Endocrine System, Part 1 - Glands & Hormones: Crash Course Anatomy & Physiology #23

Summary

This script addresses common misconceptions about hormones, emphasizing their diverse roles beyond sexual attraction and reproduction. It explains the endocrine system's function in producing hormones that regulate metabolism, sleep, stress response, and homeostasis. The script delves into the chemical structures of hormones, their solubility, and how they interact with target cells. It also highlights the importance of the hypothalamic-pituitary-adrenal (HPA) axis in managing stress and maintaining body balance, urging respect for these vital chemical messengers.

Takeaways

• 🧬 Hormones are often stereotyped and associated with behaviors and conditions related to reproduction and sexual development, but they are much more complex and influence nearly every cell and function in the body.
• 🔍 The term 'hormones' usually refers to 'sex hormones' in common discussions, but there are over 50 types of hormones that regulate various bodily processes, with only a few related to sex.
• 🌐 Hormones are chemical messengers that circulate in the blood, affecting metabolism, sleep, stress response, and maintaining overall homeostasis, which is crucial for life.
• 🔄 Hormones can trigger a 'cascade' of reactions, where one hormone's release can lead to the activation of others, creating a chain reaction throughout the body.
• 🏠 The endocrine system, which includes glands and organs, is responsible for producing, releasing, and reabsorbing hormones, and works alongside the nervous system to control the body.
• 🚀 The nervous system uses fast electrochemical signals to communicate, while the endocrine system relies on hormones traveling through the bloodstream for a slower, broader communication.
• 📍 Glands in the endocrine system, such as the pituitary, are scattered throughout the body and produce hormones that signal other glands to produce their hormones.
• 🔑 Hormones can only affect specific target cells that have the appropriate receptors for them, which can lead to either widespread or localized effects.
• 🧬 Hormones are made of amino acids or lipids, and their solubility determines whether they can cross cell membranes or need to bind externally to target cells.
• 🍰 Imbalances in hormones can occur due to over- or under-secretion, leading to conditions like diabetes or hyperthyroidism, or through complex hormonal cascades that can take time to resolve.
• 🧘‍♂️ The hypothalamic-pituitary-adrenal (HPA) axis is a key example of the endocrine system's interaction with the nervous system, particularly in the stress response and maintaining homeostasis.

Q & A

What is the common misconception about hormones discussed in the script?

The common misconception is that hormones are only related to sexual attraction, zits, or extreme emotions, when in fact they influence almost every cell and function in the body.

How many different types of hormones are mentioned as being present in the human body?

At least 50 different types of hormones are at work in the human body at any given time.

What are the two primary systems in the body that are constantly trafficking information and controlling our every move?

The two primary systems are the endocrine system and the nervous system.

How does the nervous system typically transmit information?

The nervous system uses fast electrochemical action potentials delivered by neurons to specific cells and organs.

What is the role of the endocrine system in the body's communication?

The endocrine system secretes hormones that travel through the blood to have widespread and long-lasting effects on the body.

Which gland is considered the 'master gland' in the human body?

The pituitary gland is considered the 'master gland' as it produces many hormones that signal other glands to make their own hormones.

How do hormones interact with target cells in the body?

Hormones bind to specific receptors on target cells that have the appropriate receptors for them, which can either be on the outside or inside of the cell, depending on the hormone's solubility.

What are the two hormones released by the pancreas to regulate blood sugar levels?

The two hormones are insulin, which lowers blood sugar levels, and glucagon, which raises them.

What is the hypothalamic-pituitary-adrenal axis, and why is it significant?

The hypothalamic-pituitary-adrenal axis (HPA axis) is a complex series of interactions between three glands that regulate many of the body's daily processes, including the stress response.

How does the HPA axis contribute to the body's fight-or-flight response?

The HPA axis triggers the release of stress hormones like cortisol, which ramp up blood pressure, increase glucose in the bloodstream, and shut down non-emergency services during high-stress situations.

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

The hypothalamus acts as the hub where the endocrine and nervous systems meet, monitoring the body's conditions and maintaining balance by releasing hormones like CRH to initiate the stress response.

