Homoios, “similar” in Greek, stasis “place” in that same language. It is the group of processes which collaborate towards a stable medium against an external or environmental stimulus which tries to destabilize it.
The body will try to keep itself within a status of normality when it faces resting and exercising. They are different situations. However, they are placed within a normal rank. If stimulus was to disappear, death becomes the major equilibrium level. Stress comes from the Greek and it means provoking tension. It is, in other words, to provoke a change.
Alostasis: Critical levels of stress which will produce perturbations that might stimulate pathological phenomena. This will produce a weakening of the equilibrium process. A stressing stimulus is a signal which will alert about situations which might jeopardize life or produce some change, pushing the body to adopt two basic responses: fleeing or fighting. Both are linked to a very primitive and instinctive system within our organism. Physiological processes that we might observe within our organism will prepare us for both processes. SNA and suprarenal gland are intermediaries before these responses. They will mediate as a nexus between the external stimulus and internal physiological processes. A response to stress is therefore a stereotyped response. The organism has a previously prepared plan regarding any circumstance. It just requires of the right stimulus to set it up. Stimulus’ perception will much influence the response intensity. And this changes with each individual. Some of the factors which influence.
They are: the individuals’ valuation of the resources prepared to face the problem, the novelty of the stimulus, its foreseeable quality and the individual’s personal characteristics.
Stress equals stimulus.
Response to stress
They are internal physiological changes, wide neuronal endocrinal mechanisms. They are no local but systemic. They are short and long term adjustments. We will analyze two of the mechanisms. One is short and the other long term. In other words they are the adaptation of a stressing stimulus which ensures survival through two responses: fleeing and fighting.
An important concept becomes the inhibition of the processes which are not decisive for survival: digestion, reproduction, growing and inflammation. Whatever is not related with survival is inhibited. These constant stress situations are observed in children that have difficulties with their growth. Stress will build fleeing and fighting adaptation mechanisms. However, if these are excessive they might become prejudicial and might produce pathological damage thus exacerbating preexistent sicknesses.
Afferent ways in response to stress.
Ways through which external stimulus will activate SNA or suprarenal gland and it will produce this response.
A hypothetical case: pre-surgery stress. Three different stimuli: perception, tissue damage and loss of extra-cellular liquid. An incision will take place. Our body will perceive whether submitted to anesthesia or not. There will be a stress at a tissue level (tissue damage) and there will also be a loss of extra cellular liquid, mainly blood (hemorrhage).
Perception: Our organism will suffer from something defined as anxiety. Anxiety will reach a cortex structure (since we are talking of conscious perception we will have to go to the consciousness structure, brain cortex). It will reach the brain area related with emotions, fear. This area is known as limbic system. Affection, fear, anxiety and everything related to affective and emotional links is located there. I listen to someone without seeing him and I know who he is.
Tissue damage: It will reach our central system through the nociceptive ways or pain. Again, when we analyzed the somatic system we reviewed that there was an ascendant way reaching the areas 3, 1, 2 and later area 4 descending in a motor manner. Some of the afferent ways are nociceptive.
Loss of extra cellular liquid: it will have as an afferent way extra cellular volume receptors called baroreceptors. Baro makes reference to pressure but in a practice was it is related to volume. They will be able to perceive volemia changes, extra cellular liquid changes. If they face a hemorrhage they will perceive a volemia diminution. At this level there are no mediators except the nervous ones.
It will pass through the nociceptive fibers and it will use the immune system as mediator. Before pain there exists an immune response and some molecules will function as signal molecules: IL (interleukins): IL-1, IL-6 and TNF (Tumor Necrosis Factor). They will generally be immune response triggers.
Loss of extra cellular liquid: It will be perceived by volemia receptors and its mediators will be affective introceptive tracts.
Let us analyze each one of these axis.
. Hypothalamus Pituitary Adrenal Axis AFH: adrenocorticotrofine freeing hormone. ACTH: adrenocorticotrofine hormone. A: adrenalin. NA: noradrenalin. ME: medium eminence. ANS: autonomous nervous system. S: sympathetic. PVN: Para ventricular nucleus. Hypothalamus: It is a gland located at a central level, within the encephalon. It has poorly defined limits. At a central level there is an area where we know the hypothalamus is located. We know it is there because of injuries that are produced there (we comprehend normal physiology through pathologies). We call hypothalamus this group of nuclei which will control certain hormones. These hormones will trigger hormonal cascades in the whole body which means that the hypothalamus will regulate most of our body functions. It regulates the dream-awake cycle, reproduction rhythms, hunger and satiety; it regulates the gonad (reproduction) axis, states of mind. That is way emotional reasons could lead to amenorrhea: both nucleus are one next to the other, and they influence each other. PVN will also be satiety’s center (CRH will also the satiety’s neuronal transmitter). EM and PVN are two hypothalamus nuclei.
ADH (anti diuretic hormone which will trigger thirst sensation and produce water re-absorption): we can find it within the hypothalamus.
Although the brain constitutes the master of the voluntary, the hypothalamus is regulating, the involuntary, and the primitive master.
Hypofisis: We will hierarchically find it just below the hypothalamus. The hypothalamus will mostly produce hypofisiary hormone liberating factors. Hypofisis usually sends a second hormone, the effectors hormone which will effectively produce the second reaction. Hypothalamus and Hypofisis relate themselves from nervous fibers and a vessel system: the hypothalamus hypofisiary system through which hypothalamus will deposit hormones in those vessels and blood alone will fill the hypofilisis wing. They are two mechanisms: one of them acts through nervous tracts and the other thorough blood tracts, and that is how these hormones are transported.
