在本课程中，学生将学习认识和应用说明人体九个器官系统中整体人体机能（作为完整有机体）的基本概念。
下丘脑-垂体-生殖腺轴
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來自 Duke University 的課程
人体生理学导论（中文版）
85 個評分
從本節課中
生殖系统
此模块继续讨论内分泌系统及其稳态控制。 在这一系列视频中，我们将探讨内分泌系统如何调节女性和男性体内配子（分别是卵子和精子）的产生，以及性激素的产生。
與講師見面
Jennifer CarbreyAssistant Research Professor
Department of Cell Biology
Emma JakoiAssociate Research Professor
Department of Cell Biology
Hello, were going to start talking about the male reproductive system.
Keep in mind that what were going to
be focusing on is the hypothalamus pituitary gonad
access, axis, so a lot of this is
going to be familiar to you from the endocrine system.
In this slide we have a view through the testes which is
going to be the male gonad that's going to form sperm, and
here you can see a section through a seminiferous
tubule that has the epithelial cells of the semeniferous
tubule's sertoli cells, which we'll be talking about as
well as many different types of differentiating sperm cells.
And here in the lumen of the tubule, you can see
these black, kind of flecks, which are nuclei of forming sperm.
Before we start talking specifically about the male system we're
going to talk about general principles, and one is sexual differentiation.
So how do you become a male or female?
And that requires actually several steps, and
unfortunately several steps that can go wrong.
So when, during embryo genesis,
then, germ cells are starting, to form in males and females.
Primordial germ cells.
Whether we're going to start to form, s, sperm versus egg
is going to be determined on the chromosomal sex, which is going to
be XX forming a female and XY forming, a male.
And on the Y
chromosome, the expression of a gene called SRY
is going to be, required to form a testes.
Once the decision of having a testes versus an ovary is determined based on
XX versus XY, then that will be the gonadal sex.
So that cannot, ne, sometimes the gonadal sex does not match the chromosomal sex.
So for instance, if the SRY gene is mutated on the Y chromosome,
then an ovary, will form even though the person has a chromosomal
male sex of XY, they can have a gonadal sex that is female.
Once you've established which gonads you're
going to have, the gonad is going to
be the source of hormone which is going to determine your phenotypic sex.
Basically what do you appear to be, and so that
requires that the gonad is producing the proper hormone
and that you have the proper receptors for the hormone
in order to have the correct phenotypic sex based on
the gonadal sex and then based on the chromosomal sex.
So an example of this is that you need the SRY gene so that you can form a testes,
but you also need the testosterone receptor in order to appear to be a male.
Whether or not you have the test normal testes, you still need to be
able to form testosterone and to express
the testosterone receptor to appear, as a male.
So there's many steps that are required in
order to form, properly in terms of gender.
We're going to now move to talking about
that hypothalamus pituitary gonad axis, and we're going to
call it the common axis because it's amazing
how similar it is between males and females.
Where we're going to have, production of
gonadotropin releasing hormone from the hypothalamus.
And you know from Dr. [UNKNOWN] that release is going to have to be pulsatile,
so that we don't down regulate the GnRH receptors in the pituitary.
So we're going to form GnRH in the hypothalamus.
That's going to cause production of two different hormones
in the pituitary, luteinizing hormone and follicle stimulating hormone.
Follicle stimulating hormone, when it's released by the pituitary is going to
act on the sertoli cells. The ones that are contacting the sperm.
They will ,that will cause them to promo,
and will promote the formation of the sperm.
Sertoli cells will also form inhibin, which then will negatively
regulate FSH production. LH will act on
cells that are outside of those seminiferous tubules.
Act on cells that aren't in direct contact with sperm, called leydig cells.
And it will cause leydig cells to produce testosterone.
Which will be required for forming sperm and will also
act in a negative feedback manner on the pituitary and
the hypothalamus.
So, we'll talk about, when we get to the female
reproductive system, how similar this is, in the female as well.
So Inhibin is going to affect FSH secretion, and then sex hormones, whether
your male or female, are going to affect GnRH, LH and FSH production.
Let's focus on this left portion of this diagram for right now,
the male half of it. Where this previous axis that I've already
shown was confusing because the GnRH neurons themselves,
do not have receptors for testosterone, estrogen, or progesterone.
But yet it was known that testosterone negatively regulated
GnRH production.
And so somewhat recently it's been shown why
that is, or how this system can still work.
And it's because there is a second set of neurons
that are the ones that actually have the hormone receptors.
And these are called kisspeptin neurons because
they make a neuron transmitter called kisspeptin.
Which then binds GRP54
receptors on the GnRH neurons.
So in the male, when testosterone is formed,
testosterone binds the kisspeptin neurons and causes a decrease
in kisspeptin release, which then causes a decrease
in GnRH release by those neurons in the hypothallamus.
So the kisspeptin
neurons explain why testosterone has its effects even
though GnRH neurons do not have testosterone receptors.
And we talk about this, this system in the female.
This system is also going to be important during puberty.
So, kids, express very low levels of sex hormones like testosterone and estrogen.
But yet, that small amount of estrogen or
testosterone still results in very low GnRH production.
And so, this is because at this time, the hypothalamus and
presumable the kisspeptin neurons are very sensitive to the sex hormones.
However, as the puberty approaches, somehow,
and it's not completely understood how, the neurons
in the hypothalamus become less and less sensitive to
the sex hormones so that, that same level
of testosterone will allow more GnRH to be produced.
Which will then cause more testosterone to be produced.
Until, and that will continue, the hypthalmus becoming less and
less sensitive to sex hormones until we get to the adult
amount of sensitivity.
And so that's what's are going to be, changes that are going to occur during
puberty to allow you to have the
adult, axis basically of hypothalamous pituitary gonad.
So, we've talked, really, only about, cases
that are very similar between males and females.
Where we're going to have,
the formation of germ cells, and the synthesis of sex hormones
which are going to happen in the male and female gonad.
And we're going to have secretion of GnRH from the hypap,
hypothalamus which is going to control FSH and LH from the pituitary.
Again, both in males and females, and that,
that FSH and LH are going to, be what's
responsible for producing the germ cells of
the male and female and the sex steroids.
And then, the sex steroids will feedback negatively
through kris, kisspeptin neurons on FSH and LH.
They'll be one exception in the female that we'll talk about.
And, so, these sex steroids are going to
be required for, for, fertility, for, bein able,
being able to form the gonads, but also for appearing
as a male or a female for the secondary sexual characteristics.
