Glossary Of Terms - O

Obesity Prevention of obesity Oesophagus Oedema Omega-3 Omega-6
Oncology Opioids Organic chemistry Organism acid alkali
alkyl amide amino acid amino group aryl atom
atomic number atomic weight base benzene ring under phenol carboxyl COOH compound
divalent electron element glycerol glyceryl hydroxyl group
ion isotopes ketone methyl molecule molecular weight
monovalent neutron nucleus peptide peptide bond potential of hydrogen = pH
phenol polyphenol phenobarbitone proton trivalent valency

Obesity means being overweight for one’s height and build. Thus the heart has to pump harder for the required blood flow for the increased body tissues, increasing the risk of heart failure.

In 2001, about 22% of UK adults were obese. This percentage has increased since.

Obesity increases the risks of: high blood pressure, diabetes, high cholesterol, heart attack, stroke, gallbladder disease, osteoarthritis, endometrial cancer, depression, and fertility problems; and shortens life expectancy.

Obese people risk getting Type 2 diabetes, which then increases the risk of heart disease. Until a few years ago Type 2 diabetes was found only in people over 40, or among younger people with a genetic risk such as Asians. But in the two years 2003-4 cases of Type 2 diabetes have occurred among obese children. One in four children in England is overweight or so fat that it threatens their health.

See Body mass index, Waist to hip ratio.

Try to eat sensibly – a low-fat, high-fibre diet. You need not aim for a model figure just to be within a healthy range for your height. Reduce or avoid butter, cheese, full fat milk, fried food, cakes, snacks, biscuits, chocolate, and fatty meat.

Research at the University of Texas found that men over 37 inches (94cm) waist, and women over 32 inches (81.3cm) had an increased heart disease risk. The sample was 2744 people. See Body mass index, Waist to hip ratio.

Prevention of obesity

Try to eat sensibly – a low-fat, high-fibre and high-protein diet; and reduce carbohydrates.

High-protein here is often the key – white meat, oily fish, eggs, low-fat cheese, milk – skimmed or semi-skimmed, yoghurt. That may help you reduce your total carbohydrates and fats.

Meat, fish, eggs, cheese, milk, yoghurt are complete proteins; and you may find having some incomplete proteins also helps.

You need not aim for a model figure just to be within a healthy range for your height.

Reduce or avoid: butter, full fat milk, fried food, cakes, snacks, biscuits, chocolate, and fatty meat. See If you are slightly overweight under Steps to a healthier heart.

The obesity drug sibutramine has had its licence suspended. The Medicines and Healthcare products Regulatory Agency announced on 21 January 2010 that a European-wide review had concluded the increased risk of non-fatal heart attacks and strokes from sibutramine (Reductil®) outweighs the benefit gained from weight loss. GPs have been advised not to issue any new prescriptions for sibutramine and to review the treatment of any patients taking the drug. In 2008 GPs issued 330,000 prescriptions for sibutramine.

od = once a day. bd (= bpd) = twice daily, tds = three times, qds = four times. See under Prescription terms.

Odontalgia = tooth pain. See -algia.

Oedema Pulmonary oedema means crackles or excess fluid in the lung tissues. Bilateral ankle oedema means excess fluid in the tissues of the ankles. For both see heart failure diagnosis.

Oesophagus is your gullet – the tube from the back of your mouth to your stomach for food to pass. It goes behind the heart. See transoesophageal echocardiogram under Echocardiogram.

Oestrogen is a steroid secreted by the ovaries and placenta. In mammals, not humans, it induces the period when females are 'on heat' during which ovulation occurs and copulation can occur. In humans it stimulates the changes in female reproductive organs during the menstrual cycle, and helps the development of the female secondary sexual characteristics.

Recent research in 2012 suggests that it also helps stop blood cells sticking to the walls of arteries and thus forming blockages. This could explain why women are more likely to have heart attacks after the menopause - ie when oestrogen levels decline. About 1 in 7 women die from heart attacks, whereas about 1 in 5 men do. The research findings do not mean that oestrogen could be used as a medicine or in a drug to reduce the risk of heart disease. Oestrogen also increases the risk of certain types of cancer.

om = every morning, on = every night.

Omega-3 fatty acids. See omega-3 under Fatty acids. Similarly omega-6.

Oncology is the medicine and study of tumours.

Onyx means Nail – eg finger nail, toe nail.

OPD = Outpatient department.

Opioids are analgesics related to opium, which is extracted from opium poppy seeds, and have similar properties to other drugs derived from opium – eg morphine. There are also synthetic drugs that act in a similar way to morphine, eg pethidine, methadone. See opioids under Analgesic. Opioids include drugs based on morphine and methadone, and include codeine.

