Biology

Egg incubation Processes and strategies by which animals keep eggs warm and protected until embryos develop and hatch, including parental brooding, environmental incubation, artificial incubators…

Eggshell: Structure, Function, and Human Uses Eggshell Eggshells are the mineralized outer coverings of many animal eggs. This article explains their structure, formation, roles in development, variations, and uses in culture, agricult…

Eicosanoids Eicosanoid Short-lived bioactive lipid mediators derived from 20-carbon fatty acids that regulate inflammation, vascular tone, reproduction, immunity and other local processes.

Ejaculatory duct A paired duct in the male reproductive tract that transports semen from the seminal vesicles and vas deferens through the prostate to the urethra during ejaculation.

Elastin: the elastic protein of connective tissues Elastin Elastin is a durable, highly elastic protein found in connective tissues that enables organs and vessels to stretch and recoil. It arises from tropoelastin, is cross-linked into fi…

Electrology: Permanent Hair Removal by Electrolysis Electrology Electrology is a method of permanent hair removal that destroys hair growth cells with electrical energy delivered into individual follicles; techniques, history, aftercare, and di…

Electron transport chain (ETC) Electron transport chain Membrane-bound series of protein complexes and mobile carriers that transfer electrons to build a proton gradient, driving ATP synthesis in respiration and photosynthesis.

Electrophysiology: study of electrical activity in cells and tissues Electrophysiology Electrophysiology examines electrical signals in biological systems, from single ion channels to whole organs. It covers methods, scales, history, clinical uses, and distinctions b…

Electroreception: how animals detect electrical fields Electroreception Electroreception is a biological sense allowing animals to detect electric fields. It occurs widely in aquatic species and in some terrestrial groups and supports hunting, navigati…

Elytra: the hardened forewings of beetles Elytra Elytra are the thickened, protective forewings of beetles (Coleoptera) that cover the membranous hindwings and dorsal surface; related structures include hemelytra in true bugs.

Embalming: purpose, methods, history, and cultural considerations Embalming Concise encyclopedia entry on embalming: goals, common techniques and chemicals, historical development, cultural and religious views, safety and environmental issues, legal consen…

Embioptera (webspinners): silk-producing insects of the tropics and subtropics Embioptera Embioptera, commonly called webspinners, are small insects that produce silk from glands in their front legs, build gallery shelters, and are mostly tropical; they have a fossil re…

Embryo — early stage of development in animals, plants, and other organisms Embryo An embryo is the initial developmental stage after fertilization, from the first cell divisions through major body-plan formation. This article outlines stages, processes, study, a…

Embryology: development of embryos from fertilization to organ formation Embryology Embryology is the study of embryos and their early development from fertilization through organogenesis. It informs medicine, evolutionary biology and developmental research across…

ENCODE: The Encyclopedia of DNA Elements — mapping human genome function ENCODE ENCODE is a large research effort to catalog functional elements in the human genome, producing wide-ranging maps of transcription, regulatory regions, and biochemical activity acr…

Endocardium: structure, development, function, and clinical significance Endocardium The endocardium is the thin inner lining of the heart chambers and valves. This article explains its structure, embryologic origins, roles in heart function, and common clinical co…

Endocarp: the innermost layer of a fruit's pericarp Endocarp Endocarp is the inner layer of a fruit's pericarp, varying from juicy pulp to hard stone. This article explains its structure, variation across fruit types, development, and biolog…

Endocrine gland A ductless gland that releases hormones into the bloodstream to regulate physiology; overview of major glands, function, control mechanisms, clinical relevance, and notable example…

Endocrine system: organs, hormones, functions, and clinical significance Endocrine system Overview of the endocrine system: its glands and hormones, how they work, key functions, major organs, contrasts with other systems, clinical relevance and notable distinctions.

Endometrium: structure, function, and clinical importance Endometrium The endometrium is the inner mucous membrane of the uterus that thickens and sheds cyclically. It supports implantation, responds to hormones, and is central to menstruation and fe…

Endoplasmic reticulum The endoplasmic reticulum (ER) is a membrane-bound eukaryotic organelle involved in protein and lipid synthesis, calcium storage, molecular transport, and quality control within th…

Endoskeleton: internal support systems in animals Endoskeleton An endoskeleton is an internal structural system that supports an animal's body. This article explains types, development, examples, advantages, and how endoskeletons differ from e…

Endosperm: the seed's nutritive tissue in flowering plants Endosperm Endosperm is the nutritive tissue that nourishes the embryo in most flowering plant seeds. It varies in form and composition and is a major source of human food (cereals, coconut)…

Endospore: bacterial dormant cell for survival and persistence Endospore An endospore is a highly resistant, dormant form produced by certain bacteria to survive extreme stress; this article explains its structure, formation, roles, and important distin…

Endosymbiosis: organisms living inside other organisms Endosymbiosis Endosymbiosis is a biological relationship in which one organism lives inside the cells or body of another. It shapes evolution, ecology, and physiology from organelles to insect–b…

