① Pulmonary Respiratory System

    The Structure of The Respiratory System


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     The respiratory system is composed of groups of organelles that filters and transports air into the lungs. The organs  comprising of the respiratory system include nose, nasal cavity, pharynx, larynx, trachea, bronchial tree and the lungs.

     The main function of the lungs is theexchange of gas that occurs within microscopic air sacs called alveoli. However, the upper respiratory tract (nose, mouth, trachea) has important functions that adds water vapor (H2O) to inspired air, warming it to body temperature, and trapping particulate material (dust, yeast, and bacteria) as well as noxious fumes (smoke, ozone). The pulmonary tree anatomy provides a large surface area for respiratory gas exchange between alveoli and blood (pulmonary capillaries).




     Right and left lungs are enclosed by pleura (parietal pleura and visceral pleura) which is the outer most covering of lung. These two pleura are separated by a thin layer of fluid that acts as lubricant and is able to glide one pleura on the other without friction.







    Conduction Zone


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    The conducting zone includes: trachea, bronchial tree, bronchioles from where the air passeses to reach the respiratory zone. The air enters into nasal and oral cavties first ,then moves to pharynx (throat) and then to the trachea. The trachea branches into two major bronchi: right and left. The bronchial tree branches many times before forming bronchioles. Then the bronchioles branch to form before alveolar sacs or aveoli.

     Conducting zone contributes the important function involving humidifying and filtering of the air. The air is made warm and  saturated with water vapor before it reaches the lung to preserve body temperature and prevent the delicate lung tissue from desiccation (drying out).


    Respiratory zone


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     The respiratory zone includes respiratory bronchioles, alveolus and alveolar sacs.

    Gas exchange in the lungs occurs across about 300 million tiny alveoli. The total surface of alveoli allows for diffusion in the lung. When gases move from high concentration area or higher partial pressure to lower partial pressure area, the exchange of O2 and CO2 between “alveolar air” and blood become possible. The surface of alveoli is known as 60 to 80 square meters, or about the size of a tennis court.



    Function of Lung 

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    The major function of lungs is exchanging of gases between the body and the external enviroment. The respiratory system offers the individual replacing O2 and removing CO2 between lung and blood.  These actions occur because of ventilation and diffusion. Ventilation is the mechanical process of moving air in and out of the lungs. Diffusion is random movement from a high concentration area to low concentration area.  The O2 tension in the lung is higher than in blood, so O2 moves to blood from a lungs. CO2 tension in blood is higher than in a lung, so CO2 moves to a lung from the blood. 

    Also, an important role of the lungs is regulation of acid base balance during high exercise. Exhalation of addicional CO2 is caused an increase in pulmumonary ventilation, it result in deminished of blood COand Hand it leads to increase PH. 



    Mechanics of Breathing



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    The diaphragm is the most important muscle of inspiration, it inserts into the lower ribs, and is innervated by the phrenic nerves (Cervial plexus, brachial plexus C3-5). During inspiration, the diaphragm contracts and the abdomen moves downward and forward causing ribs to lift outward. This causes the lungs to expand. This expansion results in reduction of intrapulmonary pressure below atmospher, which allows airflow into the lungs.

    During exercise, inspiration is assisted by accessory inspiratory muscles that include: external intercostal  muscle, pectoralis minor, sternocleidomastoid, scalene, and trapezius muscles. These muscles assist the action to lift the ribs and clavicles and allows for large increases in the tidal volume (normal volume of air diplacement between normal inhalation and exhalation) during exercise.

    *Inspiratory Muscles: Sternocleidomastoid, Scalenes, External intercostals, Internal intercostals, Diaphragm.




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    During rest, expiration is a passive action where the diaphragm and external internal intercostals relax. The most important muscles in expiration include: rectus abdominus, and the internal oblique. When these muscles contract, the diaphragm is pushed upward and the ribs are pulled downward and inward. These action occur during expiration.

     During exercise, expiration becomes an active movement. The contraction of the internal intercostals pull the ribs down and in. The contractions of the abdominal muscles increases abdominal pressure, allowing the diaphragm to move up into the thorax.

    * Expiratory muscles: Internal intercostals, External abdominal oblique, Internal abdominal oblique, Transversus abdominis, Rectus abdominis.




    Exercise Physiology_ Human Bioenergetics and Its Applications, 4th edition; George A.B, Thomas B.F, Kenneth M.B

    Exercise Physiology_ Theory and Application to Fintness and Performance, 7th edition ; Scott K.P, Edward T.H

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