A biogenic amine and hormone belonging to catecholamines that also functions as a neurotransmitter. It is secreted by the adrenal medulla and by neurons of the sympathetic nervous system into the bloodstream in response to anxiety, fear and stress, and thus is the most potent stimulant of the sympathetic nervous system. When secreted, it leads …
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Epiphysis
The portion of a long bone formed during secondary ossification, and initially separated from the diaphyses by cartilage. They ossify separately and eventually fuse with the diaphysis (see figure below). Epiphysis and related parts of a long bone (viz., humerus). See Adolescent growth spurt, Chrondrification, Diaphysis, Endochondral ossification, Joint capsule, Musculoskeletal system, Ossification
Epilepsy
A chronic disorder, found in cerebral palsy, that is characterized by paroxysmal brain dysfunction due to excessive neuronal discharge, and usually associated with some alteration of consciousness. The clinical manifestations of the attack may vary from complex abnormalities of behavior including generalized or focal convulsions to momentary spells of impaired consciousness. These clinical states have …
Epimere
The dorsal mesoderm portion of a somite, forming skeletal muscles innervated by the dorsal rami (branches). See Dermomyotome, Hypomere, Mesoderm, Myotome, Somites, Striated (or striped or voluntary) muscle
Epiglottis
Cartilaginous, flap-like structure that prevents the entry of food into the larynx (see figure below). In the human newborn, the entrance to the larynx is above the level of the tongue, which means it is possible to drink and breath at the same time. Within the next six months, the epiglottis descends in the pharynx …
Epigenetic landscape
A visual aid, representing a multidimensional space that includes the dimension of time, devised by Conrad H. Waddington (1905-1975) to capture some of the main features of genotype-phenotype interaction during development (i.e., those of epigenetics) such as canalization, equifinality, and homeorhesis (see figure below). The landscape varies between individuals, but nevertheless maintains its basic shape …
Epigenetics
A term credited to Waddington in 1942, although it seems to go back to Oscar Hertwig (1849-1892) who referred to it in his book Biological problem of today: preformation or epigenesis? (1896). For Waddington, it denoted a branch of biology concerned with studying how the phenotype develops as a consequence of interactions between structural genes …
Epigenetic emergence
The emergence of a structure during the development of the embryo through interactions between tissues and ongoing gene expression. For example, the heart can induce the development of the retina at an early point in development because of their proximity in the embryo. See Developmental emergence, Diachronic emergence, Dynamic systems theory (development and evolution), Emergence, …
Epidemiology
The study of the incidence, prevalence and distribution of diseases disorders and infections in specified populations (e.g., as defined by age, sex, occupation), with the aim of providing information about their causes and how they might be controlled. Other important features of epidemiology are the identification of risk factors for particular diseases (e.g., pre-eclampsia) and …
Epigenesis
‘Epi’ means something upon or addition to. Thus, development of structures and functions is not determined solely by the ‘unfolding’ of instructions in the genes nor only by environmental instruction. It involves complicated ongoing interactions between different levels of organization from genes to cells to brain parts to body parts, and all in interaction (or …