The Respiratory System (Ch. 22)

A comprehensive set of vocabulary flashcards covering the major terms in the respiratory system lecture notes.

Alveoli

Microscopic air sacs in the lungs where gas exchange occurs; each alveolus is 0.2–0.5 mm in diameter and together provide ~70 m² of surface area.

Alveolar Type I Cells

Squamous alveolar cells that cover about 95% of the alveolar surface and allow rapid gas diffusion.

Alveolar Type II Cells

Alveolar cells that cover ~5% of the surface, repair the epithelium, and secrete pulmonary surfactant.

Alveolar Macrophages (Dust Cells)

Largest population of cells in the lung that phagocytose dust and debris within alveoli.

Pulmonary Surfactant

A mixture of phospholipids and proteins secreted by Type II cells that reduces surface tension and prevents alveolar collapse.

Pleura

A serous membrane enclosing the lungs and lining the thoracic cavity.

Visceral Pleura

Membrane that covers the surface of the lungs.

Parietal Pleura

Membrane that lines the inner surface of the rib cage, mediastinum, and superior diaphragm.

Pleural Cavity

Potential space between the two pleurae containing a thin layer of pleural fluid.

Intrapleural Pressure

Slight negative pressure between the pleural membranes (about -5 cm H₂O) that keeps the lungs expanded.

Alveolar Ventilation (AVR)

Amount of air that reaches the alveoli per minute; equals (tidal volume − dead space) × respiratory rate.

Atmospheric (Barometric) Pressure

Pressure of the air surrounding the body; ~760 mm Hg at sea level and decreases with altitude.

Intrapulmonary (Alveolar) Pressure

Air pressure within the lungs that changes with lung volume to drive airflow.

Boyle’s Law

In a closed system, the pressure of a gas is inversely proportional to its volume (P ∝ 1/V) at constant temperature.

Flow Down Gradients

Fluids move from regions of higher pressure to lower pressure; flow is proportional to ΔP/R.

Pressure Gradient

Difference between two pressures that drives airflow or fluid movement.

Resistance (R)

Opposition to flow within the respiratory passages that affects airflow.

Inspiration

Breathing phase during which air flows into the lungs; muscles contract to expand the thoracic cavity.

Expiration

Breathing phase during which air flows out of the lungs; muscles relax and the thoracic cavity decreases in volume.

Negative Intrapulmonary Pressure

The pressure inside the lungs becomes negative relative to ambient pressure during inspiration, allowing air to flow in.

Sternocleidomastoid, Scalenes, External Intercostals, Diaphragm

Muscles involved in inspiration that elevate the thoracic cage and/or flatten the diaphragm to increase thoracic volume.

Internal Intercostals

Muscles that assist in forced expiration by depressing the ribs and narrowing the thoracic cavity.

Diaphragm

Primary muscle of respiration that contracts to flatten and increase the depth of the thoracic cavity during inspiration.

Trachea

The windpipe; a rigid airway that conducts air to the bronchi.

Bronchi & Bronchioles

Airways that branch from the trachea; bronchi lead to progressively smaller bronchioles culminating in terminal bronchioles.

Alveolar Ducts & Alveolar Sacs

Structures that lead to alveoli; sites of gas exchange within the lungs.

Pulmonary Capillary Bed

Network of capillaries surrounding alveoli where gas exchange with blood occurs.

Interlobular Septum

Connective tissue separating lung lobules and housing vessels and airways.

Anatomical Dead Space

Volume of the conducting airways (about 150 mL) where no gas exchange occurs.

Physiologic (Functional) Dead Space

Sum of anatomical dead space plus any pathological dead space where gas exchange is impaired.

Total Lung Capacity (TLC)

Maximum amount of air the lungs can hold after a maximum inhalation.

Vital Capacity (VC)

Total amount of exchangeable air; equals tidal volume plus inspiratory and expiratory reserve volumes.

Inspiratory Capacity (IC)

Maximum amount of air that can be inspired after a normal expiration.

Residual Volume (RV)

Air remaining in the lungs after a maximal exhalation.

Functional Residual Capacity (FRC)

Volume of air remaining in the lungs after a normal, resting expiration.

Tidal Volume (TV)

Amount of air inhaled or exhaled in a normal breath.

Alveolar Gas Exchange

Movement of O₂ from alveoli to blood and CO₂ from blood to alveoli via diffusion down their partial pressure gradients.

Dalton’s Law

Total pressure of a gas mixture equals the sum of the partial pressures of its components.

Partial Pressure (Pgas)

Pressure contributed by each gas in a mixture (e.g., PO₂, PCO₂).

Henry’s Law

Amount of gas dissolved in a liquid is proportional to its partial pressure and its solubility.

Oxyhemoglobin (HbO₂)

Hemoglobin bound to one or more O₂ molecules.

Deoxyhemoglobin (HHb)

Hemoglobin with no bound O₂.

Oxyhemoglobin Dissociation Curve

Relation between PO₂ and HbO₂ saturation; shows cooperative binding and increasing steepness at lower PO₂.

Cooperative Binding

Oxygen binding to one heme site increases affinity at remaining sites, creating a steep rise in O₂ loading.

Carbamino Compounds

CO₂ bound to amino groups of plasma proteins and hemoglobin during transport.

Carbonic Anhydrase

Enzyme in RBCs that catalyzes conversion of CO₂ and water to bicarbonate and protons.

Chloride Shift

Exchange of bicarbonate out of and chloride into RBCs during CO₂ transport.

Ventilation-Perfusion Coupling

Matching of air flow (ventilation) and blood flow (perfusion) to optimize gas exchange.

Central Chemoreceptors

Brainstem sensors that respond to changes in CSF pH, reflecting CO₂ levels.

Peripheral Chemoreceptors

Carotid and aortic bodies that detect CO₂, O₂, and pH in the blood.

Dorsal Respiratory Group (DRG)

Respiratory center in the medulla that modulates inspiration, receiving inputs from chemoreceptors.

Ventral Respiratory Group (VRG)

Medullary respiratory center that sets the basic rhythm with inspiratory and expiratory neurons.

Pontine Respiratory Group (PNG/PRG)

Pons-based center that modifies the length of inspiration or expiration.

Voluntary Breathing

Conscious control of breathing originating in the motor cortex and corticospinal tracts.

IRDS (RDS)

Infant respiratory distress syndrome; deficiency of pulmonary surfactant in premature infants.