Hi rene1899,
Let me start by quoting this paragraph from Dr. Len Kravitz, an
exercise scientist at the University of New Mexico:
?The human body regulates temperature by keeping a tight balance
between heat gain and heat loss. Your temperature regulation system is
more analogous to the operation of a home furnace, as opposed to the
function of an air conditioner. Humans regulate heat generation and
preservation to maintain internal body temperature or core
temperature. Normal core temperature at rest varies between 36.5 and
37.5 °Celsius (°C), which is 97.7 to 99.5 °Fahrenheit (°F). Core
temperature is regulated by the hypothalamus (in the brain), which is
often called the body?s thermostat. The hypothalamus responds to
various temperature receptors located throughout the body and makes
physiological adjustments to maintain a constant core temperature. For
example, on a hot day, temperature receptors located in the skin send
signals to the hypothalamus to cool the body by increasing the sweat
rate.?
http://www.unm.edu/~lkravitz/Article%20folder/thermoregulation.html
Temperature regulation by the hypothalamus is actually a feedback
loop in action, called homeostasis. The hypothalamus affects the
pituitary which affects the thyroid which produces thyroxine, which
affects the pituitary and the hypothalamus?and so on, and so on.
You can see an illustration here:
http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20102/Bio%20102%20lectures/endocrine%20system/thyroxine.gif
Homeostasis controls the ?fight or flight? response, blood pH, water
potential ,O2 and Co2 concentrations in the blood, blood glucose,
glucagon and insulin, and the one you were waiting for?..body
temperature! All of these factors influence each other, and when one
gets out of sync, the rest are affected. Many of these mechanisms rely
on negative feedback: a rise or fall in any one, such as blood
glucose, oxygen, or temperature is detected by receptors. These
receptors then send the information to the hypothalamus, which reacts
by returning to the original value, as a normal body temperature.
Homeostasis keeps the body's internal temperature constant , at 98.6
F (36.5oC), plus or minus 1 degree ?Humans maintain body temperature
within 1oC of 98.6.? There is also a natural variation during the
day. Body temperature is lower in the morning and highest on average
in the afternoon. Morning temperatures might be as low as 96.0 .
http://www.courseworkbank.co.uk/coursework/explain_is_meant_by_term_homeostasis_2472/
http://www.revision-notes.co.uk/revision/858.html
About the hypothalamus:
?Tucked deep inside the brain, this gland is an important supervisory
center, regulating many body functions. It is important for longevity
and coordinates the entire endocrine system, especially in connection
with the pituitary. The hypothalamus is located immediately below the
thalamus at the center of the brain, and controls many automatic
functions of the body. This means it has the power to govern the
autonomic (automatic or subconscious) nervous system. The hypothalamus
also controls pituitary output by secreting specific chemicals to the
pituitary's front lobe. Despite its importance in maintaining
homeostasis, the hypothalamus in humans accounts for only 1/300 of
total brain weight, and is about the size of an almond.?
http://www.diagnose-me.com/cond/C19447.html#G1087
?Once your hypothalamus sets a new temperature for your body, your
body takes action and starts to heat up. When a fever starts, your
body tries to get hotter and you may shiver without thinking about it
to create more heat. You may feel very cold even though the room isn't
cold and even though you have your pajamas or nightgown on and lots of
blankets around you. If your body reaches the new temperature that's
been set by the hypothalamus - say 102 degrees Fahrenheit (38.9
degrees Celsius) - you won't feel cold anymore. According to your
hypothalamus, your temperature is where it should be!? After the need
for a higher temperature is over, the hypothalamus will ?reset? the
thermostat back to normal, and your body will cool down.
However, just because the hypothalamus is called the body?s
thermostat, this does not mean we can just turn it up and down like
the one on our wall! The hypothalamus sends signals in the form of a
hormone called adrenaline, speeding our metabolism, causing us to
perspire if we are too hot, (cooling by evaporation) and to shiver of
we are cold, (energy from shivering muscles is converted into heat)
effectively raising or lowering the body temperature as needed.
Prostaglandins and pyrogens (fever inducers) released by the body from
inflammation and infection cause the hypothalamus to ?turn up? the
body temperature. If the temperature does not rise fast enough, we
begin to shiver with chills, boosting the body temperature quickly.
