Respiratory System Notes (Marieb ch. 22)

Functions and Processes of the Respiratory System

• Major functions include:
  • Pulmonary ventilation (breathing) – the movement of air into and out of the lungs.
  • External respiration – O₂ moves from alveoli to pulmonary capillary blood; CO₂ moves from blood to alveoli.
  • Transport of gases in the bloodstream – O₂ and CO₂ are carried to/from tissues.
  • Internal respiration – O₂ moves from systemic capillary blood to tissues; CO₂ moves from tissues to blood.
  • Cellular respiration – mitochondrial production of ATP using O₂ and producing CO₂ as a waste product.
• Additional functions cited in the slides:
  • Sound production (speech).
  • Olfactory assistance (sense of smell).
  • Protection from dust and microbes via mucus production, cilia, and coughing (defense mechanisms).
  • Maintaining acid–base balance.
  • Manufacturing substances (e.g., enzymes that participate in the RAAS system).
• Key terminology: respiration, ventilation, external respiration, internal respiration, transport of gases, cellular respiration.

Functional Anatomy: The Respiratory System at a Glance

• Major components: nose and paranasal sinuses, pharynx, larynx, trachea, bronchial tree, lungs, pleural membranes.
• Organs are organized into two functional zones:
  • Conducting zone: nasal cavity, pharynx, larynx, trachea, bronchi, and larger bronchioles – conducts, cleans, warms, and humidifies air; contains the anatomical structures involved in sound production.
  • Respiratory zone: terminal bronchioles, alveolar ducts, and alveoli – site of actual gas exchange.
• Upper vs lower respiratory tract distinction: upper includes nose, nasal cavity, paranasal sinuses, pharynx; lower includes larynx (portion involved in airflow), trachea, bronchi, and lungs.
• Alveoli and respiratory components: alveoli with respiratory membrane and surfactant; gas exchange occurs here.
• Surface protection and exchange surfaces: protective mucus, cilia, immune cells (alveolar macrophages), and a large surface area for diffusion.
• RAAS connection: lungs manufacture enzymes (e.g., ACE) that participate in the renin–angiotensin–aldosterone system.

Conducting Zone vs Respiratory Zone

• Conducting zone:
  • Nasal cavity, pharynx, larynx, trachea, bronchi, and larger bronchioles.
  • Function: air passage, cleansing, warming, and humidifying air; voice production.
• Respiratory zone:
  • Terminal bronchioles and alveoli (alveolar ducts and alveolar sacs).
  • Function: site of gas exchange (O₂ diffusion into blood and CO₂ diffusion into alveolar air).

Pathway of Air: From Nose to Lungs

• Sequence: External nose → nasal cavity → nasopharynx → oropharynx → laryngopharynx → larynx → trachea → primary bronchi → secondary (lobar) bronchi → tertiary (segmental) bronchi → bronchioles → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveoli.
• Protective mechanisms along the pathway:
  • Mucus production and ciliary action (mucociliary escalator) trap and remove dust and microbes.
  • Nasal filtration, warming, and humidification of inspired air.
• Sound production:
  • Larynx houses vocal cords; air passes through the glottis causing vocal cords to vibrate and produce sound.
• Practical implications:
  • Pathways and structures are arranged to maximize filtration, adjust air temperature/moisture, and enable phonation.

Nose and Nasal Cavity

• External nose features (as identified in the slides):
  • Root and bridge, Dorsum nasi, Ala of nose, Apex, Philtrum, External naris (nostril).
• Nasal cavity structures:
  • Vestibule, nasal mucosa with respiratory mucosa (ciliated pseudostratified columnar epithelium) for cleaning/moistening/warming air; olfactory mucosa at the roof for smell.
  • Superior, middle, and inferior conchae (turbinates) that increase surface area and aid in air conditioning.
• Functions of the nasal cavity and sinuses:
  • Provides an air passageway; inspired air is filtered, warmed, and moistened.
  • Speech resonance and sense of smell (olfactory receptors).
• Cleft palate (mentioned) and anatomy related to the palate:
  • Soft palate and hard palate separation influencing airflow and swallowing.

