Endogeny

Endogenous substances and processes are those that originate from within a system such as an organism, tissue, or cell. The term is chiefly used in biology but also in other fields. Endogenous substances and processes are those that originate from within a system such as an organism, tissue, or cell. The term is chiefly used in biology but also in other fields. Endogenous substances and processes contrast with exogenous ones, such as drugs, which originate from outside of the organism. Cell signalling systems such as hormone and neurotransmitter systems use endogenous substances. Endogenous substances can regulate sleep.:1 Examples of endogenous substances, and systems that use them, include Endogenous transcription factors are those manufactured by the cell, as distinguished from cloned transcription factors. Endogenous substances typically have some physiological utility. However substances can also be pathologically endogenous. For example, in auto-brewery syndrome, ethanol is endogenously produced within the digestive system through endogenous fermentation of sugars. Endogeneity can, in some biological systems, particularly with viruses and prokaryotes, pertain to DNA incorporated (endogenized) into the organism. However, because of homeostasis, discerning between internal and external influences is often difficult. Endogenous viral elements, which are DNA sequences derived from viruses that are ancestrally inserted into the genomes of germ cells. These sequences, which may be fragments of viruses or entire viral genomes (proviruses), can persist in the germline, being passed on from one generation to the next as host alleles. Endogenous retroviruses are a type of endogenous viral element. Endogenous effects can modulate and regulate systems, in conjunction with environmental influences.:8 Endogeny can refer to changes that originate from within a system.:8 Endogenous changes can occur in social systems and can be modelled by Marxian dialectics.:8 Orthogenesis is a similar concept to endogeny but refers to changes within separate systems that results in their evolution along similar paths.:8 The concept of orthogenesis has never been widely favored in evolutionary biology.:8