The evolution of resistance and reactivity

Phylogenesis

Reactivity and resistance of the body is the product of a long evolutionary development. Phylogenetic study of reactivity and resistance is associated with the name of I.I. Mechnikov, who first used the comparative method in pathology, and N.N. Sirotinina (1896-1977), who established the general laws of the resistance and reactivity evolution. In single-cell organisms reactivity is very limited, but the resistance to hypoxia, hypo-and hyperthermia, ionizing radiation and other factors is high. In the simplest and invertebrates reactivity and resistance is carried out at the cellular level and is limited to changes in metabolism: inhibition of metabolism allows them to transfer drying, lowering the temperature, lower oxygen content in the environment, etc.

Immunological reactivity in these organisms is absent; it begins to form in poikilothermal animals and is clearly detected in mammals, in which autoallergy is observed. In animals with a primitive nervous system the main mechanisms of reactivity and resistance are tissue reactions of poison neutralize and secure of additional sources of energy (such as glycolysis in anaerobic conditions, phagocytosis, proliferative processes). As formation in the evolution of the nervous system more opportunities appear to actively respond to stimuli, due to the protective activity of this system. Reactivity of the human as opposed to that of the animal is mediated by social factors, through the second signaling system. Word, a verbal stimulus, through the changing of person’s reactivity can have both therapeutic and pathogenic effects.

Ontogenesis

In the earliest stages of ontogenesis reactivity and resistance is carried out at the molecular level, such as in pathological conditions caused by genetic factors. In the next stage of early ontogenesis reactivity occurs at the cellular level (abnormal development leading to deformities). In the early stages of ontogenesis body is less stable than later to the long-term adverse effects (malnutrition, water fasting, cooling, overheating), and is often more resistant to short-term influences.

So, in early childhood mammals tolerate acute oxygen starvation easier because this period of ontogeny is characterized by low intensity of oxidation processes, less need for oxygen, the presence of phosphofructokinase isoenzymes in cells that are unaffected to acidotic inhibition, as well as the production of fetal hemoglobin. In addition, greater resistance to the agents of a number of infections (scarlet fever, diphtheria, measles, rubella, typhoid fever) is noted due to the presence of passive immunity due to the arrival of antibodies from the mother through the placenta and milk during breastfeeding, as well as the relevant structures perceiving effect of several stimuli are not yet formed. After 6-12 months of postnatal life, susceptibility to infections increases due to the disappearance of maternal antibodies from the child's blood. At the same time, there comes the ability to produce its own antibodies and provide allergic reactions. However, in this period, guards and barriers are insufficiently developed and undifferentiated.

Reduced sensitivity to toxins and neonatal hypoxia often can’t compensate the lack of active protection, so infections in this age group are more severe. All this is due mainly to the fact that the child is born with a nervous system that has not finished the morphological development, is functionally immature. The cerebral cortex is thinner in the new-born, their nerve cells are not fully differentiated. The formation of the cortical centers and myelination of nerve fibers of the brain is not over, pyramidal way and striatum are underdeveloped. Morphological immaturity connects with limited functionality: cortical excitability is low, all life processes occur in the prevalence of the subcortical centers, the cerebral cortex is less sensitive to changes in blood chemistry; pain centers of the thalamus are underdeveloped, pain sensitivity is weak, a high pain threshold remains to the second year. There is no degree of pain indicators (pupil dilation, peripheral vascular spasm), pain has a local character (is not localized) because there is no functional association of the hypothalamic area, the reticular formation of the brain stem, the thalamus and the cerebral cortex (it appears on the 4th week of pregnancy). There is wide irradiation of neural process, as excitatory and inhibitory, and, therefore, there is the tendency to generalized reaction that manifests as in norm and in case of pathology. So, for example, tingling skin causes diffuse tonic reaction of many muscle groups, grasping reflex is often carried out with the participation of both arms and even legs. In case of various diseases (intestinal infections, pneumo-meningococcal disease, diphtheria, influenza, etc.) there is the tendency to the cramp (generalized response); infections occur with symptoms of intoxication, often in the absence of specific local manifestations. There is low lability of the nervous system and, therefore, limited ability to adapt to the environment. And the more young the organism is, the less mature its adaptive capabilities are.

In ontogenesis reactivity of a child gradually becomes more complicated, it becomes more sophisticated and diverse due to the development of the nervous and immune systems, the establishment of the correlative relationship between the endocrine glands, improving of metabolism, enzyme systems and defensive mechanisms against infections and other harmful agents.

Due to the nature of reactivity pathology of childhood is characterized by a particular pattern: the younger the child is, the less severe the specific symptom of the disease and in the foreground is non-specific symptoms, common clinical symptoms predominate over local. Development of the nervous system and the reactivity leads to a complication of the disease manifestation, and to development of the protective mechanisms – the compensatory-adaptive reactions, barrier systems, phagocytosis, the ability to produce antibodies.

There are three changes in the age period of reactivity and resistance in ontogenesis:

a) A reduced reactivity and resistance in early childhood;

b) The period of high reactivity and resistance in adulthood (pathological processes become more pronounced);

c) A period of low reactivity and resistance in old age (due to a decrease in the reactivity of the nervous system, weakening of immune reactions, decreased barrier function; appears with sluggish course of the disease, increased susceptibility to infection, inflammations, etc.).

Date: 2015-01-11; view: 977