Respiratory

Respiratory System Anatomy & Physiology

Overview

  • Definition of Respiration: Gas exchange of oxygen (O2) and carbon dioxide (CO2)

    • Location: Between atmosphere and body cells

    • Importance: Body cells require O2 for aerobic ATP production and need to eliminate CO2 produced during this process.

General Functions of the Respiratory System

  • Passageway for Air: Facilitates the movement of air from atmosphere to alveoli.

  • Gas Exchange:

    • O2 diffuses from alveoli into the bloodstream.

    • CO2 diffuses from blood into the alveoli.

  • Olfaction: Involves olfactory receptors located in the superior nasal cavity.

  • Sound Production:

    • Air movement across vocal cords in the larynx (voice box) results in sound production through vibration of vocal cords.

General Organization of the Respiratory System

  • Structural Organization:

    • Upper Respiratory Tract: Consists of nasal cavity, pharynx, larynx.

    • Lower Respiratory Tract: Includes trachea, bronchi, bronchioles, alveolar ducts, and alveoli.

  • Functional Organization:

    • Conducting Zone: Facilitates air transport from the nose to terminal bronchioles.

    • Respiratory Zone: Involves gas exchange structures including respiratory bronchioles, alveolar ducts, and alveoli.

General Anatomy of the Respiratory System

  • Respiratory Mucosa:

    • Lining of the respiratory tract, specifically called the respiratory mucosa.

    • Composition: Epithelium with cilia, underlying lamina propria (areolar connective tissue), and mucosa-associated lymphoid tissue (MALT).

    • Epithelial changes:

    • Starts as pseudostratified ciliated columnar epithelium, transitions to simple ciliated columnar, simple cuboidal, and finally simple squamous in alveoli.

    • Exceptions: Stratified squamous epithelium found in high abrasion areas, such as oropharynx, laryngopharynx, vocal cords, and superior larynx.

Mucous Secretions

  • Source: Produced by goblet cells and mucous/serous glands in the lamina propria.

  • Function:

    • Contains mucin protein which increases viscosity, trapping dust and other particulates.

    • Active defense against microbes including antibacterial enzymes (lysozyme), proteins (defensins), and antibodies (immunoglobulin A).

    • Often referred to as sputum when coughed up.

Clinical View: Cystic Fibrosis

  • Description: Defective chloride channels preventing chloride ions from moving from cells lining the respiratory tract.

  • Consequence: Mucus becomes thick, blocking respiratory pathways and leading to frequent pulmonary infections, and potential complications in the pancreas and salivary glands.

Nose and Nasal Cavity

  • Nose: First conducting structure for inhaled air.

    • Structure: Composed of bone, hyaline cartilage, dense irregular connective tissue, and skin.

    • Bridge formed by paired nasal bones with lateral cartilages and alar cartilages providing nostril structure.

  • Nasal Cavity: Extends from nostrils to choanae (posterior nasal apertures) that lead to the pharynx.

    • Floor: Formed by the palate; Roof: Composed of nasal, frontal, ethmoid, and sphenoid bones.

    • Nasal Septum: Divides cavity into left and right sides with anterior septal cartilage and posterior bone structures.

  • Conchae: Three paired bony projections on lateral walls (superior, middle, and inferior) are known as nasal conchae, creating nasal meatuses immediately inferior to each corresponding concha.

  • Regions of Nasal Cavity:

    • Nasal Vestibule: Lined by skin and vibrissae, trapping larger particles.

    • Olfactory Region: Contains olfactory epithelium for odor detection.

    • Respiratory Region: Lined by pseudostratified ciliated columnar epithelium with extensive vascularization aiding in air conditioning (warming, cleansing, and humidifying).

Clinical View: Runny Nose

  • Causes: Increased mucus production due to allergies, viral infections, lacrimal gland secretions from crying, or exposure to cold air.

Paranasal Sinuses

  • Definition: Spaces within skull bones named for the specific bones in which they reside.

  • Types: Frontal sinuses, ethmoidal sinuses, sphenoidal sinuses, maxillary sinuses.

  • Function: Lined by respiratory epithelium; mucus is swept into the pharynx and swallowed.

Clinical View: Sinus Infections and Headaches

  • Cause: Inflammation due to respiratory infections or allergies leading to blocked drainage and accumulation of mucus, potentially resulting in headaches.

