To understand actually how food is being perceived by us we need to go through all the systems. First about endocrine control. What is endocrine control? In fact when food is being taken a lot of the time actually they carry nutrients, they carry energy containing material that would be digested. One of the most common one, in fact, is the carbohydrates, which will eventually be converted into glucose. And glucose has a lot to do with how we feel. Whether we feel hungry, we want our food, or we don't have food. Sometimes we find that when we have taken some food, and after a meal, we accumulate a lot of glucose in our blood. And over time, gradually, they will decline. And when they decline, basically our body will have a system which detects the level of glucose from that. It will tell us a signal and say, well you are running out of glucose. So they start to fire the signal to our body to tell us that you should eat more food. So we feel hungry. Now let's summarize the entire process. So what exactly would that be? Some experiment has been done to show that in fact, when we have low glucose We usually feel very weak. And when you feel weak, a lot of times you feel hungry too. So I believe that many of you have that experience. On the other hand, sometimes you know you don't need to eat the food. Because we find that using mouse or rats in experiment, when they are hungry then you simply infuse into the gut, or in this case, the duodenum, some glucose. In fact, they would feel that they have the sense of satiety. They no longer feel hungry. So that tells us that whenever there is glucose being supplied to us, that we would feel the sense of fullness. Now, so therefore, what I want to focus on is that in fact whether we feel hungry or whether we are full in fact is an integrated hormonal control. And for this hormonal control, we are monitoring the glucose level. And glucose level, a lot of times, will be regulated by insulin. You remember that when you have high level glucose, actually that's no good. So what we have is our body, the pancreas to be specific, they produce insulin. And the insulin would help us to take in all the glucose and convert it into something for storage. And by then, when the glucose level goes down, then you feel hungry again. But when the glucose levels stay high, you stop eating. So therefore, the hormonal control insulin, in this case, have a good correlation of the state of being full or hungry. Now let's look at how the insulin work. Insulin is produced by the pancreas. In fact it's something secreted into the blood and it's circulating in your body. It will be in contact with different tissues, organs, and cells. And we know that on a cell, on the surface they have some of those so called receptors. They can sense whatever surrounds them. For example insulin as a molecule, it comes in it finds a receptor. The cells that what do they do? They know that when you have a lot of insulin that means there's lots of glucose. We want to take in the glucose and import it into the cell so they produce a lot of the glucose transporter. Because there's a lot of glucose, therefore, you don't need to break down the other materials, such as the protein, lipid, or other carbohydrates. And at the same time, because there's a lot of glucose, don't need all of them. So what do you do? You assimilate them, you start producing glycogen and fatty acid. And because you have a lot of nutrients, that means that you are in a good shape so that it's time for you to start growing. You will build up more DNA and you take in more amino acid to allow the cell to grow. So in a way, insulin allows us to promote cell growth. Now when I talk about endocrine, insulin is only one component of it. There's another hormone which we call leptin. Leptin is another hormone which is produced by the fat cells, or sometimes we call that adipose tissue. This leptin, as it's produced, is secreted again into the blood. And it will be transported to the hypothalamus, where it bind on the receptor. What does it do? When it goes to the receptor, it would tell us that, well, you are full. And so, therefore, it would inhibit your appetite and you don't eat any more. So that means when you have high leptin, basically, it tells you that you don't want to eat. What happen if you don't have Leptin and you don't have the receptor just like this popular ,mouse. It doesnt know that it is full it constantly think that its hungry, it keeps on eating so gradually it becomes very fat. Now what it means that leptin is telling you that you should not eat. So inhibit your appetite. But we certainly know that this leptin whatever level they are they're telling you that whether you are at the state that you have low level of energy. You don't have food. And so basically, it's somehow using the hypothalamus as some sort of fuel gauge. That allows you to tell your body whether you have a good level of glucose in your body. And remind you that these are hormone, insulin is a hormone, leptin is a hormone. And they were secreted into the bloodstream, they travel along your body to the target site and then they trigger a response. Is it going to be very fast? The answer is no. It's relatively slow. So what do they do is when they travel over they bind onto the receptor, trigger the production of a response. It is always a time delay. So therefore, this systemic way of handling the level of glucose or nutrients in the body is always has a delay, in terms of response. Now that become a very important element that we need to remember. Now we have the leptin telling you that you should not eat. We have another hormone which is called ghrelin, which is called a hunger hormone and it tells you that you were in a hungry state. So which tissue, which organ will be the best place for you to produce this hormone? Certainly your stomach or your gut. In the stomach, in the part of it which we call the fundus, the top part of the stomach, they are the place where they produce the ghrelin. When you are starving, when you don't have energy, you don't have any food in your stomach, it is thing that tells you that, well, you are hungry. So this particular part, the fundus, which produces a lot of ghrelin, and the ghrelin one is produced it would tells you that well energy is low and so therefore produce more ghrelin and then become hungry and start eating. So what I mean is that when you feel full, now your stomach is filled And you stop producing the ghrelin. And when you produce the ghrelin when you're hungry it gives you this ravished feeling, you want to eat. Again, we call that it is a stomach defect, there's a time delay. So what happened then, is that you may recognize that when we have high level of ghrelin, when you're fasting, basically you want to eat more. When you have low level of ghrelin, you want to stop eating and usually when that happen it is after you have eaten a meal and you will have low level ghrelin. So what it suggests to us is that it makes sense if you eat more frequently. Not all the time makes you feel very full but you eat a little bit of it so it stimulate a little bit after sometime you produce the craving and then you go and eat. You eat a little bit and then the glucose go up and the craving comes down. So that's how takes place and functioning in such a hormonal cycle. So let me go through them again and remind you. When we eat something, after eating it we convert them into glucose energy and we want to convert glucose into storage using the insulin. And at the same we are stimulating the production of this hormone, leptin. From the fat cell, it tells that wow, you have a lot of energy. So stimulate hypothalamus and say well, don't eat any more, inhibit your appetite. On the other hand, if you don't any energy, you don't have any food, no insulin production, no leptin, no leptin receptor activated. So the appetite is not inhibited. At the same time ghrelin would no longer be blocked by the leptin. And so therefore, it will stimulate your appetite and tell you that you're hungry. So Ana, you will start eating more. So with this full cycle, in fact we are controlling whether you feel full or you are hungry.
