question: Why do our fingers and toes get cold before any other body part?
comment: Because they are the areas that blood takes the longest to travel to, and also have no insulation in the form of fat, or even muscle. Which is why we get cold sequentially from places further from our core inwards.
passages: Blood circulation transports heat throughout the body, and adjustments to this flow are an important part of thermoregulation. Increasing blood flow to the surface (e.g., during warm weather or strenuous exercise) causes warmer skin, resulting in faster heat loss. In contrast, when the external temperature is low, blood flow to the extremities and surface of the skin is reduced and to prevent heat loss and is circulated to the important organs of the body, preferentially.
  
  Section::::Physiology.:Rate of blood flow.
   Section::::In cold conditions.
  
  BULLET::::- Heat is lost mainly through the hands and feet.
  
  BULLET::::- Sweat production is decreased.
  
  BULLET::::- The minute muscles under the surface of the skin called arrector pili muscles (attached to an individual hair follicle) contract (piloerection), lifting the hair follicle upright. This makes the hairs stand on end, which acts as an insulating layer, trapping heat. This is what also causes goose bumps since humans do not have very much hair and the contracted muscles can easily be seen.
   When the fingers are exposed to cold, vasoconstriction occurs first to reduce heat loss, resulting in strong cooling of the fingers. Approximately five to ten minutes after the start of the cold exposure of the hand, the blood vessels in the finger tips will suddenly vasodilate. This is probably caused by a sudden decrease in the release of neurotransmitters from the sympathetic nerves to the muscular coat of the arteriovenous anastomoses due to local cold. The CIVD increases blood flow and subsequently the temperature of the fingers. This can be painful and is sometimes known as the 'hot aches' which can be painful enough to bring on vomiting.
   When core temperature falls, the blood supply to the skin is reduced by intense vasoconstriction. The blood flow to the limbs (which have a large surface area) is similarly reduced, and returned to the trunk via the deep veins which lie alongside the arteries (forming venae comitantes). This acts as a counter-current exchange system which short-circuits the warmth from the arterial blood directly into the venous blood returning into the trunk, causing minimal heat loss from the extremities in cold weather. The subcutaneous limb veins are tightly constricted, not only reducing heat loss from this source, but also forcing the venous blood into the counter-current system in the depths of the limbs.
   Vasoconstriction occurs first to reduce heat loss, but also results in strong cooling of the extremities. Approximately five to ten minutes after the start of cold exposure, the blood vessels in the extremities will suddenly vasodilate. This is probably caused by a sudden decrease in the release of neurotransmitters from the sympathetic nerves to the muscular coat of the arteriovenous anastomoses due to local cold. This cold-induced vasodilation increases blood flow and subsequently the temperature of the fingers. A new phase of vasoconstriction follows the vasodilation, after which the process repeats itself.
   In birds with webbed feet, retia mirabilia in the legs and feet transfer heat from the outgoing (hot) blood in the arteries to the incoming (cold) blood in the veins. The effect of this biological heat exchanger is that the internal temperature of the feet is much closer to the ambient temperature, thus reducing heat loss. Penguins have them also in the flippers and nasal passages.
   Warm and cold sensitive nerve fibers differ in structure and function. The cold-sensitive and warm-sensitive nerve fibers are underneath the skin surface. Terminals of each temperature-sensitive fiber do not branch away to different organs in the body. They form a small sensitive point which are unique from neighboring fibers. Skin used by the single receptor ending of a temperature-sensitive nerve fiber is small. There are 20 cold points per square centimeter in the lips, 4 in the finger, and less than 1 cold point per square centimeter in trunk areas. There are 5 times as many cold sensitive points as warm sensitive points.
   Hunting reaction
  
  The hunting reaction or hunting response is a process of alternating vasoconstriction and vasodilation in extremities exposed to cold. The term Lewis reaction is used too, named after Thomas Lewis, who first described the effect in 1930.
   BULLET::::2. Increasing body size to more easily maintain core body temperature (warm-blooded animals in cold climates tend to be larger than similar species in warmer climates (see Bergmann's Rule))
  
