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  • Have you ever thought about the way

  • the different parts of our body communicate?

  • I think we often consider the body

  • to be this one complete thing, this self.

  • But really our body is composed of lots of parts.

  • There are lots of organ systems.

  • And each of those has organs.

  • And all of those organs are made of tissues.

  • And all of those tissues are made of cells.

  • And it's crazy, but there are 100 trillion--

  • or at least roughly 100 trillion cells in our body.

  • So it's curious then how do those 100 trillion

  • different parts communicate?

  • Well, one way is through the nervous system

  • and through the pre-laid tracks of nerves.

  • But not every part of the body is connected by nerves.

  • I mean how, for example, would part of the brain

  • go about communicating with part of the kidney?

  • Well, to talk about that we're going

  • to have to talk about the endocrine system.

  • And the endocrine system is a system

  • of organs that are called glands.

  • And these glands secrete little chemical messages

  • that are called hormones.

  • And they release those little chemical messages

  • called hormones into the bloodstream

  • so that they can circulate from one part of the body

  • to another part of the body in order to initiate an effect.

  • And there are many parts of the body that

  • use these hormones to communicate.

  • But certain organs are really defined

  • by this method of communication and we

  • call them endocrine glands.

  • And so one of the major endocrine glands

  • is the hypothalamus.

  • And the hypothalamus is located right here.

  • It's a member of the forebrain.

  • And as a member of the brain, it receives a lot of those signals

  • that we talked about from the nervous system.

  • So those nerve signals are funnelling into the brain.

  • And the hypothalamus then, as a kind

  • of dual member of the endocrine system,

  • funnels those signals into the pituitary gland.

  • And so because it plays that dual role

  • between the endocrine system and the nervous system,

  • it often gets taglined as the control

  • center of the endocrine system.

  • In addition to stimulating the pituitary gland,

  • the hypothalamus actually make some hormones itself also.

  • And so it makes ADH and oxytocin.

  • And ADH is antidiuretic hormone.

  • And it's a main regulator of our fluid volume in our body.

  • And then oxytocin is a hormone that stimulates the uterus

  • to contract for females during pregnancy.

  • And so that's the hypothalamus, member

  • of the brain and member of the endocrine system

  • where it all begins, the control center.

  • And then right below the hypothalamus

  • is the pituitary gland.

  • And the pituitary gland is located right here,

  • dangling right below.

  • And so the hypothalamus is about the size of a grape.

  • And the pituitary gland is actually

  • about the size of a green pea.

  • But this little green pea is so important

  • that it's called the master gland.

  • And it's called the master gland because the pituitary gland

  • takes that stimulation from the hypothalamus

  • and it directs it to all of the other endocrine glands,

  • or at least almost all of the other endocrine glands,

  • such that their function is ultimately

  • dependent on the pituitary gland to work well.

  • And so that little green pea is a really important part

  • of the endocrine system.

  • And so one of the endocrine glands

  • that the pituitary directs is the thyroid gland.

  • And the thyroid gland is located right here in your neck.

  • It wraps around your trachea.

  • And your trachea is your windpipe.

  • And so you can feel this thyroid gland on your neck

  • as you swallow.

  • If you hold your hands right around your Adam's apple

  • and swallow, that meaty thing moving up and down,

  • that's your thyroid gland.

  • And one of its main jobs is regulating

  • your body's metabolism.

  • And it does that through the thyroid hormones T3 and T4.

  • And another name for T3 is triiodothyronine.

  • And another name for T4 is thyroxine.

  • But the thyroid uses these hormones, the thyroid hormones,

  • to stimulate the body's metabolism, which is crucial

  • because that's how our body gets energy.

  • And then right behind that thyroid gland

  • are four spots known collectively

  • as the parathyroid.

  • And the main role of the parathyroid

  • is regulating our body's blood calcium level.

  • And the level of calcium in our blood

  • is hugely important because calcium

  • does a lot of stuff in our bodies.

  • It's involved in muscle contraction.

  • It's involved in bone growth.

  • And all of those functions are really sensitive to the level

  • of calcium that's floating around in our blood.

  • And so the parathyroid glands, those four spots

  • on the back side of our thyroid, regulate calcium

  • through the parathyroid hormone, or PTH.

  • And then moving down the torso, we have the adrenal glands.

  • And the adrenal glands are located

  • right on top of the kidneys here.

  • And they're called the adrenal glands

  • because they're adjacent to or right next to the kidney

  • system, which is called the renal system in medical speak.

  • But we really need to further divide the adrenal glands

  • into two parts, the outer part and the inner part.

  • So the outer part is the cortex and the inner part

  • is the medulla.

  • And the reason for the distinction

  • is that the inside and the outside of the adrenal glands

  • have two different functions.

  • And so we'll start with the outside or the cortex.

  • And that's where the steroids, the adrenal corticosteroids,

  • are made.

  • And two major examples of steroids

  • made in the adrenal cortex are cortisol and aldosterone.

  • And cortisol is one of the body's stress hormones.

  • So it functions to increase blood sugar in times of stress

  • so we have energy.

  • And it also has some anti-inflammatory functioning.

  • And then aldosterone is one of the major regulating

  • hormones of our body's blood volume

  • and how much fluid is in our veins and arteries.

  • And so that's the cortex.

  • And then the medulla makes a class

  • of hormones called catecholamines.

  • And two major examples of catecholamines

  • are epinephrine and norepinephrine.

  • And I'm going to shorten those as epi and norepi.

  • And sometimes epinephrine is called adrenaline.

  • And that might be a little bit more familiar to you.

  • But these catecholamines are really

  • involved in our body's fight or flight response, that

  • adrenaline response that we have to a stressful or scary

  • situation.

  • And so the medulla and the cortex

  • make up the adrenal glands.

  • But moving down the list and down the body,

  • we have the gonads.

  • And in females, those are the ovaries,

  • and in males, the testes.

  • And the gonads release the sex hormones.

  • And so in males, the testes produce testosterone.

  • And in females, the ovaries produce

  • estrogen and progesterone.

  • But these sex hormones are mainly

  • involved in the development of our secondary sex

  • characteristics like pubic hair, and larger frames in males,

  • and breasts in women.

  • But they're also involved in progressing us

  • through those life stages that accompany those sex

  • characteristics, like puberty and menopause.

  • And then last, but not least, we have the pancreas.

  • And it's located right here in the upper part of the abdomen.

  • And I saved the pancreas for last

  • because it isn't involved as directly

  • with the pituitary glands as the other endocrine hormones were.

  • But it still uses those hormones to stimulate an effect

  • in a different part of the body.

  • And the effect that the pancreas stimulates

  • is control over the blood sugar.

  • And it does that through the hormones insulin and glucagon.

  • And the pancreas is vitally important

  • because without its hormones insulin and glucagon,

  • we can't regulate how much sugar is