Exercise 36 Anatomy Of The Respiratory System Review Sheet

The respiratory system, a marvel of biological engineering, orchestrates the vital exchange of gases necessary for life. Understanding its intricate anatomy is fundamental to grasping its function and potential vulnerabilities. An exercise dedicated to reviewing the anatomy of the respiratory system is more than just an academic pursuit; it's a crucial step in appreciating the delicate balance that sustains us.

Components of the Respiratory System

The respiratory system is composed of organs and structures that facilitate the intake of oxygen and the expulsion of carbon dioxide. It's conventionally divided into the upper respiratory tract and the lower respiratory tract.

Upper Respiratory Tract

The upper respiratory tract consists of:

Nose and Nasal Cavity: The primary entry point for air into the body. The nasal cavity warms, filters, and humidifies the incoming air.
Pharynx: A muscular tube that serves as a passageway for both air and food. It is divided into three regions: the nasopharynx, oropharynx, and laryngopharynx.
Larynx: Also known as the voice box, it houses the vocal cords and plays a vital role in sound production.

Lower Respiratory Tract

The lower respiratory tract consists of:

Trachea: A rigid tube reinforced with cartilage rings, ensuring that it remains open for airflow.
Bronchi: The trachea branches into two main bronchi, which enter the lungs. These further divide into smaller and smaller bronchioles.
Lungs: The primary organs of respiration, where gas exchange occurs. They contain millions of tiny air sacs called alveoli.

Detailed Anatomical Review

To truly understand the respiratory system, a deep dive into each component is essential.

Nose and Nasal Cavity

The nose, projecting from the face, is more than just a cosmetic feature; it's the first line of defense for the respiratory system. Air enters through the nares (nostrils) and passes into the nasal cavity.

Nasal Septum: Divides the nasal cavity into left and right halves.
Nasal Conchae (Turbinates): Three bony projections (superior, middle, and inferior) that increase the surface area of the nasal cavity, enhancing air turbulence, filtration, and humidification.
Mucosa: The lining of the nasal cavity, rich in blood vessels and mucus-secreting cells. The mucus traps particles, while the blood vessels warm the air.
Olfactory Epithelium: Located in the superior nasal cavity, contains sensory receptors for smell.

Pharynx

The pharynx, often called the throat, is a muscular funnel connecting the nasal cavity and mouth to the larynx and esophagus. It plays a crucial role in both respiration and digestion.

Nasopharynx: Located behind the nasal cavity, it contains the openings for the auditory (Eustachian) tubes, which connect to the middle ear. The pharyngeal tonsil (adenoids) is also found here.
Oropharynx: Located behind the oral cavity, it is a passageway for both air and food. The palatine tonsils and lingual tonsils are located here.
Laryngopharynx: Located behind the larynx, it is the point where the respiratory and digestive pathways diverge. Air enters the larynx, while food enters the esophagus.

Larynx

The larynx, or voice box, is a complex structure composed of cartilage, ligaments, and muscles. Its primary functions are to maintain an open airway, route air and food into the proper channels, and produce sound.

Thyroid Cartilage: The largest cartilage of the larynx, forming the Adam's apple.
Cricoid Cartilage: A ring-shaped cartilage located inferior to the thyroid cartilage.
Epiglottis: A flap of cartilage that covers the opening of the larynx during swallowing, preventing food from entering the trachea.
Vocal Cords (Vocal Folds): Folds of mucous membrane that vibrate to produce sound when air passes over them. The tension and length of the vocal cords determine the pitch of the sound.
Glottis: The opening between the vocal cords.

Trachea

The trachea, or windpipe, is a cylindrical tube extending from the larynx to the bronchi. Its walls are reinforced with C-shaped cartilage rings that prevent it from collapsing.

Cartilage Rings: Provide structural support and maintain an open airway. The open part of the "C" faces posteriorly, allowing the esophagus to expand during swallowing.
Trachealis Muscle: A smooth muscle that connects the open ends of the cartilage rings. It can contract to reduce the diameter of the trachea, increasing the force of exhalation (e.g., during coughing).
Mucosa: The lining of the trachea, composed of ciliated pseudostratified columnar epithelium. The cilia beat upwards, moving mucus and trapped particles towards the pharynx to be swallowed or expelled.

Bronchi

The trachea divides into two main (primary) bronchi, which enter the lungs at the hilum. The right main bronchus is wider, shorter, and more vertical than the left, making it the more common site for inhaled objects to become lodged.