Pharynx

  • Description: Funnel-shaped passageway posterior to nasal cavity, oral cavity, and larynx.

  • Sections:

    • Nasopharynx: Superior part, air passage, lined by respiratory epithelium, connects to the middle ear via the auditory tube and contains tonsils.

    • Oropharynx: Posterior to the oral cavity, extends from soft palate to hyoid bone, lined by non-keratinized stratified squamous epithelium, contains palatine and lingual tonsils.

    • Laryngopharynx: Inferior part, passageway for both food and air, lined by non-keratinized stratified squamous epithelium.

Larynx

  • Description: Pyramid-shaped airway structure situated between the laryngopharynx and trachea.

  • Functions: Produces sound via vocal folds; acts as an air passage; prevents ingested materials from entering the respiratory tract; assists in increasings abdominal pressure during actions like childbirth.

  • Anatomy: Consists of nine cartilages, including:

    • Unpaired: Thyroid cartilage (notable Adam's apple), cricoid cartilage, epiglottis.

    • Paired: Arytenoid, corniculate, and cuneiform cartilages.

    • Vocal Ligaments: Form the true vocal cords, site of sound production, modulated by tension, length, and thickness contributing to pitch and loudness.

Clinical View: Laryngitis

  • Description: Inflammation resulting in hoarseness and potential airway obstruction; may extend to epiglottis.

Lower Respiratory Tract

  • Components: Conducting pathways leading from trachea to terminal bronchioles, gas exchange structures such as respiratory bronchioles, alveolar ducts, and alveoli.

  • Trachea: Connects larynx to two main bronchi.

    • Anatomical Details: Approximately 13 cm in length, reinforced by C-shaped rings of hyaline cartilage; the trachealis muscle aids in coughing.

Clinical View: Tracheotomy and Cricothyrotomy

  • Tracheotomy: Incision into trachea for airway obstruction or compromised ventilation.

  • Cricothyrotomy: Emergency incision between cricoid and thyroid cartilage for airway access.

Bronchial Tree

  • Function: Highly branched air passage system starting at the main bronchi and ending at bronchioles.

  • Anatomy: Structures from right and left main bronchi leading to lobar and segmental bronchi, terminating at small airways and terminal bronchioles.

Clinical View: Bronchitis

  • Description: Inflammation of bronchi may be acute (often viral) or chronic (long-term irritant exposure), resulting in cough and mucus production.

Respiratory Zone: Respiratory Bronchioles, Alveolar Ducts, and Alveoli

  • Microstructures: Composed of respiratory bronchioles leading to alveolar ducts and clusters of alveoli, facilitating gas exchange.

  • Cell Types: Alveolar type I cells (95% of surface area, facilitate gas exchange), type II cells (secrete surfactant to prevent collapse), and alveolar macrophages (immune defense).

Respiratory Membrane

  • Structure: Extremely thin (0.5 microns) barrier for gas exchange between alveoli and pulmonary capillaries.

  • Function: O2 diffuses from alveoli to capillaries; CO2 diffuses from blood to alveoli.

Clinical View: Pneumonia

  • Description: Infection characterized by inflammation and fluid filling alveoli, resulting in cough, fever, and difficulty breathing.

Blood Circulation in the Lungs

  • Two Types:

    • Pulmonary Circulation: Transports deoxygenated blood from right ventricle to pulmonary capillaries for gas exchange.

    • Bronchial Circulation: Supplies bronchi and lung tissues with oxygenated blood from the aorta.

Pleural Membranes and Pleural Cavity

  • Structure: Composed of visceral pleura on lung surfaces and parietal pleura lining thoracic walls; serous fluid enables easy movement.

  • Clinical Importance: Conditions like pleurisy (inflammation) and pleural effusion (fluid accumulation) that cause chest pain or difficulty breathing.

Lung Inflation Mechanism

  • Factors: Intrapulmonary pressure, low intrapleural pressure, and the elastic properties of the lungs contribute to lung inflation.

Clinical Views: Pneumothorax and Atelectasis

  • Pneumothorax: Presence of air in pleural cavity, requiring medical intervention.

  • Atelectasis: Collapse of lung due to pressure equalization, necessitating removal of air from pleural space.