Respiratory System I-1-1.pptx

Respiratory System I By : Rakhshindah Qureshi MBBS Learning Objectives : 1.List and name the components of conducting and respiratory portions of respiratory system . 2. Describe the morphology and functions of major cell types associated with olfactory epithelium . 3. Describe the morphology and...

Respiratory System I By : Rakhshindah Qureshi MBBS Learning Objectives : 1.List and name the components of conducting and respiratory portions of respiratory system . 2. Describe the morphology and functions of major cell types associated with olfactory epithelium . 3. Describe the morphology and function of major cell types associated with respiratory epithelium . 4. Describe the morphology of true and false vocal cords . 5. Describe the morphological characteristics , and explain the consequent functional significance , for each division of the conducting portion of respiratory system . 6. Discuss the clinical correlates presented in the lecture . Reference : COLOR ATLAS & TEXT OF HISTOLOGY BY Gartner & Hiatt 7th edition . Respiratory System • The respiratory system is responsible for respiration , thereby provides oxygen for use by the cells and eliminates carbon dioxide produced during cellular metabolism . • The respiratory system is divided into 2 functionally distinct portions : • 1. CONDUCTING PORTION : • Nasal cavity • Nasopharynx • Larynx • Trachea • Bronchi • Bronchioles • Terminal bronchioles Respiratory System • 2. RESPIRATORY PORTION : • Respiratory bronchioles • Alveolar ducts • Alveolar sacs and • Alveoli . Conducting portion of Respiratory system • FUNCTIONS OF CONDUCTING PORTION : • 1. Conduit for delivering air to the lungs . • 2.Conditions incoming air by cleansing , moistening and warming it as it moves towards the lungs . • 3. Olfaction ~ a small area of conducting portion possesses the sensory receptors and other specializations necessary for olfaction . • 4. Sound production , the vocal folds in the larynx are specialized for this function . RESPIRATORY EPITHELIUM • Pseudostratified columnar ciliated with goblet cells lines most of the conducting pathway and is important in conditioning the inspired air . • A gradual transition to simple columnar and finally simple cuboidal epithelium occurs towards the end of conducting pathway . • Nonkeratinized stratified squamous epithelium is present in areas either exposed to rapid airflow (e.g vocal folds) or prone to other abrasions (e.g epiglottis) Cells associated with Respiratory epithelium • 1. Ciliated columnar cells : most numerous cells .Each cell has hundreds of cilia on its apical surface that move mucus along the epithelial surface. • 2.Goblet (mucous) cells : produce & secrete mucous. The apical region of the cell is filled with polysaccharide- rich mucous droplets. • This is the second most numerous cell type .The number of goblet cells decreases in deeper portions of the conducting portion of respiratory system . • 3.Brush cells : their apical surface is covered with microvilli. These cells are thought to be sensory receptors . • 4. Basal (stem) cells : small somewhat rounded cells that sit on the basal lamina. These cells are regenerative cells , capable of dividing and differentiating into other cell types of the epithelium . • 5. Small granule cells : are the cells of diffuse endocrine system that are located on the basal lamina and have numerous granules. Granules are hormone like substance secreted by the cell that may regulate the mucous and serous secretions of other cells . Squamous Metaplasia • The chronic presence or accumulation of toxins that occur with heavy cigarette smoking or industrial air pollution affects the respiratory epithelium beginning in the nasal cavities . • Immobilization of cilia causes failure to clear mucus containing filtered material and exacerbates the problem leading eventually to likelihood of squamous metaplasia of the epithelium . • A change from pseudostratified ciliated columnar to stratified squamous epithelium can occur . This can lead to precancerous cell dysplasia in Histological characteristics of specific regions of the conducting portion of respiratory system • Nasal cavity : • Vestibule : the portion of the nasal cavity where air enters first . • Nares ( nostrils) : the anterior dilated portion of the vestibule is lined by skin (i.e., stratified squamous keratinized epithelium) with vibrissae , sweat glands and sebaceous glands. • The keratinized stratified squamous epithelium gradually gives way to respiratory epithelium in the vestibule . • Nasal septum : hyaline cartilage that divides the vestibule into right and left halves . Internal to the vestibule the nasal septum is composed of bone . Histological characteristics of specific regions of the conducting portion of respiratory system • Nasal conchae ( turbinates) : 3 shelf like folds in the bony lateral walls of the nasal cavity. • Functions of nasal Conchae : • 1.Increasing the surface area exposed to the air • 2.Disrupting the air flow . Respiratory epithelium covers the middle and inferior nasal conchae . • Olfactory epithelium covers a portion of each superior nasal concha . Histological characteristics of specific regions of the conducting portion of respiratory system • Olfactory epithelium : • is where olfactory sensory reception takes place. This is a thick (~60μm) pseudostratified columnar ciliated epithelium covering the superior nasal concha . • Cell types of olfactory epithelium : • 1. Olfactory cells • Function : Olfactory sensory