To understand homeostasis we first need to understand the meaning- the definition buzz phrase for this word is "the maintenance of a constant internal environment". Therefore it refers to the processes which keep the balances of things such as blood sugar levels and temperature constant.
Homeostasis is essential for life as without it humans would have to live within very specific conditions- we would never be able to survive in colder climates or hot desert without mechanisms to regulate our temperature.
So how does homeostasis work? The next buzz phrase this brings us to is "negative feedback". When a change occurs there are sensors in the body which detect this. These then send signals to regulatory areas such as the hypothalamus in the brain (responsible for temperature maintenance) which then send out an appropriate response to the effectors. This is known as negative feedback because the feedback it sends is to reduce not increase the change detected. We can use the example of heat to illustrate this:
Example 1- Body temperature regulation
If the body becomes too hot sensors can detect this- they send messages to the hypothalamus in the brain which responds to this message by asking the receptors to bring about changes such as sweating and reddening of the skin (vasodilation).
Sweating decreases the body temperature by dampening the skin- this moisture then evaporates of the skin. This process of evaporation uses up some of the heat the body wants to get rid of (think about how quickly you get cold when you are wet).
Reddening of the skin is caused by vasodilation. This is where the blood vessels nearest the surface of the skin dilate allowing more blood to flow through them than normal. This causes the heat from this blood to be lost to the outside environment- cooling the body down (this is why we become so red after heavy exercise).
Example 2- Blood sugar regulation
Another important factor to be regulated is the level of sugar in the blood. Which like most of the homeostasis processes is dependent on this negative feedback loop.
If the blood sugar level is too high this is detected by the pancreas and this causes the secretion of insulin. This insulin is a hormone which converts glucose into glycogen. This is essential as glucose cannot be stored in cells but glycogen can. So insulin converts glucose in the blood into glycogen so that it can be moved out and stored in cells until needed.
So what if the blood sugar level becomes too low? The pancreas will secrete a different hormone called glucagon which can convert this stored glycogen back into glucose so it can be released back into the blood.