The Hypothalamus and Pituitary Gland - Online Tutor, Practice Problems & Exam Prep

The hypothalamus and pituitary gland are crucial in linking the nervous and endocrine systems. The hypothalamus regulates homeostasis and releases tropic hormones that stimulate the anterior pituitary to secrete hormones like growth hormone and thyroid-stimulating hormone. The posterior pituitary, an extension of the hypothalamus, releases antidiuretic hormone (ADH) and oxytocin directly into the bloodstream. Understanding these connections and hormone functions is essential for grasping endocrine system dynamics and maintaining physiological balance.

Hypothalamus & Pituitary Gland

As you learn about the endocrine system, you're almost certainly going to be responsible for the names and locations of specific glands. You're going to need to know some of the hormones they produce and specifically what some of those hormones do in the body. So to start talking about that, we are going to start with the hypothalamus and the pituitary gland. We're starting here because, while the endocrine system has many glands well distributed throughout the body that act on their own without any control, if there is something in control of the endocrine system, it's the hypothalamus and pituitary gland. And we'll explain how that works now. So, we're going to start just by saying that this is the connection or the link between the nervous and endocrine systems. Right, the nervous system and endocrine systems, those are your two major body communication systems. So it makes sense that there's this place where they talk to each other. To understand how this works, first, we'll look at our image here. We have an image of the brain, and pulled out here we have this part of the brain, the hypothalamus, right down there. And then right under the hypothalamus, we have what I always think looks like sort of this double punching bag hanging off the brain. That's the pituitary gland. Alright.

So we'll start talking about the hypothalamus. Again, the hypothalamus is part of the brain and its real main job is that it maintains homeostasis, and controls autonomic functions of the body, which are largely in charge of homeostasis. But the endocrine system also is in charge of many homeostatic variables. So, this is where they talk to each other. The hypothalamus is going to measure a lot of those variables in the body and then based on what needs to happen, it's going to tell the endocrine system what to do, and it's going to do that by controlling the release of hormones from the pituitary gland. As we go down, you'll see we have this structure that we haven't talked about yet in yellow, the infundibulum. The infundibulum is what connects the hypothalamus and the pituitary gland. Right there, it's often described as this sort of funnel-like structure connecting the hypothalamus and pituitary gland. Now, functionally, there isn't much to know about the infundibulum - it's just that sort of funnel-like connector of the two, but there is a good chance you're going to have to label it on a diagram or at least be able to describe where it is.

So as we move down, now we reach the pituitary gland. The pituitary gland, which I, again, often think of as a sort of double punching bag right there. And you'll note here, in parenthesis, we have the second name, the hypothesis. Now, almost certainly, you're not going to call it the hypothesis, and you won't hear people refer to it as the hypothesis. But if it's used as an adjective, you'll use the term hypophyseal. For example, there is this group of blood vessels right here called the hypophyseal portal system. That term, hypophyseal, comes from that other name for the pituitary, the hypothesis. The pituitary, we're going to say here its major job is that it communicates with other endocrine glands. Now, the pituitary does release hormones that don't communicate with other endocrine glands, that just sort of have more direct physiological functions. But here, in understanding this system, we want to think about the pituitary gland in its role of controlling the function of other glands. Now we're just going to say, structurally, it is inferior to the hypothalamus. So again, we can see it right here. It's just under the hypothalamus, hanging down there off the brain. And we're going to say that it's shaped like a double punching bag, so that's because it has two lobes. It has the anterior lobe and the posterior lobe that you can see here in the diagram. These are going to function differently. The anterior pituitary is going to be stimulated by hormones from the hypothalamus. So, again, we're going to go into this in more detail coming up, but for now just understand that the hypothalamus is largely in control of what's happening here. The way it controls it is that it's going to release its own hormones. They're going to go through this little blood vessel system, and that's how the hypothalamus talks to the pituitary gland, that anterior pituitary gland. The posterior pituitary is going to work differently. The posterior pituitary is made of neurons extending from the hypothalamus. So it's actually made of nervous tissue. The hypothalamus, these neurons start here and their axons come down, and the axons in the posterior pituitary sort of act both as nervous and endocrine glandular tissue. Alright.

