 So what is homeostasis? Homeostasis is the term first defined by Claude Bernard in 1865. It means maintaining a constant internal environment. Wow, great! That really explains it, doesn't it? Let me try and make it a bit clearer then. Imagine the cockpit of a plane. It is packed full of dials and it is the pilot's job to make sure they all stay in the right place. If any of them change, he will correct the plane to keep them in the right place and the plane in the air. This is a bit like how our brain works. Sensors all around the body are measuring various things and sending the information back to the brain. The brain then does its best to keep all these things stable and constant to keep the body working properly. This is homeostasis, maintaining a constant internal environment. So what kind of things need to be kept constant in the body? Well, it's very important to keep our temperature the same at around 37 degrees Celsius. You can find out more about this in the video on temperature regulation. You also need to keep the levels of sugar in the blood constant along with levels of ions and water. Your blood pressure needs to be carefully monitored along with the amounts of waste in the blood such as carbon dioxide and urea. Okay, so let's say one of these factors goes to high or low. What is the brain going to do to get it back to the normal levels? The answer to that is negative feedback. Negative feedback is the process where the brain uses either a hormone or a nervous system to send a signal to the part of the body that can rectify the problem. For example, after you eat a meal, your blood sugar level increases. You can see it on this graph. This is detected and the pancreas will release a hormone called insulin that causes the sugar to be stored in the liver. Therefore, as you can see on the graph, the blood sugar level returns to normal. Negative feedback is the loop from which the body detects a stimulus, reacts by responding accordingly and brings the body back to the normal levels. So why is homeostasis so important? Our metabolism, which is all the chemical reactions in our bodies that keep us alive, is controlled by enzymes. These enzymes only work in very specific conditions. If these conditions change, they could stop working and we could die. Luckily, all this happens without you having to think about it. If you had to do it yourself, you would spend all day and night just trying to keep all these things constant and would have no time to do anything fun like watch videos of cats on the internet.