Testosterone Explained: Your Guide to the Body's Male Master Switch and What It Does For Your Body
When people hear the word "testosterone," they
probably think about things like muscles, beards, and a deep voice, and they
are correct. However, testosterone gets a bad rap from people that generally
don’t understand it. Testosterone is indeed the main male hormone, and it plays
a huge role in developing those classic male characteristics, but its job is
far more important and extensive and starts even before birth and influencing
everything from mood to bone strength
throughout a man’s life.
The Genesis of "Maleness": How
Testosterone Shapes Men From the Start
It may come as a surprise to learn that for the first six
weeks of fetal development, every human embryo, regardless of whether it's going
to be a boy or a girl, starts out with identical reproductive parts. It's literally
a blank slate at that point. However, around week seven, there is a special
gene located on the Y chromosome (found only in males) that kick starts things
into high gear. This gene is called SRY and it acts like
a master switch and signals the body to start forming the testicles in males.
Once this happens and the testicles begin to develop, they begin
to make some very important substances. One of these crucial substances is
called Mullerian-inhibiting
substance (MIS). MIS kind of acts like a "stop sign" for female
reproductive structures like the fallopian tubes and uterus, and prevents them
from forming. Simultaneously, other cells in the developing testicles start producing
testosterone. This early testosterone production is vital for shaping both
the male urinary and reproductive tracts.
But that's not all that happens. A small amount of this
early testosterone will get converted into an even stronger form called dihydrotestosterone
(DHT).
DHT is extremely important at this stage as its responsible for the formation
of the prostate and the external male genitalia. Testosterone is also responsible
for making the testicles descend into the scrotum during the lastl two months
of pregnancy.
So, if there aren’t any Y chromosomes and no
SRY genes, female organs will begin to develop naturally. Without the presence
of early testosterone, male structures won't form, and without MIS, female
structures are free to grow normally. It's a fascinating balance and interplay of
hormones that decides our biological sex from the very beginning inside the
womb.
After Birth: Testosterone's Lifelong Influence
on Men
Testosterone doesn't stop working once you're born, quite
the contrary. It's continuously exerting its effect on men, especially during
puberty and throughout adulthood, shaping many important aspects of the males physical
and even mental well-being during their lifetimes.
The "Primary" Male Features: What
Testosterone Does for Male Reproduction
When people talk about primary sexual development, it refers
to the parts directly involved in sexual reproduction. Testosterone is vital
for several aspects of reproduction including the following:
- Testicular
Descent. As mentioned previously, it will help the
testicles move into their proper place in the scrotum during the final two
months of pregnancy and fetal development. In rare cases, a baby boy's
testicles might not descend naturally. When this happens, testosterone can
sometimes be given to help them along and allow them to move into position
without the need for surgery.
- Sperm
Production (Spermatogenesis).
Testosterone is needed for the production of healthy sperm, which is
essential for fertility. No testosterone will lead to low sperm count in
men and often infertility. Fertility specialists will often check for
testosterone, LH and FSH levels after testing for sperm count and mobility
in men with suspected fertility issues.
- Enlargement
of Penis and Testes. During puberty, testosterone drives
the growth and development of these organs. Testosterone, and more
specifically its converted form, dihydrotestosterone (DHT), are
absolutely crucial for the formation and initial growth of the penis in
the womb. If there's a significant deficiency of testosterone or a problem
with its action during this critical period, it can lead to conditions
like micropenis (an abnormally small penis at birth). Studies
confirm that fetal testosterone deficiency is a primary cause of
micropenis. Early hormonal treatment with testosterone in infancy can
often stimulate growth to a more normal length, suggesting a direct link.
- Puberty. This is the second major window
where testosterone profoundly impacts penis size. The production and
increase in testosterone during puberty drives the significant growth and
development of the penis (and other male secondary sexual
characteristics). Observational
studies have shown a correlation between testosterone levels during
adolescence and eventual adult penile length. For instance, some research
suggests that higher testosterone levels during puberty are associated
with longer penises, though many other factors (like genetics) also play a
significant role. If a boy experiences testosterone deficiency during
puberty (hypogonadism), it can result in reduced growth of the penis. Once
adulthood is reached, testosterone no longer influences penile growth,
however it can influence sex drive.
