What has changed in common disease patterns?
In recent decades, much has changed in common disease patterns. Partly due to advances in the development of pharmacy, the patterns now look very different and are no longer comparable with, for example, diseases that our ancestors died from. Nowadays , more and more people suffer from heart failure and cardio-vascular diseases than, for example , from infections and malnutrition. In connection with this change in disease patterns, the picture of how we view diseases has also undergone changes. We have discovered that there is a strong connection between emotions and the biological processes in our body. Our thoughts, feelings and personalities influence these processes in our body , which can cause that two people who get the same disease to go through a totally different course of the disease. Stress also affects our health and can even make us feel sick. However, stress can lead to adaptation of the body to certain situations in order to survive. In this way, the neurons in our brain can survive for five minutes without oxygen during a heart attack , without being permanently damaged .
In addition to differences between people of today and of the past , there are also differences between people and animals. This difference mainly concerns the area of how they experience stress. Animals experience stress only in acute physical crisis situations. Consider the following example: A zebra is hunted by a tiger. The zebra will suddenly have to run , in order to bring itself to safety . The zebra can even be injured by the tiger and still keep on trying to flee. At this point, a lot of things are physically demanded of the zebra. However, their body appears to be perfectly capable of dealing with this type of stress. People, on the other hand, more often experience chronic physical stress instead of acute stress. For example, when a farmer's crops have been eaten by animals, he will have to get his food from somewhere else for a long period of time. For example, he will have to walk much further each time to get some food . Because every time, for a long time, he has to make more effort for his food, he undergoes chronic physical stress. The human body can handle this type of stress reasonably well.
In addition to acute and chronic physical stress, there is a third form of stress, which is psychological and social stress. This type of stress is typical for humans. What stands out is that this type of stress actually only exists in our heads: There is no real physical threat. So, we can experience intense emotions that are in reality just the result of our thoughts . Our bodies can give the same reactions to psychological and social stress as to physical stress. Our bodies can adapt very well to cope with acute stress that lasts for a short time . However , this is different when the stress appears to be chronic and we activate our stress system very often for a long period of time.
The body is not prepared for this kind of activity, because the physiological defense mechanisms were originally intended to enable the body to respond quickly and efficiently to a sudden threat. For a certain period of time, the body will resist the psychological stress, but exhaustion will inevitably follow. This can cause stress-related diseases.
The body is constantly working in order to reach a state of homeostasis. Homeostasis refers to the idea that the body consists of different mechanisms and that each of these mechanisms has an optimal level; a balance. Homeostasis means that the body is fully outbalanced, in other words: all mechanisms have reached their optimum level. For example, during homeostasis; the brain receives just enough oxygen and the blood is pumped through the body at a steady pace. The body is always trying to achieve this state of homeostasis. There are, however, a number of factors that can disrupt the body's homeostasis. We call these factors stressors. Stressors are all the events that take place outside the body that can take us out of the homeostatic balance. The body responds by means of a stress response, through which it will start activities to reach the state of homeostasis again.
However, a stressor does not only have to be an event that is currently taking place. People are able to look ahead and see possible threats in the future. Humans can anticipate this. Resultingly, we can elicit a stress response only by thinking about potential stressors. The stress response is therefore not only triggered by physical or psychological threats, but also already in anticipation of a threat. This was first discovered by Selye, about sixty-five years ago. Selye did a study on rats. He injected his rats on a daily basis with an extract from an ovary. But because he was a bit clumsy, the rats often fell and he had to look for them for a long period of time before he could try to inject them again. At the end of the study, it appeared that the rats were suffering from enlarged adrenal glands and stomach ulcers. To exclude that these symptoms were the result of the injections, Selye used a control group that he injected with saline. These rats also regularly fell to the ground and were hunted by Selye in an attempt to get a hold of them. The control group appeared to show the very same symptoms as the experimental group, which led Selye to conclude that these physical symptoms were caused by the stress that arose when he followed the fallen rats.
