Principles of the Temperature Map
Thermoregulation is viewed as a complex functional system operating to achieve a useful adaptive result (UAR). This result is the maintenance of a temperature level in the tissues that is necessary for the optimal course of all metabolic processes. Since metabolic intensity varies significantly across different tissues and organs, heat indicators within them are likewise uneven.
Thus, the output of the thermoregulation system is multiparametric — it is composed of multiple local values. A constant temperature gradient exists in the body. The body temperature map represents the individual distribution of temperatures across the skin surface and internal organs. Normally, it is relatively stable, but strictly depends on two factors: the functional state of the body itself and the ambient temperature (causing tissue heating or cooling).
Normal temperature indicators at baseline points:
- Axillary (in the armpit): 36.6–36.8 °C.
- Oral (in the mouth) and rectal (in the rectum): 36.8–37.2 °C.
- Fingers: 28–32 °C.
- Toes: 24–28 °C.
Characteristics of the Core and Shell
The entire temperature structure of the body can be divided into two key functional zones.
1. Body Core (homeothermic zone) Includes deeply located internal organs and the brain. The temperature here is higher than on the surface and is maintained at a stable level due to the heat generated by internal metabolism. The "hottest" organ is the liver — the venous blood draining from it has a temperature of 37.8–38.0 °C. The universally accepted standard for assessing average core temperature is the blood in the right ventricle of the heart (its temperature is 37.5 °C).
2. Body Shell (poikilothermic zone) Represented by superficial tissues: skin, subcutaneous adipose tissue, and extremities. The shell temperature is always lower than the core temperature and is highly variable (can change by significant margins). For example, during severe cooling or heating, the tissues of the hands and feet can change their temperature in the range from 16 to 35 °C, while the person experiences no discomfort.
Temperature Distribution in Cold Conditions
When exposed to low temperatures, the centralization of heat production reaction is triggered. Peripheral vessels constrict sharply (vasoconstriction) to reliably trap heat within vital organs.
Under these conditions, the temperature core (37 °C) contracts, occupying a minimal volume — only the deep parts of the torso and the head. The temperature shell, conversely, thickens significantly.
A pronounced proximal-distal gradient is formed (a sharp drop in temperature when moving from the center of the body to the periphery of the extremities). The difference between the core and the foot under such conditions reaches 21 °C.
Exact temperature indicators in the cold:
- Superficial layers of the chest and torso: 36 °C.
- Upper extremity: shoulder cools to 34 °C, forearm to 32 °C, hand to 28 °C.
- Lower extremity: thigh — 34 °C, shin — 31 °C, ankle — 29 °C, foot — 16 °C (maximum shell hypothermia is observed in the foot area).
Temperature Distribution in Warm and Comfortable Conditions
When exposed to high environmental temperatures or in comfortable conditions, the body activates heat dissipation mechanisms. Peripheral vessels dilate (vasodilation), transporting excess heat with the blood to the body surface.
At the same time, the temperature core expands to the maximum, encompassing not only the torso but also the proximal parts of the extremities. The temperature shell thins out considerably.
The temperature gradient evens out: the skin warms up more evenly, and its indicators approach core values. The temperature difference between the core and the foot decreases to 13 °C.
Exact temperature indicators in the warmth:
- Upper extremity: shoulder and forearm warm up evenly to 36.9 °C, which practically makes them part of the homeothermic core.
- Lower extremity: the thigh fully enters the core zone (37 °C), shin temperature is 36 °C, ankle is 30 °C, and foot is 24 °C.
Briefly: answers to topical questions
Where is the main neural center of thermoregulation located, which controls the constancy of core temperature?
The main neural center of thermoregulation is located in the hypothalamus (hypothalamic region). The thermoregulation centers in the hypothalamus are divided into zones:
- Anterior hypothalamus — predominantly responsible for heat loss.
- Posterior hypothalamus — predominantly responsible for heat production.
Destruction of hypothalamic nuclei leads to impaired thermoregulation.
Which types of skin receptors record changes in the temperature of the body shell?
Changes in the temperature of the temperature shell are recorded by two main types of skin thermoreceptors, which have different sensitivity ranges:
- Cold receptors (CR) — active in the range from ~10 °C to 40 °C. Peak maximum activity is observed around 25–28 °C.
- Warm receptors (WR) — active in the range from ~30 °C to ~48 °C. Peak activity is around 42–44 °C.
Approximately in the 30–40 °C range, there is an overlap zone where both types of thermoreceptors are active simultaneously.
What physical pathways of heat dissipation are activated during shell vasodilation in warm conditions?
In warm conditions, peripheral vasodilation occurs to transport heat to the body surface. Heat dissipation from the skin surface into the external environment is carried out through the following physical pathways:
- Thermal radiation (radiative heat loss) — heat loss via the emission of electromagnetic waves in the infrared range (accounts for about 70% of heat loss).
- Conduction (thermal conduction) — direct transfer of thermal energy upon direct contact.
- Evaporation — expenditure of the body's thermal energy on the phase transition of liquid (sweat) into vapor.
- Convection — heat dissipation due to the movement of ambient volumes (air or water) around the body.
Imagine the core as a "heating pad" and the shell as a "blanket". In the cold, the body tries to save the heating pad: it shrinks to the center of the torso, and the blanket (shell) becomes very thick. In the warmth, the heating pad needs to cool down: it expands throughout the entire body, and the blanket thins out to the maximum.
Class and exam questions
Where in the body is the reference core temperature recorded?
As a standard for the average core temperature, the temperature of the blood in the right ventricle of the heart is used, which is normally 37.5 °C.
Why does the temperature difference between the torso and the foot change in warmth and cold?
Changes in isotherms are caused by vascular reactions. In the cold, vasoconstriction occurs to preserve heat (21 °C gradient), while in the warmth, vasodilation occurs to transport heat to the surface (13 °C gradient).
What are the normal temperature ranges in the axillary and rectal regions?
Axillary temperature is normally 36.6–36.8 °C, while rectal (as well as oral) is slightly higher — 36.8–37.2 °C.
What is a multiparametric result in thermoregulation?
This means that the final result of the thermoregulation system's work is composed of multiple different temperature indicators at various points of the body, since each organ requires its own optimal temperature for metabolism.
What else to study on this topic
- Mechanisms of heat production centralization and the role of vascular tone
- The relationship between internal organ metabolism and heat production
- Dynamics of the proximal-distal gradient under extreme exposures
- Multiparametric nature of the useful adaptive result (UAR)
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