>>Dr. Ketchum: In this segment of the endocrine system, we are going to be focusing on the
posterior pituitary and the hormones that are associated with that gland. And so this
segment is going to be focusing on two different hormones that are associated with the posterior
pituitary, and those two hormones are going to be ADH, which is also called vasopressin,
and oxytocin. Both of these hormones are associated with the posterior pituitary. Throughout the
next series of lectures, we’re going to be discussing various endocrine organs and what
hormones that they synthesize and secrete. So it’s very important as we go through
each of these segments that you understand for each of the endocrine organs what hormone
is synthesized and secreted. Is there a specific location from which these hormones are released?
And then if there’s a feedback loop associated with it, you need to know that feedback loop
and understand how that feedback loop functions. You have to understand the function for each
of the hormones, and also for abnormalities. So if you hypo or hyper secrete these hormones,
what would be the outcome?
So to begin, we’re just going to take a moment to describe primary versus secondary
endocrine organs. These segments on the endocrine system will focus on the primary endocrine
organs. Primary endocrine organs—their, their major function or their primary function,
in other words, is to synthesize and secret hormones. We also have what are called secondary
endocrine organs. Secondary endocrine organs have other primary functions, but secondarily
they do produce or synthesize and secrete hormones. In the segments on the endocrine
system, we were going—we are going to focus on the primary endocrine organs. Later when
we get to the cardiovascular system, we’ll discuss hormones that are secreted in the
heart. And once we get to regulation of gastrointestinal system, we will discuss various hormones that
are associated with the gastrointestinal system, such as the stomach and the liver, as well
as the small intestine. So once again, the focus for the endocrine system is to focus
on the primary endocrine organs.
So let’s go ahead and focus on the hormones of the posterior pituitary. Now these hormones
that are located in the posterior pituitary are stored in the posterior pituitary. That
is very important to understand: The posterior pituitary does not synthesize and secrete
hormones; the posterior pituitary only stores hormones. So let’s take a close look at
each of these hormones that are associated with the posterior pituitary. The first of
these is called antidiuretic hormone, ADH, which is also known as vasopressin. Vasopressin
or ADH is produced primarily by the paraventricular nuclei of the hypothalamus. The paraventricular
nuclei of the hypothalamus are part of a neurosecretory neuron that is located in the hypothalamus.
And hence, when we say periventricular nuclei, this is the nucleus that’s found within
that neurosecretory cell. So ADH has—targets the kidneys. And when it targets the kidneys,
its function is to help with osmolarity or to help maintain water balance within the
body. Now oxytocin is a hormone that’s produced primarily by the supraoptic nucleus of the
hypothalamus. Once again, it’s important to note that the supraoptic nuclei are part
of a neurosecretory neuron that’s located in the hypothalamus. So once again, now we
have antidiuretic hormone and oxytocin; they’re both synthesized and secreted by neurosecretory
neurons in the hypothalamus and they are stored in the posterior pituitary. Now in terms of
oxytocin’s target and function. So it targets a couple of different tissues within the human
body—that is the uterus, as well as the breasts or the mammary glands. When oxytocin targets
the uterus or binds to receptors on the uterus, that will cause uterine contraction that will
result in birth of a child. When oxytocin binds to cells of the mammary glands that
causes milk to be expelled from those glands; so this is very important for breastfeeding.
Now oxytocin is also involved in the mother-child bonding. And so when you think about at birth,
when a mother is introduced to her child for the very first time, that mother is bonded
to that child. And one of the reasons researchers believe that is so is because of the high
level of oxytocin, and that’s what causes that mother-child bond that occurs when that
child is born. Now there are a lot of other studies being done on the oxytocin, and there’s
a lot of exciting things being done. So as you progress through your career in the health
sciences, then you may come across some of those new discoveries. So in all with ADH
and oxytocin, these are both functionally classified as neurohormones. So hopefully
you’re asking yourself, “Why? Why are they classified as neuron hormones?” They’re
classified as neuron hormones because of the neurosecretory neuron that synthesizes and
secretes them. And remember, that neurosecretory neuron is located in the hypothalamus. Chemically,
both of these hormones are classified as peptides. So let’s focus a little more detail on antidiuretic
hormone.
So this is a hormone that is often confusing to students based on the name. So we’re
going to back up and think first off about what a diuretic causes you to do. So if you
are an ice tea drinker, you’re a coffee drinker, then you will know that those two
drinks are diuretics. So what do they do? They cause you to urinate. So if it’s an
antidiuretic, think about what the prefix “anti” means; so you’re doing the opposite.
So antidiuretic means you will urinate less, or have decreased urination. So the function
of antidiuretic hormone then is to decrease urination, so that you urinate less. And the
reason I go through this is because this is sort of a, a backwards way of thinking when
it comes to antidiuretic hormone. So let’s look at what stimulates antidiuretic hormone
release or vasopressin release. Extreme pain, having a low blood pressure, as well as stress.
These are at least three items that can stimulate antidiuretic hormone release, as well as nicotine
if you’re a smoker, or morphine. Okay, so a lot of times well have patients that are
on morphine or a morphine equivalent like Dilaudid, which all stimulate ADH release—antidiuretic
hormone. So let’s take a look at this diagram and try to interpret what this diagram means.
So at the top of this diagram, I have a low concentration of ADH. If I have very little
antidiuretic hormone, you will urinate a lot. Now that is opposite to if you have high ADH,
as illustrated by the bottom of this triangle. So if you have high ADH, you will have decreased
urination. So let’s think about a condition where you may have a patient, for example,
or even a friend of yours that has ADH, however it’s hyposecreted. So first off, think about
what hypo means. Hypo means “less,” so we’re secreting little ADH. So if you don’t
secrete a lot of ADH, you have low ADH. You’re going to urinate a lot. You will increase
your urination. Now this is a condition called diabetes insipidus. Do not confuse diabetes
insipidus with diabetes melatis. Diabetes insipidus is based on ADH, not blood sugar
levels; they are completely different. Now one of the symptoms if you have diabetes insipidus
is that you’re thirsty a lot, because you’re urinating so much. And so if you’re not
replenishing the fluids that you lose, you tend to become dehydrated and as a result
of dehydration, you can have headaches. So the treatment for this is fairly simple: You
drink a lot of water. You need to drink water in order to replenish the fluids you’ve
lost because of your increased urination. So now let’s think about what could inhibit
ADH release. So we’ve already talked about a condition where you have diabetes insipidus,
where you hyposecrete ADH. But let’s think about alcohol and drinking alcohol. So you
can think about this in terms of going off to happy hour, perhaps. And when you go to
happy hour, how frequently you visit the restroom. So if you inhibit your ADH release by drinking
alcohol, you are going to increase your urination. So often then explains why you go to the bathroom
more frequently, and it also explains why you end up with dry mouth, because you’re
thirsty, headaches because you become dehydrated because you’re not drinking enough water,
and hence, you have a hangover. So general rule of thumb: To avoid hangovers because
of this ADH, for every beer that you drink or every alcoholic drink that you consume,
drink one glass of water with it and that will help counter the effects of ADH.