Functional Anatomy of Respiratory System

Functional Anatomy of Respiratory System

Functional Anatomy of Respiratory System

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Upper & Major Airways - The Windpipe Wonders

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Lungs & Pleura - The Breathing Bags

  • Lungs: Spongy organs in thoracic cavity.
    • Right Lung: 3 lobes (Superior, Middle, Inferior); Oblique & Horizontal fissures. 10 bronchopulmonary segments (BPS).
    • Left Lung: 2 lobes (Superior, Inferior); Oblique fissure. Cardiac notch, Lingula. 8-10 BPS.
    • Hilum: Structures enter/exit. 📌 RALS (Pulmonary Artery: Right Anterior, Left Superior to bronchus).
  • Pleura: Double-layered serous membrane.
    • Visceral: Covers lungs.
    • Parietal: Lines thoracic cavity.
    • Pleural Cavity: Potential space; serous fluid.
    • Recesses: e.g., Costodiaphragmatic (lowest point). Bronchopulmonary segments of lungs, medial view and Pleura (layers, recesses))

⭐ The right main bronchus is wider, shorter, and more vertical than the left, a common site for foreign body aspiration.

Mechanics of Breathing - The Pump & Push

  • Pump: Thoracic cage & respiratory muscles. Push: Pressure gradients.
  • Inspiration (Active):
    • Muscles: Diaphragm (main, ~75%), External Intercostals. 📌 DIE (Diaphragm, External Intercostals).
    • Accessory (forced): Scalenes, Sternocleidomastoid (SCM).
    • Thoracic volume ↑ → Intrapleural pressure (IPP) ↓ (more negative, -4 to -8 cm H₂O) → Lung volume ↑ → Alveolar pressure (Palv) ↓ (-1 cm H₂O) → Air IN.
  • Expiration (Passive at Rest):
    • Elastic recoil of lungs & chest wall.
    • Thoracic volume ↓ → IPP ↑ (less negative) → Lung volume ↓ → Palv ↑ (+1 cm H₂O) → Air OUT.
  • Forced Expiration (Active):
    • Muscles: Internal Intercostals, Abdominals.
  • Key Pressures & Law:
    • Transpulmonary Pressure (Ptp) = Palv - IPP (keeps alveoli open).
    • Boyle's Law: $P \propto 1/V$.

⭐ Intrapleural pressure is always subatmospheric (negative) during normal quiet breathing.

Respiratory muscles and thoracic cage movement

Alveolar Zone - The Oxygen Exchange

Alveoli and respiratory membrane

  • Primary site of gas exchange ($O_2$ $\leftrightarrow$ $CO_2$) in the lungs.
  • Comprises: Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.
  • Alveoli: Functional units; approx. 300-500 million; provide vast surface area (~70-100 m²) for diffusion.
  • Key Cell Types:
    • Type I Pneumocytes: Squamous epithelial cells (95%); form the thin alveolar wall; primary sites for gas exchange.
    • Type II Pneumocytes (Septal Cells): Cuboidal cells (5%); secrete surfactant; can differentiate into Type I cells.
    • Alveolar Macrophages (Dust Cells): Phagocytose debris and pathogens.
  • Respiratory Membrane (Blood-Air Barrier): Extremely thin (~0.2-0.6 µm).
    • Alveolar epithelium (Type I cell)
    • Fused basal laminae of alveolar epithelium and capillary endothelium
    • Capillary endothelium
  • Surfactant: Lipoprotein complex (mainly dipalmitoylphosphatidylcholine - DPPC); reduces alveolar surface tension, prevents collapse (atelectasis), increases compliance. 📌 Mnemonic: Surfactant Stops Small alveoli from Shutting.

⭐ Surfactant synthesis begins around 24-28 weeks of gestation; deficiency leads to Neonatal Respiratory Distress Syndrome (NRDS), especially in premature infants. Type II pneumocytes are also the main progenitor cells after lung injury.

High‑Yield Points - ⚡ Biggest Takeaways

  • Type II pneumocytes produce surfactant, preventing alveolar collapse and reducing surface tension.
  • The right main bronchus is wider, shorter, and more vertical, a common site for foreign body aspiration.
  • Diaphragm is the primary inspiration muscle, innervated by the phrenic nerve (C3-C5).
  • Anatomical dead space in conducting airways is approximately 150 mL.
  • Pulmonary arteries carry deoxygenated blood; pulmonary veins carry oxygenated blood.
  • Cartilage supports bronchi; bronchioles lack cartilage, depending on smooth muscle tone.
  • Right lung: 3 lobes, 2 fissures; Left lung: 2 lobes, 1 fissure, plus cardiac notch & lingula.

Practice Questions: Functional Anatomy of Respiratory System

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In a preterm baby with respiratory distress syndrome, which of the following lipids would be deficient?

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Flashcards: Functional Anatomy of Respiratory System

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All muscles of the larynx are _____, except posterior cricoarytenoids

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All muscles of the larynx are _____, except posterior cricoarytenoids

adductors

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