Homeostasis, Thermoregulation, and the Hypothalamus: What Really Are Their Connections To Us Being Warm Blooded?

Introduction

There is this beautiful word that has been in use for a while now, by scientists all over the world, describing the way in which the body keeps everything inside it constant. It happens to be the term; HOMEOSTASIS. As brief as this word is, it explains how the body keeps its internal environment as a whole and everything related to it in a fairly constant range. From temperature, amount of water, amount of ions (calcium, sodium, chloride, etc…) and metabolic rate, to sugar level and acid/base ratio, the term just justifies everything.

However, for your pleasurable consumption today, let me bring to the table a branch of what homeostasis stands to explain; Thermoregulation.

Heat and the body (thermoregulation)

In the room you are comfortably seated, in a bid to consume this post, I could guess the temperature is not exactly 37^oc. yes! I guess so, but then, your body finds a way of keeping the temperature inside you in a fairly constant state, irrespective of the degree of change between the environmental temperature and your internal temperature. This is what makes us warm blooded (homeothermic). Our body temperature differs from the environmental temperature and is also fairly constant thus making us homeothermic.

As a matter of fact, our bodies are constantly producing, gaining and losing heat in different ways, some of which we are totally unconscious of and some of which we so much enjoy performing deliberately. Who doesn’t enjoy rubbing their palms and placing them on their cheeks?

How Does The Body Gain Heat?

As a known phenomenon, our bodies undergo what is known as metabolism. This refers to the breaking down of complex particles into simpler smaller ones and also the building up of complex particles from the simple precursors. The processes themselves have their specific names but when referring to the biological reactions of breaking down and building up as a whole in the body, the term metabolism is preferred.

Specifically, catabolism is the name for the breaking down process while anabolism is used to refer to the building up. This process of metabolism is one of the major ways through which heat is gained by the body. Metabolism of foodstuffs(referring here to catabolism); fats, carbohydrates and proteins brings about an enormous amount of heat with fats providing the highest amount of heat upon complete breakdown, carbohydrates joining the queue and proteins showing up after them all. Well, the bottom line is, food generally when completely digested and oxidized provides the body with a good amount of heat and becomes one of the body’s wonderful sources of heat.

Heat is also constantly produced by our muscles both when at rest and when carrying out an activity. During activity in muscles, heat is evolved from the mechanical contractions of the muscles probably from friction and the pulling forces involved. Also, since a biomolecule known as Adenosine Triphosphate(ATP), which is a heavy molecular compound is involved in muscular contraction reactions, the hydrolysis of ATP to form Adenosine Triphosphate (ADP) generally is accompanied by the giving off of an exothermic heat of reaction. So, hydrolysis or breakdown of ATP during muscular contractions also offers the body another avenue for heat gain.

When muscles are at rest, they do not completely seize in activity, they continuously carryout small amounts of contractions that keep them not completely collapsed but in a state where they can be up and kicking. This continuous contraction that keeps the muscles active is known as muscle tone. Tonicity is the ability of the muscles to stay non-collapsed. This whole muscle tone/tonicity stuff provides heat for the body to enjoy too.

Apart from heat grained from its production by the body itself, heat is gained directly from the surrounding through radiation and conduction. In a hot room for instance, you automatically pick up the temperature in the room with your skin through radiation. Of course, this heat is transferred from your skin to your blood, and before you can even know what is happening your blood has broadcasted the heat to the whole body and the body now, has gained the heat. This now adds to the overall heat composition of the body at the time.

Conduction seems to come into play when your skin comes in contact with any surface with a temperature higher than the body’s; heat is immediately transferred from the object to you. Actually, cuddling someone in the middle of a cold night is the only fantastic scenario my mind could offer me right now. I am sure you really don’t want to learn about the other scenarios. It absolutely is not magic that you feel warmer when you cuddle. During cuddling, your skin comes in contact with a warmer skin, heat is transferred, and then spread across the whole body by blood and yeah! Nothing really feels as good as this stuff.

From continuous observations, it is noticed that nothing can actually successfully be complete in the body without the involvement of either the nervous system or the endocrine system or both systems at once. This is one reason why it is not odd to see the involvement of two major hormones in heat production; thyroxin and adrenaline.

Presence of the hormone thyroxin always has one particular meaning which of course is, increase in rate of metabolism in every part of the body except in the brain, lungs, testes, spleen and retina. This causes the increased metabolism rate by increasing the amount of oxygen consumed by the body tissues and also increasing the overall use of foodstuffs and nutrients by the cells of the body. Adrenaline too has an effect in body heat production by increasing the body metabolism rate.

How Does The Body Lose Heat?

Every car has a steering that can either turn the tires left or right. I feel so happy saying at this point that this car, the post, has successfully been steered to the left. How about we do a little steering to the right?

Of course, this means we get a chance to look at how the body loses heat. Well, there are basically four ways in which the body loses heat and all of the heat loss mechanisms involve losing it to its environment, unlike in the heat gain mechanism where heat is also gained from within.

