Source: image endocrine system: public domain; http://commons.wikimedia.org/wiki/File:Illu_endocrine_system_New.png
Hello, class. So the nervous system provides one major way for the body to communicate. The brain processes information that's taken from all the rest of the body and sends out these responses through the nerves to be carried out for the rest of it. OK. So this provides quick, consistent sorts of responses that can be stored for later use in things like memory. OK.
But it's important to realize that the nervous system is not the only way that the body communicates. There's another system that it uses called the endocrine system. The endocrine system is a system which uses chemicals secreted by glands that travel throughout the body and cause certain kinds of reactions. OK.
So these chemical communicators that we're talking about are called hormones. OK. And hormones are chemicals that are secreted by the glands that affect different kinds of bodily functions and behaviors. They're carried throughout the body by the bloodstream and the lymph system. And they can trigger different kinds of events. Or they can be triggered by different kinds of events. So the environment might create some kind of arousal within the body. For example, when you're scared by something, you get a surge of adrenaline. OK. And that is a hormone response that the endocrine system creates.
Or there could be regular sorts of growth and life events which regulate the hormones that are being used in the body to send messages to the rest of the cells and the different parts. For example, in adolescence, there's a lot of hormones that are being sent to encourage growth in the body, especially secondary sexual characteristic growth. Those are all aspects of hormones and the communication involved with the endocrine system. So let's look more specifically at some of the glands and the hormones that are used for communication.
So some of the most important glands in the endocrine system are located in the head and the neck areas. So we're going to be looking at these right now. First, we have the pituitary gland, which is an endocrine gland that's located towards the front, in the middle of the brain. OK. And this is what we would call the master gland. It's a gland that controls the other glands within the body. It sends out signals telling when they should and should not release hormones for various kinds of functions. In this way, the pituitary gland is kind of the brain of the endocrine system. But it's important to note that it's actually being regulated largely by the hypothalamus, which is the organ that's just above it. And this provides a kind of link between these two communication systems, the nervous system and the endocrine system. OK. So that hypothalamus helps to tell the pituitary gland when it should send out those controlling hormones.
The pituitary gland also has an important function in secreting growth hormones. And growth hormones regulate the body's development over time. So at certain periods of a person's life, more growth hormones are being sent out, for example, when a child is younger, as well as certain short periods of time, like growth spurts, like in adolescence. Now too much or too little of these growth hormones can lead to different kinds of conditions, like dwarfism or gigantism.
Next we have the pineal gland, which is another endocrine gland that's located in the brain, this one, a little bit more towards the center, the middle of the brain. And the pineal gland helps to regulate the body's rhythms and cycles. Now originally, a lot of people thought that the pineal gland was useless in that it was something kind of left over from a previous time in human development, kind of like the appendix. But now we realize that it's really important, especially as a connection to the nervous system. So it actually has effects on things like our brain and personality.
The pineal gland secretes a hormone called melatonin. The pineal gland is sensitive to the amount of light within our environment. It's photosensitive. And so it'll secrete melatonin in larger amounts when there's more light. So in the beginning of the day, for example, it starts to secrete more melatonin. It secretes the most at around noontime, when we have the most light. And then it starts to go gradually downhill towards nighttime. And this actually affects the amount of arousal that we feel and our mood and activity throughout the day. So this is why we feel sluggish a lot of times on a cloudy day, things like that, because the amount of melatonin, which is keeping our body active and energetic.
Finally, we have the thyroid gland, which are these glands that are located within the neck. And they control the rate of metabolism within the body. In other words, it tells the body how quickly it should make and use different sorts of energy. So you might have heard of different disorders that have to do with the thyroid gland, things like hyperthyroidism, which is when the thyroid produces too many hormones. And this can lead to feelings of fatigue, because they're tired from using so much energy, as well as increased sweating and appetite, difficulty concentrating, nervousness or restlessness. So you can see how this creates more energy in the body than a person can really use.
And the opposite of that is hypothyroidism, which is when there are too few hormones being produced. And this can lead to feelings of depression, fatigue, weakness, as well as weight gain. So you can see it can have an effect on a person's personality and mood. If somebody has hyperthyroidism, they might be a very excitable or irritable kind of person.
A hormone secreted during childhood, from the pituitary gland, that affects the physical growth of a person; too little can result in dwarfism while too much can result in gigantism.
A chemical secreted by a gland that affects internal and external activities.
The "master gland" of the endocrine system; secretes hormones that affect other glands.
Gland located in the neck which is responsible for the regulation of metabolism.