The hypofisis is also called Pituitary gland.
The suprarenal gland has two portions: one Cx and the other Md.
Cx has three portions. Aldosterone (produces water re-absorption and potassium and hydrogen secretion) is produced by its outermost external layer. It will be liberated due to the angiotensine II stimulus. The second layer will produce cortisol or gluco-corticoids. (a great majority of gluco-corticoids are cortisol). And the internal layer will produce androgens (masculine sexual hormones). In women, the suprarenal Cx is the main source of androgens. In men, these will not have much importance within the suprarenal since most of androgens will be produced in the testicle. We will find catecholamine (A and NA, mainly A) within de medulla. NA will liberate itself in certain particular states.
Analysis of Stress Response
ANS nuclei are within the encephalic trunk. And the hypothalamus will be close to those nuclei. Through neurotransmitters the hypothalamus will stimulate ANS nuclei, triggering the sympathetic system which uses NA as neurotransmitter.
First response to stress –short term stress- will be an acute one. It could be an exam, for example. We all get nervous when we face an exam. Thus there will be an acute response to that stress. Stress will mainly stimulate hypothalamus PVN. The nucleus will liberate a hormone, CRH which will stimulate the EM. This will stimulate the ANS nuclei and through them will start that cascade which activates the sympathetic way that utilizes NA as neurotransmitter. In turn, NA stimulates the suprarenal medulla, thus producing adrenalin liberation. Then we reach a point where we have two catecolamines: A and NA. They will produce a sympathetic response within the organism. This sympathetic response will produce vessel constriction, bronco dilation, stimulation of the five cardiac properties, muscular excitability, midriasis (dilated pupils), muscular, brain and cardiac blood flow rise, diminution of the digestive apparatus blood flow, and of the gonad system. Generally we can speak of a redistribution of the blood flow redirecting it towards activities which might be necessary for survival. Glucemia’s rise will also take place in order to allow an increase of the necessary combustible. This is the sympathetic-adrenal-medullar axis (medulla of the suprarenal grand).
In chronic stress we will receive a response from the suprarenal cortex. In this case, stress is prolonged and a response to this stress continues to take place. Hypothalamus is still stimulated. PVN continues to liberate CRH using blood and not nervous ducts, reaching the hypofisis and stimulating it through cells which will liberate ACTH, this will stimulate the adrenal cortex so it might free cortisol (glucocorticoid). Cortisol will produce a long term response to stress. Generally, it is said that costisol response is mime-sympathetic or simile-sympathetic. This means that it is very similar to the sympathetic one. It will produce these same responses. The main ones are: vessel constriction and glucemia´s rise. Glococorticoids, however, will be complex hormones which will produce contradictory responses. It is the typical case of “dose makes poison”. In low doses, glucocorticoids stimulate protein synthesis and muscle mass formation. In supra-physiological conditions (high pharmacologic) will produce muscular proteolysis, or protein destruction, muscular mass destruction. In normal doses they also produce a glucemia rise and in high doses is able to produce hypo-glucemia conditions. High dosed Glucocorticoids might produce growth delays. It has oldstrong effects on the immune depression. Glucocorticoids are a very important and widely used drug but it is also a double edged weapon and might be very dangerous too.
Here, however, we are speaking of very low physiological doses triggered by the organism. In turn, cortisol will show this negative feedback through retro alimentation (sending an inhibitory response towards hypofisis in order to inhibit ACTH liberation and also send a response to the hypothalamus to impede CRH liberation). At this level homeostasis, equilibrium, concept appears. If it is small, stimulation provokes its secretion; if it is abundant it is inhibited to avoid any excess. This retro alimentation process repeats itself many times at many levels. An acute response to stress usually does not produce any pathology. A chronic response might do so. In normal chronic responses we see that a cortisol rise provokes a diminution of the CRH and ACTH levels due to this negative feedback. Pathological conditions provoke a failure of the negative feedback system, thus simultaneously provoking high cortisol, ACTH and CRH levels. It means that this mechanism it is not able to stop, the duct is exacerbated, and this we call hyper reactivity of the HPA axis.
First response to stress –short term stress- will be an acute one. It could be an exam, for example. We all get nervous when we face an exam. Thus there will be an acute response to that stress. Stress will mainly stimulate hypothalamus PVN. The nucleus will liberate a hormone, CRH which will stimulate the EM. This will stimulate the ANS nuclei and through them will start that cascade which activates the sympathetic way that utilizes NA as neurotransmitter. In turn, NA stimulates the suprarenal medulla, thus producing adrenalin liberation. Then we reach a point where we have two catecolamines: A and NA. They will produce a sympathetic response within the organism. This sympathetic response will produce vessel constriction, bronco dilation, stimulation of the five cardiac properties, muscular excitability, midriasis (dilated pupils), muscular, brain and cardiac blood flow rise, diminution of the digestive apparatus blood flow, and of the gonad system. Generally we can speak of a redistribution of the blood flow redirecting it towards activities which might be necessary for survival. Glucemia’s rise will also take place in order to allow an increase of the necessary combustible. This is the sympathetic-adrenal-medullar axis (medulla of the suprarenal grand).
