Hello there.
Welcome to endocrine with Dr. Raj.
Endocrine system,
if you had to describe it physiologically,
it would be feedback mechanism,
isn’t it?
Feedback mechanism.
Also with endocrine, it's from head to toe.
You begin at the head, in the region of hypothalamus,
that’s where we’ll begin,
we’ll go into the pituitary
and then, you want to start thinking about
all the different organs that we have in our body
that then responds via feedback mechanism.
Each one of these organs, we’ll take a look at.
For example,
from the hypothalamus,
you can generalize
and call these releasing hormones.
From the pituitary,
you’re releasing hormones.
From the thyroid gland,
you’re releasing hormones.
So, the theme from head to toe will be hormones.
What does that mean?
It means that you're going to
release these hormones into circulation,
depending as to what the stimuli will be,
as we shall see.
These hormones will then work upon a target organ,
so that you can bring about the respective response.
Welcome to the endocrine system.
Let us now begin.
Your ultimate overview of the entire body will take place with this topic.
At first,
we will take a look at pituitary hormones,
but even before we do any of that
locate where you are right now.
We’re up in the head region.
We’re in the CNS region.
And in neuroscience,
you looked at MRIs and even CTs and such.
And if you haven't, please do so.
Be able to identify the pituitary gland
and how incredibly close it is to the optic chiasm.
Are you picturing this?
Next.
When we deal the hypothalamus,
which is the upper structure here,
there are certain stimuli that will then cause the hypothalamus
to release what?
Releasing hormones.
For example,
say that you have a newborn that is suckling on a nipple.
If it's sucking on a nipple,
my goodness doesn’t that infant want to then feed upon milk.
So, therefore,
with the suckling action,
there are certain afferent sensory neurons
that are then going to signal the hypothalamus
to release a particular hormone.
Any idea as to what will be?
Good.
Oxytocin.
Oxytocin will be an example of a hormone that we’ll talk about
that has positive feedback.
And by positive feedback,
we mean that
if the stimulus takes place,
then you have more of that release of that hormone
from that organ,
which is then going to bring about a particular action.
In this case,
it would be milk ejection
when there is suckling action,
correct?
Or let's go even further back.
And this is during delivery.
During delivery,
then you are thinking about postpartum.
During delivery process,
you want the uterus to contract.
This would be more positive feedback mechanism,
wouldn’t it?
And so, therefore,
from the hypothalamus,
we are going to then release oxytocin from the posterior pituitary.
And why do I bring these two up?
Because the next question that you want to ask yourself is
where are some of these hormones being synthesized?
Guaranteed,
you’ll get certain questions
about the synthesis of your hormones.
When?
Well, when we start talking about lesions in the head,
for example,
you see the stock between the hypothalamus
and the organ down below,
we’ll talk about that stock.
And in anatomy,
you’ve talked about this being the infundibulum.
And here,
we’ll go ahead and label this
being the portal vein in just a little bit.
But before we get there, though,
there's another stimuli
that we need to take a look at.
The other set of stimuli include baroreceptors and osmoreceptors.
Our focus here will be osmoreceptors.
With osmoreceptors,
it is important that you understand,
on a day-to-day basis,
on a minute to minute basis,
our plasma osmolality,
which is approximately 300 –
sure, it’s a little bit less,
maybe 295,
but at this point,
give yourself an absolute reference point of approximately 300.
It is important that we maintain
plasma osmolality at all times.
And so, therefore,
as you and I sit here,
across from one another,
your plasma osmolality might increase.
The osmoreceptors in the hypothalamus will then be stimulated,
so that you will be releasing the appropriate hormone.
In this case,
it would be ADH,
a.k.a. vasopressin.
Here’s the portal vein that I was referring to.
You want to be really careful with this term, don't you?
The last time that you've heard of portal vein,
or more commonly
where you would hear portal vein in medicine,
would be with the drainage into the liver, correct?
I’d be very careful, though.
