So, we can now summarize the structure of the
pituitary gland, and then we can start to assign
different secretory products from those different
components of the pituitary gland. Firstly,
I did mention earlier, that the
posterior pituitary, the neurons in the
supraoptic and paraventricular nuclei
synthesize ADH and oxytocin. And they’re
released in the posterior pituitary into those
fenestrated capillaries I’ve just mentioned.
And those two hormones have
effects on various target organs that
I’ve listed there, and just basically,
they’re general function of those hormones,
what they actually bring about in those organs.
And this is just the summary.
Endocrinologists will deal with the sorts of
roles these hormones have in far more detail.
Here, I’m only giving the histological background and basis
for these hormonal products.
If we then look at the acidophils
in the anterior pituitary, then we can see that there are,
first of all, hormones we group together as being
lactotrophs, secreting prolactin.
Or there could be
somatotrophs involved with growth hormone
secretion who act via a liver and via somatomedins.
And you can see there the target organs
for each of these hormones. The lactotrophs and
the somatotrophs, or at least the somatotrophs,
occupy about 50% of all the cells in the anterior pituitary.
The lactotrophs, those that secrete
prolactin, occupy between 15% and 20%
of the cells in the anterior pituitary.
The basophils by far are the busiest group of
epithelial secretory cells in the anterior pituitary.
And again, I’ve listed the general functions of the
different hormones secreted by these basophils,
the corticotrophs that affect the adrenal cortex.
occupy about 15% to 20% of all the secretory cells in the
anterior pituitary. The thyrotrophs occupy just
a small percentage, perhaps 5%.
And the gonadotrophs occupy, again,
only about 10%. So there is
this variation in the numbers of various cell types
in the anterior pituitary that secrete all these
different hormonal products, thyroid stimulating hormone,
follicular stimulating hormone,
luteinizing hormone, and adrenocorticotropic hormone.
And I’ll refer to these hormones
in more detail when I actually cover all these
different organs in other lectures.
I’d like to now just point out the variation in this
particular slide of all the organs affected by the pituitary,
by hormones secreted by the pituitary.
And I want you to recall what I’ve said earlier
that endocrine cells secrete hormonal products
that are carried via
the blood stream to target organs at locations
a long distance away. When you look at
this diagram and you look at the various organs represented,
it makes that point very, very clear and very, very obvious.
In summary then, it’s important that
you understand the structure of
the pituitary gland, particularly, the two components
of the pituitary gland. It’s important you understand the different types of
secretory components within
both the posterior and
the anterior pituitary, and the secretory cells within them
and what the secretory products are
from each of those cells, and the general
target organ and general function of those
different hormones. It’s also very, very important
to understand that hypothalamo-hypophyseal
portal system and then
how that allows the communication between
releasing factors from the hypothalamus, and also
factors from other parts of the central nervous system, how those
releasing factors can either stimulate or
inhibit cells in the anterior pituitary and even
control their function.
So thank you for listening to this lecture. I hope you now
have a very good understanding of the pituitary gland
and the general features of hormones and the endocrine glands.