Nasal Cavity Epithelium and Mucosa

• Mucosal types:
  • Respiratory mucosa – ciliated pseudostratified columnar epithelium for cleaning, moistening, and warming air.
  • Olfactory mucosa – chemoreceptors for smell located in the roof of the nasal cavity.
• Contributing educational resources and figures referenced in slides for histology of nasal epithelium.

Functions of Nasal Cavity & Sinuses (Overview)

• Air passage and conditioning:
  • Filtered, warmed, and moistened by the mucosa.
• Speech and smell:
  • Nasal cavities contribute to voice resonance; olfactory receptors provide sense of smell.
• Questions to consider:
  • What causes sinus headaches? What is sinusitis? (Prompts for clinical correlation.)

The Larynx (Voice Box)

• Structural overview:
  • Hyaline cartilage framework anchored to the hyoid bone.
  • Thyroid cartilage (Adam’s apple).
  • Epiglottis – elastic cartilage that closes the laryngeal inlet (glottis) during swallowing to prevent aspiration.
• Vocal apparatus:
  • Vocal cords (ligaments) form true vocal cords; glottis is the opening between cords; air rushing from lungs causes cords to vibrate and produce sound.
• Primary functions:
  • Provide a patent air passageway, divert food toward the esophagus, and enable sound production.

Trachea and Bronchial Tree

• Trachea (windpipe):
  • Flexible, mobile tube extending from the larynx into the mediastinum.
  • Histology (three layers):
  • Mucosa – pseudostratified ciliated columnar epithelium with goblet cells; forms mucociliary escalator to trap and move debris toward pharynx.
  • Submucosa – connective tissue with mucous and serous glands.
  • Adventitia – C-shaped rings of hyaline cartilage and connective tissue.
• Carina:
  • The internal ridge at the end of the trachea where it splits into right and left primary bronchi.
• Bronchial tree organization:
  • Primary (main) bronchi branch into secondary (lobar) bronchi, each supplying a lung lobe.
  • Airways undergo 23 orders of branching from trachea to alveolar sacs.
  • Bronchial walls resemble the trachea but with progressively less cartilage and more smooth muscle as you go to smaller airways.
• Transition to smaller airways:
  • Bronchioles (loss of cartilage, more smooth muscle).
  • Terminal bronchioles lead to respiratory bronchioles and alveolar ducts.
• Key structural changes:
  • Bronchioles have more smooth muscle, no mucus-secreting cells, and no cartilage.
  • Epithelium changes from columnar to cuboidal in smaller airways.

Structures of the Respiratory Zone

• Respiratory bronchioles – alveolar ducts – alveoli open in alveolar ducts.
• Alveolar structures:
  • Alveolar sacs composed of alveoli (~300 million in the lungs).
  • Type I pneumocytes – primary sites of gas exchange (squamous epithelium).
  • Type II pneumocytes – produce surfactant to reduce surface tension and prevent collapse; can differentiate into Type I cells.
  • Alveolar macrophages – immune defense.
• Respiratory membrane (air–blood barrier):
  • Composed of alveolar epithelium, capillary endothelium, and fused basal laminae.
• Surfactant role:
  • Reduces surface tension in alveoli to prevent collapse during expiration and stabilize alveolar volume.

The Lungs, Pleura, and Pleural Space

• Lung anatomy:
  • Apex, costal surface, diaphragmatic surface, and hilus where vessels, nerves, and bronchi enter/leave.
  • Vital structures entering/leaving at the hilus include pulmonary arteries/veins, primary bronchi, bronchial arteries, pulmonary nerve plexuses, and lymphatics.
• Pleural membranes:
  • Parietal pleura lines the thoracic cavity.
  • Visceral pleura covers the lungs.
  • Pleural cavity contains pleural fluid; negative intrapleural pressure keeps the lungs expanded.
• Pleural pressure dynamics:
  • Intrapleural pressure is negative relative to intra-alveolar pressure, ensuring lung inflation.
• Lung perfusion:
  • Two circulations:
  • Pulmonary circulation – carries deoxygenated blood from the heart to the lungs and returns oxygenated blood to the left atrium via pulmonary veins.
  • Bronchial (systemic) circulation – supplies oxygenated blood to airways and lung tissue; drains to the right atrium via the azygos vein and SVC.
• Additional regional features:
  • Visceral pleura and parietal pleura create the pleural fluid interface critical for lung expansion mechanics.

