Homeostasis, receptors, and general control of respiration

Homeostasis, receptors, and general control of respiration...

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The basic rhythm of breathing is set by the inspiratory center, located in the medulla. Other respiratory centers, located in the medulla and pons, also control breathing. • Chemoreceptors monitor the PCO2, pH, and PO2 of arterial blood and alter the basic rhythm of breathing. • Carbon dioxide, reflected by changes in pH, is the most important stimulus controlling ventilation. • pH changes due to metabolic acids also alter ventilation. • Oxygen stimulates ventilation only when the blood PO2 is very low. • Other factors, such as voluntary control, pain and emotions, pulmonary irritants, and lung hyperinflation, also play roles in controlling ventilation. • The control of ventilation during exercise, while complex and not fully understood, involves multiple inputs including chemical and neural factors. HOMEOSTASIS AND THE CONTROL OF RESPIRATION The control of respiration is tied to the principle of homeostasis. • Recall that the body maintains homeostasis through homeostatic control mechanisms, which have three basic components: 1. receptors 2. control centers 3. effectors • The principal factors which control respiration are chemical factors in the blood. • Changes in arterial PCO2, PO2 and pH are monitored by sensory receptors called chemoreceptors. • The chemoreceptors send sensory input to
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respiratory centers in the brainstem, which determine the appropriate response to the changing variables. • These centers then send nerve impulses to the effectors, the respiratory muscles, to control the force and frequency of contraction. • This changes the ventilation, the rate and depth of breathing. • Ventilation changes restore the arterial blood gases and pH to their normal range. THE INSPIRATORY CENTER The basic rhythm of breathing is controlled by respiratory centers located in the medulla and pons of the brainstem. • Within the medulla, a paired group of neurons known as the inspiratory center, or the dorsal respiratory group, sets the basic rhythm by automatically initiating inspiration. • The inspiratory center sends nerve impulses along the phrenic nerve to the diaphragm and along the intercostal nerves to the external intercostal muscles. • The nerve impulses to the diaphragm and the external intercostal muscles continue for a period of about 2 seconds. This stimulates the inspiratory muscles to contract, initiating inspiration. • The neurons stop firing for about 3 seconds, which allows the muscles to relax. The elastic recoil of the lungs and chest wall leads to expiration. • This automatic, rhythmic firing produces the normal resting breathing rate, ranging between 12 and
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15 breaths per minute. OTHER RESPIRATORY CONTROL CENTERS
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This note was uploaded on 11/13/2010 for the course CODS 361 taught by Professor Gel during the Spring '10 term at WPUNJ.

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Homeostasis, receptors, and general control of respiration...

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