.

Nasal cavity – The hollow space behind the nose that warms, filters, and humidifies inhaled air.

Obstructive disorders – Respiratory conditions that restrict airflow due to airway narrowing (e.g., asthmaA chronic condition characterized by airway inflammation, narrowing, and excessive mucus production,, emphysemaA lung disease in which alveoli are damaged, reducing surface area for gas exchange and causing shor, bronchitisInflammation of the bronchi, leading to mucus buildup, coughing, and breathing difficulties.).

Oxygen affinity – The tendency of hemoglobinThe oxygen-carrying protein in red blood cells that gives blood its red color. to bind oxygen; affected by pHA measure of hydrogen ion concentration in a solution., temperature, and CO₂ levels.

Oxygen saturation – The percentage of hemoglobin binding sites occupied by oxygen.

Oxyhemoglobin – Hemoglobin bound to oxygen.

Parietal pleuraThe double-layered membrane surrounding the lungs and lining the thoracic cavity. – The outer layer of the pleural membrane lining the thoracic wall and diaphragm.

Partial pressure – The pressure exerted by a single gas in a mixture of gases.

Pharynx – The throat; a muscular passageway for both air and food connecting the nasal cavity to the larynx.

Pleura – The double-layered serous membrane surrounding the lungs.

Pneumonia – Infection causing inflammation and fluid accumulation in the alveoli.

Pressure – The force exerted by gas molecules colliding with surfaces.

Primary bronchi – The two main bronchi that branch directly from the trachea (right and left).

Primary muscles – The main muscles of respiration including the diaphragm and external intercostalsElevator Between ribs; lifts rib cage during breathing in..

Quiet breathing – Normal, relaxed breathing at rest that requires muscular effort only during inspiration.

Residual volume – The volume of air remaining in the lungs after maximum expiration (approximately 1200 mL).

Resistance – Opposition to airflow in the respiratory passages.

Respiration – The entire process of gas exchange including breathing, external respirationThe exchange of gases between the lungs and the blood in the pulmonary capillaries., transport, and internal respirationThe exchange of gases between the blood and body tissues..

Respiratory bronchioles – The smallest bronchioles that have scattered alveoli in their walls.

Restrictive disorders – Respiratory conditions that reduce lung expansion and total lung capacity(TLC) – The total volume of air the lungs can hold. (e.g., pulmonary fibrosis, scoliosis).

Secondary bronchi – Lobar bronchi that branch from primary bronchiThe first branches of the trachea that lead into the lungs. Also called lobar bronchi; one for each lung lobe (three right, two left).

Secondary muscles – Accessory muscles of respiration including the sternocleidomastoidFlexor / Rotator From sternum and clavicle to skull behind the ear; turns and bends the head., scalenes, and abdominal muscles used during forced breathing.

Segments – See bronchopulmonary segmentsFunctional units of the lungs, each served by its own tertiary bronchus and blood supply..

Sinuses – Air-filled cavities in skull bones that lighten the skull, warm and humidify air, and produce mucus.

Submucosal glands – Glands in the respiratory mucosaThe innermost lining of the digestive tract that contains mucus-secreting cells for protection and a that secrete mucus to trap particles and pathogens.

Surfactant – A lipoprotein mixture secreted by Type II pneumocytes that reduces alveolar surface tensionThe force exerted by the liquid lining the alveoli, which tends to collapse them; reduced by surfact and prevents collapse.

Terminal bronchioles – The smallest bronchioles that lack alveoli; they branch into respiratory bronchiolesSmallest bronchioles leading to alveolar ducts and alveoli..

Tertiary bronchi – Segmental bronchi that branch from secondary bronchiBranches from the primary bronchi that lead to each lung lobe. Also called segmental bronchi and supply bronchopulmonary segments.

Tidal volume – The volume of air inhaled or exhaled during normal quiet breathingNormal, passive breathing at rest. (approximately 500 mL).

Total lung capacity – The maximum volume of air the lungs can hold (approximately 6000 mL).

Trachea – The windpipe; a cartilage-reinforced tube connecting the larynx to the primary bronchi.

Tracheal cartilages – C-shaped rings of hyaline cartilageThe most abundant cartilage type, found in joints, ribs, and the nose. that support the trachea and prevent collapse.

Tuberculosis – A bacterial infection (Mycobacterium tuberculosis) primarily affecting the lungs.

Type I pneumocytes – Thin, flat alveolar cells that form the respiratory membrane for gas exchange.

Type II pneumocytes – Cuboidal alveolar cells that secrete surfactantA substance secreted by Type II pneumocytes that reduces alveolar surface tension..

Upper respiratory tract – Structures above the larynx including the nose, nasal cavity, paranasal sinusesAir-filled spaces in the skull that lighten it and help humidify air., and pharynx.

Ventilation – The mechanical process of moving air into and out of the lungs (breathing).

Vibrissae – Coarse hairs in the nostrils that filter large particles from inhaled air.

Visceral pleura – The inner layer of the pleural membrane adhering to the lung surface.

Volume – The amount of space occupied by a gas.