So, you’re reading this (inaudible 5:04) question.
And as you do so,
well, they’re referring to portal vein,
but you want to ask yourself immediately,
what am I referring to?
This is the connection between the hypothalamus
and this is the circulation
that is then bringing certain hormones,
such as ADH or oxytocin,
from the hypothalamus
into the posterior pituitary,
as we shall see.
Now, take a look at what we have here.
We have two major hormones of the posterior pituitary,
ADH and oxytocin.
Now, I cannot tell you
that you should be focusing upon
one part of the pituitary over the other
because, my goodness, all these hormones play amazingly critical roles.
But I can tell you that ADH,
antidiuretic hormone,
also called what?
Vasopressin.
And you'll see why in a little bit as to why it's being released.
And once again,
it comes back to understanding
that you need to maintain plasma osmolality at all times.
There are certain exceptions that we’ll go through.
But, for example,
as you get dehydrated,
you mean to say plasma osmolality starts rising,
your hypothalamic osmoreceptors will be stimulated,
your ADH will be released,
but before we get there,
where is ADH being synthesized,
do you remember?
Good.
In the hypothalamus.
Remember those neurophysins?
It is then brought into the posterior pituitary.
It's being released from your posterior pituitary.
And if you're being dehydrated and your plasma osmolality rises,
then you know that antidiuretic hormone,
also called vasopressin,
will work on the collecting ducts,
so that it can do what?
Please?
Good.
Antidiuresis.
In other words,
it's re-absorbing water
as we shall see.
What about that oxytocin?
Remember that stimuli that we just talked about earlier?
What were those stimuli please?
Good.
Suckling or delivery.
During these stimuli or processes or triggers,
you need oxytocin,
so that you can then eject the milk to the infant
or expel or deliver the infant during delivery.
Both of these are examples of positive feedback.
The more that the infant suckles,
the more that you release oxytocin.
During delivery,
you want there to be positive feedback
because you want more contraction taking place of the uterus,
so that you can deliver the child.
So, hopefully,
you're creating a picture to yourself
as to what we’re referring to here with endocrine.
Let’s move on.
Here, as we go through each one of these hormones,
as you shall see,
we’ll begin at the hypothalamus,
we’ll work on the pituitary
and you'll notice that most of these hormones –
you see the demarcation there,
above the demarcation dash line,
it represents the releasing hormones from the hypothalamus in general.
Please do this for me.
It'll be the releasing hormones coming from the hypothalamus,
working upon the pituitary,
so that you release the hormone that is necessary
to take care of the issue that the body is dealing with.
The first releasing hormone here is
TRH (thyroid releasing hormone), right?
Now, the thyroid releasing hormone
is then going to work upon the anterior pituitary.
The anterior pituitary is going to then release what?
The TSH (thyroid stimulating hormone).
And that is as far as we shall go
with this entire section here.
We’ll be referring to a releasing hormone from hypothalamus,
working upon the pituitary to release the respective hormone.
Now, a couple of big exceptions
or things that you want to keep in mind.
TRH has an incredibly important role of also releasing prolactin.
So, not only do you want to think of
TRH as releasing TSH from the anterior pituitary,
but you also,
ladies and gentlemen,
want to think of TRH as releasing prolactin from the anterior pituitary.
Is this important?
Oh my goodness, yes.
Close your eyes,
think of a particular situation
where your TSH and TRH might be elevated
and your patient is suffering from hypothyroidism.
You know –
or you should –
that TSH is the most important screening hormone that you're looking for.
So, my question earlier was
TSH was increased,
TRH was increased
and the patient was hypothyrotic.
Welcome to primary hypothyroidism.
The most common cause of primary hypothyroidism is Hashimoto.
My point is this:
if your TRH is increased,
as it is with Hashimoto,
this TRH then is going to release increasing levels of prolactin,
isn’t it?
So, how is your primary hypothyrotic patient
going to behave
with all this prolactin,
especially if she's a female.
