In immunology two types of immune response are described depending on whether there is prior contact with the antigen.
• At this first contact, only lymphocytes with receptors specific to the antigen in question are stimulated and lead to the production of antibodies capable of neutralizing it. The lymphocytes capable of recognizing a specific antigen are very few and the production of antibodies - of low intensity and limited duration - is detectable only after a period of latency of several days. This is called the primary response. The specificity of the resulting seropositivity, however, makes it possible to detect contamination (seroconversion).
• Upon re-contact with an antigen that has already triggered a primary response, specific antibody production is found to increase rapidly after a short latency period. The secretion of IgG then reaches levels much higher than those observed during the primary response, while that of IgM is of the same order. This early and intense response, called secondary response, most often results in the destruction of infectious agents before any clinical sign.
• Many centuries before the discovery of microbes, it was noted that people who developed a contagious disease without death were then specifically immunized against the disease, without being protected against others.
• The ability to react appropriately to an already received stimulus supposes the existence of a memory. The immune memory is based on the existence of memory B and T lymphocytes, resulting from the clonal expansion due to the first contact with the antigen. Their lifespan is significantly higher than that of other lymphocytes and their high reactivity gives its rapid and intense character to the secondary response.
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Stimulus is something that causes a psychological response. It can be internal or external. The stimulus is the contact with the hot pan. It is an external stimulus. Sense organs, such as the sensory receptors in the skin are sensitive to external stimulus. The quickly pull of your hand is a reflex action.
The contact causes a nerve impulse that will travel to the spinal cord via the sensory neurons.<span>To respond to the stimulus of the reflex arc, the muscle needs to contract to pull the hand quickly away from the hot pan.</span>
Oxygen cycle The cycling of oxygen between the biotic and abiotic components of the environment (see biogeochemical cycle). ... In the process of respiration oxygen is taken in by living organisms and released into the atmosphere, combined with carbon, in the form of carbon dioxide.
