Video 7: Inside the Lungs — Vocabulary Flashcards

Cranial Nerves in Pharyngeal Innervation

• Thoughts on class question: Do CN IX (glossopharyngeal) and CN X (vagus) work together in innervation of the pharynx?
  • Yes. Both CN IX and CN X innervate the pharynx, the posterior one-third of the tongue, and participate in the gag reflex.
  • Each nerve also has specific functions that it innervates independently of the other.

Lungs: Gross Anatomy Overview

• Lungs are the critical organs of the respiratory system.
• Right lung anatomy:
  • 3 lobes: superior, middle, inferior.
• Left lung anatomy:
  • 2 lobes: superior, inferior.
• Trachea serves as a central airway leading to the bronchial tree.
• Mainstem (primary) bronchi: one for each lung.
• Lobar (secondary) bronchi: subdivide the mainstem bronchi.
• Terminal divisions toward gas exchange:
  • Lobar bronchi feed each lobe.
  • Tertiary (segmental) bronchi: feed bronchopulmonary segments.
• Alveolar gas exchange structures:
  • Terminal bronchioles lead to respiratory bronchioles, which feed alveolar ducts and sacs up to alveoli.
• Alveoli:
  • More than $3.0 \times 10^8$ alveoli filled with air.
  • Site of gas exchange; surface area maximized for contact with blood.

Bronchial Tree: Structure and Divisions

• Trachea and bronchial tree provide the conduit from external air to alveoli.
• Trachea:
  • Cartilaginous with $16-20$ rings.
  • Rings are open posteriorly and connected by smooth muscle.
  • Can stretch and flex.
  • Anterior to the esophagus.
• Carina: the division point at the distal trachea where separation into mainstem bronchi occurs.
• Mainstem (primary) bronchi:
  • One per side (right and left).
• Right vs left differences:
  • The right mainstem bronchus more commonly receives aspirated material due to anatomy.
• Secondary (lobar) bronchi:
  • Right: $3$ lobar bronchi; Left: $2$ lobar bronchi.
• Tertiary (segmental) bronchi:
  • Left: $8$ tertiary bronchi; Right: $10$ tertiary bronchi.
• Bronchioles: follow tertiary bronchi; 7 respiratory divisions after tertiary division.
• Terminal bronchiole: last of the respiratory bronchioles; leads to alveolar ducts.
• Alveolar duct branches lead to alveolar sacs; alveolus is the socket-like cavity where gas exchange occurs.

Bronchial Tree: Key Details and Lab Notes

• Specimen dissections show the bronchial tree with progressively finer divisions.
• Bronchiole and terminal bronchiole levels include:
  • Alveolar duct
  • Passageway between alveoli
  • Alveolus surrounds by capillary bed
• Summary of divisions: total of $16$ divisions, with $9$ conductive (air-conducting) and $7$ respiratory (gas exchange-capable) divisions.

Alveoli and Capillary Network

• Alveolar structure:
  • Alveolus = socket/cavity at the end of the airway where gas exchange occurs.
• Population:
  • $3.0 \times 10^8$ alveoli.
• Capillary network:
  • Each alveolus is enveloped by a capillary bed with about $2.0 \times 10^3$ capillaries per alveolus.
  • Total capillaries across the lungs estimated at roughly $6.0 \times 10^{14}$ (600 trillion).
• Surface area:
  • Approximately $750 \ \text{ft}^2$ of lung surface area for gas exchange.

Terminal Adaptations: From Bronchiole to Alveolus

• Terminal bronchiole: end segment of conducting airways before gas exchange zones.
• Alveolar duct: duct through which air reaches alveolar sacs.
• Alveolar sac: cluster of alveoli.
• Alveolus: functional gas-exchange unit (socket/cavity) surrounding by capillaries.

Lungs: Functional Anatomy and Tissue Properties

• Gas exchange site: lungs are the site of gas exchange between the body and the environment.
• Lung lobes and secondary bronchi:
  • Right lung: 3 lobes and 3 secondary bronchi.
  • Left lung: 2 lobes and 2 secondary bronchi.
• Tissue properties:
  • Lungs are spongy, porous, highly elastic, and pink.
  • Lungs contain no skeletal muscle tissue; muscles involved in breathing are outside the organ.
  • The only muscle-related activity inside the lungs relates to bronchial dilation (bronchial smooth muscle).

