Chapter 23 – The Respiratory System (BIOL 2252)

Vocabulary flashcards summarizing key structures, functions, physiology, and regulation of the respiratory system as covered in Chapter 23 lecture notes.

Respiratory System

Body system that supplies O₂ for cellular respiration and removes CO₂; includes airways, lungs, and associated structures.

Pulmonary Ventilation

Movement of air into and out of the lungs (breathing).

External Respiration

Exchange of O₂ and CO₂ between alveoli and pulmonary capillary blood.

Internal Respiration

Exchange of O₂ and CO₂ between systemic capillaries and body tissues.

Gas Transport

Movement of respiratory gases in the blood between lungs and systemic cells.

Conducting Zone

Respiratory passageways that transport, warm, humidify, and cleanse air; nose through terminal bronchioles.

Respiratory Zone

Microscopic structures where gas exchange occurs: respiratory bronchioles, alveolar ducts, and alveoli.

Upper Respiratory Tract

Nose, nasal cavity, pharynx, and larynx.

Lower Respiratory Tract

Trachea, bronchi, bronchioles, alveolar ducts, and alveoli.

Respiratory Mucosa

Mucous membrane lining the respiratory tract; epithelium + lamina propria with goblet cells and glands.

Goblet Cells

Mucus-secreting epithelial cells in respiratory mucosa.

Nasal Conchae (Turbinate Bones)

Superior, middle, and inferior bony projections that create air turbulence and increase mucosal surface area.

Paranasal Sinuses

Frontal, ethmoidal, sphenoidal, and maxillary air-filled cavities that lighten skull and condition inhaled air.

Nasopharynx

Superior pharyngeal region; air passage lined with pseudostratified ciliated columnar epithelium.

Oropharynx

Middle pharyngeal region for food and air; lined with stratified squamous epithelium.

Laryngopharynx

Inferior pharyngeal region continuous with larynx and esophagus; stratified squamous epithelium.

Larynx (Voice Box)

Cartilaginous airway housing vocal cords; routes air and food and aids in sound production.

Epiglottis

Elastic cartilage flap that closes laryngeal inlet during swallowing to prevent food entry.

Vocal Folds (True Vocal Cords)

Mucosa-covered vocal ligaments that vibrate to produce sound.

Rima Glottidis

Opening between the vocal folds; part of the glottis.

Trachea

Windpipe supported by C-shaped hyaline cartilage rings; lined with ciliated mucosa.

Bronchial Tree

Branching system of airways from main bronchi to bronchioles (≈23 orders of branching).

Bronchioles

Airways <1 mm diameter; no cartilage, proportionally more smooth muscle.

Bronchoconstriction

Narrowing of bronchioles by smooth-muscle contraction; increases airway resistance.

Bronchodilation

Widening of bronchioles via smooth-muscle relaxation; decreases airway resistance.

Respiratory Bronchioles

First respiratory zone passages arising from terminal bronchioles.

Alveolar Ducts

Small passages that lead from respiratory bronchioles to alveolar sacs.

Alveoli

Tiny air sacs (300–400 million/lung) where gas exchange occurs.

Type I Alveolar Cells

Squamous epithelial cells forming most of alveolar wall; permit gas diffusion.

Type II Alveolar Cells (Septal Cells)

Cuboidal cells that secrete pulmonary surfactant and antimicrobial proteins.

Pulmonary Surfactant

Oily secretion that reduces alveolar surface tension and prevents collapse.

Alveolar Macrophages (Dust Cells)

Phagocytes that remove debris and pathogens from alveolar surfaces.

Respiratory Membrane

0.5 µm barrier of alveolar epithelium, fused basement membranes, and capillary endothelium for gas diffusion.

Pleura

Double-layered serous membrane (parietal and visceral) surrounding lungs with lubricating pleural fluid.

Intrapleural Pressure (Pip)

Pressure in pleural cavity; normally ~4 mm Hg below intrapulmonary pressure to keep lungs inflated.

Transpulmonary Pressure

Difference between intrapulmonary and intrapleural pressures; maintains lung expansion.

Boyle’s Law

At constant temperature, gas pressure is inversely related to volume (P₁V₁ = P₂V₂).

Quiet Breathing (Eupnea)

Resting, rhythmic breathing using diaphragm and external intercostals.

Forced Breathing

Vigorous inspiration or expiration involving accessory muscles.

Diaphragm

Primary muscle of inspiration; flattens to enlarge thoracic cavity.

External Intercostals

Muscles that elevate ribs during quiet inspiration.