  BULLET::::3. Having the ability to store energy as fat for metabolism
  
  BULLET::::4. Have shortened extremities
  
  BULLET::::5. Have countercurrent blood flow in extremities – this is where the warm arterial blood travelling to the limb passes the cooler venous blood from the limb and heat is exchanged warming the venous blood and cooling the arterial (e.g., Arctic wolf or penguins)
   Another example is found in the legs of an Arctic fox treading on snow. The paws are necessarily cold, but blood can circulate to bring nutrients to the paws without losing much heat from the body. Proximity of arteries and veins in the leg results in heat exchange, so that as the blood flows down it becomes cooler, and doesn't lose much heat to the snow. As the (cold) blood flows back up from the paws through the veins, it picks up heat from the blood flowing in the opposite direction, so that it returns to the torso in a warm state, allowing the fox to maintain a comfortable temperature, without losing it to the snow. This system is so efficient that the Arctic fox does not begin to shiver until the temperature drops to .
   In cold weather the blood flow to the limbs of birds and mammals is reduced on exposure to cold environmental conditions, and returned to the trunk via the deep veins which lie alongside the arteries (forming venae comitantes). This acts as a counter-current exchange system which short-circuits the warmth from the arterial blood directly into the venous blood returning into the trunk, causing minimal heat loss from the extremities in cold weather. The subcutaneous limb veins are tightly constricted, thereby reducing heat loss via this route, and forcing the blood returning from the extremities into the counter-current blood flow systems in the centers of the limbs. Birds and mammals that regularly immerse their limbs in cold or icy water have particularly well developed counter-current blood flow systems to their limbs, allowing prolonged exposure of the extremities to the cold without significant loss of body heat, even when the limbs are as thin as the lower legs, or tarsi, of a bird, for instance.
   BULLET::::- Arteriolar vasodilation occurs. The smooth muscle walls of the arterioles relax allowing increased blood flow through the artery. This redirects blood into the superficial capillaries in the skin increasing heat loss by convection and conduction.
  
  Section::::In hot and humid conditions.
   Phalanges are commonly fractured. A damaged tendon can cause significant loss of function in fine motor control, such as with a mallet finger. They can be damaged by cold, including frostbite and non-freezing cold injury (NFCI); and heat, including burns.
  
  The fingers are commonly affected by diseases such as rheumatoid arthritis and gout. Diabetics often use the fingers to obtain blood samples for regular blood sugar testing. Raynaud's phenomenon and Paroxysmal hand hematoma are neurovascular disorders that affects the fingers. 
   The condition can cause pain within the affected extremities, discoloration (paleness), and sensations of cold and/or numbness. This can often be distressing to those who are undiagnosed, and sometimes it can be obstructive. If someone with Raynaud's is placed into a cold climate, it could potentially become dangerous.
  
  When exposed to cold temperatures, the blood supply to the fingers or toes, and in some cases the nose or earlobes, is markedly reduced; the skin turns pale or white (called pallor) and becomes cold and numb.
   The phalanges are the bones that make up the fingers of the hand and the toes of the foot. There are 56 phalanges in the human body, with fourteen on each hand and foot. Three phalanges are present on each finger and toe, with the exception of the thumb and large toe, which possess only two. The middle and far phalanges of the fourth and fifth toes are often fused together (symphalangism). The phalanges of the hand are commonly known as the finger bones. The phalanges of the foot differ from the hand in that they are often shorter and more compressed, especially in the proximal phalanges, those closest to the body.
   Vascular retia mirabilia are also found in the limbs of a range of mammals. These reduce the temperature in the extremities. Some of these probably function to prevent heat loss in cold conditions by reducing the temperature gradient between the limb and the environment. Others reduce the temperature of the testes increasing their productivity. In the neck of the dog, a rete mirabile protects the brain when the body overheats during hunting; the venous blood is cooled down by panting before entering the net.
   Section::::History.
  