What do you think happens to her menses?
She doesn't have it.
She is amenorrheic, isn’t she?
Why?
Let’s take a look.
We have CRH (corticotropin releasing hormone).
Corticotropin releasing hormone
works upon the anterior pituitary
to release your ACTH (adrenocorticotropic hormone).
Now, stop here for one second.
Take a look at this.
I told you from the very beginning
that, with endocrine,
you'll be moving from head to toe.
With that said,
here on your left,
when we first looked at our TRH and TSH,
what organ is this going to work upon?
The thyroid gland.
If it’s CRH and ACTH coming from the anterior pituitary,
what is its target organ, please?
Good.
The adrenal cortex.
Now, stop here for one second.
The most important stress hormone
that you will be responsible for replenishing
– so, for example,
say that you have a patient who may have had Sheehan syndrome.
You know what Sheehan syndrome is?
Loss of blood or complications during delivery.
The mother now undergoes infarction of the pituitary.
Oh my goodness!
Infarction of the pituitary!
Look at all the hormones that might be affected
if we have infarction of the pituitary.
It's cortisol.
It is ADH. It’s prolactin.
There are a lot of hormones here.
Of all these hormones,
the hormone that you want to worry
and concern yourself
in terms of replenishing
would, in fact, be your cortisol.
We’ll talk about this over and over again.
Here we have growth hormone releasing hormone.
Growth hormone releasing hormone works upon the anterior pituitary to release of your growth hormone.
And we have another hormone that's being released from the hypothalamus,
and this one you want to pay attention to big time,
also because of pharmacology.
We have something called somatostatin.
Somatostatin is the opposite of GHRH.
It inhibits the release of growth hormone.
This will come into play incredibly when we talk about acromegaly.
Acromegaly,
a common cause might be adenoma in the anterior pituitary
releasing too much growth hormone.
So, what kind of drug might you want to use,
so that you could delay the release,
or retard the release of your growth hormone.
How about a somatostatin analog,
such as octreotide.
Same pharmacology and management,
we’ll talk about somatostatin
as being an important analog
in which you inhibit the release of growth hormone.
Lastly, gonadotropin releasing hormone.
A releasing hormone from the hypothalamus,
ha, once again,
working upon the anterior pituitary,
so that it releases what?
FSH and LH.
Now, slow down for one second here and tell me,
what is my target hormone for this axis.
These would be the gonads.
If it's a male,
it would be the testes.
And if it was a female,
it would be the ovaries, correct?
Okay.
Now, when I tie everything in here.
And I told you,
in the very beginning,
that we talked about TRH –
and in hypothyroidism,
you might have hyperprolactinemia.
Why?
Remember Hashimoto, your primary hypothyroidism.
You’re with me?
You’re going to have increased TSH.
That’s your screening test.
That's what you're looking for clinically.
You should also know that you have an increase in TRH.
So, this will go back to your physio and path.
The TRH does what to your prolactin levels?
It increases it.
Hyperprolactinemia.
What about that female again,
that patient?
She had amenorrhea.
Why?
Because prolactin has what can affect on?
Now, take a look at the right.
GNRH.
Prolactin inhibits the release of GNRH.
If you inhibit the release of GNRH, ha, I don’t release FSH and LH.
What then happens to the menstrual cycle in a female?
Oh, yeah, she doesn't have it.
She's amenorrhoeic.
Why?
She doesn't release her FSH and LH.
Any time, you have hyperprolactinemia,
your female will always be amenorrhoeic.
Why?
Inhibit the release of GNRH.
You see as to how every one of these hormones at some point in time
is tied together,
but it also begins with understanding the foundation.
Why would you need it?
When would you need it?
And what are the consequences when things go awry?
Now if TRH releases prolactin,
dopamine inhibits it.
And that is a huge topic for us
when we get into that particular pathway
of dopamine regulating the release of prolactin,
but it inhibits the release of prolactin,
must be understood at this point in time.