Interestingly, pain relievers such as aspirin, acetominophen and
ibuprofin interfere with the normal function of the hypothalamus, by
keeping us from shivering or perspiring when needed.
http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgeneral%2Fans_037.html
http://kidshealth.org/kid/ill_injure/sick/fever_p2.html
http://www.madsci.org/posts/archives/Jan2003/1042830425.Gb.r.html
?The hypothalamus regulates the endocrine system by controlling the
secretions of the pituitary gland or by producing some of the hormones
that are secreted by the pituitary. These hormones affect the body or
affect other glands in the body. Their overall affect is to maintain
homeostasis.?
http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20102/Bio%20102%20lectures/Endocrine%20System/endocrin.htm
?Our body has a normal ?set point? for its temperature, which varies
slightly from person to person. We often forget that the body
regulates its internal environment in many ways. The body senses
changes in the environment and responds by making changes in
functions. This is a dynamic process that keeps the internal
conditions of the body relatively stable? and ?Using temperature as
an example, we know that the hypothalamus in the brain can act as a
thermostat and control the body?s functioning to regulate temperature
to keep us from overheating or getting too cold. The hypothalamus
causes changes in the size of blood vessels in the skin, which then
has a direct impact on the amount of heat lost or retained by the
body. Most systems of the body maintain homeostasis by means of
negative feedback mechanisms, which reverse a response back to a
normal state.?
http://www.the-aps.org/education/k12curric/activities/pdfs/slifstein.PDF
So, how do you warm up a person who feels cold all the time? Since you
can?t raise the hypothalamus thermostat, you get your thyroid checked!
Hypothyroid (low thyroid) is the main reason people are sensitive to
cold. Women, because of a slightly lower metabolism and a different
distribution of body fat are more susceptible to feeling cold than are
men.
The hypothalamus affects the thyroid, as you saw above. Let?s digress
for a minute, and think of how a car runs. You turn the key, which
draws power from the battery, completing the circuit, to turn the
flywheel, to start combustion to start the engine. The running engine
then supplies power to the battery so you can repeat the process for
the return trip!
Your hypothalamus stimulates your thyroid?This Pharmsave site explains it best:
The thyroid gland?s hormone-producing activity is controlled by the
hypothalamus and pituitary glands in the brain. These glands can sense
when the amount of thyroid hormone in the blood is low or high and
give feedback to the thyroid accordingly. When thyroid hormone levels
drop, the pituitary gland, upon a signal from the hypothalamus, tells
the thyroid to make more. The pituitary does this by secreting a
hormone of its own called TSH, or "thyroid-stimulating hormone." As
the thyroid hormone level rises, the pituitary gland tells the thyroid
gland to shut production down. This circle of communication between
glands, called a "feedback loop," is designed to keep the amount of
thyroid hormone circulating in the blood within a fairly narrow range,
so we never have too much or too little. In hypothyroidism, TSH levels
are generally higher than normal because the pituitary pumps out more
TSH in response to low thyroid hormone levels.
http://content.nhiondemand.com/psv/HC1.asp?objID=100230&ctype=hc
?Hypothyroidism makes one feel like an engine missing a spark plug.
The mind and body are sluggish. Digestion is poor, cardiovascular
function and mental activity slow down, and muscles weaken. Low basal
metabolism causes low body temperature, leaving the hypothyroid
individual feeling chilly, with cold hand and feet, most of the time.
The old saying, "My get up and go got up and went," aptly describes
the person with hypothyroidism.?
http://content.nhiondemand.com/psv/HC1.asp?objID=100230&ctype=hc
What Causes Hypothyroidism?
?Many permanent or temporary conditions can reduce thyroid hormone
secretion and cause hypothyroidism. The most common of these are
Hashimoto's thyroiditis, an autoimmune condition, and overtreatment of
hyperthyroidism. About 95% of hypothyroidism cases occur from problems
that originate in the thyroid gland. In such cases, the disorder is
called primary hypothyroidism. In some cases, it is caused by
disorders of the pituitary gland (when it is known as secondary
hypothyroidism) or hypothalamus gland (tertiary hypothyroidism).?
http://www.reutershealth.com/wellconnected/doc38.html
From Emedicine Health: Hypothyroidism occurs when secretion of thyroid
hormones is inadequate to the point that the body begins to slow down.
