Ever wondered why a patient bleeding from a fatal accident might likely die and on the other hand, when we get bruised because of handling a sharp object we bleed for a while and feel nothing has happened? This is because the body uses two mechanism in handling blood outlet. This post this more on that.
Most of the essential control systems of the body operate by negative feedback control system averaging about a thousand in the body. The most intricate which is the genetic control systems operating in all cells to help control intracellular function as well as extracellular function.
Other control systems operate within the organs to control functions of the individual parts of the organs; others operate throughout the entire body to control the interrelation between the organs. For instance, the respiratory system, operating in association with the nervous system regulates the concentration of carbon dioxide in the extracellular fluid. The liver and pancreas regulate the concentration of glucose in the extracellular fluid, and the kidneys regulate the concentration of hydrogen, sodium, potassium, phosphate and other ions in the extracellular fluid.
While negative feedback usually result in stability, positive feedback on the other hand leads to instability and could lead to death hence it’s name viscous cycle.
An example of positive feedback is BLEEDING. An average pumping rate of a healthy heart is 5liters of blood per minute. Upon puncturing of the blood vessels which lead to excessive bleeding of about 2 liters, the amount of blood in the body is decreased to a low level such that there is not enough blood available for the heart to pump effectively. As a result, the arterial pressure falls, and the flow of blood to the heart muscle through the coronary vessels diminishes resulting in weakening of the heart, further diminished pumping, a further decrease in coronary blood flow, and still more weakness of the heart; the cycle repeats itself again and again until death occurs.
Each cycyle of the feedback results in further weakening of the heart in other words initiating stimulus causing more of the same which is termed Positive feedback it is better known as visciuos cycle but a mild degree of positive feedback can be overcome by the negative feedback mechanism leading to the termination of the viscous cycle.
If the individual were to bleed just 1liter out of the 5liters blood pumped per a minute, the normal negative feedback mechanisms for controlling cardiac output and arterial pressure would overbalance the positive feedback leading to recovering.
Source: Medical Physiology Guyton and Hall
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