Homeostasis: Thermoregulation Negative Feedback System

Introduction
“Homeostasis refers to the ability of the body or a cell to seek and maintain a condition of equilibrium or stability within its internal equilibrium when dealing with external changes” (2). “Homeostasis keeps the body’s environment under control and keeps the conditions right for cells to live and function. Without the right body conditions, certain processes (e.g. osmosis) and proteins (e.g. enzymes) will not function properly” (1). Thermoregulation is the process that allows the cyclists body to maintain its core internal temperature (between 37°C and 37.8°C). All thermoregulation mechanisms are designed to return the cyclists body to homeostasis after a disruption to the system e.g. hot or cold conditions. Throughout the duration
Negative feedback means that whenever a change occurs in a system, this automatically causes a corrective mechanism to start. This corrective mechanism brings the body temperature back towards the set point (i.e. ‘normal’). The bigger the stimulus, the bigger the corrective mechanism. The stimulus in the thermoregulation negative feedback system is the change in temperature. When there is an increase in the stimulus i.e. an increase in the cyclists body temperature, the receptors (thermo sensitive neuron cells in the skin and brain) detect this increase in body temperature. The peripheral thermoreceptors in the skin detect external temperatures whereas the anterior region of the hypothalamus in the brain detects a change in blood temperature i.e. core temperature. The message of an increase in temperature is then transmitted through neural (brain) pathways to the anterior of the hypothalamus in the brain which contains heat sensitive neurons. The hypothalamus in the brain is the thermoregulatory control centre and detects changes in both skin and blood temperature. Any difference in skin and blood temperature from the ‘set point’ e.g. 36.7 °C, will be recognised as an error. The anterior hypothalamus recognises this and has a heat loss centre that sends messages to the effectors which are nerve impulses and hormonal messages. These impulses and messages are released to the required area to signal
However, because it is not a breakdown of the system (i.e. the feedback system stops functioning and the person dies), the negative feedback system can operate to return the body to homeostasis. Although, if the enzymes are denatured this is an irreversible change. When there is an extreme increase in internal body temperature e.g. to 40 degrees celcius, skin and blood warmth receptors send a message to the hypothalamus that there is an increase in body temperature. The thermostat centre in the anterior hypothalamus activates the cooling mechanism through nerve impulses (effectors) which are sent to the required region. Therefore cooling responses will begin to re-establish homeostasis. One of these cooling responses to re-establish homeostasis is vasodilation. Vasodilation occurs when the blood vessels expand (i.e. get wider / dilate) which causes an increase in blood flow to the skin to help the cyclist lose some of its extra heat. This happens because there is a larger surface area for heat to be lost. If the heat is extreme the sweat glands will release sweat onto the skin surface which is one of the most effective response to reduce internal body temperature. The sweat evaporates off the surface of the skin which removes heat and therefore cools the body down to re-establish homeostasis. There are four ways for the cyclist to lose heat during the event: convection, conduction, radiation, and evaporation.