Ch21_Respiratory System_Part 1_Upper_slides (1)

Ch 21 - The Respiratory System

Part 1 - Anatomy of the Respiratory Tract

Functions of the Respiratory System

• Gas Exchange: The respiratory system provides an extensive surface area (approximately 70 square meters) for gas exchange between air and circulating blood, allowing oxygen to enter the bloodstream and carbon dioxide to be expelled. This process occurs primarily in the alveoli of the lungs.

• Air Movement: It facilitates the movement of air to and from the exchange surfaces of the lungs through respiratory passageways, which include the nasal cavity, trachea, bronchi, and bronchioles.

• Protection: The respiratory system protects respiratory surfaces from dehydration, temperature fluctuations, and invasion by pathogens through mechanisms like mucus production and the filtration of incoming air.

• Sound Production: It produces various sounds necessary for speaking, singing, and other forms of communication through the vibration of vocal cords in the larynx.

• Olfaction: The system detects odors through specialized olfactory receptors located in the superior portions of the nasal cavity, contributing to the sense of smell.

Structure of the Respiratory System

Components:

• The respiratory system consists of structures involved in:

  • Breathing or pulmonary ventilation (the process through which air flows to and from the lungs).

  • Gas exchange: the movement of gases into or out of the blood through the alveoli.

• Respiratory Tract: A branching passageway that transports air to and from the lungs and encompasses the upper and lower respiratory structures.

Functional Divisions of the Respiratory Tract

• Conducting Portion:

  • Anatomy: Extends from the nasal cavity down to the larger bronchioles.

  • Physiology: Functions primarily to conduct air to and from the gas exchange areas, allowing for the unobstructed flow of air.

• Respiratory Portion:

  • Anatomy: Comprised of the respiratory bronchioles and alveoli.

  • Physiology: The site where gas exchange occurs, facilitating the diffusion of oxygen and carbon dioxide across the alveolar membranes.

Respiratory Defense System

• Respiratory Mucosa:

  • Lines the nasal cavity and larger bronchioles, comprises a pseudostratified ciliated columnar epithelium interspersed with mucous cells, and is vital for trapping airborne particles.

  • Lamina Propria: Underlying supportive areolar tissue that contains mucous glands particularly concentrated in the trachea and bronchi, contributing to mucus production.

Mucociliary Escalator

• Function: The mucociliary escalator plays an essential role in moving mucus and trapped debris upwards towards the pharynx.

  • Sticky mucus, produced by mucous cells, traps debris particles, preventing them from entering the lower respiratory tract.

  • Beating cilia on the epithelial surfaces propel this mucus upwards, which can either be swallowed or expelled by coughing.

  • Damaged or old cells within the respiratory tract are replaced by epithelial stem cells to maintain tissue integrity.

Epithelia of the Respiratory Tract

• Variability: The epithelial types vary along the respiratory tract to perform specialized functions.

• Respiratory Mucosa: Lines the nasal cavity, superior pharynx, and also covers parts of the lower respiratory tract.

• Stratified Squamous Epithelium: Protects the inferior portions of the pharynx where abrasion is common (e.g., during swallowing).

• Simple Squamous Epithelium: Facilitates gas exchange across alveolar surfaces, where the distance between air and blood in capillaries measures less than 1 µm, resulting in rapid diffusion of gases.

Cystic Fibrosis

• Definition: Cystic Fibrosis is the most common lethal inherited disease affecting individuals of Northern European descent.

  • It is characterized by the production of thick, sticky mucus by mucous membranes that cannot be efficiently transported, leading to significant respiratory complications.

  • The malfunction of the mucociliary escalator results in the accumulation of mucus, creating an environment conducive to chronic infections, particularly with pathogens such as Pseudomonas aeruginosa.

  • The average lifespan of individuals affected by cystic fibrosis is approximately 37 years, with complications often resulting in death due to heart failure or chronic infections.

Upper Respiratory System

• Functionality: The upper respiratory system filters, warms, and humidifies incoming air to shield the delicate lower tract from damage and aids in reabsorbing heat and moisture from outgoing air, optimizing the air's condition for the lungs.

