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GENERAL FEATURES OF UPPER & LOWER RESPIRATORY SYSTEM LEARNING OBJECTIVES At the end of this lecture, students should be know: The general features of respiratory system Structural and functional classifications of respiratory system The general structure, function and role of each organ making up the respiratory system INTRODUCTION The respiratory system serves 3 principal purposes in the human body: gaseous exchange sound production It can be divided into 2 structural divisions: upper & lower 2 functional divisions: conducting & respiratory Respiration involves 3 separate inter-related functions: Ventilation (breathing): Delivery of Oxygen (in air) to the alveoli of the lungs Gaseous Exchange: Exchange of gases between the alveoli and the blood Oxygen Utilization: Exchange of gases between the blood and tissue (cellular respiration) Ventilation and gaseous exchange at the air blood interface are collectively known as external respiration Gaseous exchange between the blood and tissues is known as internal respiration (oxygen utilization). STRUCTURE OF RESPIRATORY SYSTEM The respiratory system is composed of : The nasal cavity Pharynx L a r yn x Trachea The bronchi Bronchioles Pulmonary alveoli in the lungs STRUCTURAL CLASSIFICATION Upper respiratory system: The nose The pharynx The larynx Lower respiratory system: Trachea Bronchial tree Alveoli and the lungs. FUNCTIONAL CLASSIFICATION Conducting part: in which gases are transported to the alveoli Nasal cavities Pharynx Larynx Trachea Bronchi & terminal bronchioles Respiratory division: where gaseous exchange takes place between the atmosphere and the blood. Respiratory bronchioles Alveolar ducts Alveolar sacs pulmonary atria & alveoli. Consists of 2 structures: External – vestibule Internal - nasal fossae NOSE VESTIBULE: Most anterior & dilated part of nasal cavity. Inner surface of nares (nostrils) have: sebaceous & sweat glands thick short hair (vibrissae) that filter out large particles from the inspired air. NASAL FOSSAE: Two chambers separated by nasal septum. 3 bony shelf-like projections extend from each lateral wall known as conchae. Superior Conchae are covered by olfactory epithelium. Middle & inferior conchae are covered by respiratory epithelium PHARYNX Divided into: Nasopharynx and oropharynx Lined with respiratory epithelium. LA R Y NX Connects the pharynx to the trachea. Lamina propria contains 9 cartilages: 3 unpaired Thyroid Cricoid epiglottis 3 paired Arytenoids Corniculate Cuneiform LARYNGEAL EPITHELIUM - Lining epithelium varies in type in different parts of the larynx: stratified squamous noncornified epithelium covers: - - laryngeal inlet most of the epiglottis true vocal cords. Typical respiratory epithelium (i.e., pseudostratified columnar ciliated epithelium with goblet cells) covers: - the rest of the larynx. LARYNX TRACHEA 10 cm long extends from the base of the larynx to sternal angle (2nd costal cartilage/ T4 vertebrae) At sternal angle bifurcates into two primary bronchi. Respiratory epithelium with numerous goblet cells. Lamina Propria contains 16-20 C-shaped rings of hyaline cartilage Gaps b/w posterior ends of each cartilage is bridged by a band of fibro-elastic ligament & bundle of smooth muscle called Trachealis BRONCHI Extra-pulmonary or primary bronchi Resembles the trachea D-shaped smaller diameter. Intra-pulmonary or secondary bronchi • • • • It differs from the Extra-pulmonary by: Smaller diameter round contour. Smooth muscles appear in the form of complete ring. Hyaline cartilage occur as irregular cartilaginous plates BRONCHIOLES 1 mm or less diameter Gradual changes occurs in the epithelium as follows: • • First simple columnar Then simple cuboidal ciliated epithelium. They differ from the bronchi in 2 respect: No cartilage in their wall. No glands in their mucosa. TERMINAL BRONCHIOLES: (0.5 mm diameter) Epithelium simple cuboidal with no goblet cells Has scattered non-ciliated, dome-shaped clara cells. RESPIRATORY BRONCHIOLES: Transitional zone between conducting and respiratory divisions Distinguishing feature is presence of saccular outpocketing (alveoli) on its wall. - ALVEOLAR DUCTS Thin walled conical tubes Wall studded with alveolar sacs & alveoli Alveoli open into the lumen of the duct Epithelium – simple squamous Lamina propria - consists of smooth muscle & C.T. Terminate by opening into the pulmonary atria ATRIA : Irregular spaces, from which alveolar sacs & alveoli diverge. Two or more alveolar sacs arise from each atrium. A network of elastic and fibers encircles the openings of alveolar sacs and alveoli. No smooth muscle in the wall of and alveolar sacs. reticular atria, ALVEOLAR (AIR) SAC: Collection of alveoli opening central chamber. into a PULMONARY ALVEOLI the atria Sac-like evaginations (~200 µm in diameter) of the respiratory bronchioles, alveolar ducts & sacs. Terminal portion of the bronchial tree Lined by 2 types of epithelial cells: Squamous alveolar cells or type – I cells. Great alveolar cells or type – II cells or septal cells. Main sites where exchange of oxygen & carbon dioxide take place between the inspired air & blood. RESPIRATORY DIVISION