00:01
There are few types of feedback
loops that we need to go through
for endocrinophysiology.
00:07
Let's talk through more of a
standard negative feedback loop.
00:11
And then we'll talk about how
axis differ from these standard
feedback loops.
00:17
So often times you have an
endocrine gland that's going
to secret the hormone.
00:22
And that hormone goes to
a target organ binds
to a receptor, causes
a physiological effect.
00:30
And then you measure
the physiological effect
and that is the negative feedback back to the gland.
00:43
And you just go
through this process.
00:46
If that negative feedback
isn't strong enough,
you'll continue to
secrete the hormone.
00:51
If negative feedback comes
back and is high enough,
you'll stop hormonal secretion.
00:56
So this is this
general response.
00:59
Axis are a little different.
01:01
Let's go through how
these work.
01:04
In this case you have
the hypothalamus releases
a releasing hormone which
then binds to the pituitary.
01:12
The pituitary then
releases a hormone.
01:16
And then that hormone goes to
the gland or the target gland,
releases a second hormone that
goes to end organs and then you
have a physiological effect.
01:30
Seems like a lot of
steps, doesn' it.
01:32
But why might this be important.
01:35
Well, you are regulating here
the hormone
rather than the physiological effect.
01:44
Let's go through the pituitary
gland in the little bit
more detail.
01:48
The pituitary gland can be
split into an anterior
and the posterior pituitary.
01:53
The anterior pituitary recieves
input from the hypothalamus.
01:58
These particular neurons project
down from the hypothalamus.
02:03
And go into the vasculature
of the anterior pituitary.
02:08
So there is direct signals
that can be sent
from the hypothalamus to
the pituitary
by this circulatory method.
02:22
The posterior pituitary works
in a little different format.
02:26
Instead of using blood flow,
it has direct neural projection
from the hypothalamus to
the posterior pituitary.
02:35
And when it releases
it's substance,
it goes directly into
the circulation there.
02:42
So again, anterior pituitary,
hypothalamic nerve,
releasing the trophic factor
which then bathes the anterior
pituitary cell versus
the posterior pituitary.
02:54
We have the nerve going
all the way to spot
which is going to release
the hormone.
03:02
Let's talk now through what
are the cells that the anterior
pituitary have and what are
those trophic hormones
that are going to cause
the anterior pituitary cells
to release their substance.
03:20
Those anterior pituitary targets
for these trophic or releasing
factors are either
corticotropes, gonadotropes,
lactotropes, somatotropes
or thyrotropes.
03:36
The important thing to think about here is,
what are the cells
types, what is it doing?
And how it is distributed across
all anterior pituitary cells.
03:47
So somatotropes are going
to be the most numerous.
03:50
About have fo the
cells are somatotropes.
03:54
Then we have both lactotropes
and corticotropes,
about 15 to 20 percent.
04:00
Finally, gonadotropes
and thyrotropes
one with 10 and 5
respectively.