Negative Feedback Mechanism
A negative feedback mechanism is a system that initiates physiological changes in the body to return the conditions to a normal or ideal state. For the process of a negative feedback mechanism to be successful, a series of steps occur in what is referred to as the negative feedback loop. The negative feedback mechanism works to oppose particular stimulus in the body. Stimuli are therefore the changes that require correction such as high blood glucose levels or high temperatures. The setpoint is the desirable levels or the normal range under which the body performs its activities at an optimum range. For temperature, the set point is 37 degrees Celsius.
Receptors enable the process of negative feedback on the body. The receptors can either be in the form of nerve endings on the skin or hormones in the body system that detects these changes. Temperature changes are usually detected by nerve cells on the skin, and changes in the blood glucose are detected by the pancreatic cells. The nerve cells and pancreatic cells, therefore, act as the sensors in the process of negative feedback. Once the receptors detect the changes, they are relayed the control center of the brain. The function of the control center is to process the information and decide on the necessary course of action to undertake. An example of the control center in the brain that oversees temperature changes is referred to as the ‘temperature-regulatory control center' (Marieb & Hoehn, 2007).
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Thermoregulatory Negative Feedback Mechanism
Body temperature is controlled through the action of the thermoregulatory center found in the hypothalamus. The thermoreceptors responsible for sending input originate from two areas, the hypothalamus, and the skin region. All these are important to enable the body to adjust appropriately to changes. When the body is under optimal temperature conditions, usually 37 degrees Celsius the thermoregulatory center is not stimulated hence no corrective measure is undertaken. However, factors such as fever may result in the increase or decrease of body temperature necessitating the need for adjustment.
In response to increased temperature past the optimum, the skin and the hypothalamus send impulses to the thermoregulatory center. The effectors that are targeted in this case include muscles of blood vessels, sweat glands, erector pili muscles, skeletal muscles, and adrenal and the thyroid glands. Muscle relaxation in the blood vessels causes vasodilation leading to loss of heat to the environment via convection and radiation. Sweat glands release sweat leading to loss of heat through evaporation. Erector pili muscles relax allowing free circulation of air hence enhancing heat loss by convection and evaporation. The skeletal muscles prevent shivering hence inhibiting production of extra heat. The adrenal and thyroid gland stops producing adrenaline and thyroxin.
The opposite happens when the body responds to decreased temperature. The muscles of the blood vessels contract leading to vasoconstriction leading to conservation of heat in the body. The erector pili muscles contract hence elevating the skin hair causing them to trap air that acts as an insulator . The skeletal muscles begin to contract and relax leading to shivering, a factor that generates heat for the body. Adrenaline and thyroxin glands are activated leading to activation of metabolic activity.
Pathological Positive Feedback Mechanisms
Hypothermia is a situation where the body temperature lowers to below 35 degrees Celsius. On the other hand, hyperthermia is a situation where the body temperature goes beyond 37 degrees Celsius. During hypothermia, the negative feedback systems that are geared towards increasing the temperature of the body have failed. The result is that metabolic reactions and respiration slow down leading to an even decreased temperature. Because the conditions are moving away from the normal, it becomes a positive feedback that is pathological.
The same scenario can happen during hyperthermia. The body may get dehydrated due to sweating leading decrease of heat loss. If the humidity is high, sweat may fail to evaporate at the required rate leading to a marked increase in body heat leading to heat stroke.
Reference
Marieb E.N & Hoehn, K. (2007). Human Anatomy & Physiology . Pearson Education. 10 th Ed. ISBN: 978-0-321-92704-0
