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This article provides an overview of the functions, organs, and structures of the respiratory system. It discusses the process of gas exchange, the organs involved, and the physiology of ventilation.
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Functions of the Respiratory System • Provides structures and mechanisms for gas exchange • Intake of O2 • Elimination of CO2 • Helps maintains body’s pH
Respiration • The exchange of gases between the atmosphere, blood, and cells • Pulmonary Ventilation - the exchange of air between the atmosphere and lungs • External (Pulmonary) Respiration - gas exchange between the lungs and blood • Internal (Tissue) Respiration - gas exchange between the blood and cells
Organs of the Respiratory System • Nose • Pharynx • Larynx • Trachea • Bronchi • Lungs
Nose • External Portion • Supporting bony framework • Cartilage - Skin • Mucous membranes • Nostrils or external nares • Internal Portion - large cavity within the skull • Connects the external nose to the pharynx through two openings (Internal Nares)
Nose • Nasal Cavity - large cavity that contains both the external and internal nose cavities • divided into the right and left sides by the NASAL SEPTUM
Functions of the Nose • Warming, moisturizing and filtering incoming air • Smell (reception of olfactory stimulus) • Resonating chamber for speech
Pharynx • Funnel-shaped tube about 13 cm long • Extends from the internal nares down to the cricoid cartilage of the larynx • Walls composed of skeletal muscle lined with a mucous membrane • Divided into three areas • Nasopharynx • Oropharynx • Laryngopharynx
Functions of the Pharynx • Passageway for food and air • Resonating chamber for speech
Larynx (Voice Box) • A short passageway that connects the pharynx with the trachea • Walls of the larynx is composed of 9 pieces of cartilage • Three single pieces of cartilage • epiglottic cartilage (Epiglottis) • thyroid cartilage (Adam’s Apple) • cricoid cartilage (attaches the Larynx to the Trachea) • Three paired pieces of cartilage • arytenoid - corniculate - cuneiform
Epiglottis • Large leaf-shaped piece of cartilage lying on top of the larynx • The stem of the epiglottic cartilage is attached to the thyroid cartilage • Leaf portion of the cartilage is unattached and acts like a trap door covering the opening to the trachea which is called the glottis. • Dependent upon breathing or swallowing
Glottis • The opening from the pharynx to the larynx that contains the vocal cords • Vocal Cords - mucous membrane folds that extend across the glottis in two layers • upper layer or folds - false vocal folds • lower layer or folds - true vocal folds • Sounds originate from vibration of these true vocal cords
Trachea • Tubular passageway about 12 cm long and 2.54 cm in diameter • Anterior to the esophagus • Extends from the larynx to about the 5th thoracic vertebrae • Composed of 16 - 20 C-shaped cartilage rings stacked upon one another • Hyaline cartilage rings • Covers the anterior and lateral walls
Trachea • Non-cartilaginous posterior softer portion of the trachea allows for expansion of the esophagus during swallowing • Lined with ciliated epithelium • The point where the trachea bifurcates is called the carina • About the 5th thoracic vertebrae
Bronchi • Tubes that branch off of the trachea at the carina and extend into the lungs • Left Primary Bronchus (Left Mainstem Bronchus) • Right Primary Bronchus (Right Mainstem Bronchus) • Shorter and more vertical • Swallowed objects more likely to lodge in the right primary bronchus than the left
Bronchi • Also composed of cartilaginous rings • Continue branching as they enter the lungs into a structure called the bronchial tree • Trachea -Mainstem (Primary) Bronchi - Secondary (Lobar) Bronchi - Segmental (Tertiary) Bronchi - Terminal Bronchioles - Respiratory Bronchioles - Alveolar Ducts
Lungs • Paired - cone shaped organs that occupy most of the thoracic cavity • Separated from each other by the heart and other structures of the mediastinum • Surrounded by a double layered serous membrane called the pleural membrane
Pleural Membrane • Parietal Pleura - outer layer of the pleural membrane • Attached to the thoracic wall • Visceral Pleura - inner layer of the pleural membrane • Attached to the lungs themselves • Between the parietal pleura and the visceral pleura is a potential space called the pleural cavity • Contains pleural (serous) fluid (reduces friction)
Alveoli • A cup shaped out pouching of epithelial tissue • Place where external respiration occurs (gas exchange between the lungs and the blood) • Lungs contain 300 - 500 million alveoli • Surface area of about 750 sq. ft. • The size of a Tennis Court
Physiology of Ventilation • Ventilation - the process of inhaling and exhaling air in and out of the lungs • Pulmonary Ventilation - the process by which air flows between the lungs and the external environment • Due to a change in pressure between the atmosphere and the air in the lungs
Inspiration (Inhalation) • Bringing air into the lungs from the external environment • The lungs themselves contain no muscles and thus depend upon the relationship with the muscles of the walls of the thoracic cavity to alter lung volumes
Expiration (Exhalation) • Movement of air from the lungs to the external environment • Normally a passive process (no energy or muscular contractions required) • Dependent upon muscle and lung elasticity • May become active during high levels of physical activity • Most people require ventilation rates above 55% - 65% of their vital capacity for expiration to become active