Discuss Factors That Control Respiration.

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DISCUSS FACTORS THAT CONTROL RESPIRATION.

Stimuli that drive respiration can be classified as either chemical or voluntary... Chemical control has evolved to meet the following general needs; to insure a supply of oxygen for tissue metabolism and to remove the by product carbon dioxide and to help maintain the acid base balance of the body. Voluntary control is necessary to fine-tune the respiratory output for purposeful activities such as speech, sneezing, coughing and other behaviours but it is overridden if blood carbon dioxide rises (hypercapnia) (Medical Education, 2002 p1).

        The basic rhythm of respiration is controlled by groups of nerve cells that control the rate and depth of inspiration. The area which nerve impulses are sent to the respiratory muscles is called the respiratory centre and consists of groups of neurons divided into three areas; the medullary rhythmicity areas, the pneumotaxic area and the apneustic area (Tortora & Grabowski, 2000 p836). They are situated in the brainstem, the medulla oblongata. The medulla oblongata looks like a swollen tip to the spinal cord (Jenkins, 2002 p2). It ensures that the correct level of gas exchange is maintained according to the body’s demands.

        These nerve cells send a rhythmic pattern of impulses to the diaphragm and the intercostals, the muscles of respiration. When intense respiratory effort is required, the accessory muscles of respiration are used. The most important is the sternocleidomastoid. Contraction of these muscles in addition to the diaphragm and the intercostals muscles ensures the maximum increase in the capacity of the thoracic cavity.  The rhythm is supplemented by stretch receptors situated in the lungs. These stretch receptors inhibit nerve impulses when the lungs are inflated, and stimulate nerve impulses when they are deflated (Fitness Complete, 2002 p3). The Hering- Breuer reflex prevents over inflation of the lungs. Stretch receptors situated in the thoracic wall generate nerve inhibitory impulses when the lungs have inflated. They travel via the vagus nerves to the respiratory centre.

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        Automatic and rhythmic discharge of neurons in the medullary respiratory centre produce inspiration. Impulses travel via the phrenic nerve to the diaphragm.

        Other neurons in the brainstem, known as expiratory neurons, are active when ventilation is increased over resting rates. Inspiratory and expiratory neurons also have inhibitory connections to one another. In the pons, the pneumotaxic centre acts as an integrator of inspiratory and expiratory outputs to coordinate and make the process of breathing smooth (E- breathing. 2002 p3).

        Although the basic rhythm of respiration is set and coordinated by the inspiratory area, the rhythm can be modified in response ...

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