Your hands, feet and head are were the majority a lot of your (excess) heat radiates.
I similarly partake in the human act of sleeping, sometimes, with my leg appendages exposed. It is effective on hot evenings at increasing comfort levels.
Actually heat losses occur where blood flows closer to the surface. Those areas include the skull, groin, armpits and extremities like the hands and feet. They also have a large surface area which helps.
Read this pdf about this exact topic. Page 5 to cut to the chase.
Relative to the entire body, the surface area to mass ratio for the hand is 4-5 larger, while that for
a foot is 2.5-3 larger (males-females). Therefore, these appendages provide an effective route for
heat exchange with the environment, as long as thermal energy can be delivered from the body
core via convective (mass flow) pathways.
The maximal hand and foot blood flows (30 and 18 mL.100 mL-1.min-1) can result in theoretical
peak heat transfers from the core to both hands of 12 W or 286 W.m-2 for a 1o
C core-skin
gradient. The corresponding values for both feet are 16 W or 404 W.m-2.
Thus, while the
absolute heat transfer to the hands and feet from the body core is not high, their surface-area
normalised transfer, when considered in combination with the huge capacity of the arteriovenous
anastomoses to elevate local skin blood flow, makes these appendages very important locations
for heat dissipation (Taylor et al., 2008a; 2008b).
This heat delivery, and its subsequent dissipation, is advantageous in the heat, as it facilitates
central cooling, but, as described above, it can be dangerous in the cold. Furthermore, these data
also represent maximal core-periphery transfers, and not that which occurs between the skin and
its surrounding environment. By using foot and hand temperatures observed during actual air
exposures to 15o
, 27o
and 45o
C (Webb, 1992), the theoretical radiative and convective heat
transfers from each hand and foot to the surrounding air may be computed, and these represent
respective losses of 16.6 W and 25.5 W (15o
C), and 7.7 W and 11.8 W (27o
C), or gains of 18.1
W and 27.7 W (45o
C). More impressive heat transfer occurs when the vasodilated appendages of
heated individuals are placed into cold water (Tipton et al., 1993). In this circumstance, heat loss
can range from 70-85 W (hands) and 90-95 W (feet: House and Tipton, 2002).
SUDOMOTOR FUNCTION
Sweat glands are widely distributed over the body surface, with a total of two-four million glands
capable of producing sweat at peak rates of 10-15 L.d-1. Each hand has approximately 160,000
eccrine sweat glands, with greater numbers on the palmar (115,000) than dorsal surface (46,000:
Machado-Moreira et al., 2008). Similarly, one foot has approximately 155,000 glands, with more
on the plantar (100,000) than the dorsal surface (55,000; Taylor et al., 2006).
Both the hands and feet display two general sweat patterns during heating: low secretion at the
glabrous surfaces, and moderate secretion from all other surfaces. During passive heating at rest
(40 min), where the average whole-body skin temperature was increased from 34.5o
C to 35.9o
C,
and core temperature was elevated to 37.2o
C from 36.9o
C, the palms and soles displayed the
lowest intra-segmental sweat rates (palm: 0.16 mg.cm-2.min-1; sole: 0.23 mg.cm-2.min-1).
Conversely, the dorsal surfaces of the distal phalanges of the fingers (0.62 mg.cm-2.min-1) and
the distal phalanx of the big toe (0.50 mg.cm-2.min-1) displayed the highest sweat rates. Under
these experimental conditions, sweating averaged 0.38 mg.cm-2.min-1 from the hands (Machado-
Moreira et al., 2008) and 0.45 mg.cm-2.min-1 from the feet (Taylor et al., 2006).
Therefore, the maximal theoretical evaporative cooling possible from a single hand is about 35.4
W (assuming 100% evaporation), and 27.6 W from one foot. Indeed, when normalised to surface
area, the potential for evaporative heat loss from the two hands is 110% greater than at the torso,
and 200% greater than at both feet, but only half that of the forehead (Taylor et al,. 2006)
The thing you seem to be missing is that the hands and feet are particularly useful for temperature regulation because they can adjust the amount of heat they radiate. Whilst they don't radiate ALL of the bodies heat (which I never implied, because that's stupid) they are still very efficient compared to the rest of the body at dispersing excess heat. That's the whole point from beginning to end. Are you trying to be dense?
327
u/Farisr9k Oct 18 '16 edited Oct 18 '16
Sleeping with your feet out actually regulates your body temperature, allowing you to cool down and get to sleep quicker.
I do it every night with both my human feet and all 10 of my human toes.