PI

Chapter 13: The Respiratory System

13.1 Functional Anatomy of the Respiratory System

  • Learning objectives:
    • Name the organs forming the respiratory passageway from the nasal cavity to the alveoli of the lungs, and describe the function of each.
    • Describe several protective mechanisms of the respiratory system.
  • The respiratory system functions:
    • Provides oxygen to body tissues.
    • Disposes of carbon dioxide.
    • Helps regulate blood pH.
  • Why this matters:
    • Without oxygen, cells die; excess CO₂ makes blood acidic and interferes with cellular function.
    • Cells continuously use O₂ and produce CO₂, creating a need for ongoing gas exchange.
  • Relationship with the cardiovascular system:
    • Cardiovascular and respiratory systems share responsibility for supplying oxygen and disposing of CO₂.
    • Respiratory system organs oversee gas exchange between blood and external environment.
    • Blood transports respiratory gases between lungs and tissues.
  • Gas exchange targets:
    • Occurs in alveoli (air sacs) and at capillary beds around the body.
  • Key concepts:
    • Gas exchange relies on diffusion across membranes.
    • If either system fails, cells experience oxygen starvation and CO₂ accumulation.
  • 13.1a The Nose
    • Air enters through nostrils (nares) into the nasal cavity.
    • Nasal cavity is divided by the nasal septum.
    • Olfactory receptors are located in the superior part of the nasal cavity, beneath the ethmoid bone.
    • The mucosa lining the nasal cavity includes:
    • Olfactory mucosa (smell).
    • Respiratory mucosa (warms, humidifies, and moistens air) with a rich venous network.
    • Functions of nasal mucosa:
    • Warms air via venous plexuses.
    • Moistens air with mucus; mucus traps bacteria and debris.
    • Lysozyme and other enzymes chemically destroy bacteria.
    • Ciliated cells move mucus posteriorly toward the pharynx (mucociliary clearance).
    • Cilia sluggishness in very cold air explains runny noses in winter.
    • Nasal conchae (superior, middle, inferior) increase mucosal surface area, and turbulence helps trap particles.
    • The nasal cavity is separated from the oral cavity by the palate:
    • Hard palate (bone) anteriorly; soft palate posteriorly.
    • Paranasal sinuses surround the nasal cavity (frontal, sphenoid, ethmoid, maxillary);
    • Lighten the skull, act as resonance chambers for speech, and produce mucus.
    • Mucus drains into nasal cavities; nasolacrimal ducts drain tears into the nasal cavity.
    • Clinical notes:
    • Rhinitis is inflammation of nasal mucosa from viruses/allergens; excess mucus causes congestion and postnasal drip.
    • Sinusitis is sinus inflammation; blocked sinus ostia lead to air absorption and pressure -> sinus headaches.
    • Cleft palate (failure of facial bones to fuse) leads to breathing and oral function difficulties; in normal development, the palate separates nasal and oral cavities.
  • 13.1b The Pharynx
    • The pharynx is a muscular passageway (~13 cm long) that serves as a common passage for air and food.
    • Regions (from nasal to laryngeal):
    • Nasopharynx (air passage behind nasal cavity).
    • Oropharynx (air and food; behind the mouth).
    • Laryngopharynx (food directed to esophagus posteriorly by the epiglottis).
