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RESPIRATORY SYSTEM REVIEWER INTRODUCTION ▪ Body requires abundant and endless supply of molecular oxygen (O2) ▪ The respiratory system helps us in what we commonly call breathing, but is more appropriately termed respiration ▪ Respiration includes four processes: 1. Ventilation – the movement of air into and out of the lungs 2. Gas exchange between air in the lungs and blood (external respiration) 3. Transport of oxygen and carbon dioxide in the blood 4. Gas exchange between the blood and the tissues (internal respiration) ▪ Respiration and cellular respiration; what’s the difference? ▪ The two processes are related 1. Respiration provides the O2 needed in cellular respiration to make energy 2. Respiration also removes CO2, a waste product during cellular respiration ▪ Two organ systems that share the responsibility of supplying O2 and eliminating CO2 1. Cardiovascular system 2. Respiratory system ▪ In addition to respiration, the respiratory system performs the following functions: 1. Regulation of blood pH 2. Production of chemical mediators 3. Voice production 4. Olfaction 5. Protection 1 FUNCTIONAL ANATOMY OF THE RESPIRATORY SYSTEM Functional division respiratory system: of the Conducting zone • From the nose to the terminal bronchioles • Exclusively for air movement • Cleaning, warming, and humidification of air Respiratory zone • From the respiratory bronchioles to alveoli • Where actual gas exchange between air and blood takes place, a process known as external respiration 2 Functions of the Nasal Conchae 1. Increase surface area 2. Increase air turbulence within the nasal cavity 3. Increase trapping of inhaled particles 3 Functions of the Paranasal Sinuses 1. Lighten the skull 2. Act as resonance chambers for speech 3. Produce mucus Functions of the Nasal Cavity 1. Serves as a passageway for air 2. Cleans the air 3. Humidifies and warms the air 4. Contains the olfactory epithelium 5. Helps determine voice sound 4 Functions of the Pharynx 1. Serves as a passageway for air and food 2. Drains the middle through the opening of the pharyngotympanic tube (nasopharynx) 3. Protects the body from infection Tonsils are clusters of lymphatic tissues that play a role in protecting the body from infection Larynx ▪ Commonly called the voice box ▪ Located inferior to the pharynx ▪ Made of eight rigid hyaline cartilages and one elastic cartilage ▪ Paired (hyaline) ▪ Arytenoid ▪ Corniculate ▪ Cuneiform ▪ Made of eight rigid hyaline cartilages and one elastic cartilage ▪ Unpaired cartilages ▪ Thyroid (hyaline) ▪ Largest ▪ Also known as Adam’s apple ▪ Cricoid (hyaline) ▪ Forms the base of the larynx where the other cartilages rest ▪ Epiglottis (elastic) ▪ Attached to the thyroid and projects superiorly as a free flap toward the tongue ▪ Vocal folds (true vocal cords) ▪ ▪ Vibrate with expelled air ▪ Allow us to speak Glottis includes the vocal cords and the opening between the vocal cords 5 Functions of the Larynx 1. Thyroid and cricoid cartilages maintain an open passageway for air movement 2. The larynx prevents swallowed materials from entering the lower respiratory tract and regulates the passage of air into and out of the lower respiratory tract 3. The vocal folds are the primary source of sound production 4. The pseudostratified ciliated columnar epithelium lining the larynx produces mucus, which traps debris in air; the cilia move the mucus and debris into the pharynx Trachea ▪ Commonly called the windpipe ▪ 4-inch-long tube (10-12 cm) descending from the larynx to the level of the fifth thoracic vertebra ▪ Consists of dense regular connective tissue and smooth muscle reinforced with 15-20 Cshaped pieces of hyaline cartilage ▪ Cartilages support the anterior and lateral sides of the trachea ▪ Cartilages protect the trachea and maintain an open passageway for air ▪ Posterior wall of the trachea is devoid of cartilage ▪ However, it contains an elastic ligamentous membrane and bundles of smooth muscle called the trachealis muscle ▪ Contraction of the trachealis muscle can narrow the diameter of the trachea 6 ▪ During coughing, this action causes air to move more rapidly through the trachea, which helps expel mucus and foreign objects ▪ Lined by pseudostratified columnar ciliated epithelium with numerous goblet cells ▪ Goblet cells produce mucus, which traps inhaled foreign particles ▪ Cilia beat continuously in the opposite direction of incoming air ▪ Cilia move the mucus and foreign particles into the larynx, from which they enter the pharynx and are swallowed ▪ Constant, long-term irritation to the trachea, as observed in smokers, can cause the tracheal epithelium to become stratified squamous epithelium that lacks cilia and goblet cells ▪ Consequently, the normal function of the tracheal epithelium is lost 7 Main Bronchi ▪ Formed by division of the trachea ▪ Each bronchus enters the lung at the hilum (medial depression) ▪ Right bronchus is wider, shorter, and straighter than left ▪ Bronchi subdivide into smaller and smaller branches Lungs ▪ Occupy the entire thoracic cavity except for the mediastinum ▪ Apex of each lung is near the clavicle (superior portion) ▪ Base rests on the diaphragm ▪ Each lung is divided into lobes by fissures ▪ Left lung – two lobes ▪ Right lung – three lobes ▪ Visceral pleura covers the lung surface ▪ Parietal pleura lines the walls of the thoracic cavity ▪ Pleural fluid fills the space or cavity (pleural space or cavity) between the layers ▪ ▪ Allows the lungs to glide over the thorax ▪ Decreases friction during breathing Pleural space is more of a potential space 8 Bronchial Tree ▪ Main bronchi divide into lobar bronchi, or secondary bronchi, within each lung 9 ▪ Two lobar bronchi exist in the left lung ▪ Three exist in the right lung ▪ Lobar bronchi, in turn, give rise to segmental bronchi, or tertiary bronchi ▪ These bronchi continue to branch, finally giving rise to bronchioles (smallest conducting passageways), which are less than 1 mm in diameter ▪ Bronchioles also subdivide several times to become even smaller terminal bronchioles ▪ Approximately 16 generations of branching occur from the trachea to the terminal bronchioles 10 ▪ As the air passageways of the lungs become smaller, the structure of their walls changes ▪ Like the trachea, the main bronchi are supported by C-shaped cartilage connected by smooth muscle ▪ In the lobar bronchi, the C-shaped cartilages are replaced with cartilage plates, and smooth muscle forms a layer between the cartilage and the mucous membrane ▪ As the bronchi become smaller, the cartilage becomes more sparse, and smooth muscle becomes more abundant ▪ Terminal bronchioles have no cartilage, and the smooth muscle layer is prominent ▪ Bronchi are lined with pseudostratified columnar ciliated epithelium ▪ Larger bronchioles are lined with ciliated simple columnar epithelium ▪ Ciliated simple cuboidal epithelium lines the terminal bronchioles ▪ Ciliated epithelium functions as a mucus-cilia escalator, trapping debris in the air and moving it to the larynx Respiratory Zone ▪ Terminal bronchioles lead into respiratory zone structures and terminate in alveoli ▪ Respiratory zone includes the: ▪ ▪ Respiratory bronchioles ▪ Alveolar ducts ▪ Alveolar sacs ▪ Alveoli (air sacs) – the only site of gas exchange Conducting zone structures include all other passageways 11 ▪ ▪ ▪ Alveoli ▪ Simple squamous epithelial cells largely compose the walls ▪ Alveolar pores connect neighboring air sacs ▪ Pulmonary capillaries cover external surfaces of alveoli Respiratory membrane ▪ Air-blood barrier ▪ On one side of the membrane is air, and on the other side is blood flowing ▪ Formed by alveolar and capillary walls Respiratory membrane ▪ A thin layer of fluid lining the alveolus ▪ The alveolar epithelium composed of simple squamous epithelium ▪ The basement membrane of the alveolar epithelium ▪ A thin interstitial space ▪ The basement membrane of the capillary endothelium ▪ The capillary endothelium, composed of simple squamous epithelium 12 ▪ ▪ Gas crosses the respiratory membrane by diffusion ▪ Oxygen enters the blood ▪ Carbon dioxide enters the alveoli Alveolar macrophages (“dust cells”) add protection by picking up bacteria, carbon particles, and other debris ▪ Surfactant ▪ Lipid molecule ▪ Coats gas-exposed alveolar surfaces ▪ Secreted by cuboidal surfactant-secreting cells 13
