Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.
Ruchi Mathur, MD, FRCP(C) is an Attending Physician with the Division of Endocrinology, Diabetes and Metabolism and Associate Director of Clinical Research, Recruitment and Phenotyping with the Center for Androgen Related Disorders, Department of Obstetrics and Gynecology at Cedars-Sinai Medical Center.
Testosterone is produced by the testes in males and ovaries in females. The
testes are under the hormonal control of the hypothalamus and pituitary in the
brain and make testosterone in response to stimulation by FSH and LH.
Primary hypogonadism occurs because of the inability of the testes to
produce testosterone.
Causes of secondary and tertiary hypogonadism are due to a variety of
illnesses or diseases that affect the hypothalamus-pituitary-gonadal axis.
Symptoms of low testosterone depend upon when in the life cycle it occurs.
Osteoporosis and loss of muscle mass are significant complications of low testosterone.
In the United States, testosterone replacement therapy is available as an
FDA-approved treatment in men only. It may be administered by injection, patch
or gel, or gum and cheek putty.
What is testosterone?
Testosterone is an anabolic-androgenic steroid hormone which is made in the testes in males and in
the ovaries in women (a minimal amount is also made in the adrenal glands).
Testosterone has two major functions in the human body.
Testosterone is needed
to form and maintain the male sex organs and promote secondary male sex
characteristics (in both men and women) such as voice deepening and hair growth
patterns. This function is related to its androgenic properties.
Testosterone is the facilitation of muscle growth as well as bone
development and maintenance. This is a result of its anabolic properties.
Testosterone production is regulated by hormones released from the brain. The
hypothalamus and pituitary gland located in the brain produce hormonal signals
that ultimately result in the production of testosterone. The hypothalamus is
located just above the brain stem, and among its many functions, it produces
gonadotrophin releasing hormone (GRH). GRH travels a short distance to the
pituitary gland located in the base of the brain stimulating the gland to release FSH (follicle stimulating hormone) and LH (luteinizing
hormone). These hormones travel through the bloodstream to activate the sex
organs in both men and women. Subsequently, these hormones also have a role in
regulating testosterone levels in the bloodstream.
The majority of testosterone circulates in the blood bound to a carrier
protein (a hormone is produced in one are of the body and has its effect on
another area. Often a carrier protein that assists the hormone travel through
the bloodstream). In this
case the carrier protein is called "sex hormone binding globulin," or SHBG. When
testosterone is being carried by SHBG, it is considered "bound". Bound
testosterone does not play an active role in the body; only the unbound or "free" testosterone is able to enter the different cells of the body and exert
its androgenic and anabolic effects. Thus, anything that affects the function or
the amount of SHBG can also affect the total circulating amount of active
testosterone.
Picture of the endocrine system including the testes and ovaries
What is low testosterone?
The human body functions within a relatively narrow range of normal; when
chemicals such as hormones fall outside those normal levels, there can be
consequences that affect the body at a cellular, organ, or systemic (body-wide)
level.
Blood tests used to measure testosterone are usually performed in the morning.
Testosterone sampling is difficult since the levels normally tend to bounce
around a fair bit during the course of the day. The normal value for total
testosterone in males is 270-1070 ng/dl. However, this depends to some extent
on the individual laboratory being used, and the range can vary as a result. In
women, there is debate about the accuracy of testosterone measurements, because
the circulating values are so much lower than in males and are harder to
accurately measure.
As people age, the amount of testosterone the
body produces gradually falls in both men and women. Free testosterone levels can be measured and
normal levels depend upon an individual's age. Interestingly,
menopause
itself does not seem to play a role in a reduction of testosterone levels in
women beyond that of advancing age.
Reviewed by Ruchi Mathur, MD, FRCP(C) on 9/12/2012
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