    • The pharyngotympanic (Eustachian) tubes open into the nasopharynx, linking the middle ears.
    • Lymphatic tissue clusters (tonsils) are located in the pharynx: adenoids (pharyngeal tonsil) in nasopharynx; palatine tonsils in oropharynx; lingual tonsil at the base of the tongue; tubal tonsils near pharyngotympanic tube openings.
    • Tonsils protect against infection; inflammation can obstruct the pharynx (tonsillitis).
  • 13.1c The Larynx
    • The larynx (voice box) routes air and food into proper channels and contributes to speech.
    • Structure: eight rigid hyaline cartilages and the elastic cartilage epiglottis.
    • Thyroid cartilage is the largest (Adam’s apple).
    • The epiglottis protects the superior opening of the larynx during swallowing by acting as a lid; air passage is unimpeded during normal breathing.
    • Vocal folds (true vocal cords) form the glottis; vibration of the folds enables speech.
    • If non-air substances enter the larynx, a cough reflex is triggered to protect the lungs.
  • 13.1d The Trachea
    • The trachea (windpipe) conducts air to the lungs (approximately 10–12 cm or ~4 inches).
    • Walls reinforced with C-shaped rings of hyaline cartilage; the open parts face posteriorly toward the esophagus.
    • The trachealis muscle completes the posterior wall.
    • The trachea is lined with ciliated mucosa containing goblet cells that secrete mucus.
    • Cilia beat upward toward the pharynx to propel mucus and debris out of the lungs; mucus can trap irritants.
    • Smoking damages cilia, reducing mucus clearance and increasing infection risk; the cough reflex is a key protective mechanism.
    • Clinical notes:
    • Heimlich maneuver can expel an obstructing object by using air from the lungs to pop it out.
    • In severe obstruction, an emergency tracheostomy may be performed.
  • 13.1e The Main Bronchi
    • The trachea divides into right and left main (primary) bronchi.
    • Right main bronchus is wider, shorter, and more vertical than the left, making it a common site for inhaled objects to lodge.
    • Inside the lungs, bronchi subdivide into secondary and tertiary bronchi and beyond, delivering air to the air sacs.
  • 13.1f The Lungs
    • The lungs occupy most of the thoracic cavity except the mediastinum, which houses the heart, great vessels, bronchi, esophagus, and other organs.
    • Pleural membranes and cavity:
    • Visceral pleura covers each lung; parietal pleura lines the thoracic wall.
    • Pleural fluid in the pleural cavity provides lubrication and surface tension that keeps lungs adhered to the thoracic wall.
    • The pleural space is a potential space; pleurae resist being pulled apart, enabling normal breathing.
    • Lung anatomy:
    • The lungs contain lobes: left lung has two lobes; right lung has three lobes.
    • The root of the lung is at the hilum (entry/exit point for vessels and airways).
    • Additional lung features:
    • Apex near the clavicle; base rests on the diaphragm.
    • Pleurae and pleural fluid enable the lungs to glide with chest wall movements during breathing.
  • 13.1g (Summary of conducting vs respiratory zones)
    • Conducting airways purify, humidify, and warm air; gas exchange occurs primarily in the alveoli of the respiratory zone.
    • Alveoli are the site of external respiration and gas exchange with pulmonary capillaries.

