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The Control of Breathing Mechanisms in Humans

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The Control of Breathing Mechanisms in Humans All living things require energy. This energy is obtained by breaking down sugars and other substances through the process of respiration. As a consequence of respiration, gaseous exchange takes place. Breathing is essential to humans in order to provide the oxygen required for aerobic respiration and also to get rid of carbon dioxide produced as a waste product of respiration. The breathing mechanism in humans is more complex than small animals because of the need for an intricate system that delivers all over the body. We know that air needs to be taken in and out of the body. These processes, called inspiration and expiration, take place due to pressure gradients created in the lungs. These pressure changes are brought about by changes in the volume of the thorax. The volume of the thorax in turn changes as a result of movements of the ribs and diaphragm caused by muscle contractions. ...read more.


Nerve impulses arising here: > rhythmically stimulate the intercostal muscles and diaphragm > regulate heartbeat > regulate the diameter of arterioles thus adjusting blood flow. Therefore destruction of the medulla causes instant death. The pons, as well as serving as a relay station carrying signals, also participates in the reflexes that regulate breathing. It is thought that there are at least three kinds of cell in the respiratory centre: some are active throughout inspiration, some start to produce action potentials late in inspiration and some are active in expiration. Breathing occurs automatically through involuntary reflex action controlled by motorneurones in the spinal cord which in turn are controlled by the control centre which continually adjusts the rate of breathing to meet the body's immediate needs. For example, when at rest the breathing rate may be at normal. Then when performing activities the breathing rate increases to provide enough extra oxygen required for respiration to carry out the activity. ...read more.


If either of these fluids has a high concentration of CO2 then ventilation will increase. So the central chemoreceptors are influenced by the composition of these two fluids. When CO2 dissolves in these fluids the following reaction takes place: CO2 + H2O ? H+ + HCO3- As you can see, the protons produced when CO2 dissolves in water decrease the pH of the solution as it becomes more acidic. So in fact, it is the pH which is sensed by the receptors and not directly the CO2 concentration. Basically, falls in pH increase the breathing and rises in pH decrease it; when the pH falls, the increase in ventilation reduces the CO2. Carbon dioxide is therefore not directly detected and so there are some consequences to this system. As carbon dioxide can diffuse freely across the blood-brain barrier, which hydrogen ions cannot pass, the CO2 in the blood plasma and the cerebrospinal fluid will be the same, but the pH's of the two may differ. Therefore the blood-brain barrier has made a hydrogen ion receptor specific to CO2. ...read more.

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