Components of the Upper Respiratory System

• Includes:

  • Nose

  • Nasal cavity

  • Paranasal sinuses

  • Pharynx

    • Nose: Serves as the primary route for air entry, featuring external nares that act as paired openings into the nasal cavity.

Nasal Cavity Functions

• Lamina Propria: Contains a comprehensive network of blood vessels that release heat, warming inhaled air, along with mucus that ensures the air is humidified.

• Temperature Maintenance: Air is heated nearly to body temperature and saturated with water vapor by the time it transitions from the nasal cavity to the lungs, enhancing respiratory efficiency.

• Exhalation: The mucosa reabsorbs heat and water during exhalation, reducing environmental loss, which is particularly important in dry or cold conditions.

• Mouth Breathing: Bypasses the nasal cavity, eliminating filtration and humidification benefits, which may lead to respiratory complications.

Nasal Conchae and Meatuses

• Structures: Comprised of superior, middle, and inferior nasal conchae (bony structures) and corresponding meatuses (spaces) that increase air turbulence.

• Function: These structures aid in swirling incoming air, which effectively traps small particles and directs chemicals to olfactory receptors, ensuring that air is adequately warmed and humidified during the process.

Nasal Cavity Structures

• Paranasal Sinuses: Include the frontal, ethmoidal air cells, maxillary, and sphenoidal sinuses, which contribute to the overall function of the nasal cavity.

  • The mucous produced by these sinuses moistens and cleans the nasal surfaces, with drainage through the nasolacrimal duct causing a runny nose during tears.

• Nasal Septum: Formed by the vomer bone and the perpendicular plate of the ethmoid bone, dividing the nasal cavity into two nostrils.

Pharynx

• Definition: Functions as a muscular passageway shared by the respiratory and digestive systems, facilitating both air and food passage.

• Nasopharynx: Superior part extending to the soft palate, housing the pharyngeal opening of the auditory tube, which connects the middle ear to the throat.

• Oropharynx: Lies between the soft palate and the base of the tongue, lined with stratified squamous epithelium to withstand the friction during swallowing.

• Laryngopharynx: The inferior section from the hyoid to the larynx, explaining why liquids may come out of the nose when laughter or coughing occurs while drinking.

Anatomy of the Lower Respiratory System

• Function: This system conducts air to and from the gas exchange surfaces situated within the lungs.

Larynx

• Role: Protects the glottis, the opening that leads to the trachea, and is involved in sound production.

• Composition: A cartilaginous tube encircling the glottis, featuring three large cartilages: the epiglottis (covers the glottis during swallowing), the thyroid cartilage (contains laryngeal prominence, known as the Adam's apple), and the cricoid cartilage (forms the base of the larynx).

Epiglottis

• Shape: Resembles a shoehorn, projecting superiorly over the glottis during rest.

• Function: During swallowing, the epiglottis folds back over the glottis, preventing the entry of solids and liquids into the respiratory tract, thereby protecting the air passage.

• Etymology: From Greek, "epi" means upon, reflecting its position above the glottis.

Glottis of the Larynx

• Function: Facilitates the passage of air through the larynx and is comprised of vocal folds (vocal cords).

• Vocal Folds: These tissues contain vocal ligaments; their vibrations during airflow produce sound waves, which can be modified for speech.

Sound Production

• Phonation: The process of sound production occurring in the larynx via vibrations of the vocal cords.

• Articulation: Modifies basic sounds through the actions of the tongue, teeth, and lips.

• Amplification and Resonance: Enhanced in the pharynx, oral and nasal cavities, as well as the paranasal sinuses, leading to varied vocal tones and pitches.

The Trachea (Windpipe)

• Structure: A robust, flexible tube measuring about 2.5 cm in diameter and 11 cm length, creating a clear passageway for air entering the lungs.

• Contains 15-20 C-shaped cartilages, preventing collapse and overexpansion during breathing.

• Trachealis Muscle: Connects the ends of the tracheal cartilages, allowing for the expansion of the esophagus during swallowing and regulates tracheal constriction and dilation based on autonomic nervous stimulation.

