Let's talk about testosterone. Testosterone is a very well-known
hormone and it has multiple important functions throughout the human body.
So, we need to discuss these important functions so of which I think are going to surprise you
as well as talk about where this hormone is produced. Now, it's no secret that testosterone
is typically referred to as a male hormone but do females produce it? And if so,
what would it do for them? The answers to those questions and much more coming up.
[Intro]
First, what is testosterone? Testosterone is the primary male sex hormone. It is also
classified as an androgen. Androgens are steroid hormones that promote the development of masculine
characteristics and we'll talk about the details of these characteristics a little bit later
but keep in mind there are multiple androgens throughout the human body. It's just that
testosterone is much more abundant and therefore has greater effects. Hence,
testosterone is referred to as the primary male sex hormone.
Again, we will discuss if females produce it and what it does but to help us with
that we're going to talk about where the testosterone is produced and it's likely
not going to be a shocker that we're going to take a look at the testis, testosterone,
testis, make sense that it's produced there so let's take a look at this cadaver dissection.
You are taking a look at the right side of the groin zoomed in here and you can see a right
testis - testis is just singular for testes, you can see we've obviously removed it from
the scrotal sac. on this side of the testis we kept some of the connective tissues there
but removed it on this side and if we open up, you can see how amazing the internal structure
of testicles and those tiny little tubes called seminiferous tubules, those will produce sperm
cells and we've covered that in a different video but interspersed in between there,
we'd see another cell type called interstitial or leydig cells and those interstitial or
leydig cells are going to be responsible for producing and secreting the testosterone.
Now, what's really cool about the section as well is that there's this other structure called the
spermatic cord here that I'm pulling up with the probe. Now, the spermatic cord contains veins,
arteries, and nerves that serve the testis and it also contains a tube here that we've
actually dissected out that you can see called the vas deferens that would transport sperm
cells out of the testis but when we're talking again about those leydig cells
inside secreting the testosterone, that will secrete the testosterone into the bloodstream.
And like I said, there are veins inside of here and the veins will transport that testosterone
outside of the testis so it can circulate throughout the entire body and therefore, have
its widespread effects. Now, before we discuss the effects of testosterone, is testosterone produced
in other regions throughout the body besides the testis? And if you're curious about that,
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So, back to answering this question of is testosterone produced in other regions
throughout the body? and based on how I've been building this up, you probably guess the answer
is yes and one of those places is the adrenal gland. So, let's take a look at this adrenal
gland by looking at a cut that we made through the midline of the body or the sagittal plane.
So, here's where that midline cut was. Here would be the left side of the chest and the
lower margin of the rib or what we'd refer to as the costal margin. We've removed the
intestines but you can see some cool organs like the spleen here and the left kidney right here.
Now, interestingly enough about the name "adrenal", if you break that term down,
renal means kidney ad means neurobecide.
So, we should find this adrenal gland next to the kidney here specifically on top of it
and the central portion where my probe is here is actually referred to as the adrenal medulla or
the central portion of the adrenal gland and the outer portion is referred to as the adrenal cortex
and it's the adrenal cortex that produces some other androgens and testosterone in both sexes.
So, that gives us that answer about females. Do females produce some androgens and
testosterone? Yes, from the adrenal cortex but how much are we talking here? Well,
the effect or the amount that's released from the adrenal cortex is quite minimal,
especially when we compare it to males and the overall effect here.
The overall effect that we get from the adrenal cortex
only contributes to about 5%. That means that the testosterones created from the testis is
doing the majority of the worker creating the greatest overall effect throughout the human body.
Now, another place that you can find where testosterone is being produced is specific to
females and that is the ovaries. The ovaries will produce a small or minimal amount of
testosterone and therefore, would only have a minimal effect. Most of us have a pretty good
idea that the main sex hormones released from the ovaries are estrogen and progesterone. Both
of which have some amazing effects but we'll have to talk about those in a different video.
So, we keep mentioning all of these effects or at least leading to the effects of what
testosterone can do. So, let's talk about its effects on both males and females
starting with when males are developing inside of mom.
During male fetal development or in other words,
when developing inside mom's wonderful cocoon of love that we call
the uterus, testosterone is being secreted in promoting the development of male body parts.
Things like the penis, scrotum, prostate gland, seminal vesicles, and other male genital ducts.
It also helps promote the descent of the testis prior to birth. Now, what's interesting about
this, when you look at testosterone secretion during fetal life, it's actually being secreted
in moderate amounts. However, when you compare that to soon after birth and throughout childhood,
there is virtually no testosterone being secreted from the testis during childhood.
That doesn't change until about age 10 to 13 when we all know that magical time
of life occurs that we call puberty and in that case in males, testosterone will spike
which will make it responsible for some other effects that it has throughout the body
for example, it's major effect on bone tissue.
It promotes this major growth spurt that we see during the teenage years.