reception . • Structure : each olfactory cell is a bipolar neuron with an olfactory bulb on its apical surface projecting slightly above the surface of surrounding cells . • Olfactory cilia : 6-10 long nonmotile projections extending from the bulb >> generate a nervous impulse in response to binding of odiferous molecules • The round nucleus of the olfactory cell is found in the basal half of the cell .The cell's axon project from the basal surface and joins other axons below the basal lamina , forming nerve fiber bundles in the lamina propria . Histological characteristics of specific regions of the conducting portion of respiratory system • Cell types of olfactory epithelium : • 1. Olfactory cells • Olfactory nerve ( cranial nerve I) forms from these fiber bundles after they pass through the cribriform plate of the ethmoid bone and join other nerve fiber bundles . Histological characteristics of specific regions of the conducting portion of respiratory system • Cell types of olfactory epithelium : • 2. Sustentacular cells : • Function : To support and electrically insulate the olfactory cells . • Structure : These are the most numerous cell type in olfactory epithelium. • Each cell has microvilli on its apical surface and an oval nucleus situated in the apical third of the cytoplasm . • They form junctional complexes with each other and with olfactory cells ( in the region of olfactory bulb ) Histological characteristics of specific regions of the conducting portion of respiratory system • Cell types of olfactory epithelium : • 3.Basal cells : • Function : can replace and proliferate both olfactory cells and sustentacular cells . (one of the few instances in adult where nerve cells can be replaced ) • Structure: basal cells are short, pyramid – shaped cells at the base of the epithelium that do not extend all the way to the apical surface . • Olfactory glands ( Bowman's glands) : produce a serous secretion that traps and dissolves odiferous substances. • Constant flow from these glands can remove old scents and permits detection of new scents. • The secretory portion of these glands are found in lamina propria deep to the olfactory epithelium and their ducts open on the epithelial surface Olfactory mucosa of nasal cavity Histological characteristics of specific regions of the conducting portion of respiratory system • Paranasal sinuses : relatively large , blind cavities present in 4 skull bones (frontal , ethmoid , sphenoid and maxilla ) that communicate with the nasal cavity via small openings . • Respiratory epithelium lines the sinuses .The thin lamina propria is continuous with the periosteum and possesses seromucous glands. • Cilia on the respiratory epithelium beat in such a way that mucous is moved towards the nasal cavity . • Sinusitis : a common condition in which paranasal sinuses are inflamed .This painful condition results from an upper respiratory tract infection . • Chronic sinusitis and chronic bronchitis are components of primary ciliary dyskinesia or Kartagener’s syndrome , an inherited disorder characterized by defective ciliary function . Histological characteristics of specific regions of the conducting portion of respiratory system • Larynx : an irregular rigid tube that serves as a : • Passageway for air between oropharynx and trachea . • The organ involved in producing sounds for speech . • Larynx possesses several irregularly shaped cartilaginous plates some of which are hyaline while others are elastic cartilage. These plates are joined by ligaments and are moved with respect to one another by intrinsic skeletal muscle of the larynx. Histological characteristics of specific regions of the conducting portion of respiratory system • Epiglottis : a spoon shaped plate with an elastic cartilage core that serves as a cover for the larynx. • During Respiration : • The epiglottis is in a vertical position and uncovers the laryngeal opening • During Swallowing : • The epiglottis moves to a horizontal position covering the larynx . • Stratified squamous epithelium covers the lingual surface and the apical portion of the epiglottis . The epithelium gradually changes to respiratory epithelium at the base of the laryngeal surface . Histological characteristics of specific regions of the conducting portion of respiratory system • Larynx : • Two pairs of mucosal folds are present in the larynx wall distal to the epiglottis : • False vocal cords (ventricular folds ) : are named so because they lack the associated musculature and are immovable. These folds can create resonance of sound . • Superior part of false vocal cords is covered by respiratory epithelium . Histological characteristics of specific regions of the conducting portion of respiratory system • Larynx : • Ventricle : out pocket of the larynx lumen located between the false and true vocal cords . • The ventricle affects the resonance and volume of the sound . Histological characteristics of specific regions of the conducting portion of respiratory system • Larynx : • Vocal folds ( true vocal cords): lower pair of folds , covered by stratified squamous non keratinized epithelium . • Movement of air against the edges of these folds produces sound . • Vocal ligament : located with in the vocal folds and consists of parallel elastic fibers bundles . • Vocalis muscle : skeletal muscles attached to the ligament that can modify both the tension on the true vocal cords and the amount of space between the folds . Histological characteristics of specific regions of the conducting