Now, to really understand how this connection between the hypothalamus, the pituitary, and other glands work, we need to knock off one more vocab word, and that will be tropic hormones. A tropic hormone is a hormone that will trigger the release of other hormones. So a tropic hormone has target cells in other glands, and the response, when those target cells recognize the hormone, is to release more hormones. So we're going to say here that tropic hormones from the hypothal...

The Hypothalamus and Pituitary Gland Example 1

Our example tells us that a scientific study demonstrated that studying for exams can lead to an increase in a student's cortisol levels due to stress. Some of the steps of the stress response involving cortisol are shown below, and we want to circle any steps that involve tropic hormones. So first, let's just remind ourselves of that definition of tropic hormones. A tropic hormone is a hormone that has a target cell in another gland and causes the release of another hormone. So, we have this sort of flowchart here showing some hormones, glands, and other tissues. We'll start out, we have an image of the hypothalamus, and that seems to be releasing this corticotropin-releasing hormone. That then goes to our next image here of the anterior pituitary, which you see right there. It seems to be releasing adrenocorticotropic hormone. That hormone seems to be going to the adrenal glands, which you see here drawn on top of the kidneys, where they are in the body. The adrenal glands seem to be releasing the hormone cortisol, and that seems to be going to the liver. Alright. So, remembering that definition of a tropic hormone, well, our first hormone here, corticotropin-releasing hormone, is going to the anterior pituitary, and the response seems to be that the anterior pituitary is releasing another hormone. So, that seems to me like it's a tropic hormone; it's causing the release of another hormone from another gland. So, I'm going to circle this first hormone here. Next, we have the adrenocorticotropic hormone. Well, again, it's right there in the name tropic. Adrenocorticotropic hormone. This hormone, what's happening? It's going to the adrenal glands. And how do the adrenal glands respond? They respond by releasing another hormone, cortisol. So, I am going to circle adrenocorticotropic hormone. Lastly, we have the hormone cortisol. Cortisol here is going to the liver, and that seems to be where this pathway stops. It looks like, from this diagram, that the physiological effect from cortisol is going to happen in the liver, and there aren't going to be any more hormones released. That means that cortisol, at least in this diagram, is not a tropic hormone. So, our first two hormones there, I have circled corticotropin-releasing hormone and adrenocorticotropic hormone. From this diagram, those look like tropic hormones to me. That's my answer.

Which of the following describes a tropic hormone?

• A. Insulin is a hormone that causes the body to produce glycogen, removing sugar from the bloodstream.
• B. Thyroid stimulating hormone signals the thyroid gland to release the hormone thyroxin.
• C. Epinephrine is a hormone that leads to many different physiological changes in many different tissues.
• D. Estrogen is a lipid soluble hormone, and therefore can pass through the cell membrane.

Anterior Pituitary

The hypothalamus and the pituitary gland serve as the link between the nervous system and the endocrine system. We also said that if there's anything in charge of the endocrine system, it's the hypothalamus and the pituitary gland. Specifically, the anterior pituitary releases hormones that affect the release of other hormones throughout the body. Before we get going, let's orient ourselves to our picture here. Here we have the pituitary gland, color-coded in light brown for the anterior pituitary, the front part of the gland we are discussing. You can also see some blood vessels here, and upward, the hypothalamus in gray. We can also observe some neurons in the hypothalamus, that part of the brain that run downward, and we'll discuss how they function shortly.

We'll start by mentioning that the anterior pituitary is stimulated by tropic hormones from the hypothalamus. Remember, a tropic hormone is one that causes the release of other hormones. The way the hypothalamus directs the anterior pituitary is by releasing its hormones that have target cells in the anterior pituitary. However, this system works differently from the general hormone release. Typically, hormones enter the bloodstream and spread throughout the body. Not here. Here, they're released into what's called a portal system. To understand a portal system, consider our drawing: the first capillary bed where these hormones are released funnels into veins, which unusually lead to more capillaries rather than going straight to the heart. This is called the hypothalamic-hypophyseal portal system because it connects capillaries from the hypothalamus to those of the anterior pituitary.

Looking again, remember the hypothalamus comprises nervous tissue. Neurons at the top have axons running down to the base of the hypothalamus or the top of the infundibulum, where these hormones enter the portal system efficiently reaching the anterior pituitary without dispersing into the overall body's circulation. We want to focus on what hormones the anterior pituitary releases and their effects. The table's middle column highlights likely important hormones released by the anterior pituitary, noting generally what they do based on their target cell locations. This quick review provides an understanding of the hormones released from the anterior pituitary and their functions.

