Review Sheet 36 Anatomy Of The Respiratory System

Review Sheet 36: Anatomy of the Respiratory System

This comprehensive review sheet delves into the intricate anatomy of the respiratory system, covering key structures, their functions, and clinical correlations. We'll explore the system from the nose to the alveoli, emphasizing the interconnectedness of its components and the importance of understanding their individual roles in respiration. This resource is designed to aid students in their understanding and preparation for examinations.

I. Upper Respiratory Tract

The upper respiratory tract is the initial point of entry for air into the body. It functions to filter, warm, and humidify incoming air before it reaches the lower respiratory tract. Key components include:

A. Nose and Nasal Cavity:

• External Nose: Composed of bone (nasal bones, frontal process of maxilla) and cartilage (septal, alar). Its shape and structure are crucial for directing airflow.
• Nasal Cavity: A large, air-filled space above the palate, divided by the nasal septum. The nasal conchae (superior, middle, and inferior) increase surface area for air conditioning.
• Olfactory Receptors: Located in the superior nasal cavity, these chemoreceptors detect odors.
• Paranasal Sinuses: Air-filled spaces within the frontal, maxillary, ethmoid, and sphenoid bones. These sinuses lighten the skull, contribute to voice resonance, and produce mucus. Sinusitis, inflammation of these sinuses, is a common ailment.

B. Pharynx:

The pharynx is a muscular tube that serves as a common passageway for air and food. It's divided into three regions:

• Nasopharynx: Posterior to the nasal cavity, it's the passageway for air only. The pharyngeal tonsil (adenoids) is located here. Enlarged adenoids can obstruct airflow, leading to mouth breathing and sleep apnea.
• Oropharynx: Posterior to the oral cavity, it's a passageway for both air and food. The lingual and palatine tonsils are located here. Tonsilitis, inflammation of the tonsils, is a common infection.
• Laryngopharynx: Extends from the hyoid bone to the larynx and esophagus. It is a passageway for both air and food. The epiglottis, a flap of cartilage, prevents food from entering the trachea during swallowing.

II. Lower Respiratory Tract

The lower respiratory tract is responsible for gas exchange, where oxygen is taken up into the blood and carbon dioxide is removed. The major components are:

A. Larynx (Voice Box):

The larynx is a cartilaginous structure connecting the pharynx to the trachea. Its primary functions are:

• Protection of the airway: The epiglottis prevents food from entering the trachea.
• Vocalization: The vocal cords, located within the larynx, vibrate to produce sound. The tension and position of the vocal cords determine pitch and volume. Laryngitis, inflammation of the larynx, results in hoarseness or loss of voice.
• Cough reflex: Initiated by irritants in the trachea, this reflex helps to clear the airways.

B. Trachea (Windpipe):

The trachea is a flexible tube reinforced by C-shaped hyaline cartilage rings. These rings prevent the trachea from collapsing during inhalation. The trachea branches into two main bronchi.

• Cartilaginous rings: Provide structural support and prevent collapse.
• Trachealis muscle: Connects the ends of the C-shaped cartilage rings, allowing for adjustment of tracheal diameter during breathing.
• Mucociliary escalator: The lining of the trachea is covered with cilia that move mucus containing trapped particles upwards, away from the lungs.

C. Bronchi and Bronchioles:

The trachea branches into two main bronchi, one for each lung. These bronchi further subdivide into smaller and smaller bronchi, eventually leading to bronchioles.

• Main bronchi: Enter the lungs at the hilum. The right main bronchus is wider and shorter than the left, making it more susceptible to foreign object aspiration.
• Lobar bronchi: Further divide the airways within each lung lobe.
• Segmental bronchi: Supply air to specific lung segments.
• Bronchioles: The smallest airways, lacking cartilage support. They contain smooth muscle which regulates airflow through bronchoconstriction and bronchodilation. Asthma is characterized by bronchospasm, resulting in airway narrowing and difficulty breathing.
• Terminal bronchioles: The final branches before the respiratory zone begins.

