 Let's explore hormones in animals. Remember, hormones are messenger molecules which are used for control and coordination. But why do we need hormones? Because you also have nervous system. Nervous system also can be useful in controlling and coordination, right? Well, to understand that, let's look at the difference between hormones and the nervous system, the hormonal system and the nervous system. Well, the first major difference is that this is a chemical system, meaning you need to use molecules to control and coordinate. Nervous system uses electrical impulses, okay? The second main difference, and this is the big difference, is that the medium over here is blood. So hormones are sent into the blood, and then the blood goes to all the parts of the body. Versus nervous system uses specialized cells called nerves, so it uses that. And now we can understand why you need hormones. See, hormones can reach all the cells because the blood reaches all the cells. So you can control all the cells using this system. But nervous system has very limited reach. Nerves don't reach all the cells. That's why hormone system is also super important. But then I wondered, well, if that is the case, why do we need nervous system? Hormonal system would be enough to control and coordinate, right? Well, no, because hormone system is very slow because it takes a lot of time for it to go into the blood and then get circulated and then finally reaches the cell. Versus nervous system is super fast. So you see, both systems have their advantages and disadvantages. So we need both the systems. Okay, now that we understand what hormone systems are and how useful hormones are, let's look at some of the important hormones and hormone secreting glands in our body. Now the hormone secreting glands in our body are called endocrine glands. Well, glands means organs that secrete things and endocrine because it is duct less, meaning there are no pipe systems over here. For example, if you look at salivary gland, then you can see there is a pipe over here. But these endocrine glands, they do not have any pipe. They don't need a pipe because their job is to secrete it into the blood. Okay, so that's the whole idea behind this. So let's look at the various endocrine glands and look at their major hormones and the functions. We start with the testes. The major hormone, the secret is testosterone. And what's their main job? Well, in creation of sex cells and secondary development in males. Similarly, in females, ovaries give out estrogen or progesterone. These are useful again for developing sex cells and secondary development in females. Then we have the pancreas. One of the main hormone it secretes is insulin. You probably heard about it. Insulin's main job is to absorb blood sugar whenever the sugar level increases in the blood. Because if the blood sugar level increases in the blood vessels, then it can damage the blood vessels. And people who have diabetes, well, their problem is that they don't have like insulin secretion is a problem. So that's the whole idea behind diabetes. Okay, then you have these two hat shaped glands over here above the kidneys. We call them the adrenal glands. One of the main hormone that they secrete is adrenaline. What does adrenaline do? You know, it is called the fight or flight hormone, one of the most important hormones. What happens is when you are in a situation when you are in danger, this hormone will increase your heart rate, will increase the blood supply to your skeletal muscles and it'll either prepare you to fight or flight, go away from the danger, run away from the danger. Okay, then we come focus to come to our neck. Here you have an important gland called the thyroid gland. One of the important hormones it secretes is called the thyroxin. The thyroxin's main job is to regulate the metabolism of fat, carbon, carbs and proteins. Now, when the thyroxin glands are not working properly, they either they will you will have increased metabolism, in which case, you know, people tend to become very thin, or you can have decreased metabolism, in which case, the people tend to get obese. And this is also the reason why we intake iodized salt, because iodine is super important for the creation of thyroxin. That's why we take iodized salt. Finally, the last important gland for us is the pituitary gland, which is situated in the brain. What does it do? Well, it releases a lot of growth hormones. It's responsible for our growth. It's also responsible for our height. Sometimes some people are dwarf because the growth hormones are not secreted enough. And sometimes people are very, very tall because their growth hormones are secreted a lot. But another thing about pituitary is that it's also called the master gland. And the reason for that is because it controls all the other glands. For example, if you want thyroid to release a sacred thyroxin, the pituitary will actually release a hormone that stimulates the thyroid, which releases the thyroxin. So it's the pituitary that actually controls all the other glands, which is why it's called the master gland.