Minute Ventilation

Total air moved each minute = tidal volume × respiratory rate.

Anatomic Dead Space

150 mL of tidal volume remaining in conducting zone with no gas exchange.

Alveolar Ventilation

Air reaching alveoli per minute = (tidal volume − dead space) × rate.

Tidal Volume (TV)

≈500 mL of air inhaled or exhaled in a quiet breath.

Inspiratory Reserve Volume (IRV)

Additional air that can be inhaled beyond tidal inspiration; reflects compliance.

Expiratory Reserve Volume (ERV)

Additional air exhaled after tidal expiration; reflects elasticity.

Residual Volume (RV)

Air remaining in lungs after maximal expiration; prevents alveolar collapse.

Vital Capacity (VC)

Maximum air expired after maximal inspiration (TV + IRV + ERV).

Total Lung Capacity (TLC)

Sum of all lung volumes (VC + RV).

Spirometer

Instrument that measures respiratory volumes and capacities.

Dalton’s Law

Total gas pressure equals the sum of partial pressures of each gas in the mixture.

Henry’s Law

At a given temperature, the amount of gas dissolved in a liquid is proportional to its partial pressure and solubility.

Partial Pressure

Pressure exerted by a single gas in a mixture; symbolized as Pgas (e.g., PO₂).

Ventilation–Perfusion Coupling

Matching of airflow to blood flow by local regulation of bronchioles and arterioles to optimize gas exchange.

Bohr Effect

Lowered blood pH or higher PCO₂ reduces hemoglobin’s affinity for O₂, enhancing O₂ unloading.

Haldane Effect

Lower PO₂ and reduced hemoglobin increase CO₂ loading and H⁺ buffering in blood.

2,3-Bisphosphoglycerate (2,3-BPG)

RBC metabolite that decreases hemoglobin affinity for O₂, promoting release.

Hyperventilation

Breathing faster or deeper than metabolic need, causing hypocapnia and respiratory alkalosis.

Hypoventilation

Slow or shallow breathing leading to hypercapnia, hypoxemia, and respiratory acidosis.

Hypocapnia

Below-normal blood PCO₂ often due to hyperventilation.

Hypercapnia

Elevated blood PCO₂ usually from hypoventilation.

Respiratory Alkalosis

Blood pH rises due to excessive CO₂ exhalation (low PCO₂).

Respiratory Acidosis

Blood pH falls from CO₂ retention (high PCO₂).

Carbonic Anhydrase

RBC enzyme catalyzing CO₂ + H₂O ⇌ H₂CO₃ reaction for bicarbonate formation.

Chloride Shift

Exchange of HCO₃⁻ out of and Cl⁻ into RBCs during CO₂ transport.

Oxygen Reserve

O₂ still bound to hemoglobin (≈75 % saturation) after systemic capillary exchange at rest.

Oxyhemoglobin (HbO₂)

Hemoglobin bound to oxygen.

Carbaminohemoglobin

Hemoglobin bound to carbon dioxide on globin chains.

Surface Tension (Alveolar)

Attraction of water molecules lining alveoli; countered by surfactant.

Lung Compliance

Ease with which lungs and chest wall expand; influenced by elasticity and surface tension.

Airway Resistance

Friction encountered by air in passages; affected by airway diameter and mucus.

Respiratory Center

Brainstem nuclei (medulla + pons) that generate and regulate rhythmic breathing.

Ventral Respiratory Group (VRG)

Medullary neurons that set basic rhythm and drive inspiratory muscles.

Dorsal Respiratory Group (DRG)

Medullary center that integrates sensory input and communicates with VRG.

Pontine Respiratory Center

Pons nuclei that smooth transitions between inspiration and expiration.

Chemoreceptors

Specialized sensors detecting CO₂, H⁺, and O₂ levels to adjust ventilation.

Central Chemoreceptors

Medullary receptors responsive to CSF pH (reflecting blood CO₂).

Peripheral Chemoreceptors

Carotid and aortic bodies sensing blood PO₂, PCO₂, and pH.

Pulmonary Circulation

Low-pressure, high-volume circuit delivering deoxygenated blood from heart to lungs and back oxygenated.

Bronchial Circulation

Systemic vessels supplying oxygenated blood to lung tissue (except alveoli).

Bronchopulmonary Segments

Structurally and functionally independent lung regions each served by a segmental bronchus and artery.

Respiratory Distress Syndrome (RDS)

Alveolar collapse due to insufficient surfactant, common in premature infants.