16 Anatomy of resp tract 3 - Alveoli

Anatomy of the Respiratory Tract

• Overview of the respiratory system, focusing on the alveoli.

Alveoli

• Function:

  • Site of gas exchange between air and blood.

• Arrangement:

  • Scattered throughout respiratory bronchioles.

  • Connects respiratory bronchioles to alveolar ducts.

  • Alveolar ducts are elongated airways made up of alveoli leading to:

    • Alveolar sacs: spaces surrounded by clusters of alveoli.

Structure of the Alveoli

• Quantity: 150-250 million alveoli per lung.

• Surrounding Support: A dense network of capillaries aids gas exchange.

• Significance: Provides extensive surface area essential for efficient gas exchange.

Blood Supply to Alveoli

• Components of blood flow:

  • Bronchioles (terminal and respiratory)

  • Pulmonary arterioles

  • Pulmonary venules

  • Alveolar sacs and alveoli are enveloped by a capillary network, facilitating the transport of gases.

Structure of an Alveolus

• Cell Types:

  • Type I alveolar cell: Simple squamous epithelium that forms walls of alveoli.

  • Type II alveolar cell: Produces surfactant that reduces surface tension.

  • Macrophages: Aid in phagocytosis of small inhaled particles and bacteria.

• Components:

  • Surfactant

  • Capillaries

  • Respiratory membrane comprised of:

    • Epithelium of type I cells

    • Basement membrane of type I cells

    • Endothelium of capillaries

    • Basement membrane of capillaries (these two basement membranes are typically fused together).

Functional Organisation of the Respiratory Tract

• Two Portions:

  • Conductive Portion: Filter, warm, and moisten air before reaching lungs.

    • Includes: nasal cavity, paranasal sinuses, pharynx, larynx, trachea, primary bronchi, secondary bronchi, tertiary bronchi, bronchioles, terminal bronchioles.

  • Respiratory Portion: Areas where gas exchange occurs.

    • Includes: respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli.