Respiratory System


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Respiratory System

  1. 1. Functions of the Respiratory System Chapter 17 • Cooperates with the cardiovascular The Respiratory system in supplying oxygen to cells and System removing CO2 • Warms, moistens and filters debris and pathogens from inspired air • Contains receptors for smell • Produces sound • Helps eliminate wastes RESPIRATORY SYSTEM OVERVIEW Organs • The upper respiratory tract includes: • the nose, • the pharynx and • associated structures (tonsils, sinuses,etc.) • The lower respiratory tract includes: • the larynx, • the trachea • the bronchi and • the lungs which contain branches of bronchi that ultimately end in alveoli. Functional Divisions Transition from Conducting to • Conducting Structures that conduct air into the Respiratory Portions of the RT lungs and condition it before it enters the lungs: • the nose, • The cells and tissues of the conducting • the pharynx, portion of the RT gradually change such that • the larynx, there is a decrease in: • the trachea • goblet cells • the bronchi, bronchioles and terminal bronchioles. • cartilage • Respiratory Structures where gas exchange • ciliated cells occurs: • height of cells • the respiratory bronchioles, • and an increase in: • alveolar ducts, • smooth muscle • alveolar sacs • alveoli. • elastic fibers. 1
  2. 2. Air Conditioning Respiratory Epithelium • A major function of the conducting portion • PSCCE gradually changes to: of the RT is to condition the inspired air, i.e., to warm, moisten and filter it. • simple columnar ET, then • Structures that carry out these functions • simple cuboidal ET in terminal are: bronchioles • vibrissae (specialized hairs) • which lacks goblet cells but retains • The mucous, ciliated respiratory epithelium ciliated cells • highly vascularized underlying CT • simple squamous ET in alveoli • nasal conchae (turbinates) within the nasal fossae The Respiratory Epithelium SEM of Surface of Respiratory Epithelium PSCCE lines most of the respiratory tract except the terminal branches of the bronchioles, the alveoli and inferior portions of the pharynx. The lamina propria contains serous glands The movement of these cilia propels mucus and that contribute to moistening inspired air. trapped particles toward the pharynx. Five Cell Types in the Respiratory Epithelium Figure 24-02a (in order of abundance) • Ciliated columnar cells • Goblet (mucous) cells • Basal (stem) cells • Brush cells • sensory receptors with numerous microvilli • Small granule cells • endocrine - may act on caliber of bv or airway Note: all cell types sit on the basement membrane 2
  3. 3. The Nasal Cavity Paranasal Sinuses and • Consists of: Conchae • the Vestibule • the external portion of the nasal cavity • contains external nares lined with keratinized stratified squamous ET that gradually changes into respiratory ET before entering • the Nasal Fossae, • two convoluted openings within the skull • whose lateral walls contain three nasal conchae. Nasal Conchae Paranasal Sinuses • Function to increase the surface area of • Air-filled chambers that occur in the the respiratory epithelium for filtering, frontal, maxillary, ethmoid and sphenoid warming and moistening inspired air. bones of the skull. • The lamina propria under the RE • They are lined with a thinner RE that contains large venous plexuses called contains few goblet cells. swell bodies • They communicate with the nasal cavity • that alternately become engorged with through small openings. blood, shifting air flow to allow RE to • They function to lighten the skull and act recover from desiccation as resonating chambers for the voice. Upper Respiratory Tract The Larynx The nasopharynx contains the openings into the Eustachian tubes and pharyngeal tonsil. The oropharynx contains the The larynx is a box supported by 9 cartilages. lingual and palatine tonsils. 3
  4. 4. Larynx, posterior view Larynx, sagittal section The lingual surface of the epiglottis is covered with stratified squamous ET which changes to PSCCE at the base of the laryngeal surface. The Vocal Cords Vocal Cords • Below the epiglottis, the mucosa forms two pairs of folds that extend into the lumen of the larynx: • The upper pair are the ventricular folds (false vocal cords) covered with RE. • The lower pair are the true vocal cords containing the elastic vocal ligaments and vocalis muscles covered by stratified squamous ET. The Glottis, closed Laryngoscopic View Anterior Intrinsic laryngeal muscles close the glottis during swallowing. 4
  5. 5. Larynx, human VF The Trachea VoF l.s. x14 • Extends from the base of the larynx to the point at which it bifurcates into the two VM = vocalis muscle primary bronchi (about 10 cm or 4 in). VoF = vocal fold • It is lined in RE and contains 16-20 C-shaped VF = vestibular fold GL = mucous and VM rings of hyaline cartilage in the lamina propria. seromucous glands LC = laryngeal • These incomplete rings keep the tracheal cartilage GL lumen open and allow changes in its diameter. • A fibroelastic ligament (annular ligament) and the trachealis muscle (smooth muscle) bridge LC the open ends. Trachea and Esophagus, cs Trachea and Esophagus, cs The incomplete rings of cartilage permit expansion of the esophagus into the trachea during swallowing. The Thoracic Cavity Trachea, monkey l.s. x270 Identify: Goblet cell Lamina propria Submucosa Mucous and glands Perichondrium C-shaped hyaline cartilage The Right lung is thicker, broader and shorter and has 3 lobes separated by 2 fissures. The L lung has 2 lobes separated by a single oblique fissure. 5
  6. 6. Trachea and Bronchi, anterior view The Bronchial Tree • After entering the lungs, the primary bronchi give rise to 3 bronchi in the R lung and 2 in the L. • These are the secondary (lobar) bronchi which are characterized by 5-6 cartilagenous plates around their circumference. • The lobar bronchi divide repeatedly (about 12 times) giving rise to smaller bronchi with fewer and smaller plates of cartilage in their walls. • Tertiary (segmental) bronchi have 3 plates of cartilage. The right primary bronchus is shorter, wider and more vertical than the left. Implications? The Bronchial Tree Each lobe receives its own secondary (lobar) This is a plastic cast of an adult bronchus which branches multiple times. As long as bronchial tree. cartilage is present, these branches are bronchi. Bronchi and Bronchioles Bronchus, x.s. x132 SM L HC LT 6
  7. 7. Photomicrograph of a section of Lung A Large Bronchus Bronchi have cartilage in their walls, bronchioles do not. Bronchioles Bronchiole, x.s. • The terminal branches of bronchi are x270 bronchioles. • Bronchioles lack cartilage and glands but retain PSCCE that gradually changes to simple ciliated columnar with few goblet cells and finally to simple cuboidal epithelium. • They are 1 mm or less in diameter and have scalloped lumens. • Their lamina propria is composed largely of smooth muscle and elastic fibers. • Vagal (parasympathetic) stimulation causes constriction and sympathetic stimulation causes dilatation of the bronchioles. Sm LT Terminal Terminal Bronchioles Bronchioles, x.s. RB • Lack cartilage, x132 • Lined in ciliated simple columnar TB epithelium without goblet cells, • Accompanied by branches of the TB pulmonary artery, • Branch to form 2 or more respiratory bronchioles. TB • The epithelium of terminal bronchioles contains nonciliated, secretory Clara cells. 7
  8. 8. A Lung Lobule Clara Cells Pulmonary lobules are pyramid-shaped with the apex (containing a bronchiole) pointed toward the hilum of the lung. Each bronchiole divides to form 5- 7 terminal bronchioles within the lobule. Organization of a Lung Lobule Respiratory Bronchioles • Lined with ciliated cuboidal epithelial and Clara cells, • With underlying smooth muscle and elastic CT. • Walls are interrupted by numerous alveoli where gas exchange occurs. • At the distal portions, alveoli become more numerous and the cuboidal epithelial cells lose their cilia. Alveolar Ducts Alveolar Sacs • The walls of alveolar ducts consist of • Common areas for openings of a alveoli with smooth muscle bundles in cluster of alveoli, the lamina propria, • Supported by elastic and reticular • Smooth muscle disappears at the distal fibers. ends of alveolar ducts, • Elastic and collagen fibers provide the only support for the duct and its alveoli. 8
  9. 9. Diagram of Lung Tissue SEM of Alveoli Note: Smooth muscle bundles in the walls of alveolar ducts appear as knobs between adjacent alveoli. Cell Types in Alveoli Alveoli • Sac-like evaginations of the respiratory bronchioles, alveolar ducts and alveolar sacs; The • The terminal portions of the bronchial tree; alveolar • Covered by the richest capillary network in the septum has body. thin and • Walls contain: thick • Type I (squamous alveolar) cells, portions. • Type II (great alveolar or septal) cells and • macrophages (dust cells). Type I (squamous alveolar) cells make up • A few brush cells may be present to serve as 97% of the alveolar surface and receptors monitoring air quality. Type II (septal or “great alveolar”) cells are most of the remaining 3%. Respiratory Membrane The Respiratory Membrane (Blood-air Barrier or Alveolar-capillary Barrier) The thinnest membrane in the body is found where the alveolar The squamous Type I cells provide a barrier of air space minimal thickness that is readily permeable to meets a gases. The Type II cells secrete surfactant which capillary. lowers alveolar surface tension preventing collapse of alveoli. 9
  10. 10. RB Lung TB x14 LN ? HC ? 10