13.2 Respiratory Physiology

  • Overview:
    • The major function is to supply the body with O₂ and dispose of CO₂.
    • Gas exchange involves four processes: pulmonary ventilation, external respiration, gas transport, and internal respiration.
    • Gas exchanges follow diffusion principles (move from high to low concentration).
  • 13.2a Mechanics of Breathing
    • Fundamental rule: Volume changes lead to pressure changes, which drive gas flow to equalize pressure.
    • Inspiration (inhalation):
    • Inspiratory muscles (diaphragm and external intercostals) contract; thoracic cavity volume increases.
    • The diaphragm moves inferiorly (flattens); rib cage expands (increases AP and lateral dimensions).
    • Lungs stretch with the chest wall due to pleural linkage; intrapulmonary (intrapulmonary) volume increases and intrapulmonary pressure drops, creating a partial vacuum that draws air in.
    • Expiration (exhalation):
    • Lungs recoil due to elasticity; rib cage descends; diaphragm relaxes and moves superiorly.
    • Intrapulmonary volume decreases; intrapulmonary pressure rises above atmospheric, causing air to flow out.
    • In quiet breathing, expiration is largely passive; active expiration uses internal intercostal and abdominal muscles during forceful breathing or bronchiole constriction (asthma, disease).
    • Intrapleural pressure:
    • Always negative relative to intrapulmonary pressure; keeps lungs from collapsing.
    • If intrapleural pressure equals atmospheric pressure (pneumothorax), lungs collapse (atelectasis).
    • Hyperpnea: increased rate and depth of breathing during exercise.
    • Figures referenced: rib cage and diaphragm movements (Figure 13.7) and intrapulmonary pressure changes (Figure 13.8).
  • 13.2b Respiratory Volumes and Capacities
    • Define and note typical values (adult, average):
    • Tidal Volume (TV) = 500 ext{ mL}
    • Inspiratory Reserve Volume (IRV) = 3100 ext{ mL}
    • Expiratory Reserve Volume (ERV) = 1200 ext{ mL}
    • Residual Volume (RV) = 1200 ext{ mL}
    • Vital Capacity (VC) = TV + IRV + ERV = 4800 ext{ mL}
    • Total Lung Capacity (TLC) = VC + RV = 6000 ext{ mL}
    • Dead Space Volume (anatomical dead space) ≈ 150 ext{ mL} per breath.
    • Alveolar ventilation per breath (functional volume contributing to gas exchange): ≈ 350 ext{ mL} per breath.
    • Alveolar ventilation rate depends on respiratory rate (RR):
    • Alveolar ventilation per minute ≈ (TV − Dead Space) × RR.
  • 13.2c External Respiration, Gas Transport, and Internal Respiration
    • External respiration (pulmonary gas exchange):
    • Occurs at the respiratory membrane: alveolar epithelium, fused basement membranes, and capillary endothelium.
    • Oxygen (O₂) diffuses from alveolar air into blood; carbon dioxide (CO₂) diffuses from blood into alveoli.
    • Structure of the respiratory membrane:
    • Squamous (Type I) alveolar cells; alveolar epithelium.
    • Endothelial cells of capillaries; fused basement membranes.
    • Alveolar pores connect neighboring alveoli for alternate routes if a feeder bronchiole is blocked.
    • Surfactant-secreting cuboidal cells line alveolar surfaces to reduce surface tension and keep alveoli from collapsing.
    • Gas transport in the blood:
    • Oxygen transport: mainly bound to hemoglobin as oxyhemoglobin (HbO₂); a small amount is dissolved in plasma. Represented as: ext{Hb} + ext{O}2 ightleftharpoons ext{HbO}2
    • Carbon dioxide transport: mostly transported as bicarbonate (HCO₃⁻) in plasma; some bound to hemoglobin; a portion remains dissolved in plasma.
    • Conversion inside RBCs: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ with the enzyme carbonic anhydrase catalyzing the reaction.
    • The bicarbonate diffuses into plasma; hydrogen ions contribute to pH buffering in blood (pH 7.35–7.45 is normal).
    • Central idea of gas exchange:
    • External respiration exchanges gases between alveolar air and pulmonary blood; internal respiration exchanges gases between systemic blood and tissue cells.
    • Carbon monoxide (CO) risks:
    • CO binds Hb more readily than O₂, forming COHb and reducing O₂ delivery; CO poisoning is a dangerous cause of hypoxia.
  • 13.2d Control of Respiration
    • Neural regulation (rhythm and depth):
    • Medulla oblongata contains the VRG (ventral respiratory group) and DRG (dorsal respiratory group).