In the first column, we see hormones released by the hypothalamus that either stimulate or inhibit the anterior pituitary. Names like growth hormone-releasing hormone, thyrotropin-releasing hormone, corticotropin-releasing hormone, and gonadotropin-releasing hormone are self-explanatory. They stimulate the anterior pituitary to release growth hormone (GH), thyroid stimulating hormone (TSH), adrenocorticotropic hormone, luteinizing hormone, and follicle-stimulating hormone. Moreover, prolactin inhibiting hormone does the opposite by blocking the release of prolactin (PRL), which has target cells in the breasts and is involved in milk production.

Remembering these hormones can be challenging, so a mnemonic device could be helpful. For the anterior pituitary hormones, consider 'FLAT PEG': F for follicle-stimulating hormone, L for luteinizing hormone, A for adrenocorticotropic hormone, T for thyroid-stimulating hormone, P for prolactin, and G for growth hormone. 'FLAT' refers to the tropic hormones, while 'PEG' denotes hormones with direct physiological actions. Next, we will discuss the posterior pituitary, which has fewer hormone releases, but first, review the examples and try the practice problems.

The Hypothalamus and Pituitary Gland Example 2

This example asks you to imagine that you are a doctor. You have a male patient showing low levels of thyroid hormone or T4, low levels of cortisol, produced in the adrenal cortex, and low levels of testosterone in a male, which would be produced in the testes. You believe the cause is a tumor in the hypothalamus. Now, based on your understanding of the role of the hypothalamus in the endocrine system, would you expect the tumor to be blocking the normal function of the hypothalamus or causing overstimulation of the hypothalamus? And explain your reasoning.

Alright. Take a second and think that through. If you are not producing enough thyroid hormone, cortisol, and testosterone and the cause is a tumor in the hypothalamus, would you think that is due to blocking the hypothalamus function or overstimulating the hypothalamus? Well, let's think about that, and let's sort of walk this all back. We are talking about thyroid hormone made in the thyroid gland, cortisol made in the adrenal cortex, and testosterone made in the testes. Now the release of all those hormones is going to be influenced by tropic hormones from the anterior pituitary gland. Specifically, thyroid-stimulating hormone (TSH) will stimulate the release of thyroid hormone. Adrenocorticotropic hormone (ACTH) will stimulate the release of cortisol. And, luteinizing and follicle-stimulating hormones will influence the release of testosterone.

So, if you're not producing enough of those hormones, there is a good chance the pituitary gland is not producing enough of those tropic hormones. But those tropic hormones from the anterior pituitary get released when the pituitary gland is stimulated by tropic hormones from the hypothalamus. So if the anterior pituitary gland isn't producing enough, there is a good chance it's because the hypothalamus is not producing enough of its tropic hormones. And so, if it's not producing enough, that says to me that this would be blocking the function of the hypothalamus.

Now, my reasoning we have just sort of gone through. Now, in I'm going to state it in real simple terms. I would just say that tropic hormones cause the release of other hormones. And now if this were a test, obviously, I would say a lot more than that. I'd start with that, and then I would say how the hypothalamus releases tropic hormones that affect the pituitary gland, which causes the release of hormones from the pituitary gland. The pituitary gland releases tropic hormones, which cause the release of these hormones we are talking about. So, if these hormones are not being released at a high enough level, there is a decent chance that we can follow it all the way back, and the tropic hormones from the hypothalamus are also not being released at a high enough level. That is my answer. We have more practice problems to follow. I'll see you there.

The following hormones are all produced by the pituitary gland. Which hormone is NOT released by the anterior pituitary?

• A. Oxytocin.
• B. Prolactin (PRL).
• C. Adrenocorticotropic Hormone (ACTH).
• D. Thyroid Stimulating Hormone (TSH).

What is the primary function of the hypothalamic-hypophyseal portal system in hormone transport?

• A. It transports hormones from the anterior pituitary to the hypothalamus.
• B. It allows hormones from the hypothalamus to reach the anterior pituitary directly.
• C. It carries hormones from the anterior pituitary to the general circulation.
• D. It carries tropic hormones directly from the hypothalamus to the different endocrine glands around the body.

