Respiratory System: Gas Exchange Structures

Functional Units of Gas Exchange

• Primary lobules, also known as lung parenchyma, encompass respiratory bronchioles, alveoli, alveolar ducts, and alveolar sacs.
• Respiratory bronchioles consist of four generations that conduct air and partake in minimal gas exchange.

Alveoli and Structures

• Alveoli are tiny balloon-like structures, the primary sites of gas exchange, separated by septal walls, and represent the terminal portion of the respiratory tree.
• Alveolar ducts connect respiratory bronchioles to alveolar sacs and consist of four generations.

Alveolar Sacs

• Clusters of 15-20 alveoli form alveolar sacs, resembling grape-like structures that maximize surface area for gas exchange.

Pneumocyte Types

• Type I squamous pneumocytes make up about 95% of the alveolar surface, essential for efficient gas exchange due to their broad, thin design (thickness: 0.1μ to 0.5μ).
• Type II granular pneumocytes produce surfactant, preventing alveolar collapse and assisting in the repair of the alveolar epithelium.

Pores of Kohn

• Pores of Kohn, with sizes ranging from 3μ to 13μ, are small openings in the interalveolar septa that facilitate gas movement between adjacent alveoli, crucial for maintaining even gas distribution.

Alveolar Macrophages

• Type III alveolar cells, also known as alveolar macrophages, perform phagocytosis of foreign particles and pathogens, playing a protective role in maintaining lung health.

Interstitium

• The interstitium serves as a gel-like support for the alveolo-capillary system, comprised of collagen fibers and extracellular matrix components, which aids in structural support and tissue repair.

Collagen and Alveolar Distensibility

• Collagen in the interstitium grants tensile strength and limits alveolar stretching, thereby preventing capillary occlusion.

Pulmonary Circulation

• Pulmonary arteries transport deoxygenated blood from the right ventricle to the lungs, traversing through the hilum and following the tracheobronchial tree.
• Arterioles provide nutrients to respiratory structures and consist of three layers: endothelial, elastic, and smooth muscle, which diminish prior to entering the alveolar-capillary system.
• Capillaries, less than 0.1μ thick, constitute the primary site for gas exchange, forming a network around alveoli while also playing roles in biochemical processes.

Pulmonary Venous System

• Venules and veins extend from arterioles, leading to pulmonary veins, characterized by three tissue layers, diminished smooth muscle and elastic tissue, and flap-like valves to facilitate blood return to the heart.

Alveolar Statistics

• The human lungs contain approximately 300 million alveoli, each measuring between 75μ and 300μ.

Explore the vital components of the respiratory system in this quiz, focusing on structures distal to the terminal bronchioles. Learn about respiratory bronchioles, alveoli, and their roles in gas exchange and lung function.