- Increased
Libido. Testosterone plays a significant role in
a man's sex drive. Men with higher testosterone often have higher libidos
and anyone who is on TRT can tell you the difference between pre and post commencement
of hormone therapy.
The "Secondary" Male Features: What
Makes a Man Look and Feel Like a Man
Testosterone is known as the “Male hormone”, even though make
and need testosterone as well just in much smaller amounts. Beyond the hormone’s
role in reproduction, it’s the driving force behind the "masculine"
traits we commonly recognize.
- Hair.
Thick facial hair, body hair, and even certain patterns of hair loss or
male pattern baldness are all associated with either too much or not
enough testosterone. There is certainly a genetic factor involved however studies
have shown testosterones effect in men.
- Voice
Deepening. This characteristic change in puberty is
a direct result of testosterone affecting the vocal cords especially in
puberty when boys voicers begin to “crack”. It’s an awkward stage that
marks the change from childhood to adolescence in men.
- Muscle
Growth (Anabolic Effects). We’re not talking about
steroids however testosterone is a powerful anabolic hormone, meaning it
promotes protein
synthesis and muscle growth. This is why you see significant muscle
development in boys during puberty. It also contributes to growth spurts
in height, though it eventually signals the growth plates in the bones to
close. Bodybuilders or athletes looking to put on muscle will often take
testosterone at much higher dioses that one needs for TRT to help build
and put on muscle during “cycles” of anabolic steroid abuse which is not
good for overall health and not recommended.
- Red
Blood Cell Production. Higher hematocrit
levels can be a side effect of testosterone due to the fact that it stimulates
the production of red blood cells, which is why men typically have a
higher red blood cell count than women. This helps carry oxygen throughout
the body and needs to be monitored for any patients on TRT.
The Body's Balancing Act: How Testosterone
Levels are Controlled by The Brain
The human body is incredibly smart and automated. Men have
a sophisticated system in place to keep testosterone levels in check. This
system is called the hypothalamic-pituitary-gonadal
axis (HPG), and it's like a finely tuned thermostat that contantly
checks and monitors hormone levels in the body.
Here's how it works:
1.
The Brain's Command Center (Hypothalamus). Your
hypothalamus is a small but powerful part of the brain, which detects
testosterone levels and releases a hormone called Gonadotropin Releasing
Hormone (GnRH) in small, regular bursts when low levels are
detected.
2.
The Master Gland (Pituitary). GnRH
travels to your pituitary gland (another small gland at the base of your
brain), which then secretes and releases two important hormones: Luteinizing
Hormone (LH) and Follicle-Stimulating
Hormone (FSH).
3.
The Testicles Respond (Gonads): LH
and FSH then travel through your bloodstream to your testicles. LH specifically
tells the Leydig cells in your testicles to produce testosterone and sperm.
Negative Feedback: Keeping Things in Balance
Once testosterone levels rise, a signal is sent back to the
hypothalamus and pituitary, which then tells them to ease up on GnRH, LH, and
FSH production. This is called negative feedback, and it's how your body
prevents testosterone levels from getting too high and keeps the male hormone system
balanced.
Before puberty, testosterone levels in children are low
because this entire system is relatively quiet. However, one puberty begins,
there's both a dramatic and rapid increase in GnRH, which kicks off the whole
process, leading to the sudden surge in testosterone that starts all of those
pubertal changes and hits teenagers like a ton of bricks.
How Testosterone is Made and Used
Inside the testicles, specialized Leydig cells are busy
converting cholesterol into testosterone. While most of the testosterone in
your blood is attached, or "bound" to special proteins (like sex
hormone-binding globulin and albumin), a small amount remains "free" or
bio-available, if you will. It's this free testosterone that's
biologically active and can directly influence your tissues, like your muscles,
bones, and prostate and is the important testosterone in your body. A man could
have total testosterone levels in upper ranges however if its tied up by SHBG,
for example, it’s useless, so the free testosterone in the hormone that matters
as its what’s available to the body.
Do you remember earlier when we talked about DHT? That’s the
powerful form of testosterone created when an enzyme called 5-alpha-reductase
converts regular testosterone in your cells. Both testosterone and DHT then
bind to receptors on cells, signaling them to make new proteins and carry out
their functions.