Hypothyroidism was first diagnosed in the late nineteenth century when
physicians observed that after surgically removing the thyroid gland,
a patient developed swelling of the hands, face, feet, and tissues
around the eye. They named this syndrome myxedema and correctly
concluded that it was the outcome of the absence of substances,
thyroid hormones, normally produced by the thyroid gland.
Hypothyroidism is usually progressive and irreversible. Treatment,
however, is nearly always completely successful and allows a patient
to live a fully normal life.
http://www.emedicinehealth.com/articles/15503-1.asp
?Mammals respond to cold weather with the hypothalamus releasing thyrotropin
releasing factor. This production increases with the severity of the cold
weather and the length of the exposure to cold over a long period of time
(at least three to four weeks). The thyroid responds by slowly increasing
in size and releases thyroxine at higher quantities. Thyroxine increases
the sensitivity of the entire nervous system. As a matter of fact, as you
probably know, it increases the metabolism wholesale! within the
body. This gets complicated so I'm keeping it simple. So, the bottom line
is thyroxine. It just heightens our sensitivity not only to cold but our
entire nervous system is enhanced.?
http://www.newton.dep.anl.gov/askasci/bio99/bio99966.htm
?Sluggishness, mental dullness, feeling cold, or muscle cramps may
persist. Even mild hypothyroidism without any symptoms can lead to an
increase in cholesterol levels. To avoid these problems, patients
should take the proper dosage of levothyroxine as prescribed and have
regular check-ups that include measurement of blood TSH.?
http://www.stopgettingsick.com/Conditions/condition_template.cfm/1367/76/1
From Reuter?s Health :
·An understanding of the complex thyroid hormone process begins with
iodide, a salt that is extracted from the blood and trapped by the
thyroid gland.
·Iodide is converted to iodine in the thyroid gland. (Here, 80% of the
body's iodine supply is then stored.) Iodine, in turn, is the raw
material used in the manufacturing of thyroxine (T4), the key thyroid
hormone.
·Thyroxine itself is converted into triiodothyronine (T3) , which is
the more biologically active thyroid hormone. (Only about 20% of
triiodothyronine is actually formed in the thyroid gland, however. The
rest is manufactured from circulating thyroxine in tissues outside the
thyroid, such as those in the liver and kidney.)
·Once the T4 and T3 thyroid hormones are in circulation, a large
fraction binds to other substances called thyroid hormone transport
proteins, after which they become inactive. (In fact, only 0.03% of
thyroxine and 0.5% of triiodothyronine are free, that is, unbound, and
chemically active.)
·Two other important hormones in the process are thyroid-stimulating
hormone ( TSH or thyrotropin) and thyrotropin-releasing hormone (
TRH).
·TSH directly influences the whole process of iodine trapping and
thyroid hormone production.
·This hormone is secreted by the pituitary gland and monitored by TRH,
which is produced in the hypothalamus gland. (Both the pituitary and
hypothalamus glands are located in the brain.)
·When thyroxine levels drop even slightly, the pituitary gland goes
into action to pump up secretion of TSH so that it can stimulate
thyroxine production.
Any abnormality in this intricate system of glands and hormone
synthesis and production can have far-reaching consequences.
http://www.reutershealth.com/wellconnected/doc38.html
The hypothalamus produces a hormone called thyrotropin-releasing
hormone (TRH), which stimulates the pituitary gland to produce
thyroid-stimulating hormone (TSH). TSH, in turn, regulates the amount
of thyroid hormone produced and released into the bloodstream by the
thyroid gland. A problem in the hypothalamus can result in decreased
release of thyroid hormone by the thyroid gland.
http://www.meritcare.com/hwdb/showtopic.asp?module_abbrev=HWKB4&pd_hwid=sth150007-sec&topic_name=Hypothalamus&sequence=1
Risk factors for hypothyroid disease include a family history, having
given birth in the previous 9 months, goiter, partial thyroidectomy
and Graves Disease.
http://thyroid.about.com/cs/hypothyroidism/a/checklist.htm
Thyroid tests
Most commonly ordered thyroid function tests include T3, T4, FT3, FT4,
and TSH. Should any of these be abnormal, further testing will be
ordered.
