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Introduction to Respiratory System | Respiratory Tract | Respiratory System

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    RESPIRATORY SYSTEM Respiration - The process by which food is oxidized in the body to releaseenergy is called as respiration. This involves the exchange of gases i.e.Oxygen and carbon dioxide between the body and the external environment.the various organs required for this exchange of gases together constitutethe respiratory system.The various organs of the respiratory system are:1.   Nose2.   Pharynx3.   Larynx4.   Trachea5.   Bronchi6.   Bronchiole7.   LungsThe  nose is first part of the respiratory system through which the air entersand passes through the various parts of the respiratory system to the lungs.The main function of nose is to moisten the air and make it warm alongwith this; it also filters the various impurities present in the air.The pharynx communicates with posterior nose, Eustachian tube , mouth ,esophagus and larynx.The larynx is a passage for the air from the pharynx to the trachea and likenose it also helps in further moistening and filtering of the air. It is called as voice box. The trachea is a cylindrical cartilaginous tube, 11-12 cm long , from thelarynx to the bronchial tubes. It extends from the 6 th cervical to the 5 th dorsalvertebrae. Here it divides at a point called carina into two bronchi, oneleading to each lung. It is lined with mucous membrane and its inner surfaceis lined with ciliated epithelium .It is also called as wind pipe.STRUCTURE OF LUNGS The two lungs lie on each side of midline, in thoracic cavity. They are coneshaped and consist of an apex and base. The right lung is larger then the left.The lower surface of the lung is concave and is present very close to the  diaphragm, which divides the body into the thoracic cavity and theabdominal cavity. The lungs are divided by the double layered membranecalled pleura which contains a small amount of serous fluid in it.Each major branch from the trachea enters the root of the lung anddivides and subdivides to give progressively smaller bronchi and then stillsmaller bronchioles. The small terminal bronchioles branch into respiratorywhich branch into alveolar ducts ending ultimately into alveoli.The walls of alveoli are surrounded by a dense network of capillaries. Thewalls of the alveoli and capillaries are made up of a single layer flattenedepithelial cells. The exchange of gases between the alveoli and capillariestakes place across this thin layer   TRACHEOBRONCHIAL TREE 1.   Made up of cartilage, smooth muscle, and epithelium containing cilia andglands.2.   Function: passage of gas movement from to alveoli.3.   Divide into conducting and respiratory zone.4.   Weibel’s classification of airway generations from trachea to alveolarsac.Airways division occurs 23 times.Zero generation – trachea,1- 16 - conducting zone (bronchi, bronchioles and terminalbronchioles.)17 – 23 - respiratory zone. (respiratory bronchioles, alveolar ductsand alveoli.TIPS TO REMEMBER1.   Cartilage and glands are present only in trachea and bronchi.2.   Cilia present up to respiratory bronchiole.Two type of alveolar epithelial cells:1.   TYPE I2.   TYPE II ( granular pneumocytes) cells secrete surfactant. PROPERTIES OF GASES:PARTIAL PRESSURE OF GASES .:Pressure exerted by any one gas ina mixture of gases.P = nRT / V.P IS PRESSURE,  n is number of moles,R IS gas constant,T is absolute temperature.,V is volume. DALTON’ S LAW: Total pressure exerted by mixture of gases = sum of partial pressure of allgases present. COMPOSITION OF AIR ( mmHg)INSPIREDAIRALVEOLARAIRARTERIALBLOODVENOUSBLOOD.PO 2 158 100 97 -100 40.PCO 2 0.3 40 40 46. FUNCTIONS OF LUNG : 1.   Gaseous exchange. 2.   Humidification. 3.   Prevents foreign bodies from entering the alveoli. 4.   Phagocytic action by pulmonary alveolar macrophages. 5.   Surfactant release that prevents the development of surface tension inalveoli. 6.   Conversion of Angiotensin I to Angiotensin II by activating theenzyme, ACE. 7.   Removal of various substances from blood - prostaglandins,bradykinin, serotonin, nor epinephrine.  
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