When Testosterone Goes Awry: Too Much or Too
Little
There can be several problems with testosterone like when the
body produces too much, too little, or if a person’s cells don't respond to it
properly.
Too Little Testosterone (Hypogonadism)
This is becoming more and more common and there are several
reasons why a man’s T levels could decline. Lifestyle, genetics, medications
and other environmental factors like chemicals or food additives could be
reasons for declining testosterone levels. Testosterone levels also naturally
decline with age, and this can lead to a variety of symptoms, including:
- Decreased
testicular size
- Lower
libido and sex drive
- Reduced
bone strength and density (which can lead to osteoporosis)
- Loss
of muscle mass and increased body fat
- Decreased
production of red blood cells, potentially leading to anemia
If a patient or doctor suspects low testosterone, they'll
usually get a blood
test to confirm, ideally between 8 AM and 10 AM, when testosterone levels
are typically at their highest due to the body producing the hormone over night
when a male usually sleeps. Depending on the lab results, the healthcare
provider might run further tests to determine why levels are low. For example,
if testosterone levels are low but LH and FSH levels are high, it suggests that
there could be a problem with the testicles themselves (primary hypogonadism).
If all three are low, it might point to an issue with the hypothalamus or
pituitary (secondary hypogonadism). An experienced doctor is important
in helping to determine the cause and best course of action for treatment.
In many cases, Low testosterone can be treated with testosterone
replacement therapy (TRT). It’s a great option for many men, especially
when it's causing significant symptoms or medical problems.
Too Much Testosterone (Hyperandrogenism)
While much less common in adult men, too much testosterone
(or other similar hormones called androgens) can cause concerning issues. In
younger boys, this could show up as early puberty symptoms like penile
enlargement and excessive hair growth. Although these might not seem like bad
problems to have, they can negatively impact an adolescent and should be
addressed. In women, high androgen levels are more impactful can lead to
symptoms like acne, excessive hair growth (hirsutism), menstrual
irregularities, and even male-pattern baldness which can be devastating to a female.
Conditions like Polycystic Ovarian Syndrome (PCOS) in women, or certain tumors
of the adrenal glands or ovaries/testicles, can lead to excess androgen
production and are normally responsible for the higher testosterone levels.
When the Body Doesn't Process Testosterone
(Androgen Insensitivity)
Even if testosterone is present in normal amounts, problems
could manifest themselves if the body's cells can't "hear" its
signals. Androgen insensitivity syndrome is a condition where
individuals will have male chromosomes (XY) and produce testosterone, however
their cells lack functional androgen receptors which means their bodies don’t
respond to testosterone, leading to external female characteristics, even
though internal male structures might be present but undescended.
Another condition where the cells aren’t capable of processing
testosterone is called 5-alpha reductase deficiency. It involves a
problem with the enzymes that convert testosterone to DHT. Since DHT is crucial
for the development of male external genitalia, those individuals with this
deficiency might have ambiguous or female-like genitalia at birth, despite
having male internal organs. Interestingly, at puberty, the surge of
testosterone can lead to the development of some male secondary sexual characteristics.
What it All Means
Testosterone is much more than just a "male
hormone." It's both a vital and fundamental part of human development from
fetal development well into adulthood. It’s a critical regulator of countless
bodily functions throughout a man's life. From shaping our earliest development
in the womb to maintaining bone strength and mood in adulthood, its influence
is profound and undeniable. Understanding its roles, how it's regulated, and
what happens when it's out of balance can empower men to have more informed
conversations with their healthcare providers about your own health and
well-being with confidence that it can be treated to improve health, wellness
and quality of life.
Dr. Timothy Wray Mackey, a distinguished physician at NovaGenix, brings extensive expertise in internal medicine and a specialized focus on hormone replacement therapy. A licensed DO with years of experience in both men and women's hormone replacement therapy and weight loss treatments, including a background in the U.S. Army, Dr. Mackey provides personalized care to patients seeking solutions for low testosterone, bioidentical hormone replacement, and various wellness needs. He is certified in anti-aging medicine and bio-identical hormone replacement therapy, ensuring a comprehensive and evidence-based approach to optimizing patient health and well-being.
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