D. Respiratory Zone:

This is where gas exchange actually takes place. The respiratory zone includes:

• Respiratory bronchioles: These are the smallest bronchioles that participate in gas exchange.
• Alveolar ducts: Small tubes leading to alveolar sacs.
• Alveolar sacs: Clusters of alveoli.
• Alveoli: Tiny air sacs where gas exchange occurs. The alveoli are surrounded by capillaries, allowing for efficient diffusion of oxygen into the blood and carbon dioxide out of the blood. Alveoli are lined with Type I and Type II alveolar cells. Type I cells facilitate gas exchange, while Type II cells secrete surfactant, a substance that reduces surface tension and prevents alveolar collapse. Emphysema is a disease characterized by the destruction of alveoli, reducing surface area for gas exchange.

III. Lungs and Pleurae

The lungs are paired organs located within the thoracic cavity. Each lung is surrounded by a double-layered serous membrane called the pleura.

A. Lungs:

• Right lung: Three lobes (superior, middle, inferior)
• Left lung: Two lobes (superior, inferior) The left lung is smaller than the right due to the presence of the heart.
• Hilum: The region where the bronchi, pulmonary vessels, and nerves enter and exit the lungs.
• Lung lobes and segments: Understanding the lobar and segmental anatomy is crucial for diagnosing and treating lung diseases.

B. Pleurae:

The pleurae are composed of two layers:

• Visceral pleura: Adheres directly to the surface of the lungs.
• Parietal pleura: Lines the thoracic cavity.
• Pleural cavity: The potential space between the visceral and parietal pleurae. It contains a small amount of pleural fluid which reduces friction during breathing. Pleurisy, inflammation of the pleurae, causes sharp chest pain with each breath. Pneumothorax, air in the pleural cavity, causes lung collapse.

IV. Muscles of Respiration

Several muscles are involved in the mechanics of breathing:

• Diaphragm: The primary muscle of inspiration. Contraction flattens the diaphragm, increasing the volume of the thoracic cavity.
• External intercostal muscles: Located between the ribs. Contraction elevates the ribs, further increasing thoracic volume.
• Internal intercostal muscles: Located between the ribs. Contraction depresses the ribs, decreasing thoracic volume (primarily involved in forced expiration).
• Accessory muscles: These muscles are recruited during forced inspiration (e.g., sternocleidomastoid, scalenes) or expiration (e.g., abdominal muscles).

V. Clinical Correlations

Understanding the anatomy of the respiratory system is crucial for diagnosing and treating various respiratory conditions. Some common examples include:

• Pneumonia: Inflammation of the lungs, often caused by infection.
• Bronchitis: Inflammation of the bronchi.
• Asthma: Chronic inflammatory disorder of the airways characterized by bronchospasm.
• Emphysema: A chronic lung disease characterized by the destruction of alveoli.
• Lung cancer: A malignant tumor that arises in the lungs.
• Cystic fibrosis: A genetic disorder that affects mucus production in the lungs and other organs.
• Tuberculosis: A bacterial infection that primarily affects the lungs.

VI. Review Questions

To solidify your understanding, consider these review questions:

1. Describe the pathway of air from the nose to the alveoli.
2. What are the functions of the paranasal sinuses?
3. What is the role of the epiglottis?
4. Explain the mucociliary escalator.
5. Describe the differences between bronchi and bronchioles.
6. What is the function of surfactant?
7. Explain the structure and function of the pleurae.
8. What are the primary muscles of inspiration?
9. Briefly describe the clinical significance of understanding respiratory anatomy.
10. Differentiate between the right and left lungs.

This detailed review sheet provides a comprehensive overview of the respiratory system's anatomy. By understanding the structure and function of each component, you can better appreciate the complexity and importance of this vital system. Remember to consult your textbook and other resources for further in-depth information and visual aids. Good luck with your studies!