Alveoli and Gas Exchange Details

• Alveolar surface features:
  • Approximately 300 million alveoli provide a massive surface area for diffusion.
  • Alveolar ducts terminate in alveolar sacs lined by alveoli.
• Alveolar cell types and roles:
  • Type I cells – thin squamous cells specialized for gas exchange.
  • Type II cells – synthesize and secrete surfactant; serve as a progenitor for Type I cells.
  • Alveolar macrophages – immune defense against inhaled pathogens.
• Respiratory membrane components:
  • Alveolar epithelium + capillary endothelium + fused basal laminas – forms the air–blood barrier for gas exchange.
• Surfactant function (revisited):
  • Reduces surface tension to prevent alveolar collapse at end-expiration; essential for keeping alveoli open and ensuring efficient gas exchange.

Gas Exchange, Transport, and Cellular Respiration

• External respiration:
  • Oxygen moves from alveolar air into blood; carbon dioxide moves from blood into alveolar air.
• Internal respiration:
  • Oxygen moves from systemic capillary blood into tissues; carbon dioxide moves from tissues into blood.
• Transport of gases in the blood:
  • Oxygen is carried bound to hemoglobin and dissolved in plasma; carbon dioxide is carried dissolved, as bicarbonate, or bound to hemoglobin.
• Cellular respiration:
  • Occurs in mitochondria of cells to produce ATP, consuming O₂ and producing CO₂ as a waste product.

Lung Volumes and Capacities (Clinical Relevance)

• Key volumes:
  • Tidal volume (TV) – volume of air per normal breath.
  • Inspiratory reserve volume (IRV) – additional air that can be inspired beyond a restful inspiration.
  • Expiratory reserve volume (ERV) – additional air that can be expired beyond a restful expiration.
  • Residual volume (RV) – air remaining in lungs after maximal expiration; keeps alveoli inflated.
• Example values shown in the slides:
  • TV ≈ 500 ml
  • IRV ≈ 3100 ml
  • ERV ≈ 1200 ml
  • RV ≈ 1200 ml
  • Vital capacity (VC) ≈ 4800 ml
  • Total lung capacity (TLC) ≈ 6000 ml
• Important formula:
  • $VC = IRV + TV + ERV$
• Clinical significance of VC and lung function tests:
  • Measuring VC provides a diagnostic benchmark for respiratory disorders and treatment effectiveness.
  • VC is reduced in restrictive disorders; not necessarily reduced in purely obstructive disorders.
• Forced expiratory volume (FEV1):
  • Definition: the volume of air expelled in the first second of a forced expiration.
  • Normal reference: $FEV<em>1\% = \frac{FEV</em>1}{VC} \times 100\% \ge 75\%.$
  • Reduced in obstructive disorders.

Notable Conditions and Concepts (from the slides)

• Rhinitis, sinusitis, laryngitis, pleurisy – conditions mentioned as part of the respiratory system’s related disorders.
  -Sinus headaches and sinusitis are referenced as examples of clinical questions related to nasal cavities and sinuses.

Additional Connections and Practical Implications

• Sound production and voice quality depend on laryngeal function and vocal cord tension.
• The nose’s conditioning of air (warming, humidifying, filtering) is essential for protecting lower airways and optimizing gas exchange.
• The respiratory membrane and surfactant are critical for efficient oxygen diffusion and keeping alveoli open; disruptions can lead to impaired gas exchange or respiratory failure.
• The dual blood supply to the lungs (pulmonary and bronchial circulations) reflects both gas exchange needs and metabolic support for lung tissue.
• Negative intrapleural pressure and pleural fluid dynamics are key to lung inflation mechanics during breathing.

Forms of Respiration Summary (Cross-Sectional)

• Four stages of respiration:
  • Pulmonary ventilation (breathing)
  • External respiration
  • Transport of gases
  • Internal respiration
• Cellular respiration occurs in mitochondria within tissues.
• Anatomic organization supports both air conditioning and gas exchange: conducting zone cleans/warms air; respiratory zone maximizes surface area for diffusion.