Outlines

00:00

🧬 Hormones and the Endocrine System Overview

This paragraph introduces the topic of hormones and the endocrine system, challenging stereotypes that associate hormones primarily with sex and reproduction. It clarifies that hormones are chemical messengers that regulate a wide range of bodily functions, including metabolism, sleep, stress response, and homeostasis. The paragraph explains that hormones are part of a complex system involving various glands and organs, such as the pituitary and thyroid, which produce hormones that trigger reactions in target cells with the appropriate receptors. The chemical structure of hormones determines their solubility and method of action, with water-soluble hormones binding to external receptors and lipid-soluble hormones, like steroids, penetrating the cell membrane to bind internally. The endocrine system works alongside the nervous system, with the former using a slower, broader approach to communication compared to the rapid, targeted signals of the latter.

05:01

🍰 Hormonal Imbalances and the HPA Axis

The second paragraph delves into how hormonal imbalances can occur, using the example of blood sugar regulation by insulin and glucagon as a case study. It discusses endocrine-related illnesses like diabetes and hyperthyroidism, which result from the over- or under-secretion of hormones. The paragraph then focuses on hormone cascades, particularly the hypothalamic-pituitary-adrenal (HPA) axis, which is central to the body's stress response and involves a series of interactions between three glands. The HPA axis is highlighted as an example of the endocrine system's coordination with the nervous system, particularly in the fight-or-flight response. The paragraph describes the process from the release of CRH by the hypothalamus to the eventual release of stress hormones by the adrenal glands, which can lead to a range of physiological effects. It concludes by emphasizing the importance of understanding hormones beyond the stereotypes and recognizing their critical role in maintaining bodily balance.

Keywords

💡Hormones

Hormones are chemical messengers produced by the endocrine system that regulate various functions in the body. They are crucial for maintaining homeostasis and are involved in a wide range of processes, from metabolism to the stress response. In the video, hormones are discussed as being more than just 'sex hormones,' highlighting their diverse roles in the body, such as regulating metabolism and stress response.

💡Endocrine System

The endocrine system is a collection of glands and organs that produce hormones. It plays a vital role in coordinating many of the body's functions through the secretion of these hormones into the bloodstream. The video emphasizes the endocrine system's role in producing hormones that have widespread effects on the body, contrasting it with the nervous system's faster, more direct communication method.

💡Homeostasis

Homeostasis refers to the body's ability to maintain a stable internal environment despite changes in external conditions. Hormones play a key role in achieving this balance by regulating various physiological processes. The video script mentions homeostasis in the context of hormones' influence on keeping the body functioning optimally and maintaining balance, such as regulating blood sugar levels.

💡Sex Hormones

Sex hormones are a subset of hormones that are primarily involved in the development of sexual characteristics, reproduction, and sexual behavior. The script challenges the stereotype that equates all hormones with sex hormones, explaining that while they do play a role in sexual attraction and development, they are just one type among many different hormones in the body.

💡Metabolism

Metabolism is the set of life-sustaining chemical reactions in the body that allow it to grow, maintain, and repair cells, and produce energy. Hormones, such as thyroxine produced by the thyroid gland, play a critical role in regulating the rate of metabolism. The script uses metabolism as an example of one of the many functions influenced by hormones.

💡Hormone Cascades

Hormone cascades refer to a series of hormonal interactions where one hormone triggers the release of another, creating a chain reaction. This concept is important in understanding how complex hormonal responses are orchestrated in the body. The video script discusses hormone cascades in the context of the body's response to stress, illustrating how one hormone can lead to a series of hormonal releases.

💡Hypothalamic-Pituitary-Adrenal (HPA) Axis

The HPA axis is a critical communication pathway in the body that links the hypothalamus, the pituitary gland, and the adrenal glands, playing a central role in the body's response to stress. The script explains how the HPA axis is activated during stress, leading to the release of hormones that prepare the body for a fight-or-flight response.

💡Stress Response

The stress response is the body's reaction to a perceived threat or challenge, which can include physiological changes such as increased heart rate and blood pressure. Hormones, particularly those released through the HPA axis, are central to this response. The video script uses the example of waking up to a burning house to illustrate the activation of the stress response and the role of the endocrine system in this process.

💡Insulin and Glucagon

Insulin and glucagon are hormones produced by the pancreas that regulate blood sugar levels. Insulin decreases blood sugar levels by promoting the storage of glucose, while glucagon raises blood sugar levels by stimulating the release of stored glucose. The script uses these hormones to explain how the body maintains blood sugar balance in response to food intake.

