Temperature control is very important in living things. In this article I will talk about temperature and the mechanisms we can carry out to regulate body temperature. Last week there have been unique temperature events, such as the Valley of Death that have reached the temperature of 54.4º.
Types of body temperature control
Not all animals have equal temperature control. You can create a classification like the following depending on how they perform that control:
- Homeotherms. They are warm-blooded animals, they maintain their body temperature regardless of the ambient temperature. Mammals and birds would fall under this definition.
- Poiquilotermos. They have poor control of their body temperature. Changes in the environment follow, it depends on the environment.
Body temperature control is not identical in all organisms. In homeotherms two types of temperature are distinguished:
- Central temperature, always constant, around 37 °C in humans. The parts of the body with this temperature would be the head, chest and abdominal cavity.
- Surface temperature, skin and muscle. Temperature variations can be important. It’s more variable.
The mechanisms of heat genesis (generation) occur in the central compartment. Losses occur in the surface compartment. Body temperature is going to be a weighted sum of the 2 factors.
The body temperature controller
En el control de la temperatura vamos a tener un centro termorregulador que es el hipotálamo. Llegan aferencias cutáneas que informan cual es la temperatura de la piel. Al hipotálamo llega información del compartimento central, en función de esta información el hipotálamo regula la termogénesis (generación de calor) y la termolisis (el calor corporal es eliminado).
To remove heat the body can perform several actions:
- Heat conduction. The organism comes into direct contact with another body with a lower temperature. The skin conducts quite bad heat which is a way to help maintain our internal temperature.
- radiation. The body emits characteristic wavelength radiation that falls into infrared rays. We can also capture energy from the environment lying in the sun.
- convection. It occurs whenever the body is in contact with a fluid. When these are heated they establish convective currents.
- Evaporation of water or sweating. It is very effective and is always used for thermolysis. When fluids change state they capture a large amount of heat. Up to a liter of water can be lost from sweating.
- Another thermolithic mechanism is for heating air/water. The air that enters is at 25 ºC and the air that comes out at 37 ºC. We also heat large amounts of water.
- We can also lose heat from feces and urine (at 37 °C). In addition, food is not always ingested at 37 °C.
Thermogenesis are mechanisms of heat generation. Among them we find:
- radiation. We receive infrared radiation from the sun.
- conduction. Temperature of the electric blanket, for example.
- Ingestion of hot food supplies heat to the body.
- basal metabolism. The cells produce a lot of heat. The metabolic efficiency of cells does not exceed 20%. The potential energy only 20% is used in work, the rest is removed as heat.
- Muscle tone. If heat is needed, it increases muscle tone. If we are cold we start to pull, involuntary contraction, very high energy use, chills are caused, etc..
- Neuroendocrine mechanism. It modifies basal metabolism and muscle tone. The hormone triiodothyronine (T3) and catecholamine hormones are used. They modify mitochondrial metabolism, couple or decoupl certain enzymes. Cells use energy to produce heat. One of the stimuli of these hormones is the drop in temperature. Catecholamines cooperate with thyroid hormones. Brown fat is located in the lungs, heart, is used exclusively in the production of heat, regulated by catecholamines. Within the body there is heat transfer between the different organs.
Heat conduction internally
Heat is generated in the central compartment and removed in the surface compartment. From the central compartment to the surface compartment is heat is moved by:
- Blood. The blood collects the heat in the abdominal cavity and distributes it through the limbs. The circulatory system carries heat.
- By conduction between the different organs, they can be heated or cooled. The hand can be used to transmit heat that is anti-inflammatory to other areas of the body.
- Countercurrent affects the circulatory system. In one arm, arteries and veins go their separate ways. The most important is the brachial arterial, the artery of the arm. By the distribution of the vessels, which carry the opposite direction, the blood has a temperature of 37 °C while the blood of the hand is about 20 °C. By the path through the arm in man there is heat transfer from arteries to veins in such a way that the greater the gradient is greater heat transfer. This mechanism facilitates the forming of a temperature gradient from the central compartment to the surface compartment.
