9.07 Chapter Summary

Key Components:

Lungs

• Location: Situated in the thoracic cavity, protected by the rib cage.
• Structure: Divided into lobes (three on the right, two on the left).
• Function: Primary organs for gas exchange; house the alveoli.

Trachea (Windpipe)

• Structure: A rigid tube reinforced with C-shaped hyaline cartilage rings to prevent collapse.
• Length: Approximately 10-12 cm in adults.
• Function: Conducts air to and from the lungs.

Bronchi

• Structure: The trachea bifurcates into the left and right primary bronchi, each entering a lung and branching into secondary and tertiary bronchi.
• Cartilage Presence: Contains more cartilage than bronchioles, maintaining airway integrity.
• Function: Distribute air into each lung and further into bronchial branches.

Bronchioles

• Structure: Smaller air passages without cartilage; walls contain smooth muscle.
• Subdivision: Terminal bronchioles lead to respiratory bronchioles.
• Function: Regulate airflow and direct air to alveolar ducts.

Alveoli

• Structure: Tiny, balloon-like sacs surrounded by a dense capillary network.
• Epithelium: Composed of thin squamous epithelial cells facilitating gas diffusion.
• Function: Site of gas exchange between air and blood.

Capillary Network

• Structure: Extensive network of thin-walled blood vessels enveloping alveoli.
• Function: Transport blood to and from the alveoli for gas exchange.

Cartilage

• Locations: Trachea and bronchi.
• Function: Provides structural support to keep airways open.

Ciliated Epithelium

• Locations: Trachea, bronchi, and bronchioles.
• Function: Moves mucus and trapped particles upward toward the throat.

Goblet Cells

• Locations: Trachea, bronchi, and bronchioles.
• Function: Secrete mucus to trap inhaled debris and pathogens.

Squamous Epithelium

• Locations: Alveoli.
• Function: Facilitates efficient gas diffusion due to thin cell layers.

Smooth Muscle

• Locations: Bronchioles.
• Function: Regulates the diameter of airways, controlling airflow resistance.

Capillaries

• Locations: Surround alveoli.
• Function: Enable gas exchange between alveolar air and blood.

Cartilage

• Appearance: Rigid, white, and translucent with a distinctive, patterned structure.
• Identification Tip: Look for the semi-rigid matrix with embedded chondrocytes.

Ciliated Epithelium

• Appearance: Cells with hair-like projections (cilia) on their apical surface.
• Identification Tip: Observe coordinated movement of cilia under higher magnification.

Goblet Cells

• Appearance: Larger cells interspersed among epithelial cells, containing mucin granules.
• Identification Tip: Identify cells with a prominent, mucous-filled cytoplasm.

Squamous Epithelium

• Appearance: Flat, scale-like cells forming a thin layer.
• Identification Tip: Recognize the closely packed, thin cells facilitating gas exchange.

Smooth Muscle

• Appearance: Spindle-shaped cells with elongated nuclei, no striations.
• Identification Tip: Locate circular or longitudinal arrangements within airway walls.

Capillaries

• Appearance: Extremely narrow blood vessels with single-layered walls.
• Identification Tip: Identify small, thin structures surrounding alveolar spaces.

Trachea:

• Features: Presence of C-shaped cartilage rings, pseudostratified ciliated columnar epithelium with goblet cells.
• Identification: Look for repetitive cartilaginous rings maintaining airway shape.

Bronchi:

• Features: Similar to trachea but with a complete ring of cartilage and branching structure.
• Identification: Observe branching patterns and presence of more extensive cartilage compared to bronchioles.

Bronchioles:

• Features: Lack of cartilage, presence of smooth muscle, and smaller diameter.
• Identification: Notice the absence of cartilage and the presence of smooth muscle fibers.

Alveoli:

• Features: Clusters of thin-walled sacs with extensive capillary networks.
• Identification: Identify numerous small, spherical structures facilitating gas exchange.

Plan Diagrams of Transverse Sections:

• Trachea Section: Visible C-shaped cartilage rings with the open part facing the esophagus.
• Bronchus Section: Complete cartilage rings with increased branching patterns.
• Bronchiole Section: Smooth muscle presence, absence of cartilage, narrower lumen.
• Alveolar Section: Simple squamous epithelium with dense capillary networks surrounding sac-like structures.

Ciliated Epithelial Cells

• Function: Utilize coordinated ciliary movements to propel mucus and trapped particles upward toward the pharynx for expulsion or swallowing.
• Importance: Maintains airway cleanliness and prevents infection by removing debris.

Goblet Cells

• Function: Produce and secrete mucus, which traps inhaled dust, pathogens, and other particles.
• Importance: Forms a protective barrier, facilitating the removal of harmful substances.

Mucous Glands

• Function: Extend deeper into the respiratory tract, continuously supplying mucus to the airways.
• Importance: Ensures a constant mucus layer for trapping particles and maintaining humidified air.

Cartilage

• Function: Provides structural support to keep airways open during inhalation and exhalation.
• Importance: Prevents collapse of trachea and bronchi, ensuring continuous airflow.

Smooth Muscle

• Function: Contracts or relaxes to adjust airway diameter, regulating airflow and resistance.
• Importance: Facilitates airflow control during varying respiratory demands (e.g., exercise, stress).

Elastic Fibres

• Function: Allow lungs and airways to stretch during inhalation and recoil during exhalation.
• Importance: Maintains lung elasticity, essential for efficient breathing mechanics.

Squamous Epithelium

• Function: Provides a thin barrier for rapid gas diffusion between alveolar air and blood.
• Importance: Maximizes the efficiency of oxygen and carbon dioxide exchange.

Mechanism of Gas Exchange:

• Diffusion Process: Gases move from areas of higher partial pressure to lower partial pressure.
  • Oxygen (O₂): Moves from alveolar air (high partial pressure) into blood (low partial pressure).
  • Carbon Dioxide (CO₂): Moves from blood (high partial pressure) into alveolar air (low partial pressure).

Structural Facilitation:

• Thin Walls: Alveolar and capillary walls are one cell thick, minimizing the distance for gas diffusion.
• Large Surface Area: Millions of alveoli provide an extensive surface area (~70 m²) for efficient gas exchange.
• Close Proximity: Alveoli are tightly enveloped by capillaries, ensuring rapid gas transfer.

Partial Pressures:

• Oxygen Partial Pressure: Higher in alveoli (~100 mmHg) than in deoxygenated blood (~40 mmHg).
• Carbon Dioxide Partial Pressure: Higher in blood (~45 mmHg) than in alveolar air (~40 mmHg).

Hemoglobin Role:

• Oxygen Binding: Hemoglobin in red blood cells binds oxygen, facilitating its transport.
• Carbon Dioxide Transport: CO₂ is carried dissolved in plasma, bound to hemoglobin, or as bicarbonate ions.