💡Nervous System

The nervous system is a complex network of nerves and cells that transmit signals between different parts of the body. It is responsible for rapid communication and control of body functions. The video contrasts the nervous system's fast, electrical communication with the slower, chemical communication of the endocrine system, highlighting the interplay between these two systems in controlling the body's functions.

💡Target Cells

Target cells are specific cells in the body that have receptors for particular hormones, allowing them to respond to those hormones. This concept is important for understanding how hormones exert their effects in a highly regulated and specific manner. The script explains that hormones can only trigger a reaction in cells that have the appropriate receptors, giving examples such as thyroxine affecting many cells and follicle-stimulating hormone affecting specific cells in the reproductive system.

Highlights

The talk addresses common stereotypes about hormones, emphasizing that they are often unfairly associated with behaviors and conditions related to reproduction and sexual development.

Hormones are not just about sexual attraction or zits; they play a crucial role in regulating almost every cell and function in the body, including metabolism, sleep, and stress response.

There are at least 50 different types of hormones in the human body, with only a few directly related to sex.

Hormones are chemical messengers that maintain homeostasis, influencing a wide range of bodily functions from birth to death.

The endocrine system and the nervous system are the body's two bosses, working together to control every aspect of the body through different methods.

The endocrine system uses hormones to send slower, widespread signals through the bloodstream, unlike the nervous system's fast electrochemical action potentials.

Glands in the endocrine system are scattered throughout the body and include the pituitary, thyroid, adrenal, and pineal glands, among others.

The pituitary gland is considered the master gland, producing hormones that signal other glands to produce their own hormones.

Hormones can only trigger a reaction in specific target cells that have the appropriate receptors for them.

Hormones are either water-soluble, requiring external receptors, or lipid-soluble, allowing them to pass through the cell membrane to internal receptors.

The thyroid hormone thyroxine is an example of a hormone that affects most cells in the body, while follicle-stimulating hormone is more specific to cells in the ovaries and testes.

Endocrine-related illnesses such as diabetes and hyperthyroidism are often the result of an imbalance in hormone secretion.

Hormone cascades are a series of interactions where one hormone controls the release of another, creating a chain reaction within the body.

The hypothalamic-pituitary-adrenal (HPA) axis is a key hormone cascade that regulates the body's response to stress and is integral to the fight-or-flight response.

The HPA axis involves the hypothalamus, pituitary gland, and adrenal glands, and is a critical example of the endocrine system coordinating with the nervous system.

During stress, the hypothalamus releases CRH, which triggers a series of hormone releases leading to the fight-or-flight response, including increased blood pressure and glucose levels.

The stress response regulated by the HPA axis is slower to initiate and longer to subside compared to the nervous system's electrical signals.

The talk concludes by encouraging a deeper understanding and respect for hormones, highlighting their essential role in maintaining bodily balance and responding to stress.

Transcripts

I’ve invited you all here today because I wanted to talk to you about some

ugly stereotypes that are going around.

I’ve been hearing a lot of unfair, unseemly, and unscientific generalizations being made lately.

And they mostly have to do with sex. And your hormones.

People have a nasty habit of equating “hormones” with a particular set of behaviors and conditions,

most of which have to do with reproduction, or sexual development, or acts that include

what my brother John has referred to as “skoodilypooping.”

For example, people will say that “hormones” are why Kevin has zits, and is being all moody,

or why Hannah, who’s three months pregnant, just cried watching a commercial for car insurance

-- which, let’s be honest, I do that too.

Now, I’m not saying that hormones aren’t at the root of sexual attraction, or zits,

or occasional bouts of extreme emotion, because they are. That’s just not all that they do.

Not even close.

When people talk about “hormones” in the contexts that I just mentioned,

what really they mean is "sex hormones."

But sex hormones are just one kind of hormone that you have coursing through your body right now.

In fact, there are at least 50 different types of these chemical messengers at work in your

body at this very minute, but only a very few of them have anything at all to do with sex.

The truth is, from birth to death, just about every cell and function in your body is under

your hormones’ constant influence.

They’re floating through your blood, regulating your metabolism, your sleep cycle, your response

to stress, and the general and incredibly important overall homeostasis that keeps you not dead.

Some hormones are just there to make other hormones trigger even more hormones -- in

a kind of chemical relay race that biologists refer to, rather elegantly, as “cascades.”

These hormones run through you no matter what your mood is, or whether you have zits.