Main (Primary) Bronchi: One bronchus enters each lung.
Lobar (Secondary) Bronchi: Each main bronchus divides into lobar bronchi, with two on the left (to the two lobes of the left lung) and three on the right (to the three lobes of the right lung).
Segmental (Tertiary) Bronchi: The lobar bronchi divide into segmental bronchi, which supply specific bronchopulmonary segments of the lungs.
Bronchioles: Small branches of the segmental bronchi. They lack cartilage and are primarily composed of smooth muscle.
Terminal Bronchioles: The smallest bronchioles, which lead to the respiratory bronchioles.

Lungs

The lungs are the primary organs of respiration, located in the thoracic cavity. They are surrounded by the pleurae, which are serous membranes that reduce friction during breathing.

Lobes: The right lung has three lobes (superior, middle, and inferior), while the left lung has two lobes (superior and inferior).
Fissures: Separate the lobes of the lungs. The right lung has a horizontal and an oblique fissure, while the left lung has only an oblique fissure.
Pleura: A double-layered serous membrane surrounding each lung. The visceral pleura covers the surface of the lung, while the parietal pleura lines the thoracic cavity. The pleural cavity, between the two layers, contains a small amount of serous fluid that reduces friction during breathing.
Alveoli: Tiny air sacs where gas exchange occurs. They are surrounded by a network of capillaries. The walls of the alveoli are composed of simple squamous epithelium, which facilitates the diffusion of oxygen and carbon dioxide.
Alveolar Sacs: Clusters of alveoli.
Respiratory Membrane: The interface between the alveoli and the capillaries, consisting of the alveolar wall, the capillary wall, and their fused basement membranes. This thin membrane allows for rapid gas exchange.

Microscopic Anatomy

The microscopic structure of the respiratory system is intricately designed to facilitate gas exchange.

Epithelial Lining

The respiratory tract is lined with various types of epithelium, depending on the location and function.

Pseudostratified Ciliated Columnar Epithelium: Lines most of the respiratory tract, from the nasal cavity to the bronchi. The cilia propel mucus and trapped particles towards the pharynx.
Simple Squamous Epithelium: Lines the alveoli, providing a thin barrier for gas exchange.
Goblet Cells: Scattered throughout the epithelial lining, these cells secrete mucus to trap particles.

Alveolar Cells

The alveoli contain two main types of cells:

Type I Alveolar Cells: Thin, squamous epithelial cells that form the majority of the alveolar surface. They are responsible for gas exchange.
Type II Alveolar Cells: Cuboidal epithelial cells that secrete surfactant, a substance that reduces surface tension in the alveoli and prevents them from collapsing.

Alveolar Macrophages

Also known as dust cells, these macrophages patrol the alveoli and engulf any foreign particles that make it past the respiratory defenses.

Mechanics of Breathing

Breathing, or pulmonary ventilation, involves two phases: inspiration (inhalation) and expiration (exhalation). These processes are driven by changes in pressure within the thoracic cavity.

Inspiration

Diaphragm Contraction: The diaphragm, a dome-shaped muscle at the base of the thoracic cavity, contracts and flattens, increasing the volume of the thoracic cavity.
External Intercostal Muscle Contraction: These muscles lift the rib cage, further increasing the volume of the thoracic cavity.
Pressure Changes: As the volume of the thoracic cavity increases, the pressure inside decreases (Boyle's Law). This creates a pressure gradient, with the pressure in the lungs being lower than the atmospheric pressure.
Airflow: Air flows into the lungs down the pressure gradient, from an area of higher pressure to an area of lower pressure.

Expiration

Diaphragm Relaxation: The diaphragm relaxes and returns to its dome shape, decreasing the volume of the thoracic cavity.
External Intercostal Muscle Relaxation: These muscles relax, allowing the rib cage to descend, further decreasing the volume of the thoracic cavity.
Pressure Changes: As the volume of the thoracic cavity decreases, the pressure inside increases. This creates a pressure gradient, with the pressure in the lungs being higher than the atmospheric pressure.
Airflow: Air flows out of the lungs down the pressure gradient, from an area of higher pressure to an area of lower pressure.

Factors Affecting Ventilation

Several factors can affect the ease with which air flows into and out of the lungs:

Airway Resistance: The resistance of the respiratory passageways to airflow. Constriction of the bronchioles (e.g., during asthma) increases airway resistance and makes breathing more difficult.
Lung Compliance: The ability of the lungs to expand. Conditions like pulmonary fibrosis can decrease lung compliance, making it harder to inflate the lungs.
Surface Tension: The attraction of water molecules to each other. Surfactant, secreted by type II alveolar cells, reduces surface tension in the alveoli and prevents them from collapsing.

