Endocrine system introduction

What you see in these pictures is a forward view of a transparent man or a semi-transparent man, and this is a posterior back view of a semi-transparent woman. But what are these organs that are depicted?

These organs secrete molecules into the bloodstream. An organ that secretes things is called a gland, and they secrete these molecules into the bloodstream that regulate other parts of the body—things that might be quite far away from the organs, the glands that actually do the secretion.

So, these molecules that regulate other parts of the body are called hormones. The word hormone comes from Greek "ormo," which means to set in motion. So, one way to think about it is that these are molecules that set things in motion in other parts of the body. This is really to regulate body function.

Now, this entire system of glands is referred to as the endocrine system. "Endo" refers to the fact that it's acting within the body; "crin" originally comes from Greek "krinein," meaning to sift or to differentiate something. It's a system of organs, or I guess you could say glands, that secrete these molecules (hormones) into the bloodstream to regulate the body.

I'm not going to go in depth in all of these endocrine glands, but just to give you an appreciation of what they do and what these hormones are all about, we can list some of the more common ones that you might hear about.

For example, the thyroid gland produces thyroid hormone. This is a version of thyroid hormone; you see your carbons in the dark gray, your hydrogens in the white, oxygens in the red, nitrogen in blue, and these big atoms right over here—these are iodine. Thyroid hormone plays an important role in your metabolism.

In fact, if you have too much thyroid hormone, that's a disorder called hyperthyroidism, which would make your metabolism overactive. Likewise, if you have too little thyroid hormone, that's a disorder known as hypothyroidism, in which case your metabolism isn't active enough.

You have hormones like adrenaline that are released by the adrenal glands; that's where it gets the word adrenaline from. It's often known as epinephrine. You might hear things like, "Hey, so-and-so is an adrenaline junkie," which means they really like a thrill.

Adrenaline actually plays a role there; it's involved in the fight or flight response where it will increase your heart rate and increase blood flow to the muscles.

What's really interesting about all of these hormones is they have so many impacts on the body because they're released into the bloodstream and to different cells; they might do different things.

This right over here is a variation of estrogen, which is produced primarily in females in the ovaries, but it also exists in a male body. It's associated with a lot of female bodily function, but once again, not strictly female; estrogen also exists in males.

Similarly, you have testosterone, which is associated with male function, but it also exists in females and it's primarily produced in men in the testes—thus the name testosterone. But it can also be produced by the adrenal glands, and in women, it can be produced by the ovaries.

But you could also have a molecule like insulin, which you can see is much larger than the other hormones that we have looked at. It's produced in the pancreas and it plays a super important role in how we process sugars and how we store fat.

Scientists are constantly discovering new roles for these various hormones. Insulin, in particular, you might associate with diabetes. People with type 1 diabetes aren't able to produce enough insulin to take sugar out of their bloodstream to have the cells absorb the sugar.

Insulin will bind to the surface of a cell so that it will start taking in sugar from the bloodstream. People with type 2 diabetes have an insensitivity to insulin, so they might have to take extra insulin in order for their cells to take in the proper amount of sugar.

But the big idea here is that the endocrine system, although it might not be as obvious or it might not be as well known as something like, say, the nervous system, plays a pivotal role in your body. It helps regulate your body; it helps keep it at the right temperature, the right blood pressure, your heart pumping at the right rate.

One way to think about this is the notion of homeostasis, which is derived from "similar" and "staying the same." So, keeping your body at the right temperature, regardless of what the temperature is outside or regardless of what your body is doing, there's a whole series of roles that these hormones, which are released by these endocrine glands, actually do.