In addition, there are thermal responses that will allow the body to cool or warm up. The most important thermal responses are:
- Cutaneous motility vessel (arteriovenous anastomosis).
- Neuroendocrine activity.
At the level of the skin there is a fairly thick capillary plexus. Deeper there are arteriovenous anastomosis, small vessels that connect the arterial circuíto with the venous circuíto.
We can avoid cooling if we prevent them from passing near the skin, which is the area where heat is lost in such a way that according to the needs of the organism can occur entry and exit to the subcutaneous circle. This glass motility mechanism is the main mechanism for adjusting heat losses.
Body temperature drop
When a drop in temperature occurs our body has mechanisms to counteract that drop. The general action is called hypothermia. It is a body temperature of less than 35 °C. It occurs when the ambient temperature is very low and we are poorly sheltered and there are also air currents and heat dissipation in considerable ways. A wind of 20 ºC is as if we had an ambient temperature of 4 ºC. The wind complicates the situation.
If we are in contact with water, the body loses large amounts of heat by conduction. Snow is low heat conductive. Heat losses are minimized.
Thermogenic failure can occur. It does not occur in normal people but in the elderly, or children. The elderly have less muscle activity, worse overall temperature control, less fat and deficiencies in the hypothalamus. In children the mass-surface ratio is reduced with size. The ratio of surface area to volume is greater the smaller the radius. A pigeon has a higher volume surface ratio than we do. In children it also occurs and they have worse thermal control. There may also be hypothalamic lesions. Therefore, the thermal control is poor.
Responses to the cold
They’re pretty consistent. The most common are:
- Cutaneous vasoconstriction (can increase the level of isolation up to 6 times), narrowing of blood vessels.
- Piloererección is important because it generates a layer under the hair that isolates the individual from the outside. Air is a bad conductor of heat.
- Increase in the production of metabolic heat, due to the secretion of thyroid hormones and catecholamines.
- Increase in muscle activity, i.e. tiritone. It is possible to produce heat. This tiritone increases the core temperature to 0.5 °C.
- Increased respiratory, cardio-vascular activity.
- Protective behaviors that are involved in reducing body surface area, we can reduce body surface area to less than half. In conditions of extreme cold the head is where more heat is lost (even more than half of the heat) and possibly in man the only place where hair is maintained is in areas where there are heat losses.
Continued exposure to cold leads to acclimatization to the cold. Man has colonized climates as aggressive as polar areas and deserts. It involves an increase in metabolic rate at the expense of an increase in thyroid production.
Phases of hypothermia
Hypothermia occurs in three phases:
- Phase of struggle or adaptation, the individual has feeling of internal cold and pain in the extremities. Responses to cold are manifested. There is tachycardia (increased heart rate), tachypnea (accelerated breathing), increased blood pressure, etc.. The body shrinks.
- Implementation phase. Depression of functions, decrease in cardiac output. Sensory enlotment and you enter a period of apathy. Muscles become stiff and non-functional.
- If this is not restored it is passed to a phase of poiquilotermia. The core temperature varies with the atmospheric one, which can lead to unconsciousness.
Types of temperature drops
In this case there are large temperature drops and they affect the surface compartment, especially the extremities. Maybe:
The most important is the freezing that affects the aerial parts, protruding parts of the corportal structure, the extremities. They are further away from the central compartment, losing heat more easily. The effect of freezing is due to different processes, the water of the cells crystallizes and prevents the transfer of information and normal operation. Crystals facilitate the denaturation of proteins and organelles of the cytoplasm.
Rupture coupled with vasoconstriction produces ischemia in the distal parts (lack of blood supply, associated with anoxia). An ischemia is infarctions, deaths of cells due to lack of blood supply. It will also facilitate the aggregation of lymphocytes which is an embolism, foreign particles inside a vessel or contents. The problem appears when embolisms clog small vessels producing ischemia. This occurs especially in arteriosclerosis.