So the reality is: We’re all hormonal ... all of the time.

OK, to begin to understand our hormones -- and the endocrine system that produces, releases,

and re-absorbs them -- we have to step back and take a broad view.

Not just by emphasizing that sex hormones aren’t the only hormones you have -- but also by

looking at how your hormones interact with your other organ systems.

Because, if anything, your body has two bosses -- two complementary systems that are constantly

shouting instructions over each other, to all of your bits and pieces.

Both your endocrine system and your nervous system are constantly trafficking information

around your corpus, gathering intel, making demands, controlling your every move. They

just have totally different ways of doing it.

Your nervous system uses lightning-fast electrochemical action potentials,

delivered by an expressway made of neurons to specific cells and organs.

But your endocrine system prefers a slower, wider stream of data.

It secretes hormones that travel through your blood -- NOT through neurons -- so they move more

slowly, but they also produce widespread effects that last a whole lot longer than an action potential.

Now, compared to your heart or brain or other, arguably more glamorous organs, your endocrine

system’s organs and glands are kinda small and lumpy.

They’re also rogues -- instead of being all nestled together like in your other organ systems,

these guys are scattered all over the place, from your brain to your throat, to your kidneys, to your genitals.

A gland is a just any structure that makes and secretes a hormone. And the master gland

in your body is the pituitary, which produces many hormones that signal other glands -- like

the thyroid, parathyroid, adrenal, and pineal glands -- to make their own hormones.

The endocrine system also includes a few organs -- like the gonads, the pancreas, and the

placenta in pregnant women -- all of which have some other non-hormonal functions and

are made up of multiple tissue types.

And technically the hypothalamus in your brain is in the endocrine club too, since in addition

to all of its busy brain duties, it does produce and release hormones.

So, thanks to these glands and organs, you’ve got all these hormones diffusing through your blood,

doing all sorts of different things, but the thing to remember about them is that a hormone can only

trigger a reaction in specific cells -- their so-called target cells -- that have the right receptors for it.

So, just like some keys can open many locks, while others only work with one, so too can

the hormone-target-cell relationship either be widespread or localized.

You’re probably gonna want an example of that. So, your thyroid -- at the bottom of

your throat -- produces the hormone thyroxine, which stimulates metabolism and binds to receptors

in most of the cells in your body.

But your pituitary -- which is nestled all comfy under your brain -- produces follicle-stimulating

hormone, which helps regulate growth and triggers sexual maturity, and it only targets specific

cells in the ovaries and testes.

So how do hormones bind to their target cells?

Well, chemically, most hormones are either made of amino acids -- including their more

complex structures like peptides or proteins -- or they’re derived from lipids, like cholesterol.

And this is key, because a hormone’s chemical structure determines if it’s water soluble,

like most amino acid-based ones are, or lipid soluble, like steroids are.

Solubility is important because your cell membranes are made of lipids.

That means that water soluble ones can’t get across them. So target cells for those

kinds of hormones have receptors for them on the outside of their membranes.

Lipid-soluble hormones, on the other hand, can just basically glide right through that

cell membrane, so their receptor sites are inside their target cells.

Either way, when a target cell is activated, the hormone alters its activity, by either

increasing or decreasing some of its functions -- usually with the goal of maintaining your

body’s homeostasis in one way or another.

So, if hormones are keeping your body IN balance, what’s putting your body out of balance?

I don’t know -- could I interest you in some pie?

If you have a couple of nice, generous helpings of strawberry-rhubarb pie -- and just to make

things interesting, let’s say they’re a la mode -- your blood glucose level is gonna go through the roof.

And the pancreas regulates your blood sugar by releasing two different hormones -- insulin and

glucagon. Once you have a belly full of that pie, beta cells in your pancreas release insulin, which

helps lower your blood sugar by increasing the rate at which your cells store the sugar

either as glycogen or as fat for later use.

Now, let’s say you’ve done the opposite: You’ve eaten no pie -- you’re pie-less

-- in fact, you’ve eaten nothing for hours.

If your blood sugar drops too low, then alpha cells in the pancreas will instead send out

glucagon, which helps raise your blood sugar levels, in part by decreasing the storage

of sugar in your cells, and triggering their release of glucose back into the blood.

Lots of different endocrine-related illnesses -- like diabetes or hyperthyroidism -- tend

to be the result of either hyper (too much) or hypo (too little) secretion of certain

hormones, which throw your homeostasis off balance.

