Chapter 18 – Respiratory System Fundamentals

Vocabulary flashcards covering key terms, structures, molecules, volumes, and physiological principles from Chapter 18 on the Respiratory System.

Ventilation

Mechanical process that moves air into and out of the lungs.

External Respiration

Gas exchange within the lungs: O2 moves from alveoli to pulmonary capillaries; CO2 moves from capillaries to alveoli.

Internal Respiration

Gas exchange within body tissues: O2 moves from systemic capillaries to cells; CO2 moves from cells to capillaries.

Airway Pathway

Nasal cavity → Pharynx → Larynx → Trachea → Primary bronchi → Secondary bronchi → Tertiary bronchi → Respiratory bronchioles → Terminal alveolar sacs.

Alveoli

Tiny air sacs that are the primary site of gas exchange in the lungs and secrete surfactant while reabsorbing Na⁺ and water.

Respiratory Zone

Region where gas exchange occurs; includes respiratory bronchioles and terminal alveolar sacs.

Conduction Zone

Passageways that transport, warm, moisten, and filter air but do not perform gas exchange.

Bicarbonate (HCO₃⁻)

Weak base that buffers blood pH; its formation and elimination are influenced by CO₂ levels ventilated by the lungs.

Erythropoietin (EPO)

Kidney hormone released at high altitude to stimulate red bone-marrow production of hemoglobin/RBCs.

2,3-Diphosphoglyceric Acid (2,3-DPG)

RBC molecule that decreases hemoglobin’s affinity for O₂, enhancing O₂ off-loading—especially at low PO₂.

Inspiration Pressure Gradient

During inhalation, intrapulmonary pressure becomes lower than atmospheric pressure, drawing air into the lungs.

Expiration Pressure Gradient

During exhalation, intrapulmonary pressure rises above atmospheric pressure, pushing air out of the lungs.

Surfactant

Mixture of phospholipids and hydrophobic proteins that reduces alveolar surface tension, preventing lung collapse.

Type I Alveolar Cells

Flattened epithelial cells that form the majority of the alveolar wall and facilitate gas exchange.

Type II Alveolar Cells

Cuboidal alveolar cells that secrete surfactant and help reabsorb Na⁺ and water to keep alveoli dry.

Diaphragm

Primary muscle of quiet breathing; its contraction enlarges thoracic volume and decreases intrapulmonary pressure.

Pulmonary Ventilation

Bulk flow of air into (inspiration) and out of (expiration) the respiratory tract, driven by pressure changes.

Tidal Volume (TV)

Volume of air inhaled or exhaled in one quiet, resting breath.

Expiratory Reserve Volume (ERV)

Extra volume of air that can be forcefully exhaled after a normal tidal expiration.

Inspiratory Reserve Volume (IRV)

Extra volume of air that can be forcefully inhaled after a normal tidal inspiration.

Residual Volume (RV)

Volume of air remaining in the lungs after maximal exhalation; prevents lung collapse.

Henry’s Law

Amount of gas that dissolves in a liquid is proportional to its partial pressure, solubility, and inversely to temperature.

Rhythmicity Center

Neuronal network in the medulla oblongata that sets the basic rhythm of breathing.

Chemoreceptors

Sensors that detect changes in arterial pH, PCO₂, and PO₂ to adjust ventilation rate.

Oxygen–Hemoglobin Dissociation Curve

Sigmoidal graph showing the percent saturation of hemoglobin at varying PO₂; illustrates cooperative O₂ binding.

Affinity Factors (4)

Temperature, pH (Bohr effect), PCO₂, and 2,3-DPG—all decrease hemoglobin’s affinity for O₂, shifting the curve right.

Carbamino Compounds

Form in which ~23 % of CO₂ binds reversibly to amino groups of hemoglobin for transport.

CO₂ Transport Forms

Dissolved in plasma (7 %), as carbamino compounds (23 %), and as bicarbonate ions (70 %).

Feedback Loop for Respiratory Rate

Elevated PCO₂ or lowered pH/PO₂ → chemoreceptors → medullary rhythmicity center → increased ventilation → restores homeostasis.