When you introduce yourself into a cold room, it is often noticed that the cool nature of the room at first does not just on the point make you feel cold, it takes a while. While in the course of your stay in the room, your body constantly loses heat to the environment by radiation and this eventually makes you feel like your body temperature has dropped and you feel cold. This is the body losing heat through radiation.

Heat is also lost through conduction. This shows up when the body, the skin, comes in contact with a cold surface, the body loses heat to the cold surface and thus there is a drop in its overall temperature. If you have never laid down on a bare tile floor, you probably shouldn’t be anywhere near this part of the post. You may not know how good it feels for your body to lose heat in this manner. Well, I still owe you an explanation though. When you lay on the floor and your skin comes in contact with the floor which is a good conductor of heat, heat is lost by the body to the floor and this decreases the overall temperature of the body.

Convection too is a means of heat loss and fans are major conveyors of this style. You get blown by a fan and your sorrows in form of heat are blown away, how do you think that happens? Convection is when a medium, in this case air is involved in the transfer of heat from one point to the other. Unlike radiation where heat just jumps from one place to another, convection requires something that carries the heat from the releasing medium and moves to the receiving medium. The drop in temperature when blown by a fan is because the air from the fan carries heat from the body away to wherever the fan pleases.

The most useful mechanism and probably the first resort to the body when it notices an increase in temperature tends to be evaporation. During evaporation of water from the skin, heat is carried along and this apparently reduces the heat content of the skin from which the water had been evaporated from. Sweating uses this mechanism by offering the skin more and more amount of water for evaporation and cooling.

What Business Does The Hypothalamus Have With This?

Somewhere seated on everyone’s head is a part of the brain known as the hypothalamus. This part of the brain is involved in homeostasis as a whole (water balance, ionic balance, temperature, etc…). It also controls sleep, thirst, emotions, hunger and many other functions of the body. So when next hunger descends on you like a wounded lion, you know exactly what to do; a knock on the head might help.

Somehow, this part has something really large to do with temperature regulation too. This is so because the two sites for the regulation of temperature as to when high or low are both located on it. The hypothalamus has two distinct heat control portions located on it; a heat gain center and a heat loss center.

Heat loss center is located on the preoptic nucleus of the anterior hypothalamus and is brought into action when the body has a need to send off heat while the heat gain center is located on the posterior hypothalamic nucleus and is brought into action when the overall body temperature drops and there is need for the body to gain or produce heat.

When the body experiences an increase in temperature which obviously denotes a rise in the amount of heat circulating in the body at the time, the blood which is the main medium of transfer between organs in the body becomes hotter than normal. This hot blood eventually gets to the brain and passes through the hypothalamus. The preoptic nucleus of the hypothalamus which is endowed with enormous thermoreceptors senses the heat in the blood and starts a cascade of events to help decrease the temperature.

First, it stimulates sweat glands to produce sweat. This way, the sweat produced gets to the surface of the skin, evaporates and causes a cooling effect on the body as a whole. It also sends inhibitory signals to the sympathetic centers of the brain, also in the hypothalamus. This part of the brain controls cutaneous vasoconstriction (decrease in blood flow to the skin) and this inhibitory signal makes that part to stop functioning, allowing for cutaneous vasodilation (increase in blood flow to the skin). This increased blood flow to the skin is in a bid to increase the amount of blood carrying heat to the external environment and freeing the body of its troubles.

On the other hand, when there is a drop in temperature of the body, the preoptic nucleus is not activated and thus the part of the brain controlling cutaneous vasodilation is not inhibited. This decreases the amount of blood supplied to the skin which furthermore leads to a decrease in the amount of heat sent off to the surroundings. The posterior hypothalamus also houses a center that controls shivering. This center is activated by the heat gain center when the temperature is low and causes muscle contractions which are called shivering. Shivering produces a large amount of heat due to increased muscular activities and hydrolysis of ATP.

This same heat gain center of the hypothalamus causes the release of adrenaline and noradrenaline which causes an increase in the body’s metabolism rate. The hypothalamus itself secretes a hormone which finally leads to the secretion of the thyroid hormone from the thyroid gland. This hormone acts particularly to also increase metabolic rates in the body.

Summary

The hypothalamus plays a very vital role in keeping any man alive and awake or asleep. In terms of everything that needs to be maintained in the body, the function of the hypothalamus cannot be overemphasized. Its ability to sense when the environment is either giving too much heat to us or taking too much heat from us to help cause a thermometric change to keep our temperature fairly constant is one of the reasons why we are still warm blooded. The hypothalamus is thus the only thing standing between man, and cold bloodedness.

References

_{Guyton, A. C., & Hall, J. E. 1. (2006). Textbook of medical physiology (11th ed.). Philadelphia : New Delhi: Elsevier Saunders.
Sembulingam K., Sembulingam M.. Cardiac output, in Essentials of Medical physiology, ed 5. New Delhi; Jaypee Brothers Medical Publishers (p) ltd, 2010, p 553.
Warm and cold blooded animals
Thermoregulation in humans
Homeostasis}

Image sources

All images are from Max Pixel and wikicommons licensed under creative commons and eligible for commercial use.

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