But there are lots of more common -- and less obvious -- ways your hormones can get out

of balance, not because of some disorder, but because these signaling chemicals are

just caught up in a chain reaction, which can take a while to subside.

Some hormones just exist to control other hormones, which in turn control still more hormones.

So as soon as one starts to trickle out, you can pretty quickly wind up with a cascade on your hands.

You’ve got a few different hormone cascades going on at any given moment, but one of the

big ones -- one that’s really worth understanding -- is the hypothalamic-pituitary-adrenal axis,

or the HPA axis, because you don’t want to have to say that every time.

This is a complex series of interactions between three glands that ultimately regulates lots

of your body’s daily processes, like digestion, sexuality, immune response, and how you handle stress.

And it’s complex not just because of all the glands involved -- it’s also one of

the more crucial instances of your endocrine system coordinating with your nervous system.

Specifically, it’s behind that fight-or-flight response that everybody keeps talking about.

The HPA Axis is essentially the endocrine system’s companion to the sympathetic nervous system.

The sympathetic system, in times of high stress, does things like speed up your heart rate

and direct blood away from the digestive organs and to the muscles.

But many of the other effects of the stress response are carried out by your endocrine

system. And getting your nervous and endocrine systems to work together in times of crisis

is where the hypothalamus comes in.

It’s the hub of where the two systems meet -- it keeps tabs on what’s going on all

over your body, analyzing your blood for signs that something might be off.

So, let’s revisit our fight-or-flight scene from a few lessons ago -- the old Burning House Scenario.

So you’re sleeping, dreaming about petting pandas with Emma Watson or whatever, when the smoke alarm

goes off. Well, action potentials in your brain trigger neurons in your hypothalamus to release the peptide

hormone CRH, or corticotropin releasing hormone.

The CRH makes the very short trip through the bloodstream to the anterior pituitary

gland, where, because it’s water soluble, it binds to receptors on the outside of its target cells.

There, it triggers the release of adrenocorticotropic hormone, or ACTH. The ACTH travels -- again

through the bloodstream -- to the adrenal cortices of the adrenal glands on top of your kidneys.

When the ACTH binds to receptors on cells in an adrenal cortex, it triggers the release

of a frenzy of different freak-out compounds known as glucocorticoid and mineralcorticoid hormones.

Typically these guys help us deal with day-to-day stress by keeping our blood sugar and blood pressure

balanced. But under major stress -- like waking up in a burning building stress -- these hormones,

like cortisol, cause the classic fight-or-flight response: ramping up your blood pressure,

dumping glucose into your bloodstream, shutting down non-emergency services like your immune

system and sperm and egg development.

And guess what? Now that all these stress hormones are pulsing through your blood, the

hypothalamus back in the brain senses them.

And because its job is to monitor and maintain balance whenever possible, it then stops secreting

CRH, which -- eventually -- causes the other glands to stop secreting their panic hormones.

Now, because this element of the stress response is hormonal rather than electrical, it comes

on more slowly than the nervous system part, and it takes longer to subside, too, as those

stress hormones linger in the blood before being broken down by enzymes.

So. We’re a long way from teenage crushes and zits and crying over commercials at this point, aren’t we?

As a life-long owner of hormones, I hope you’ll join me in dispelling the stereotypes that

surround these powerful and important chemicals, and give them the respect they rightly deserve.

Today we looked at the endocrine system, and how it uses glands to produce hormones. These

hormones are either amino-acid based and water soluble, or steroidal and lipid-soluble, and

may target many types of cells or just turn on specific ones. We also touched on hormone

cascades, and how the HPA axis effects your stress response.

Thank you to our Headmaster of Learning, Thomas Frank, and to all of our Patreon patrons who

help make Crash Course possible through their monthly contributions. If you like Crash Course

and you want to help us keep making free educational content for the whole world, you can go to

patreon.com/crashcourse.

Crash Course is filmed in the Doctor Cheryl C. Kinney Crash Course Studio. This episode

was written by Kathleen Yale, edited by Blake de Pastino, and our consultant is Dr. Brandon

Jackson. It was directed by Nicholas Jenkins, the editor is Nicole Sweeney, the script supervisor

was Stefan Chin, our sound designer is Michael Aranda and the graphics team is Thought Café.