Unit 6: Respiratory System

Unit 6: The Respiratory System

Overview of the Respiratory System

Functions:

• Airflow to/from the lungs: Ensures the delivery of oxygen to tissues and the removal of carbon dioxide from the body.

• Gas exchange (pulmonary ventilation): Facilitates the essential process of exchanging gases between the bloodstream and the air.

Divisions:

• Upper Respiratory Tract: Includes the nose, nasal cavity, sinuses, pharynx, and larynx. Responsible for filtering, warming, and humidifying air before it reaches the lungs.

• Lower Respiratory Tract: Comprises the trachea, bronchi, bronchioles, and alveoli. Key to conducting air to gas exchange areas.

Structure of the Respiratory Tract

The respiratory tract is a complex branching passageway that allows air to move in and out. It is vital for gas exchange in the lungs, divided into two portions:

• Conducting Portion: Extends from the nasal cavity through terminal bronchioles; this portion does not allow for gas exchange but prepares air for the lungs.

• Respiratory Portion: Connects the respiratory bronchioles to alveoli; this is where gas exchange occurs as oxygen is absorbed into the bloodstream and carbon dioxide is released.

Upper Respiratory Tract

Functions:

• Air Quality Management: The mucosa filters out particulates, humidifies the air to prevent cellular damage, and warms the air, which is vital for efficient gas exchange in the lungs.

• Protection & Reabsorption: Protects the lower respiratory tract from pathogens and environmental contaminants, while facilitating the reabsorption of heat and moisture from exhaled air

Lower Respiratory Tract

Function:

• Conducts air efficiently to and from the lungs where gas exchange surfaces are located.

Respiratory Defense System

Components:

• Respiratory Mucosa: This specialized lining spans the nasal cavity and extends to large bronchioles, primarily composed of pseudostratified ciliated columnar epithelium interspersed with mucous cells. This architecture allows for effective trapping of foreign particles.

• Mucociliary Escalator: A protective mechanism where sticky mucus traps inhaled debris; cilia move this mucus upward toward the pharynx for expulsion through swallowing or coughing. Stem cells within the mucosa are vital for repairing damaged cells after injury or infection.

Types of Epithelium in the Respiratory Tract

• Respiratory Mucosa: Found in the nasal cavity, trachea, and bronchi, aiding in air filtering and gas exchange.

• Stratified Squamous Epithelium: Provides protection against abrasion in areas like the oropharynx and laryngopharynx.

• Simple Cuboidal Epithelium: Present in smaller bronchi and bronchioles, facilitating gas exchange and fluid movement.

• Simple Squamous Epithelium: Critical for gas exchange in alveoli due to its thin barrier that allows for efficient diffusion of gases.

Cystic Fibrosis (CF)

Cystic fibrosis is a genetic disorder, primarily affecting individuals of Northern European descent. Affected individuals experience the production of thick, viscous mucus that obstructs normal respiratory function. This condition leads to:

• Chronic Infections: Increased susceptibility to lung infections due to impaired clearance of mucus.

• Decreased Life Expectancy: A significant impact on quality of life, resulting in an average life expectancy of around 37 years due to respiratory failure and complications.

Structures of the Upper Respiratory System

• Nose & Nasal Cavity: The primary air entry route, supported by a combination of cartilage (for flexibility) and bone (for structure).

• Nasal Conchae & Meatuses: These structures help to swirl and direct airflow, ensuring that air is effectively humidified and warmed.

• Nasal Septum: Comprises cartilage and bone, dividing the nasal cavity into left and right nostrils, facilitating airflow regulation.

• Paranasal Sinuses: Include four paired sinuses (frontal, ethmoidal, maxillary, sphenoidal) that help warm and moisten inhaled air while also lightening the skull’s weight.

Pharynx

Divisions:

• Nasopharynx: The upper section, which includes the opening for the auditory tube that connects to the middle ear, helping to equalize ear pressure.

• Oropharynx: The middle section that serves as a passageway for both air and food, critical for swallowing.

• Laryngopharynx: The lower section that connects to the larynx, leading to the trachea.

The Larynx

Structure:

The larynx serves as both a protective structure for the airway and a sound-producing organ. Major cartilages include:

• Epiglottis: A flap that covers the glottis during swallowing, preventing food from entering the airway.

• Thyroid Cartilage: The largest cartilage, prominent in the neck.

• Cricoid Cartilage: Forms a complete ring around the trachea, providing structural support.

The Trachea and Bronchi

The trachea is a flexible, tube-like structure made of C-shaped cartilages that maintain its shape while allowing flexibility. It bifurcates into two main bronchi that lead to each lung. Key anatomical features include:

• Bronchi: Branch into secondary and tertiary bronchi, further dividing into smaller bronchioles.

• Airflow Regulation: Sympathetic stimulation can dilate bronchi, reducing resistance and optimizing airflow during increased physical activity.

The Lungs

Lobes:

• Right Lung: Comprising three lobes (superior, middle, inferior), allowing for efficient air distribution.

• Left Lung: Slightly smaller with two lobes (superior, inferior) to accommodate the heart's position.

• Bronchopulmonary Segments: Each lobe contains multiple segments, each with its own bronchus and blood supply, optimizing functional independence during various conditions.

Alveoli

Function:

Alveoli are the small air sacs surrounded by capillary networks, where gas exchange occurs. Efficient design includes:

• Alveolar Ducts & Sacs: These structures are where gas is exchanged with blood, with thin walls to maximize diffusion.

Respiratory Physiology

External Respiration:

Gases are exchanged between the blood, lungs, and the environment, with high efficiency due to factors such as alveolar surface area and partial pressure gradients.

Pulmonary Ventilation:

This involves air movement into and out of the lungs, which can be described by:

• Boyle's Law: Pressure and volume are inversely related; an increase in lung volume results in a decrease in pressure, allowing air influx during inhalation, and vice versa during exhalation.

Respiratory Muscles:

• Primary Inspiratory Muscles: The diaphragm (responsible for 75% of breathing) and the external intercostals (accounting for 25%).

• Accessory Muscles: Assist in more intense breathing during exertion.

• Exhalation Mechanics: Mostly passive during normal conditions, becoming active during forceful exhalation.

Respiratory Volumes and Capacities

• Tidal Volume (VT): The standard volume of air inhaled or exhaled with each breath (approximately 500 mL).

• Inspiratory Reserve Volume (IRV): The additional air that can be inhaled beyond the tidal volume.

• Expiratory Reserve Volume (ERV): The additional air that can be exhaled beyond the tidal volume.

• Residual Volume: The volume of air remaining in the lungs after full exhalation.

• Lung Capacities: Include total lung capacity, vital capacity, and functional residual capacity, important for assessing pulmonary function.

Regulation of Pulmonary Ventilation

Control centers in the brainstem (medulla and pons) and input from chemoreceptors and stretch receptors finely tune respiratory rates to maintain homeostasis by responding to changes in:

• Chemoreceptors: Detect variations in CO2, O2, and pH levels, causing adjustments to breathing rates and depths for optimal gas exchange.

Effects of Aging and Smoking

• Age-Related Changes: Deterioration in lung elasticity, decreased vital capacity, and an increase in the prevalence of respiratory disorders.

• Smoking Effects: Detrimental alterations in bronchial epithelium lead to chronic obstructive pulmonary disease (COPD), dysplasia, and metaplasia, significantly elevating lung cancer risk and overall health complications.