We want to continue looking at this link between the nervous system and the endocrine system, between the hypothalamus and the pituitary gland. And so here, we're going to be talking about the posterior pituitary. Just like when we talked about the anterior pituitary, we're first going to discuss that link between the hypothalamus and the posterior pituitary. We'll explore it structurally and how it functions, and then we will look at what hormones the posterior pituitary actually releases. So let's get started. Alright. We're going to start just by orienting ourselves to our image here. We have the pituitary gland hanging down there, and the posterior part, this rear part, we have color-coded in pink. You can see there are some blood vessels on there. And then the other thing you'll notice are these neurons that start up here in the hypothalamus and then run down into the posterior pituitary there. And again, I said they start up here in the hypothalamus, that part of the brain there.
Alright. We're going to start just by saying that the posterior pituitary is this rear portion. That's just what posterior means. It's in the back. This rear portion of the pituitary, and it's made largely of nervous tissue. And this nervous tissue has a direct connection to the hypothalamus. So, again, that's what we just looked at in this drawing here. These neurons start up in the hypothalamus, and they run all the way down, and they actually make up the majority of tissue in this pituitary gland. This direct connection is very different from the anterior pituitary gland. Remember, the anterior pituitary gland was connected to the hypothalamus through blood vessels, and its tropic hormones that sort of instructed the anterior pituitary what to do. Here, we have a direct connection. It's really the same tissue. It's cells that start in the hypothalamus and then extend down and make up the posterior pituitary. So we're going to say the posterior pituitary really functions as an extension of the hypothalamus. Right? Again, it's the same cells.
Now, these cells start in 2 very specific places, so we want to call those out, and we have them color-coded here. They start in the paraventricular and supraoptic nuclei. So paraventricular nuclei, that's this region sort of here in blue in the hypothalamus. Paraventricular para means beside and ventricular it's beside the 3rd ventricle in the brain. And supraoptic nuclei, that's this one color-coded in purple. Supraoptic supra means above, and optic, it's just above the optic tract.
Now you probably don't need to know need to break down those words like that, but if you want to know where they come from, that's where they come from. Alright. So this paraventricular and supraoptic nuclei, these actually make the hormones. So the hormones are going to be synthesized up here in the hypothalamus. Now they need to travel down these cells to get to the posterior pituitary. So we're going to say they travel down the hypothalamic hypophyseal tract. Now that should sound familiar. Remember, in the anterior pituitary, we had the hypothalamic, hypophyseal portal system. Hypothalamic means the hypothalamus. Hypophyseo is an adjective that means pituitary gland. And the portal system was this group of blood vessels that connected them in the anterior pituitary gland. But the posterior pituitary, again, it's the same cells, so it travels down a tract. And a tract refers to a group of neurons, like the optic tract. So we have this group of neurons, these axons that are running down through the infundibulum. So the hypothalamic, hypophyseal tract, that is going to allow these hormones to travel down axons through the infundibulum and into the posterior pituitary.
Once we're in the posterior pituitary down here, well, this is where these hormones are actually going to get released from the axon terminals, and it's going to be action potentials that start up in the hypothalamus that lead to the release of the hormones. So the hormones have to travel down these axons to be released by the axon terminals, but it's the same axons that carry the action potential down and stimulate the release. Now, you may note that's very similar to how a lot of the nervous system works. Right? You have an action potential that comes down that leads to the release of a neurotransmitter, which is a chemical messenger. The key difference, a neurotransmitter travels from one neuron across a synapse to another neuron. But here, these chemical messengers are released from an axon terminal and into the blood. Well, if you release a chemical messenger into the blood, you call it a hormone.
Let's see what hormones are released from this posterior pituitary gland. Now we've set up this table just like we did for the anterior pituitary, but you'll see there's a lot less going on here. In this case, on the left, it's always going to be stimulated by hypothalamic neurons. The action potentials are always going to cause the release of these hormones. There are no tropic hormones. We don't have to worry about those here.
The hormones of the posterior pituitary, again, this is very likely something that you need to know to be able to know what hormones are released by this gland. And then we're also going to say what target cells they affect, and just very generally what they do in the body. Now again, you may need to know what these hormones do in more detail, but we're not talking about that here. Right now, we just want to talk very generally what they do and ass