      • VRG: inspiratory and expiratory neurons; sets quiet breathing rate (eupnea) at ~12–15 ext{ respirations/min}.
      • DRG: integrates chemoreceptor and stretch receptor info and modulates VRG output.
    • Pons centers modulate timing and smooth transitions between inhalation and exhalation (e.g., during singing, sleeping, or exercise).
    • Protective reflexes: stretch receptors in bronchioles and alveoli trigger reflexes to prevent overinflation via vagal pathways.
    • Volition and reflexes: cortex can influence breathing (e.g., singing, breath-holding) but reflexive control dominates; if CO₂ or pH signals demand, voluntary control yields to automatic regulation.
    • Non-neural factors:
    • Talking, coughing, exercising can modify rate and depth.
    • Temperature, emotional factors, and body temperature affect breathing rate.
    • Chemoreceptors as primary chemical regulators:
    • Central chemoreceptors in brain respond to CO₂ and pH (brain interstitial fluid pH).
    • Peripheral chemoreceptors (aortic body, carotid body) respond to O₂ and CO₂ levels; low O₂ or high CO₂ stimulates breathing.
    • Important concepts:
    • Primary stimulus to breathe in healthy individuals is CO₂/pH; low O₂ becomes a major stimulus only when hypoxemia is severe or chronic lung disease is present (e.g., emphysema).
    • Hyperventilation and apnea:
    • Hyperventilation increases rate/depth of breathing and can cause alkalosis (low CO₂). Apnea can occur if breathing stops; hyperventilation followed by apnea can occur in anxiety or stress.
  • 13.3 Respiratory Disorders
    • COPD (Chronic Obstructive Pulmonary Disease): predominantly includes chronic bronchitis and emphysema; smoking is a major risk factor.
    • Chronic bronchitis: mucosa of lower respiratory passages inflamed with excessive mucus production; ventilation and gas exchange impaired; risk of infections.
    • Emphysema: destruction of alveolar walls, loss of lung elasticity, airway collapse during expiration; difficulty with exhalation; barrel-shaped chest and pink puffer phenotype.
    • Common features: history of smoking; dyspnea, coughing, frequent infections; hypoxia, CO₂ retention, and respiratory acidosis; many COPD patients eventually progress to respiratory failure.
    • Lung cancer:
    • Leading cancer killer; strongly linked to smoking; aggressive and rapidly metastasizes; low 5-year survival once metastasis has occurred.
    • Three major types:
      • Adenocarcinoma (~40%): solitary peripheral nodules; arises from bronchial glands and alveolar cells.
      • Squamous cell carcinoma (~25–30%): arises in epithelium of larger bronchi; tends to form masses that bleed.
      • Small cell carcinoma (~20%): lymphocyte-like cells in main bronchi; grows aggressively in mediastinum.
    • Cystic fibrosis (CF): defective CFTR gene; thick mucus production; affects other secretory processes and pancreas; reversible with therapies; inhaled hypertonic saline can thin mucus.
    • Infant respiratory disorders: IRDS (infant respiratory distress syndrome) due to insufficient surfactant in preterm infants; treated with positive-pressure ventilation to keep alveoli open.
    • SIDS (crib death): sudden infant death syndrome; risk factors and prevention via safe sleep practices (Back to Sleep).
    • Other conditions mentioned: rhinitis, tonsillitis, pleurisy, pneumothorax, atelectasis (lung collapse).
  • 13.4 Developmental Aspects of the Respiratory System
    • Fetal life: lungs are fluid-filled; placental gas exchange occurs before birth.
    • At birth: fluid drains; alveoli inflate and begin gas exchange; surfactant is critical to prevent alveolar collapse; adequate surfactant typically develops by 28–30 weeks gestation.
    • IRDS risk: premature infants, particularly before week 28 or born to diabetic mothers, may lack sufficient surfactant and develop IRDS; modern support helps alveolar stabilization.
    • Birth defects and genetic conditions:
    • Cleft palate and CF are highlighted as important developmental concerns.
    • Postnatal development and aging:
    • Newborns have high respiratory rates (~40–80 breaths/min); rates drop with age; lungs mature with more alveoli into young adulthood.
    • Smoking in adolescence can impair complete maturation of lungs.

