呼吸是向组织提供氧气的现象，并从组织中清除二氧化碳。外部呼吸是肺与大气之间的气体交换的过程。内呼吸是组织气体交换的过程。这些气体在血液中的吸收和排泄之间的平衡被保持为呼吸活动。在吸气过程中氧气增加血液水平并降低在呼气。化学感受器在血液检测氧气和血液中的二氧化碳水平的感官受体，并向大脑发送信号。然后大脑使咽喉和声带的开放，其次是扩大胸腔和膈肌。胸腔扩大，使氧气流入肺部，从而导致吸入过程。同样，胸腔闭塞呼气过程中排出肺部的二氧化碳。更多的氧气流入的结果，在最大的潮汐量和一个正常的呼吸流。图1.1显示了正常的呼吸信号，呼吸频率为每分钟12次。

Respiration is the phenomenon of supplying oxygen to the tissues and removing the carbon dioxide from the tissues. 美国Essay代写 External respiration is the process of exchange of gases between the lungs and atmosphere. Internal respiration is the process of gas exchange in the tissues. The balance between the absorption and excretion of these gases in blood are maintained as breathing activity. During inspiration the level of blood in oxygen increases and it decreases during exhalation. Chemoreceptors are the sensory receptors in the blood stream that senses the level of oxygen and carbon dioxide in blood ,and sends signals to the brain. Then the brain allows the opening of larynx and vocal cords, followed by the expansion of ribcage and diaphragm muscles. The chest cavity enlarges to allow the inflow of oxygen into the lungs thus resulting in inhalation process. Similarly the chest cavity occludes during the process of exhalation and expels the carbon dioxide from lungs. More of oxygen inflow results in maximum tidal volume and a normal respiratory flow. Fig 1.1 shows the normal respiratory signal with respiration rate of 12 breaths per minute.