Selye came to two conclusions:
The body uses the same responses for multiple different stressors. Selye called this the general adaptation syndrome, and nowadays this phenomenon is called the stress response.
Stressors that persist for too long can lead to illness.
What is allostase?
The original concept of homeostasis was based on two ideas:
There is one optimum level or optimum amount for all measurable things in the body, such as the ideal blood pressure, temperature, etc.
You achieve this optimum level or this optimum amount through a local regulatory mechanism.
However, this concept was proved to be incorrect and has therefore been extended with the theory of allostase. With regard to the first idea, this means that there are different optimal levels, depending on what you are doing. The optimum value for heart rate is much lower when you are sleeping than when you are training for the marathon. So there is not one optimum level, but multiple different optimum levels. Considering the second idea, this means that there is not one way in which the ideal level can be achieved, but this can be done in multiple different ways. Every way will have its own outcome. Roughly speaking, the difference between homeostasis and allostase is that in the case of a deficiency, homeostasis only addresses the responsible mechanism but allostase causes the brain to direct changes in the entire body, and often in behavior too. An example : suppose your body lacks water . With homeostasis, only the kidneys would be directed to produce less urine . Allostase does this as well, but it also extracts water from other body parts and causes you to get thirsty.
The body does not have to stop all complex regulatory processes to restore a certain value. Moreover, the body is able to anticipate values that will deviate from their optimum level. The brain can therefore control certain bodily functions in advance, which will ensure that a certain value will not lose its optimum level. This corresponds to the fact that the body can respond to a stressor before it actually occurs.
How to adapt to an acute stressor?
In this adapted theory, a stressor is seen as all factors that could possibly get you out of your allostatic balance. The stress response concerns your body's attempts to restore allostasis. Although it is logical to think that specific challenges for the body require specific adjustments, every stressor yields the same stress response.
In people, the key point of the stress response lies in the fact that the muscles in the body have to work much harder than normal. Firstly, glucose must be mobilized, which provides energy. The glucose is then rapidly transported through the body by increasing its heart rate, blood pressure and speed of breathing. The sympathetic system is activated, while other processes in the body are ceased . Examples of this are digestion, growth and reproduction.
The immune system will also be suppressed temporarily . The energy that is saved by this will be used to make the sympathetic system work harder. The parasympathetic system is temporarily switched off. Remember the story about the zebra running from the tiger: The perception of pain can also be switched off during acute stress. Another example, think of a soldier who does not realize that he was injured during the time that the fight is still going on. Only once the battle is over, the perception of pain returns.
During acute stress there is also a change in cognitive and sensory skills. Certain parts of the memory improve, so you can quickly remember whether you have been in a similar situation before and how you can get out of it. Moreover, your senses become sharper. During an acute stress situation you can be startled by the squeaking of a door, while normally, you would barely notice this .
Selye designed a three-phase theory about stress responses. The first phase is the alarm phase, in which the stressor is noticed. This can be compared to an alarm that goes off in your head and at that point you can tell that something is wrong. The second phase is the phase of adaptation or resistance, in which the stress response system is mobilized and the body attempts to return to its allostatic balance. With persistent stress, the third phase of exhaustion can start . However, Selye made the mistake of thinking that you became ill because the hormones that are secreted during the stress response ran out . However, this cannot be the case, because these hormones are so crucial that we can't possibly ever run out of it. The stress response can have a harmful effect on the body if it is activated sufficiently. The stress response is especially harmful if the stressor is psychological. The consequences can be enormous , especially in the case of long-term (psychological) stress or when you suffer from stress very often. Because you spend your energy in response to stress so often, the body does not have time to recover and rebuild its reserves . Because you do not build up your reserves, your body will be exhausted faster. People who are under chronic stress also often suffer from reproductive disorders. You are also more likely to suffer from diabetes and high blood pressure, because the cardiovascular system is activated chronically . In addition , the immune system is often suppressed, making you more susceptible to infectious diseases. You will also have more trouble eliminating these diseases from your body . Finally, certain brain functions can also be affected if a certain hormone that is secreted during stress is produced excessively. When you have a lot of stress and therefore often excrete stress hormones, it will always be harder to find the balance of allostase. The following problems may arise:
It takes a lot of energy to keep on trying to find this balance. This energy can no longer be used for processes that take place in the long term, such as storing energy.
