Homoeostasis:
Homoeostasis is the maintenance of a constant internal environment in the body despite changes in the external environment. It is a fundamental concept in physiology and is essential for the survival of an organism. The internal environment of the body includes factors such as temperature, pH, and the concentration of various substances, such as glucose, sodium, and calcium.

Constant Temperature:
The maintenance of a constant body temperature is a crucial aspect of homoeostasis. The normal body temperature of humans is around 37°C, and this temperature is maintained through various physiological mechanisms that regulate heat generation and dissipation. The hypothalamus, a part of the brain, acts as the body's thermostat and helps to maintain a constant body temperature.

Role of Negative Feedback Loop:
The body uses a negative feedback loop to maintain a constant body temperature. A negative feedback loop is a process in which the body's response to a stimulus is to counteract and reverse the stimulus. In the case of body temperature, when the body temperature rises above the set point, the hypothalamus initiates a series of responses to cool the body down. These responses include vasodilation, sweating, and increased respiration, which all help to dissipate heat from the body. On the other hand, when the body temperature falls below the set point, the hypothalamus initiates responses to generate heat, such as vasoconstriction, shivering, and increased metabolism.

Conclusion:
In conclusion, the maintenance of a constant body temperature is an excellent example of homoeostasis. The body uses physiological mechanisms to regulate heat generation and dissipation to maintain a constant body temperature of around 37°C. The hypothalamus acts as the body's thermostat and uses a negative feedback loop to maintain this constant temperature by initiating responses to counteract and reverse any changes in body temperature.