Overview of the Respiratory System
The respiratory system is a crucial organ system responsible for gas exchange, supplying oxygen to the body, and removing carbon dioxide. Histologically, it comprises various structures, including the nasal cavity, pharynx, larynx, trachea, bronchi, and lungs.Nasal Cavity
The nasal cavity is lined with a specialized mucosa known as the respiratory epithelium, which is primarily composed of pseudostratified ciliated columnar epithelium. This epithelium is rich in goblet cells that secrete mucus, trapping particles and pathogens. The cilia move the mucus towards the pharynx for expulsion.Pharynx and Larynx
The pharynx is a muscular tube lined with stratified squamous epithelium in its upper parts, transitioning to pseudostratified ciliated columnar epithelium in the lower parts. The larynx, responsible for voice production, is supported by cartilaginous structures and lined with a similar type of epithelium.Trachea
The trachea is a flexible tube supported by C-shaped cartilaginous rings. Its inner lining consists of pseudostratified ciliated columnar epithelium. The submucosa contains seromucous glands that help in moistening the air and trapping foreign particles.Bronchi and Bronchioles
The bronchi are extensions of the trachea and are also lined with pseudostratified ciliated columnar epithelium. As the bronchi branch into smaller bronchioles, the epithelium transitions to simple ciliated columnar and then to cuboidal epithelium. The cartilage and glands gradually disappear in the smaller bronchioles.Lungs
The lungs are composed of alveoli, which are the primary sites for gas exchange. Alveoli are lined with a simple squamous epithelium, known as type I alveolar cells, facilitating efficient gas exchange. Type II alveolar cells are interspersed and secrete surfactant, reducing surface tension and preventing alveolar collapse.Alveolar-Capillary Barrier
The alveolar-capillary barrier is a thin membrane composed of the alveolar epithelium, a fused basement membrane, and the capillary endothelium. This thin barrier ensures efficient diffusion of oxygen and carbon dioxide between the alveoli and the blood.Questions and Answers
Q: What type of epithelium lines the nasal cavity?
A: The nasal cavity is lined with pseudostratified ciliated columnar epithelium.
Q: What is the primary function of goblet cells in the respiratory epithelium?
A: Goblet cells secrete mucus that traps particles and pathogens in the respiratory tract.
Q: How does the trachea maintain its structure?
A: The trachea is supported by C-shaped cartilaginous rings that maintain its open structure.
Q: What are the key differences between bronchi and bronchioles?
A: Bronchi are lined with pseudostratified ciliated columnar epithelium and contain cartilage and glands, while bronchioles have simple ciliated columnar or cuboidal epithelium and lack cartilage and glands.
Q: What role do type II alveolar cells play in the lungs?
A: Type II alveolar cells secrete surfactant, which reduces surface tension and prevents alveolar collapse.
Q: Describe the alveolar-capillary barrier.
A: The alveolar-capillary barrier is a thin membrane consisting of the alveolar epithelium, a fused basement membrane, and the capillary endothelium, facilitating gas exchange.