Trachea Cross-Section

• Structure: The ends of C-shaped tracheal cartilages are anchored by elastic ligaments and the trachealis muscle.

• During contraction of the trachealis, the trachea's diameter reduces, potentially affecting airflow.

• Sympathetic stimulation causes bronchial dilation, increasing airflow by widening the trachea. When necessary, cartilages are incomplete posteriorly to accommodate the esophagus’s expansion when swallowing.

Bronchial Branches

• Structure: The trachea bifurcates into right and left primary bronchi, each leading to respective lungs. The Respiratory Tree refers to the extensive branching of bronchi and bronchioles within the lungs.

• Bronchitis: Refers to inflammation of the bronchi, leading to coughing, production of mucus, and difficulty breathing.

The Bronchial Branches

• Bronchioles: Smaller branches that lack cartilage but possess smooth muscle, allowing for significant changes in diameter and airflow regulation.

• Sympathetic Nervous System: Mediates bronchodilation (enlargement of bronchioles), facilitating increased airflow.

• Parasympathetic Nervous System: Induces bronchoconstriction (narrowing of bronchioles), reducing airflow.

Types of Bronchioles

• Terminal Bronchioles: The last branches leading to pulmonary lobules, playing a role in conducting airflow effectively toward areas of gas exchange.

• Respiratory Bronchioles: The first branches where gas exchange begins, transitioning from conducting to respiratory function.

Lobes of the Lungs

• Lung Lobes: The right lung consists of three lobes (superior, middle, inferior), while the left lung has two lobes (superior and inferior).

• Functionality: Each lobe can function independently, which is critical for lung health; any lobe can be surgically removed if necessary without significantly impeding overall function.

Pulmonary Lobules and Alveoli

• Definition: Pulmonary lobules are the smallest functional subunits of the lungs containing alveoli, where gas exchange takes place.

• Each terminal bronchiole supplies one pulmonary lobule, branching into respiratory bronchioles, leading to alveolar ducts, and subsequently to alveolar sacs (sac-like structures made of multiple alveoli).

Structure of Alveoli

• Quantity: Approximately 150 million alveoli per lung, creating a spongy texture and significantly expanding the surface area for gas exchange.

• Capillary Network: An extensive capillary network envelops each alveolus, ensuring efficient transfer of gases between air and blood.

• Elastic Fibers: Comprised of elastic fibers surrounding the alveoli to aid in their expansion during inhalation and recoil during exhalation, facilitating air movement.

Pleural Layers

• Pleurae: These are serous membrane sacs that surround the lungs, composed of two layers:

  • Visceral Pleura: Covers the outer surface of the lungs, adhering closely to lung tissue.

  • Parietal Pleura: Lines the thoracic wall, diaphragm, and mediastinum, providing a protective covering.

• Pleural Cavity: The potential space between the visceral and parietal pleurae contains pleural fluid that reduces friction during respiratory movements, enhancing smooth lung expansion and contraction.

Alveolar Epithelium

• Cell Types: Various cell types are present in the alveoli:

  • Pneumocytes Type I: Thin and delicate cells that form the alveolar wall for efficient gas diffusion.

  • Pneumocytes Type II: Responsible for the production of surfactant, a substance that reduces surface tension within the alveoli, preventing their collapse.

  • Alveolar Macrophages: Wandering immune cells that identify and phagocytize foreign particles and pathogens, ensuring alveolar health.

Blood-Air Barrier

• Gas Exchange Interface: Gas exchange occurs between blood and alveolar air through three essential layers:

  • Alveolar Cell Layer: The thin layer of alveolar epithelium.

  • Fused Basement Membranes: Composed of both alveolar and capillary membranes.

  • Capillary Endothelium: The layer of endothelial cells lining the capillaries.

The Respiratory Membrane

• Efficiency: This interface allows for very rapid diffusion of gases due to the minimal distance (average of approximately 0.5 µm) separating the air within the alveoli and the blood within the capillaries.

• Solubility: Both oxygen and carbon dioxide are lipid-soluble gases, allowing for their diffusion through the phospholipid bilayer of the cell membranes, enhancing the effectiveness of gas exchange.