Landmarks and Surface Anatomy

• Lung apex and base:
  • Apex is the uppermost part;
  • Base sits over the diaphragmatic surface and is concave to fit the diaphragm.
• Diaphragmatic impression: on the lung base where the diaphragm contacts the lung.
• Cardiac impression: indentation on the left lung where the heart sits.

Lobes, Fissures, and Segmentation

• Left lung:
  • Superior and inferior lobes.
  • Oblique fissure separating the two.
• Right lung:
  • Superior, middle, and inferior lobes.
  • Fissures: horizontal fissure (separating superior and middle) and oblique fissure (separating middle and inferior).

In Situ Anatomy and Pleural Relations

• Lungs in their anatomical location with pleural coverings:
  • Pleural membranes form continuous lining around lungs.
  • Costal (parietal) pleura lines inner rib cage.
  • Visceral pleura covers the surface of the lungs.

Mediastinum and Phrenic Nerve Considerations

• Mediastinum: central compartment containing the heart and other structures.
• Phrenic nerve:
  • Provides motor and sensory innervation to the diaphragm.
  • Recall its role in diaphragmatic movement during respiration.

Pleurae: Function and Mechanics

• Pleural linings provide a friction-free interface between the rib cage and lungs.
• Surfactant:
  • A slippery fluid between parietal and visceral pleurae that reduces surface tension.
• Lung-rib cage dynamics:
  • When the rib cage elevates, the lungs expand transversely.
  • When the diaphragm contracts (pulls downward), the lungs expand vertically.
• Postnatal development:
  • At birth, the lung is relatively small compared to the thorax; the thorax grows more than the lung, placing lungs in dynamic suspension within the thoracic cavity.

Respiratory Physiology: Gas Exchange and Motion

• Primary goal: move oxygen into the blood and carbon dioxide out of the blood.
• Four stages of gas exchange:
  • Ventilation: actual movement of air through the respiratory pathway.
  • Distribution: delivery of air to the alveoli.
  • Perfusion: flow of blood to the alveolar capillaries (the blood arriving to become oxygenated).
  • Diffusion: gas exchange across the alveolar-capillary membrane.
• Oxygen diffusion: O2 from alveolar air moves into the blood in nearby capillaries to be distributed to tissues.
• CO2 diffusion: CO2 from blood travels back to the lungs to be exhaled.

Ventilation, Perfusion, Diffusion in Life and Speech Breathing

• Primary function of breathing: O2 delivery to the body and CO2 removal.
• Variations in air movement:
  • Hyperventilation: excessive rate or depth of breathing leading to too little CO2 in the blood.
  • Hypoventilation: insufficient ventilation leading to elevated CO2 in the blood.
• Speech breathing:
  • During running speech, we often experience hyperventilation (relatively lower CO2) compared to resting quiet breathing.

Quick Recap and Exam Preparation Cues

• Remember the directional flow: trachea -> mainstem bronchi -> lobar bronchi -> segmental (tertiary) bronchi -> bronchioles -> terminal bronchioles -> alveolar ducts -> alveoli.
• Key quantitative figures to memorize:
  • Right vs left lobes: $3$ vs $2$.
  • Tracheal rings: $16-20$.
  • Bronchial divisions: $9$ conductive + $7$ respiratory = $16$ total divisions.
  • Alveoli count: $3.0 \times 10^8\,$.
  • Alveolar capillaries per alveolus: $2.0 \times 10^3$.
  • Total capillaries: $6.0 \times 10^{14}$.
  • Surface area: $750\ \text{ft}^2$.
• Clinical correlations:
  • Aspiration risk favors the right mainstem bronchus due to anatomy.
  • Surfactant is crucial for reducing surface tension and keeping alveoli open; lack of surfactant is a life-threatening issue in premature infants.
  • Phrenic nerve function is essential for diaphragmatic-driven ventilation; diaphragmatic movement is central to vertical expansion of the lungs.
• Connections to broader physiology:
  • The four-stage gas exchange model connects anatomy to respiratory physiology and supports speech-language pathology considerations in healthy vs. disordered breathing.

Knowledge Check and Next Steps

• Review the relationships between ventilation, perfusion, and diffusion and how disruptions in any stage affect gas exchange.
• Watch Video 8 to learn about lung volumes and complete Quiz 8 by the designated deadline.