Human Physiology 5, Your Brain - Your Thermostat,
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Review: How does it all work? (or...how do you 'work' in sensing
The sensors in your skin are part of the nervous system.
Information about temperature, pressure, and humidity etc...is
picked up at the sensors and sent to your brain through the
nerve fibers up into the spinal cord passing through the
thalamus to your cerebral cortex.
This is an illustration1of all the skin "comfort" sensors
in your body which ultimately have to be satisfied by the
environment created by the
It doesn't matter if you are standing on a
(conductive heat loss) or next to a
cold window or wall
(radiative heat loss) your sensors pick up the loss of energy
and your brain says..."hey...I'm cool, cold ..maybe darn right
It is the very essence of why we say we are not in the
business of conditioning buildings, rather we are in the
business of conditioning people.
The thalamus acts as a gatekeeper for messages passing through
the spinal cord into the cerebral hemispheres.
This is an
illustration1 of the spinal cord carrying thermal
information (left side) as it enters the thalamus
(right side). Note
the similarities between this and the wiring of an HVAC
system...the body is a great metaphor for designing radiant
based HVAC systems.
Click graphic for a larger image.
hypothalamus regulates your body's temperature and is responsible for
crucial urges — such as eating, sleeping and sexual behavior.
It says..."if I'm hot -
I need to sweat, if I'm cold -
I need to
This is an illustration1 of the hypothalamus and the parts which
regulate body temperature.
Click graphic for a larger image.
"If, due to an increased environmental temperature or metabolic
rate, the body begins to heat up, a process called
vasodilation is initiated in the hypothalamus. This
involves the dilation of blood vessels near to the surface of
the skin to increase its temperature. This leads to increased
radiant and convective heat loss.
If the body temperature is still increasing, the sweat glands
are activated to produce moisture on the skin surface. When this
moisture evaporates, latent heat of vaporisation is drawn from
both the surrounding environment and the skin. As sweat flows
directly onto the surface of the skin, conduction from
circulating blood immediately beneath forms one of the most
significant components. Sweat can be produced at up to four
litres per hour for short periods and is supplemented by the
evaporation of moisture from within the lungs and respiratory
If heat build up continues, hyperthermia sets in and heat
stroke may develop. This occurs when deep-body temperature
reaches about 40 deg C and can cause fatigue, headache, nausea,
shortness of breath and, in some cases, mental disturbances such
as apathy, poor judgment and irritability. After heat stroke is
developed, sweating stops, rapidly increasing body temperature
until serious brain damage results in coma and imminent death.
In cold conditions the body’s first response to heat loss is
vasoconstriction. This involves the contraction of blood
vessels near to the surface of the skin, increasing its
insulative value and reducing heat loss. If heat loss continues,
blood supply to extremities such as fingers and toes may be cut
off completely before deep-body temperature is affected. If
these extremities subsequently freeze, this is known as
frostbite and often results in their loss.
Vasoconstriction is often accompanied by the erection of hair
follicles (also known as goose pimples or pilo-erection) which,
if enough matted hair were present, would greatly increase its
insulation potential. With even greater heat loss, shivering is
initiated. This is simply involuntary spasms within certain
muscle groups designed to increase metabolic heat production.
When deep-body temperature falls below 95 deg F (35 deg C), hypothermia
sets in. Metabolic controls cease to function and body cooling
is increased. In some extreme cases, where body cooling occurred
very quickly, individuals have survived long periods of almost
suspended animation. If body cooling occurs at slower rates,
death results at a temperature of between 77 deg F (25 deg C) and 86
deg F (30 deg C)."
Copyright (c) Dr Andrew
One Research PTY LTD and the Welsh School of Architecture
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GIUNTI PUBLISHING GROUP, Atlas of Anatomy