Endothelium: the cellular lining of blood and lymphatic vessels Endothelium Endothelium is the monolayer of cells lining blood and lymphatic vessels. It serves as a selective barrier, regulates vascular tone, coagulation, inflammation and angiogenesis, and…

Enkephalin: endogenous opioid peptides involved in pain and brain signaling Enkephalin Enkephalins are short opioid peptides in the brain and nervous system that modulate pain, mood and motor control. They are pentapeptides occurring as methionine- or leucine-ending…

Ensifera: Long-horned orthopterans including crickets and katydids Ensifera Ensifera is the suborder of Orthoptera that contains crickets, katydids and relatives. Members have long antennae, many produce songs by wing rubbing, and females often bear a long…

Entamoeba histolytica: biology, disease, diagnosis and prevention Entamoeba histolytica Entamoeba histolytica is a single-celled parasitic protozoan that causes amoebiasis. This article explains its biology, transmission, clinical effects, diagnosis, treatment and pub…

Enteric nervous system (ENS) Enteric nervous system The enteric nervous system is the intrinsic neural network of the gut that controls digestion, motility and local reflexes and communicates bidirectionally with the central nervous…

Enterobacteriaceae: overview of a major family of Gram-negative bacteria Enterobacteriaceae Enterobacteriaceae are a diverse family of Gram-negative, rod-shaped bacteria found in intestines and the environment; members include harmless commensals and important pathogens,…

Enterococcus — biology, habitats, and clinical importance Enterococcus Enterococcus is a genus of Gram-positive lactic acid bacteria found in the intestines of humans and animals; some species are benign commensals while others are notable opportunist…

Enterotype: classification of the human gut microbiome Enterotype Enterotypes are categories used to describe dominant microbial communities in the human gut. They relate to digestion, drug metabolism, diet, early development and are a focus of m…

Enterovirus: biology, diseases, transmission and public health significance Enterovirus Enteroviruses are common RNA viruses that often inhabit the gut and cause illnesses from mild febrile disease to meningitis and, rarely, paralytic disease; they include poliovirus…

Entognatha: the entognathous hexapods Entognatha Entognatha are small, wingless hexapods with internalized mouthparts. This group includes springtails, diplurans and proturans, important in soil ecology and early hexapod evolutio…

Entomology — the scientific study of insects Entomology Entomology is the branch of zoology concerned with insects: their biology, classification, ecology, economic importance, and roles in ecosystems and human affairs.

Entoprocta (Kamptozoa): small sessile cup-shaped aquatic animals Entoprocta Entoprocta (Kamptozoa) are tiny mostly marine, sessile invertebrates with a ciliated tentacular crown; this article summarizes their morphology, life cycle, ecology, fossil record,…

Enzyme: Biological Catalysts — Structure, Function, History, and Applications Enzyme An enzyme is a biological catalyst—usually a protein—that accelerates specific chemical reactions in living organisms. This article covers structure, mechanism, classification, reg…

Eosinophil granulocyte (eosinophil) Eosinophil granulocyte Eosinophils are a type of granulocytic white blood cell that play roles in defense against parasites, modulation of allergic inflammation and tissue repair; they contain distinctiv…

Epidermis — the outer cellular layer of plants and animals Epidermis The epidermis is the outermost living cell layer in animals and plants. It forms a protective interface, renews by mitosis, senses the environment, and shows adaptations such as ke…

Epididymis: structure, function and clinical significance Epididymis The epididymis is a coiled duct along the posterior testis where sperm mature, are stored and transported. This article covers anatomy, development, function and common clinical is…

Epigenetics: how genes are regulated without changing DNA sequence Epigenetics Overview of epigenetics: mechanisms that alter gene activity without changing DNA sequence, their stability, historical development, biological roles, and applications in medicine,…

Epigynum: the external female genital structure of spiders Epigynum Epigynum (plural epigyna) is the external reproductive aperture on female spiders. It receives sperm from the male's pedipalps and leads to internal storage organs used for later f…

Epistasis: genetic interactions between loci Epistasis Epistasis describes how alleles at one genetic locus can modify or mask the effects of alleles at another locus, affecting phenotype, genetic architecture, and evolutionary dynamic…

Epistaxis (Nosebleed): Causes, First Aid, Treatment and Prevention Epistaxis Epistaxis, commonly called a nosebleed, is bleeding from the nasal cavity. This article explains causes, anatomy, first aid, treatment options, prevention and when to seek medical…

Epithelium: structure, types, functions and clinical significance Epithelium Summary of epithelial tissue: cellular arrangement, common types (simple, stratified, pseudostratified), key functions (barrier, secretion, absorption), and clinical relevance incl…

Erection: physiology, types, and clinical considerations Erection Overview of erection as a physiological change in penile, clitoral, or nipple tissue: mechanisms, triggers, normal patterns, clinical problems (e.g., erectile dysfunction, priapism…

Erythropoietin (EPO): physiology, therapeutic uses, and notable facts Erythropoietin Erythropoietin (EPO) is a kidney-derived hormone that stimulates red blood cell production. This article covers its biology, clinical uses, synthetic forms, risks, and issues such…