The use of stress hormones helps to relieve the stressor, but it often gets small processes in the body out of balance. Thus, a complete allostase is still not achieved.
Illness can also occur when the stress response is turned off too slowly , or when different components are turned off at different times . For example, the values of one stress hormone may return to normal, while the values of another hormone are still very high.
Having a stress response is important, which has become evident from the studies of people who do not have the stress response due to an illness. Two important hormones are secreted during stress. In Addison's disease and 'Shy-carrier syndrome' people are unable to secrete certain hormones, which results in the fact that no stress response is triggered. When people with Addison's disease are confronted with a trauma , they go into a so-called 'Adissonian' crisis, which means that blood pressure falls and they fall into shock.
Shy carrier syndrome is a disease in which the blood pressure drops sharply when the patient stands up . The amount of sweat, tear fluid and saliva diminishes, vision is poor, urination is difficult and often, there is impotence.
If you repeatedly activate your stress response or if you have difficulty turning off the stress response again when the stressful situation is over, it is possible that the stress response may ultimately be harmful to your body . However , it is not the stress or the stressor that makes you sick. Chronic stressors or recurring stressors only increase the risk of getting sick. They also increase the chance that defense mechanisms cannot win the fight against a disease. There are different steps between getting a disease and actually getting sick. This also causes individual differences.
Practice questions
1. What is allostase?
2. Which of the following is no function of the biological 'fight or flight' stress response?
A) Limiting damage
B) Transporting oxygen to the muscles
C) Causing negative emotions
D) Saving energy by suppressing unnecessary bodily activities
3. During the stress response the sympathetic nervous system is active / deactivated and the parasympathetic nervous system is active / deactivated.
Answers to the practice questions:
1. Allostase is a balanced state of the body. Attaining the state of allostase in the body happens through the secretion of stress hormones and mediators by the brain.
2. C
3. Active, deactivated
Thoughts can end up affecting your entire body. The thought of something frightening can cause you to start sweating, even though in reality there is nothing wrong. What happens in your body is controlled by the brain.
What is the connection between stress and the nervous system?
Your brain controls the rest of your body by sending signals to the nerves that run down from the brain through the spinal cord. This can happen deliberately when, for example, you control your muscles to walk home. These actions are driven by the voluntary nervous system . But actions can also happen unconsciously. When you get cold, you often get goosebumps without consciously controlling your body to get these goosebumps. These signals are therefore automatic and are involuntary. For example, when you blush, you often do not want this at all, but you cannot help it.
The set of nerves that control this kind of automatic, involuntary processes is called the autonomic nervous system . This system is very important for the stress response . Half of this autonomic nervous system is activated during a stress response, the other half is suppressed . The half that is activated is called the sympathetic nervous system . Half that is suppressed is called the parasympathetic nervous system . Both systems start in the brain and go through the spinal cord to practically all places in your body, such as organs, blood fibers and sweat glands.
The sympathetic nervous system is activated in the case of an emergency, or when you suspect that there is an emergency. You could also say that it is activated in case of flight, fighting, fear and sex.
The sympathetic nerve cells secrete epinephrine (adrenaline) and norepinephrine (noradrenaline). Epinephrine is excreted by the glands that are just above the kidneys (the adrenal glands) . Norepinephrine is excreted by all other sympathetic nerve endings.
The parasympathetic nervous system controls the quiet, time-consuming activities in the body such as energy storage and growth. The sympathetic and the parasympathetic nervous system are therefore opposite to each other and cannot work simultaneously on the same process in the body .