It also influences bone thickness and density and even the shape of the male pelvis. Now,
you've probably heard things in general where we say the female pelvis is wider
than the male pelvis. Let me give you a couple things that you can look at with the pelvis.
For example, here, this is referred to as the pubic arch. This is much more
sharp of an angle where on females, it's about - it gets close to about a 90° angle or wider.
Also, the pelvic outlet where potential baby could pass through in the female pelvis,
this is much more narrow in the male pelvis and that's influenced by testosterone.
They've seen certain situations or disorders where the testis aren't
secreting enough testosterone or that male isn't producing enough testosterone
during development and the pelvis tends to mirror more of the female shape of the pelvis.
Another function of testosterone is its effect on metabolic rate.
Testosterone can increase metabolism by about 10 to 15%
and again, we know this by comparing it to situations when the testis aren't producing
enough testosterone. This effect of increased metabolic rate is linked to testosterone's
anabolic effect on skeletal muscle tissue which is another function of testosterone.
Testosterone promotes enlargement of those skeletal muscles especially during those years
of puberty and when you compare after puberty, you'll see about an increase on average of about
40 to 50% increase in muscle mass to that which occurs during puberty with the female.
Testosterone is also related to an increased number of red blood cells and this has been
shown when normal amounts of testosterone were injected into castrated males. Now, I know that
sounds horrible and I'm sure they weren't donating their testis to science or for the specific study,
I'm pretty sure they were castrated for other reasons and then the study
found them. At least that's what I'm telling myself.
Nonetheless, when this testosterone was injected,
they saw an increase of 15 to 20% in the number of red blood cells. Now, to be fair,
they think this is more of an indirect result. Meaning, that when they injected the testosterone,
they didn't actually see an increase in this hormone called erythopoieten or EPO
and as the hormone directly responsible for stimulating red blood cell production.
Instead, they think it was more of a secondary effect from things like increase in muscle mass
and protein production and the blood cells kind of followed suit from these other effects of
testosterone. Now, testosterone also increases things like sperm production or regulates sperm
production, increases libido which is that feeling of wanting to do stuff - amorous stuff.
Testosterone also has a powerful effect on primary and secondary sex characteristics.
Primary sex characteristics we've actually already talked about - that's the presence of say like
penis, testis and scrotum and during puberty, testosterone causes the penis, testis and scrotum
to increase in size by about eight fold, which many teenage males are quite excited about.
Secondary sex characteristics would be things like hair distribution. So,
facial hair, hair over the chest and abdomen, axillary hair, pubic hair,
and yes, sometimes hair on the back. It also influences the pattern of distribution of
the hair of the head. So, testosterone does influence male pattern baldness.
Another secondary sex characteristic example would be the deepening of the voice or the
changes of the voice box of the larynx that I'm pointing at on me but I can show you on
an actual could ever hear. So, here is the actual larynx right above the thyroid gland.
I was pointing about right there on myself and testosterone tends to enlarge the larynx
which has a result of yes, making it look more pronounced but also makes the voice deeper.
Another example of a secondary sex characteristic would be testosterone's
influence on the skin. It tends to make the skin thicker, tougher, more rugged, and more desirable
to a potential mate - maybe. Okay, everything before "desirable" was actual science.
And finally, what does testosterone do for females? Now, we've already established
that testosterone and other androgens are produced in the adrenal cortex as well as the ovaries but
again, those are much much lower levels when compared to that produced by the testis.
So, we logically have to think if we're producing a much lower amount of testosterone,
those overall effects are going to be much less in females when compared to the effect
that testosterone has in males. Now, that doesn't mean zero effect. Testosterone does
still influence the development of say like pubic hair and axillary hair in females and "axillary
hair" is a fancy pants name for armpit hair. It does have some influence on bone health, libido,
mood, even follicular development within the ovaries and even tissue maintenance.
Now, notice that I said "some influence" because for example,
if we took bone health as the example, estrogen has a much more important role
in the health and wellness and density of female bones than that of testosterone and if we were to
have a discussion about what estrogen does to the body, which we are going to, we're going to make
a future video on that - our conversation would almost flip flop where we talk about
all these effects that it has on anatomy and physiology of females and much more minimal
effects on the anatomy and physiology of males if we were to flip flop and talk about estrogen.
Now, can we have situations where females have too little testosterone or too much of test
testosterone? Yeah, but often, you typically see a more widespread symptomology from too much rather
than too little because again, we're already dealing with fairly small amounts. But what if
a female had too much testosterone? You might see things like excess distribution of hair or other
masculinizing effects and there are disorders or conditions like PCOS where this can occur.
Now, take a step back on this and I always tell my students,
let's first learn what the hormones are supposed to do at normal levels. Then,
we can have the discussion of what if there's too little or too much in certain conditions and
we will go there in future videos and I'm giving you all these little teasers
but, hopefully you learned something amazing about testosterone in this video.
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have, any comments or concerns that you may have about testosterone and if you feel like it,
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go ahead and stay safe out there until Geoffrey and I see you in the next video.