In biology, most biochemical processes strive to maintain equilibrium (homeostasis), a steady state that exists more as an ideal and less as an achievable condition. Environmental factors, internal or external stimuli, continually disrupt homeostasis; an organisms present condition is a state of constant flux moving about a homeostatic point that is that organisms optimal condition for living. Factors causing an organisms condition to diverge too far from homeostasis can be experienced as stress. A life-threatening situation such as a major physical trauma or prolonged starvation can greatly disrupt homeostasis. On the other hand, an organisms attempt at restoring conditions back to or near homeostasis, often consuming energy and natural resources, can also be interpreted as stress.The ambiguity in defining this phenomenon was first recognized by Hans Selye (1907–1982) in 1926. In 1951 a commentator loosely summarized Selyes view of stress as something that "...in addition to being itself, was also the cause of itself, and the result of itself".First to use the term in a biological context, Selye continued to define stress as "the non-specific response of the body to any demand placed upon it". Neuroscientists such as Bruce McEwen and Jaap Koolhaas believe that stress, based on years of empirical research, "should be restricted to conditions where an environmental demand exceeds the natural regulatory capacity of an organism".
Combined immunodeficiencies (or combined immunity deficiency) are immunodeficiency disorders that involve multiple components of the immune system, including both humoral immunity and cell-mediated immunity. This category includes conditions such as bare lymphocyte syndrome, as well as severe combined immunodeficiency. Combined immunodeficiencies are commonly distinguished from SCID by low but not absent T-cell function.ICD-9 divides immune deficiencies into three categories: humoral (279.0), cell-mediated (279.1), and combined (279.2). However, ICD-10 does not include a category for cell-mediated immune dysfunction (antibody is D80, and combined is D81), thus grouping T-cell mediated conditions with combined conditions. References


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