Posterior Pituitary

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

The Hypothalamus and Pituitary Gland Example 3

Anterior Pituitary	Posterior Pituitary
Structure Connecting to Hypothalamus: Hypothalamic-hypophyseal portal system	Structure Connecting to Hypothalamus: Hypothalamic-hypophyseal tract
Hormones Released: Follicle-Stimulating Hormone (FSH) Luteinizing Hormone (LH) Adrenocorticotropic Hormone (ACTH) Thyroid-Stimulating Hormone (TSH) Prolactin (PRL) Growth Hormone (GH)	Hormones Released: Antidiuretic Hormone (ADH) Oxytocin

The anterior pituitary is connected to the hypothalamus by the hypothalamic-hypophyseal portal system, which is a network of blood vessels. This system carries tropic hormones directly from the hypothalamus to the anterior pituitary.

The posterior pituitary is essentially an extension of the hypothalamus, connected by the hypothalamic-hypophyseal tract. This tract consists of axons of neurons that originate in the hypothalamus and terminate in the posterior pituitary, where they release hormones into the bloodstream.

The anterior pituitary secretes several hormones, memorably summarized by the mnemonic "FLAT PEG": FSH, LH, ACTH, TSH, Prolactin, and Growth Hormone, each targeting specific organs and regulating various bodily functions.

In contrast, the posterior pituitary releases two main hormones, using the mnemonic "powerful antioxidants" for easy recall: ADH, which targets the kidneys and influences water reabsorption, and Oxytocin, which stimulates labor contractions and milk release.

This understanding of the pituitary gland's structure and function highlights its crucial role in the endocrine system and its complex relationship with the hypothalamus.

Which of the following statements about the posterior pituitary is true?

• A. The posterior pituitary is connected to the hypothalamus via the hypothalamic-hypophyseal portal system.
• B. The posterior pituitary releases hormones that are synthesized in the hypothalamus.
• C. The posterior pituitary relies on tropic hormones to signal when to release ADH and oxytocin.
• D. The posterior pituitary releases tropic hormones that target other endocrine glands.

Here’s what students ask on this topic:

What is the role of the hypothalamus in the endocrine system?

The hypothalamus plays a crucial role in the endocrine system by maintaining homeostasis and regulating autonomic functions. It acts as a bridge between the nervous and endocrine systems. The hypothalamus releases tropic hormones that stimulate the anterior pituitary gland to secrete hormones like growth hormone and thyroid-stimulating hormone. Additionally, it directly influences the posterior pituitary, which releases antidiuretic hormone (ADH) and oxytocin. These hormones are essential for various physiological processes, including growth, metabolism, and water balance.

How does the anterior pituitary gland function?

The anterior pituitary gland functions by releasing hormones in response to tropic hormones from the hypothalamus. These tropic hormones travel through the hypothalamic-hypophyseal portal system, a network of blood vessels connecting the hypothalamus to the anterior pituitary. The anterior pituitary then secretes hormones such as growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), and others. These hormones regulate various endocrine glands and physiological processes, including growth, metabolism, and stress response.

What hormones are released by the posterior pituitary gland?

The posterior pituitary gland releases two main hormones: antidiuretic hormone (ADH) and oxytocin. ADH, also known as vasopressin, helps regulate water balance in the body by reducing urine production and increasing water reabsorption in the kidneys. Oxytocin is involved in uterine contractions during labor and the release of milk during breastfeeding. It also plays a role in social bonding and emotional connections.

What is the hypothalamic-hypophyseal portal system?

The hypothalamic-hypophyseal portal system is a network of blood vessels that connects the hypothalamus to the anterior pituitary gland. This system allows tropic hormones released by the hypothalamus to travel directly to the anterior pituitary without entering the general circulation. This targeted delivery ensures that the anterior pituitary receives precise signals to release specific hormones, such as growth hormone (GH) and thyroid-stimulating hormone (TSH), which regulate various physiological processes.

What are tropic hormones and their function?

Tropic hormones are hormones that stimulate other endocrine glands to release their hormones. They are crucial for regulating the endocrine system. For example, the hypothalamus releases tropic hormones like thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH), which stimulate the anterior pituitary to release thyroid-stimulating hormone (TSH) and adrenocorticotropic hormone (ACTH), respectively. These hormones then act on the thyroid gland and adrenal cortex to release thyroid hormones and cortisol, respectively, thereby regulating metabolism and stress response.