Frostbite trigger the inflammatory reaction. According to the severity of the freeze they are classified into three groups:
- First degree: Redness and pain, symptoms of inflammatory reaction.
- Second degree: Blisters from subcutaneous edemas.
- Third degree: Member gangrene. They include severe ischemic processes. Gangrene usually includes infections by certain gas-producing pathogens. Clostridium are anaerobic and attack areas that do not receive enough oxygen.
There are also freezes like trench foot. It occurs because the foot cools in a humid and unhygienic environment, produces ischemia in the feet and the humid environment facilitates infection and infected yagas are formed, but without pain.
There is also the appearance of chilblains. Lesions with a bluish-red appearance and itching are due to small varicose veins in the superficial veins.
The cold starts pathophysiological processes are not frequent but they are not due to the drop in temperature. Redness effect, Raynoud phenomenon, if we put the hand in cold water and a progressive vascular process occurs, vasoconstriction and vasodilation after, white, blue and red hand edemas occur.
Temperature increase in body temperature
When there is an increase in heat we have three fundamental mechanisms:
- Skin vasodilation.
- Conduct, take off your clothes.
In addition, people who live in warm climates, suffer acclimatization processes that are optimizations of individuals. It is based on lowering the temperature threshold to produce sweating. They are refrigerated before. It also increases sweating, it has a risk which is dehydration.
Ambient humidity can be an adjuvant factor to heat. The air is saturated at a certain temperature. The lower that temperature, the sooner the air becomes saturated. The best mechanisms to remove heat is sweating that depends on ambient humidity. The sweating ability is greatly reduced.
Heat can have a direct general action called heat stroke which is due to the inability of the body to cool to certain temperatures. It happens to marathon runners. The temperature was not very high but the atmosphere completely saturated and could not be properly cooled. Also inappropriate discharges in a humid and warm atmosphere. It affects athletes, welders and soldiers.
Mechanism of action
It is due to the inability to cool and if the temperature greater than 41 °C the proteins are denatured. When an egg is fried there is a change in appearance, the proteins are functional, they stop performing their function.
There is an increase in metabolism as well as increased heat production. Metabolism is the main generator of heat. You get into a vicious circle and that makes the situation worse. This will affect the organs that make up the body, the most sensitive are the central nervous system, muscle, liver, pancreas and kidney.
In addition another alteration is that by effect of heat this releases large amounts of coagulation proteins. Under normal conditions the blood does not coagulate since the anticoagulant factors if the balance is broken there are disseminated intravascular coagulations, in such a way that in any situation the coagulation that produces the disseminated vascular intravascular coagulation occurs. It produces generalized embolisms and will affect the function of the organs. One situation that occurs is in certain children suffering from meningitis. It can lead to death in a very short time.
Manifestations of heat stroke
There are 2 phases:
- Adaptation phase. The individual feels embarrassment, reddened, and very hot skin, profuse sweating, tachycardia and dehydration may appear. It results in muscle cramps and exhaustion.
- Phase of organic suffering. If this phase of adaptation is overcome, the phase of organic suffering by denaturation of proteins is reached. They are characterized by hypotension, apathy, renal liver failure, C.I.D. coagulation, coma, death, headache, asthenia, lack of appetite, sensory bottling.
Indirect heat actions in body temperature
The most common is syncope due to heat. It is produced by a physiological conflict between 2 different stimuli. It happens in people who are standing. Heat produces vasodilation. The bipedal position involves vasoconstriction of the arteries of the upper mids.
Sometimes vasodilation predominates, displacement of the volume of fluid to the legs, blood pressure drops, the individual becomes dizzy.
There is also exhaustion. They are due to electrolyte disorders. Sweat is composed of water and is salty. Due to this salt loss disorders occur in the membrane potentials in the cells. Vasodilation on the descent instead of recovering the volume with salty liquid since the water needs water and salts. If they drink water, they suffer from cramps and exhaustion due to lack of electrolytes.