Alright.
In this video, we are going to go over some more important hormones in the body, including
epinephrine, or adrenaline is another name for epinephrine, as well as norepinephrine.
We're also going to talk about calcitonin and parathyroid hormone as well as insulin
and glucagon.
So let's first talk about epinephrine and norepinephrine.
These two hormones are catecholamines that are released by the adrenal medulla - so that's
the inside of the adrenal gland - in response to acute stress.
So if you are being chased by a bear, that would be acute stress, and that would kick
off your body's flight or fight response and result in the release of epinephrine and norepinephrine.
These hormones will cause a number of changes in the body, including vasoconstriction, increase
of heart rate and blood pressure, bronchodilation, pupil dilation, increase blood flow to the
muscles, and increase blood glucose levels.
Your body's basically preparing to run from the bear, and it wants to make sure that you're
getting enough oxygen in those lungs and that the blood is circulating throughout the body
and getting that oxygen and nutrients to your skeletal muscles and everywhere else.
So those are the changes you can expect when epinephrine and norepinephrine are released.
Keep in mind that epinephrine has more of an effect on the heart, versus norepinephrine
which has more of an effect on the blood vessels.
So in terms of what controls release of epinephrine and norepinephrine, when you have an acute
stress situation, the sympathetic nervous system is activated, which activates nerves
that are connected to that adrenal medulla, which allows for the secretion of epinephrine
and norepinephrine.
All right, now let's talk about calcitonin, which is a hormone that decreases blood calcium
levels.
It opposes the action of parathyroid hormone, which we'll talk about next.
So it decreases blood calcium levels by doing two different things.
The first thing it does is it decreases the activity of osteoclasts.
So osteoclasts are cells that break down the bone and move that calcium into the bloodstream.
And we don't want that, right, because we're trying to decrease levels of calcium in the
bloodstream.
So it opposes the action of osteoclasts.
Then the other thing that calcitonin does is it increases excretion of calcium at the
kidney.
So we're just getting rid of extra calcium so it doesn't build up in the bloodstream.
So the way that I remember what calcitonin does is if you look at the word calcitonin,
you can remember that calcitonin tones down the calcium.
And that little hint is here on card 11.
So what stimulates release of calcitonin?
When the body senses that we have too much calcium in the bloodstream, or hypercalcemia,
this stimulates a release of calcitonin from the thyroid gland.
Okay.
Now, let's talk about parathyroid hormone, or PTH.
This basically does the opposite of what calcitonin does.
So PTH wants to increase the amount of calcium in the bloodstream, and it does this by doing
three different things.
The first thing it does is it pulls calcium out of the bones and into the bloodstream.
The second thing it does is it causes the kidneys to reabsorb more calcium, and it also
causes the kidneys to release vitamin D, which helps with the absorption of calcium in the
body.
And then the third thing it does is it increases absorption of calcium in the intestines.
So it does all of these three things to bring those calcium levels up in the bloodstream.
So what controls release of PTH?
When the body senses that there's not enough calcium in the bloodstream, so hypocalcemia,
that stimulates the release of PTH from the parathyroid gland.
All right.
Let's talk about insulin and glucagon.
So insulin decreases blood glucose levels.
Insulin allows glucose to move from the bloodstream into the body's cells, where it can be used
for energy.
So when the body senses that blood glucose levels are rising, insulin is released from
the beta cells in the pancreas to help escort that glucose into the body's cells.
Glucagon is basically doing the opposite.
It wants to increase blood glucose levels, as opposed to insulin, which wants to decrease
blood glucose levels.
Glucagon increases blood glucose levels in three different ways.
The first way is through glycogenolysis.
So this is where we convert glycogen in the liver into glucose and then release that into
the bloodstream.
The second way that glucagon increases blood glucose levels is through gluconeogenesis,
so this is production of new glucose.
And then the third way that glucagon increases blood glucose levels is it causes the adipose
tissue to break down fat for use as energy.
So it does these three things to bring up those blood glucose levels.
So when the body senses that blood glucose levels are low, then glucagon is released
from the alpha cells in the pancreas.
So we got through all of those hormones, so good job in sticking with me through all those.
Next, we're going to talk about that negative feedback mechanism that I mentioned in a previous
video, as well as the positive feedback mechanism that is used by just a couple of the hormones
in the endocrine system, so stay tuned for that information in my next video.
Take care!