http://www.endocrineweb.com/tests.html
Normal Ranges for Thyroid Tests, from EndocrineWeb
===================================================
Test Abbreviation Typical Ranges
===================================================
Serum thyroxine T4 4.6-12 ug/dl
Free thyroxine fraction FT4F 0.03-0.005%
Free Thyroxine FT4 0.7-1.9 ng/dl
Thyroid hormone binding ratio THBR 0.9-1.1
Free Thyroxine index FT4I 4-11
Serum Triiodothyronine T3 80-180 ng/dl
Free Triiodothyronine l FT3 230-619 pg/d
Free T3 Index FT3I 80-180
Radioactive iodine uptake RAIU 10-30%
Serum thyrotropin TSH 0.5-6 uU/ml
Thyroxine-binding globulin TBG 12-20 ug/dl T4 +1.8 ugm
TRH stimulation test Peak TSH 9-30 uIU/ml at 20-30 min
Serum thyroglobulin l Tg 0-30 ng/m
Thyroid microsomal antibody titer TMAb Varies with method
Thyroglobulin antibody titer TgAb Varies with method
http://www.endocrineweb.com/TFT.html
Interpreting these tests:
http://thyroid.about.com/library/howto/htthyroid-test.htm
Treating Hypothyroid:
Levothyroxine, whose brand names are Eltroxin, Levothroid, Levoxine,
Levoxyl, Thyrolar and Synthroid. Armour also makes a porcine(pig)
thyroid medication that is better tolerated by many patients as it
closer resembles the human form of the hormone. This medication is
taken, once a day, in the morning and with food. It may take up to two
weeks before beneficial effects are seen.
http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a682461.html
http://www.armourthyroid.com/
http://www.synthroid.com/
?Well treated hypothyroid patients should enjoy a vibrant life with
lowered risks of all of the degenerative diseases including arthritis,
cancer and heart disease. I personally have seen a number of patients
whose arthritis pains have completely cleared when treated with proper
doses of thyroid. With regard to cancer, the well known alternative
cancer treatment developed by Max Gerson, involves the use of Armour
Desiccated Thyroid in virtually all of his cancer patients. High serum
cholesterol and the development of atherosclerosis are well known
effects of hypothyroidism. Therefore, all patients with coronary
artery disease and other atherosclerotic conditions should be checked
carefully for evidence of a low functioning thyroid condition and
treated cautiously and appropriately if a low thyroid condition is
found. Psychiatrists have found that the addition of thyroid hormone
to patients suffering from refractory depression often is helpful,
even when the blood tests are normal.?
http://www.healthy.net/asp/templates/article.asp?PageType=Article&ID=528
Another good regulator of the hypothalamus is simple, exercise!
?Resistance exercise may directly reset the body clocks in skeletal
muscle, according to research published in Genome Biology this week.
This result may partly explain how exercising early in the day helps
jet-lagged bodies readjust to their new time zone.
Many processes in the body vary in a 24-hour rhythm called the
circadian rhythm. These rhythms are controlled by molecular clocks, in
organs such as the liver, in tissues such as skeletal muscle, and in
the hypothalamus, a part of the brain. The clock in the hypothalamus
is the central controller and keeps all the peripheral clocks in
synch.
Exercise can reset circadian rhythms. Most scientists thought this
process was mediated purely by inputs to the hypothalamus, which can
alter the expression of genes in the central clock. Now researchers,
from the Gladstone Institute of Cardiovascular Disease, the University
of California, and Northwestern University, have found that exercise
can also alter the expression of clock genes in the muscles
themselves.?
http://www.eurekalert.org/pub_releases/2003-09/bc-rer092403.php
http://www.scienceblog.com/community/modules.php?name=News&file=article&sid=1986
Additional Reading:
CNN
http://www.cnn.com/HEALTH/library/DS/00353.html
Physioweb
http://physioweb.med.uvm.edu/Endocrine/301HYPO03F.pdf
There you have it, rene1899! Rather than bundle up in sweatshirts and
blankets, get your thyroid checked! If it turns out that your thyroid
is causing you to be cold-sensitive, following appropriate treatment,
you will effectively raise your hypothalamic setpoint! If your thyroid
is normal (hopefully) exercise may be the best way for you to warm up!
If any part of my answer is unclear, or if I have duplicated sites you
have already seen, please request an Answer Clarification, before
rating. This will allow me to assist you further, if possible.
Sincerely,
crabcakes
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