13.2, 13.3, 13.4 (Key Formulas, Terms, and Concepts)

  • Gas exchange and diffusion principles:

    • Gas exchange follows diffusion down partial pressure gradients across the respiratory membrane.
    • Oxygen diffusion from alveoli to blood:
    • Carbon dioxide diffusion from blood to alveoli:

  • Gas transport equations and processes:

    • Oxygen binding to hemoglobin:
    • ext{Hb} + ext{O}2 ightleftharpoons ext{HbO}2
    • Carbon dioxide transport in blood:
    • CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ (catalyzed by carbonic anhydrase in red blood cells).
    • Majority of CO₂ is transported as bicarbonate (HCO₃⁻) in plasma after conversion.

  • Gas exchange products and barriers:

    • Respiratory membrane comprises:
    • Alveolar epithelium (Type I cells), alveolar macrophages, surfactant-secreting Type II cells; endothelial cells of pulmonary capillaries; fused basement membranes.
    • Surface area of gas exchange in a healthy adult is extremely large (estimate: on the order of 50–70 m²).

  • Lung volumes and capacities (example values):

    • TV = 500 ext{ mL}
    • IRV = 3100 ext{ mL}
    • ERV = 1200 ext{ mL}
    • RV = 1200 ext{ mL}
    • VC = TV + IRV + ERV = 4800 ext{ mL}
    • TLC = VC + RV = 6000 ext{ mL}
    • Dead space = 150 ext{ mL}
    • Alveolar ventilation per breath ≈ 350 ext{ mL}

  • 13.3, 13.4 Conceptual connections

    • Gas exchange depends on differences in partial pressures (O₂ and CO₂) between alveolar air and blood.
    • The bicarbonate buffering system helps maintain blood pH within a narrow range (7.35–7.45).
    • Surfactant reduces alveolar surface tension; without it, alveoli collapse, particularly in IRDS.
    • Smoking impairs mucociliary clearance and alveolar macrophages, increasing infection risk and contributing to COPD and lung cancer.
    • The hygiene hypothesis (closer look) links reduced antigen exposure in developed societies to higher allergy and autoimmune risks; regulatory T cells require antigen exposure during development to become tolerant.

  • Practical and ethical implications:

    • Smoking cessation is a major public health goal due to COPD and lung cancer risks.
    • Public health measures impacting air quality and pollen exposure can influence respiratory disease prevalence.
    • Early screening and treatment for COPD, lung infections, and CF are critical for quality of life and survival.
    • Understanding surfactant biology informs neonatal care and IRDS management.

  • Did You Get It? sample study prompts (from the transcript):

    • What is the most basic function of respiration? (External respiration’s gas exchange in lungs; overall oxygen delivery and CO₂ removal.)
    • Why is nose breathing preferable to mouth breathing? (Air is filtered, warmed, and humidified before reaching lungs.)
    • What protects the trachea from collapse and keeps airways open? (C-shaped hyaline cartilage rings and the trachealis muscle.)
    • Which main bronchus is more likely to lodge an inhaled object, and why? (Right main bronchus; wider, shorter, and more vertical.)

  • Connections to prior lectures and real-world relevance:

    • Roots in foundational principles of diffusion, gas exchange, and respiratory membrane structure.
    • The respiratory system as an integrated unit with the cardiovascular system for gas transport and pH regulation.
    • Real-world relevance includes understanding disorders like COPD, emphysema, chronic bronchitis, lung cancer, CF, and IRDS; emphasizes lifestyle choices (smoking) and public health strategies.

  • Key terms to memorize (quick list):

    • Alveoli, alveolar ducts, alveolar sacs, alveolar pores, surfactant, macrophages (dust cells), pleura (visceral and parietal), pleural fluid, pleural cavity, bronchial tree, mucociliary escalator, glottis, vocal cords, epiglottis, conducting zone, respiratory zone, tidal volume, vital capacity, residual volume, dead space, eupnea, hyperpnea, hypoventilation, hyperventilation, atelectasis, pneumothorax, COPD, emphysema, chronic bronchitis, adenocarcinoma, squamous cell carcinoma, small cell carcinoma, CF, IRDS, SIDS.

Title

Chapter 13 Notes: The Respiratory System — Comprehensive Overview and Study-Ready Details