 Okay. If a hormone is not a steroid hormone, so it's not derived from cholesterol and it's not an amino acid hormone, so it's not derived from tryptophan or tyrosine, then it must be a peptide hormone and that truly is the process of elimination. Everything else are peptide hormones. And I'm going to tell you about the mechanism. First of all, peptide hormones are like all hormones. They start in the blood. And they are hydrophilic. They're made out of protein, so they're not going to be hydrophobic. And oh my gosh, I'm having a very hard time deciding on what color to make my peptide hormone. I can't remember what my other colors were. Because they are not hydrophobic, they're cool with water. Water, homey. Let's hang out. They don't need a carrier. Sometimes they like to be in a boat. Sometimes, just, and I'm going to put my little flag on this boat just so you remember it's a boat and not a receptor. Sometimes they like the protection offered by a boat, but they don't need the boat in the same way that a steroid hormone would. The second mechanism, this is awesome. Peptide hormones initiate a second messenger response. And this is something that we will see again and again and again in lots of different environments. Peptide hormones, this is how they, this is the mechanism by which they get a response. Other systems, I believe a smell involves a second messenger response. And so this technique, this tool, this mechanism can be seen in other systems. But let's draw ourselves a cell. And I'm going to illustrate for you what a second messenger system or mechanism looks like. First of all, your hormone is your first message. So what does this tell you right here? Somewhere along the line, we're going to get a second message. And here's how it works. First of all, the hormone binds to the receptor. The receptor is embedded in the cell membrane. So first hormone binds. It binds to the receptor. And we already know that a key tool in the communication toolbox is that proteins, when they bind to their people, they change shape. So the receptor, when it binds to the hormone, it's going to change its shape. And the act of changing shape. The receptor changes shape. The triangle means change in windy land. And the shape change causes a cascade of chemical reactions. Now you can go and find out what the G protein and all the proteins involved in the cascade. And most of the time, these things are known. For this class, all we're going to have to do is know that you know what, it's going to initiate a cascade of chemical reactions to result in our second messenger. And our second messenger, receptor changes shape, initiates a cascade of chemical reactions to produce my second message. And in most cases, guess who my second message is? If you know me, you know that I pick orange for my favorite high-energy things. And this is related to my very favorite high-energy thing, which is ATP. This is something called cyclic adenosine monophosphate, or CAMP. Do you want me to write that down for you? Cyclic adenosine, like adenosine triphosphate, ATP, but it's only monophosphate. Oh, show. Cyclic adenosine monophosphate, CAMP. CAMP is my second message. Now, CAMP, depending on where it is and what's going to happen, CAMP is the enzyme, or the CAMP activates. CAMP is then going to activate the enzymes or whatever needs to be activated to make an action happen. And so, number six, and I wanted to draw like a little enzyme, okay, here I go, ready? Enzymes always look cool, like Pac-mans, but watch this. This enzyme isn't going to work unless it gets some CAMP hooked up in there. So when CAMP hooks in, then that enzyme is like, I'm a Pac-man, and it goes around. And this is one of the characteristics of the second message or response. One CAMP can go around and activate a whole bunch of enzymes. So actually, now that I've drawn it like this, it makes me think that, no, that's not an appropriate way to draw it because it's not like the CAMP gets used up. The CAMP can go around and activate and activate and activate, which means that a second messenger response can be amplified, so it is fast. That means one hormone can come in and activate 1,000 enzymes. Two hormones can activate 2,000 or 5,000 or 12,000 hormones, or enzymes, and so essentially where with the steroid hormones, if you wanted one outcome, you needed to put in one hormone. Here you put in one hormone and you can get holy madness of response. And that's one of the really unique things. Now, since the response can be amplified and it's fast, now think back to the amino acid derivatives that had a peptide hormone-like mechanism. That means that you're adrenaline, you're epinephrine and norepinephrine. These guys have a very fast and amplifiable effect on the cell. Dude, that's perfect. Throw one hormone in, one. I mean, don't you get that feeling? Like now we know why. When you almost get into a car accident, you don't even have to be in the car accident. You don't even have to know what the hell just happened. And you have this rush of adrenaline and the response is instantaneous. Your heart rate increases, your blood pressure increases, you start to sweat, you start to dilate your pupils, let more light in. Your responses are immediate. And you get that feeling. Like the stimulus comes in, here's the car accident about to happen or the bear about to chase me. And all of a sudden, the effectors are like, whoa, seriously? Like I didn't even process in my brain that that was actually a bear over there. And yet all of this already happened. Evidence that the second messenger response is not messing around. What a great strategy. We're going to take, you now have some tools. You have some mechanisms to understand different hormones and how they act. And we're going to look at similar mechanisms and hormone actions all the way through the course. Most likely in your integration project, you're going to have some kind of hormonal thing going on. So you're probably going to need to be aware of or feel comfortable with these processes. Now we're going to look at, take a step back and look at some of the endocrine anatomy and some specifics between the hypothalamus and the pituitary.