How does the brain work during a stress response?
The brain controls the stress response through the nerves in the sympathetic nervous system. Yet, this is not the only way in which the brain creates a stress response. The brain also secretes hormones.
A neuron (a cell from the nervous system) can secrete a neurotransmitter. A neurotransmitter is a chemical messenger that can travel super fast to another neuron to make it do something different from what it is currently doing. For example, a sympathetic nerve endings can secrete norepinephrine into the heart, causing the heart muscle to work differently.
However, a neuron can also send a messenger that ends up in the blood instead of another neuron and can travel great distances through the body. Such a messenger is a hormone. Some hormones are activated during stress, while others are suppressed.
It used to be thought that the parts of the body that secret the hormones (peripheral glands), such as the pancreas and the testes, knew themselves when and when not to excrete hormones.
For example, they thought that the fact that the sexual urges of men decrease with age is because the testicles excrete less testosterone. The solution to this problem would then be easy: give the men testosterone! The testosterone extracts that were used were taken from animals and injected into the men. However, this did not work. Patients were in fact injected with a water-based extract, and testosterone does not dissolve in water. But if it would have dissolved, it would also not have worked. The fact that the testes excrete less testosterone is not due to the testes, but because another organ (namely the brain) no longer tells them to do that. Scientists also came to this discovery. At first they thought that the pituitary gland controlled these peripheral glands . They only release hormones after the pituitary gland has secreted a hormone, which causes the peripheral glands to take action. When the pituitary gland is damaged, the hormone balance is disrupted.
In the 1950s it was discovered that the pituitary gland was not the 'master gland'. In a study, a pituitary gland had been removed and replaced in a kind of bottle with nutrients. The result was that certain hormones that are normally excreted were not released now, while other hormones were released in very large numbers. For example, it was discovered that the pituitary gland does not work on its own, because if this had been the case, the pituitary gland would have had to release the same amounts of hormones during the study as it normally did. It was found that the pituitary gland follows the orders of the brain. This was investigated by damaging parts of the brain that were close to the pituitary gland, with the result that the pituitary gland became disrupted and started to secrete hormones.
One question remains: how does the brain accomplish this? There are no nerves from the brain to the pituitary gland. In 1944, physiologist Geoffrey Harris came up with the idea that it could be that the brain also releases hormones, which then go to the pituitary gland and regulate the actions of this organ. Some hormones stimulate the secretion of hormones, other hormones suppress the release that hormones . Guillemin and Schally investigated this and discovered after years of research that this is indeed the case.
We now know that the brain is at the head of secreting hormones. This is based on the hypothalamus, which can secrete a large amount of different hormones. The hypothalamus can control the pituitary gland by secreting only one hormone. This hormone has an activating function and an inhibitory function. The hypothalamus can also control the pituitary gland by means of an activating and an inhibiting hormone. We then speak of dual control. Moreover, it is possible that the hypothalamus secretes several different hormones in order to control the pituitary gland.
What is the connection between hormones and stress?
Hormones are very important for stress. The two hormones that are most important in the stress response are the previously discussed epinephrine and norepinephrine ; which are both excreted by the sympathetic nervous system. Glucocorticoids are also very important for the stress response. Glucocorticoids are among the steroid hormones (including: androgen, estrogen, progestin, mineralocorticoids and glucocorticoids). They are excreted by the adrenal glands, which lie just above the kidneys.
The glucocorticoids resemble the effect on epinephrine. But epinephrine already works within a few seconds, while glucocorticoids only work after a few minutes to a few hours. It could be argued that glucocorticoids take over the activities of epinephrine.