portion of respiratory system Trachea :  A tube ~10cm , extending from the base of the larynx and bifurcates into 2 primary bronchi . • The wall of the trachea is divided into 4 layers Starting from the lumen side these are : • 1.Mucosa : respiratory epithelium , underlying loose elastic – rich connective tissue layer , the lamina propria . Histological characteristics of specific regions of the conducting portion of respiratory system • Trachea : • 3. Cartilaginous layer : stack of ~ 1020 horse-shoe shaped hyaline cartilages that keep the tracheal lumen open . The open end of the tracheal rings are situated posteriorly. Adjacent rings are held together by fibroblastic connective tissue . • Trachealis muscle : smooth muscle bridging the two end of each tracheal ring, thus regulating the lumen size . • 4. Adventitia : loose connective tissue , often with many adipose cells , binding the trachea to the adjacent structures . Histological characteristics of specific regions of the conducting portion of respiratory system • The bronchial tree : • The trachea divides into 2 primary bronchi , each of which enters a lung .Primary bronchi are histologically comparable to trachea, but they are smaller in diameter and have thin walls . • Each primary bronchus gives rise to lobar bronchi (secondary bronchi) , each of which enters a lobe of the lung .The right primary bronchus splits into 3 lobar bronchi and the left primary bronchus divides into 2 lobar bronchi . • The lobar bronchi further divide into segmental (tertiary) bronchi .The lobar bronchi give rise to 10 segmental bronchi in each lung , with each bronchus going to a discrete Broncho pulmonary segment . • Arterial blood vessels supplying the lung follow the same branching pattern as bronchi . • This segmental nature of the lung and parallel course of bronchi and blood vessels are clinically important as it facilitates segmental resections during surgical procedures . Segmentation of the intrapulmonary bronchial tree • As the bronchial diameter decreases , cartilage rings are replaced by isolated plates of hyaline cartilage . • Small mucus and serous glands are abundant , their ducts open into the bronchial lumen . • Crisscrossing bundles of spirally arranged smooth muscles and elastic fibers are present in the lamina propria , which become more prominent in smaller bronchi . • Numerous lymphocytes are present in lamina propria , smaller bronchi , aggregates of lymphocytes (MALT) becomes more prominent Histological characteristics of specific regions of the conducting portion of respiratory system • The bronchial tree : • The segmental bronchi branch into smaller and smaller bronchi until they eventually form: •Bronchioles : • Bronchioles begin at 10 th to 15th level of branching in the bronchial tree and are a few millimeters in diameter. • In contrast to bronchi , bronchioles do not possess cartilage in their wall. • Epithelium varies from thin respiratory epithelium ( ciliated pseudostratified columnar) in larger bronchioles to more commonly simple columnar ciliated to simple cuboidal ciliated epithelium . Histological characteristics of specific regions of the conducting portion of respiratory system • The bronchial tree : • Terminal bronchioles : represent the end of conducting portion of respiratory epithelium • They are <0.5 mm in diameter and lined by simple cuboidal epithelium ( ciliated ) . • The lamina propria is thin and has fibroelastic connective tissue • There is a layer or two of smooth muscle . Histological characteristics of specific regions of the conducting portion of respiratory system • The bronchial tree : • Terminal bronchiole : • Clara cells : specialized cells of the terminal bronchioles found interspersed among the cuboidal cells . • Clara cells are also called club cells . • Histology : • Clara cells have a rounded apical surface without cilia , although they do have microvilli (not resolved in light microscope) Histological characteristics of specific regions of the conducting portion of respiratory system • Functions of Clara cells : • 1. Secretion of glycosaminoglycan that coat and protect the lining of the bronchioles • 2. Synthesis of enzymes believed to degrade certain inhaled toxins . • 3. Synthesis of a surfactant that reduces surface tension in bronchioles • 4. Regeneration of bronchiole epithelium via mitotic division . Histological characteristics of specific regions of the conducting portion of respiratory system • Other cells in the terminal bronchiole : • Brush cells -------- chemosensory • DNES small granule cells • A small proportion of stem cells provide for replacement of other bronchiolar cell types . Segmentation of the intrapulmonary bronchial tree • A terminal bronchiole supplies a pulmonary lobule • Each respiratory bronchiole --- derived from a terminal bronchiole – organizes a pulmonary acinus . Asthma : • Is a common condition produced by chronic inflammation within the bronchial tree of the lungs . • The disorder is characterized by sudden constrictions of the smooth muscle in the bronchioles --- bronchospasms or bronchial spasms . • Constriction is caused by mast cell degranulation triggered by the presence of specific antigens . • The resulting difficulty in breathing may be mild to severe . • Epinephrine and other sympathomimetic drugs relax the smooth muscles and increase the bronchiolar diameter by stimulating the sympathetic nervous system , and they are administered during asthma attacks . Review of Respiratory system Review of Respiratory System