  Section::::History.:Early years.
   Dorsal venous arch of the foot
  
  The dorsal venous arch of the foot is a superficial vein that connects the small saphenous vein and the great saphenous vein. Anatomically, it is defined by where the dorsal veins of the first and fifth digit, respectively, meet the great saphenous vein and small saphenous vein.
  
  It is usually fairly easy to palpate and visualize (if the patient is barefoot). It lies superior to the metatarsal bones approximately midway between the ankle joint and metatarsal phalangeal joints.
   BULLET::::- The "palm" (Volar), which is the central region of the anterior part of the hand, located superficially to the metacarpus. The skin in this area contains dermal papillae to increase friction, such as are also present on the fingers and used for fingerprints.
  
  BULLET::::- The "opisthenar" area (dorsal) is the corresponding area on the posterior part of the hand.
   The climate here is mild, and generally warm and temperate. When compared with winter, the summers have much more rainfall. This location is classified as Cwa by Köppen and Geiger. The temperature here averages 21.7 °C. The rainfall here averages 2012 mm. At an average temperature of 30.3 °C, May is the hottest month of the year. At 15.5 °C on average, December is the coldest month of the year.
  
  Section::::Tourism.
   Pathways for touch-position and pain-temperature sensations from the face and body merge in the brainstem, and touch-position and pain-temperature sensory maps of the entire body are projected onto the thalamus. From the thalamus, touch-position and pain-temperature information is projected onto the cerebral cortex.
  
  Section::::Function.:Summary.
  
  The complex processing of pain-temperature information in the thalamus and cerebral cortex (as opposed to the relatively simple, straightforward processing of touch-position information) reflects a phylogenetically older, more primitive sensory system. The detailed information received from peripheral touch-position receptors is superimposed on a background of awareness, memory and emotions partially set by peripheral pain-temperature receptors.
   A glomus body (or glomus apparatus) is a component of the dermis layer of the skin, involved in body temperature regulation. The glomus body consists of an arteriovenous shunt surrounded by a capsule of connective tissue. Glomus bodies are most numerous in the fingers and toes. The role of the glomus body is to shunt blood away from the skin surface when exposed to cold temperature, thus preventing heat loss, and allowing maximum blood flow to the skin in warm weather to allow heat to dissipate. The glomus body has high sympathetic tone and potentiation leads to near complete vasoconstriction.
   BULLET::::- Anime:Strawberry Tart (using Inverted Fold)
  
  BULLET::::- Manga: Tarte Tatin (using Inverted Fold)
  
  Section::::Techniques and special terms.
  
  Normally, extremities such as the hands are lower in temperature than the rest of the body, but if one can increase blood flow to the hands, that difference decreases. In France, those that possess this ability are said to have "Solar Hands".
  
  Note: Gran Kayser has hands that are a combination of the cumulative techniques of Solar Hands and Solar Gauntlets known as the "Solar Hand, Gigantis."
   BULLET::::- Type II: Also called a "spoon" or "mitten" hand. This is a more serious anomaly since the thumb is fused to the index finger by simple complete or incomplete syndactyly. Only the distal phalanx of the thumb is not joined in the osseous union with the index finger and has a separate nail. Because the fusion of the digits is at the level of the distal interphalangeal joints, a concave palm is formed. Most of the time, we see complete syndactyly of the fourth webspace.
   BULLET::::- Resting a laptop computer on the thigh (laptop computer-induced erythema ab igne). In a 2012 review, Riahi and Cohen describe the characteristics of laptop computer-induced erythema ab igne. Temperatures between 43-47 °C can cause this skin condition; modern laptops can generate temperatures in this range. Indeed, laptops with powerful processors can reach temperatures of 50 °C and be associated with burns. Positioning of the laptop on the thighs can allow for direct exposure to the heating elements of the laptop, which include the central processing unit (CPU) and the graphics processing unit (GPU). At least 15 cases have been reported by 2012 with the condition usually affecting the left anterior thigh. In these reports, 9 of the 15 patients were women (60%) with an average age of 25 years at diagnosis.
  