The secretion of glucocorticoids is also controlled by the brain. When something happens that is stressful or that the person involves perceives to be stressful, the hypothalamus secretes different hormones into the pituitary gland. This is a circulating system. The most important hormone secreted by the hypothalamus is CRH (corticotropin releasing hormone). Within about fifteen seconds, the CRH stimulates the pituitary gland to secrete the hormone ACTH (corticotropin). ACTH then enters the bloodstream and reaches the adrenal glands. In the adrenal glands, ACTH ensures that glucocorticoids are excreted.
Together with the action of the sympathetic nervous system (in particular the excretion of epinephrine and norepinephrine), the glucocorticoids cause the body's most important reactions to stress.
Your pancreas is also stimulated during stress to excrete the hormone glucagon . Glucagon, glucocorticoids and the sympathetic nervous system ensure that the sugar level (glucose) in the body is increased. This provides more energy. The brain and pituitary gland also secrete endogenous, morphine-like substances, namely endorphins and enkephalin . These hormones ensure, among other things, that you hardly notice any pain. The pituitary gland also secretes an anti-diuretic hormone (vasopressin), which ensures that little urine is excreted for water conservation in the body.
In addition to the activation of certain hormones, there are also hormones that are suppressed during the stress response. This mainly concerns hormones that are related to reproduction, growth and the release of insulin, which normally causes the body to store energy for later use.
What are the possible complications?
So the aim of the stress response is to 'fight or flight'. However, researcher Taylor disputes whether this response is the same for men and women. Research has shown that the fight or flight response actually only occurs in men. Men are often much more aggressive than women. That is why men will fight a lot faster. However, women must also take their children into account, making them often unable to fight or to flee; Since in that case, they would need to leave their children behind. 'Be careful and be a friend' (tend and befriend) is therefore a more common stress response in women. This is, from an evolutionary perspective, much more useful for them than fighting or fleeing.
During stress, the pituitary gland also secretes the hormone oxytocin in women . Among other things, this hormone causes women to stay with one man and to therefore be monogamous. That is why this hormone fits much better with Taylor's theory about being careful and becoming friends. There are opponents who say that women might as well be aggressive and flee, but often women tend to be aggressive only when there is a threat to their children.
Taylor's theory is generally accepted. It is recognized that the body does not only respond to stress by preparing the body for fighting and fleeing. Moreover, it has become common knowledge that there are important sex differences in the physiology and psychology of stress.
Another complication is that some characteristics of the stress response are different for different animals: Take, for example, the difference in time of the effects of epinephrine and glucocorticoids. In humans, epinephrine works within seconds, while glucocorticoids only work after a few hours. For some animal species, however, this is not at all convenient. If you are the zebra that is being hunted, you do not have to sustain the flight response for hours. The effect of the glucocorticoids would therefore occur too late. In this type of animal, glucocorticoids appear to be more responsible for recovery after the stress response. In some cases, glucocorticoids can also act as preparation for the next stressor.
Epinephrine and glucocorticoids can each cause the other to be excreted because they are both excreted by the adrenal gland.
Because of this your stress response is often the same for all stressors. However, it has been found that not all stressors provide the same stress response. The speed and amount of the sympathetic system and the glucocorticoids vary per stressor. Moreover, not all other endocrine components of the stress response are always activated. This differs per stressor as well. Similarly, the secreted hormones and their exact amount differ per stressor. However, two different stressors may result in a secretion of exactly the same amount of the same hormones. In this case the sensitivity for the two stressors differs in different parts of the body. This means that some parts of the body will not respond to one stressor, but will respond to the other.
Practice questions
1. From an evolutionary perspective, what does one try to do in the case of a stress response?
2. True or untrue: The adrenal gland is responsible for excreting adrenalin.
3. What order of events is correct?
A) CRH > ACTH > cortisol
B) ACTH > CRH > cortisol
C) ACTH > cortisol > CRH
D) CRH > cortisol > ACTH
4. Why does the body suppress the production of insulin during a stress response?
Answers to the practice questions
1. Fight or flight.
2. True
3. A
4. In order to conserve energy and fuel needed for the fight or flight response.
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