Gas Exchange

Gas exchange, or respiration, involves the movement of oxygen and carbon dioxide across the respiratory membrane. This process occurs in the alveoli of the lungs.

External Respiration

Oxygen Diffusion: Oxygen diffuses from the alveoli into the blood in the capillaries. This is driven by the difference in partial pressure of oxygen between the alveoli and the blood.
Carbon Dioxide Diffusion: Carbon dioxide diffuses from the blood in the capillaries into the alveoli. This is driven by the difference in partial pressure of carbon dioxide between the blood and the alveoli.

Internal Respiration

Oxygen Diffusion: Oxygen diffuses from the blood in the capillaries into the cells of the body. This is driven by the difference in partial pressure of oxygen between the blood and the cells.
Carbon Dioxide Diffusion: Carbon dioxide diffuses from the cells of the body into the blood in the capillaries. This is driven by the difference in partial pressure of carbon dioxide between the cells and the blood.

Control of Respiration

Breathing is controlled by the respiratory centers in the brainstem (medulla oblongata and pons). These centers regulate the rate and depth of breathing in response to various stimuli.

Medullary Respiratory Center

Ventral Respiratory Group (VRG): Contains neurons that control both inspiration and expiration. It sets the basic rhythm of breathing.
Dorsal Respiratory Group (DRG): Receives input from sensory receptors and modifies the activity of the VRG.

Pontine Respiratory Center

Pneumotaxic Center: Inhibits the inspiratory neurons in the medulla, limiting the duration of inspiration.
Apneustic Center: Stimulates the inspiratory neurons in the medulla, prolonging inspiration.

Factors Influencing Respiratory Rate and Depth

Several factors can influence the rate and depth of breathing:

Partial Pressure of Carbon Dioxide (PCO2): An increase in PCO2 is the most potent stimulus for breathing. Chemoreceptors in the medulla and carotid and aortic bodies detect changes in PCO2 and signal the respiratory centers to increase ventilation.
Partial Pressure of Oxygen (PO2): A decrease in PO2 can also stimulate breathing, but to a lesser extent than PCO2.
pH: A decrease in pH (increase in acidity) can stimulate breathing.
Other Factors: Exercise, pain, emotions, and body temperature can also influence breathing.

Common Respiratory Diseases

A comprehensive understanding of the respiratory system is incomplete without knowledge of common respiratory diseases. These conditions can significantly impair respiratory function and overall health.

Asthma

A chronic inflammatory disease of the airways characterized by:

Airway Inflammation: The airways become inflamed and swollen.
Bronchoconstriction: The smooth muscles around the airways tighten, narrowing the airways.
Mucus Production: Excess mucus is produced, further obstructing the airways.

Chronic Obstructive Pulmonary Disease (COPD)

A group of lung diseases that block airflow and make it difficult to breathe. The two main types of COPD are:

Emphysema: Damage to the alveoli, leading to a loss of elasticity and impaired gas exchange.
Chronic Bronchitis: Inflammation and narrowing of the bronchi, leading to chronic cough and mucus production.

Pneumonia

An infection of the lungs caused by bacteria, viruses, or fungi. The alveoli become filled with fluid and pus, impairing gas exchange.

Lung Cancer

A malignant tumor that originates in the lungs. It is often caused by smoking or exposure to other carcinogens.

Cystic Fibrosis

A genetic disorder that causes the production of thick, sticky mucus that can clog the airways and lead to chronic lung infections.

Clinical Significance

A thorough understanding of respiratory anatomy is crucial for healthcare professionals. It aids in:

Diagnosis: Identifying the location and nature of respiratory problems.
Treatment: Guiding interventions such as intubation, bronchoscopy, and surgery.
Patient Education: Explaining respiratory conditions and treatments to patients.

Conclusion

The respiratory system, with its intricate network of structures and functions, is essential for life. A comprehensive review of its anatomy is vital for anyone seeking to understand the complexities of human physiology. From the nasal cavity to the alveoli, each component plays a critical role in ensuring the efficient exchange of gases that sustains us. This exercise serves as a foundation for further exploration into the mechanics of breathing, gas exchange, and the various diseases that can affect this vital system.