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Medical and Healthy Living Glossary - E

This page of our online glossary of medical and healthy living is for medical and healthy living terms beginning with the letter 'E'.

• ECG (Electrocardiogram) - tracing of electrical activity in the heart.
• EEG (Electroencephalogram) - tracing of electrical activity in the brain.
• Electrolytes - Charged particles that circulate in the blood and help to regulate the body's fluid balance. They include sodium, potassium, chloride and bicarbonate.
• Electron - An indivisible particle that is negatively charged and free to orbit the positively charged nucleus of every atom. In the traditional model, electrons move around in concentric shells. However, the latest concept, based on quantum mechanics, regards the electron moving around the nucleus in clouds that can assume various shapes, such as a dumb-bell (two electrons moving) or clover leaf (four moving electrons). The shape and density of the outermost electronic shell will help determine what reactions are possible between particular atoms and molecules, e.g. whether an atom will easily gain or lose electrons to form an ion.
• Embryo - The first 8 weeks of life inside the womb when tiny organs are being formed.
• Emulsifiers - Additives that allow oils to be blended with water, overcoming their natural reluctance to mix.
• Enamel - Tooth coating; it is the hardest substance in the body.
• Endocrine Glands - Ductless glands that produce hormones for secretion directly into the bloodstream or lymph. Some organs, such as the pancreas, also release secretions via a duct. In addition to the pancreas, the major endocrine glands are the thyroid, pituitary, parathyroid, ovary and testis. Imbalances in the secretions of endocrine glands can produce a variety of diseases.
• Endorphins - Natural painkillers and tranquillisers produced in the brain. Their effects are similar to drugs such as morphine. They are released at times of severe mental stress, and during strenuous exercise. Eating chocolate is believed to boost the endorphin levels in the brain.
• Enteric Infections - Infections of the digestive system.
• Enzymes - Protein substances produced in the cells of plants and animals that act as catalysts, helping to speed up biological processes without being affected themselves. They work by combining with the substance which is to be processed, and help to convert it into another substance. Enzymes in the saliva, stomach, pancreas and small intestine all play a vital part in digestion. They help to change food into a form in which it can best be used by the body or excreted as waste. Each enzyme has a specific role, so that one which breaks down fats, for example, cannot deal with proteins or carbohydrates. Enzymes are vital for the normal functioning of the body, and their lack or inactivity can produce metabolic disorders. Any failure, even by a single enzyme, can cause a serious disorder. The names of enzymes mostly end with the suffix - ase.
• Epidemiology - The study of the incidence and distribution of disease or toxicity in human populations.
• Epidermis - The outer layer of skin, including the dead skin on the surface.
• Epiglottis - A cartilage flap at the root of the tongue which moves to block the windpipe when food is being swallowed, so that the food cannot go down the trachea.
• Erysipeloid - A bacterial skin infection which is caused by touching infected fish or meat.
• Erythroblast - A cell occurring in the red bone marrow that develops into a red blood cell (a erythrocyte). The cell is colourless at first but accumulates haemoglobin and becomes red. In mammals, the nucleus is lost.
• Essential Amino Acids - An amino acid which is necessary for growth but which cannot be synthesised in the body and therefore must be obtained from food. The essential amino acids are: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.
• Essential Fatty Acids - Some types of polyunsaturated fatty acids are not made in the body and must be supplied by polyunsaturated fat in the diet to maintain health. There are two main types: omega-6, which is found in foods such as corn oil and sunflower oil, and omega-3, which is found in rapeseed oil, walnuts and oily fish. These fatty acids maintain cell membranes, transport fats around the body and are needed to make prostaglandins (important hormone-like chemicals). The essential fatty acids are linoleic acid, linolenic acid and arachidonic acid.
• Exocrine Gland - A gland that secretes its products through a duct into particular parts of the body such as the liver, the sweat glands, the pancreas and the salivary glands.