They act on sites in the central nervous system that are involved in pain perception, and block or reduce the pain signals. Normally brain cells pass pain signals to other cells that interpret them. Opioids combine with receptors on brain cells to block the passing of the pain signals. This blocking can occur both in the brain as above and also in the spinal cord. Compare non-opioids.

Opioids are the strongest analgesics and so are used to relieve the pain from surgery, serious injuries and cancer. They also help the patient to relax and relieve the stress associated with pain.

Organic chemistry is the chemistry involving carbon compounds, including particularly compounds of or produced by living organisms, and nowadays also including similar manufactured substances such as plastics and drugs.

The following explains in summary some of the terms and concepts of the relevant organic chemistry, gradually building up the explanations.

An organism is any animal or plant, including any bacterium or virus, or anything resembling a living creature in structure and behaviour.

An atom is the smallest quantity of an element that can take part in a chemical reaction. An atom can be thought of as a very tiny amount with a heavy central nucleus and with light electrons in orbits around.

The nucleus (plural nuclei) is the core of the atom, consisting of protons – which have a positive electrical charge, and neutrons – which are electrically neutral. Protons have a mass about 1836 times the mass of an electron; neutrons have about 1839 times. Each electron has a negative electrical charge and can be thought of as in an orbit around the nucleus. The number of electrons equals the number of protons in the nucleus so the totality has an equal number of positive and of negative electrical charges.

An element is any of the substances such as listed below. The nucleus of each atom has the same number of protons. Eg each oxygen atom nucleus has 8 protons.

Where two isotopes of the same element exist, they have the same number of protons but different numbers of neutrons in their nuclei. Over 110 elements are known or created in laboratories, including (from lightest to heaviest in atomic number order): hydrogen, helium, carbon, nitrogen, oxygen, fluorine, neon, sodium, magnesium, aluminium, silicon, phosphorus, sulphur, chlorine, potassium, calcium, chromium, iron, cobalt, nickel, copper, zinc, selenium, silver, tin, iodine, gold, mercury, lead, uranium, plutonium. Isotopes have the same number of protons; isotones have the same number of neutrons.

See Minerals for those elements needed for health.

Each element has an atomic number, which is the number of protons in the nucleus of an atom of the element. Some of the light elements have the same number of neutrons as protons; heavy elements generally have more neutrons than protons.

Each element has an atomic weight, which is its atomic mass relative to other elements; and is about equal to the number of protons plus the number of neutrons in its nucleus.

A molecule consists of two or more atoms held together by chemical bonds.

A compound is a chemical structure with atoms of two or more different elements held together by chemical bonds. The structure is represented by a formula – with some conventions explained there including that in what follows here: H is hydrogen, C is carbon, N is nitrogen, O is oxygen, – represents a single bond, and = represents a double bond.

Molecular weight is the sum of the atomic weights (the relative atomic masses) of the atoms in a molecule or compound. High molecular weight implies a big structure.

An acid is a substance that dissociates in water and gives a sour taste or corrosive solution, having hydrogen ions.

An ion is an atom or group of atoms that has lost or gained one or more electrons, so is electrically charged. An electron is negatively charged.

An alkali is a base that is soluble in water.

A base is a metal oxide (a metal and oxygen only) or involves an –OH or similar structure. -OH is short for -O-H, a hydroxyl group. A hydroxyl group is an –OH structure.

The potential of hydrogen, written pH, measures how acid or alkaline a liquid is. Pure water has a pH value of 7; acids are less than 7; and alkalines are more than 7. Remember as 'acid' is a short word of less than 7 letters; and 'alkaline' is longer.

An amino acid is a compound that contains an amino group of atoms of the form –NH2 and also contains one or more carboxyl groups of the form –COOH.

The –NH2 is an amino group and represents an N with three bonds: one to the rest of the compound, and the other two each to an H. Each H has one bond.

The carboxyl –COOH is a shorthand representation for a structure that is common in organic acids. Each O has two bonds; and the C has four bonds: one to the rest of the compound, two to an oxygen =O, and one to –OH.

More widely, an amide is formed from an organic acid by the substitution of an amino (NH2, NHR, or NR2) group for the OH of a carboxyl (COOH) group. Here R represents any appropriate carbon chain structure. See eg Angiotensin sensitivity test.

Methyl means containing a monovalent CH3 group of atoms.

mono- means having one of something. Monovalent means having a valency of one.

Valency is a property of atoms or a group of atoms equal to the number of atoms of hydrogen that it could combine with or displace in forming compounds. So a CH3 group is a carbon atom with four bonds – three going to a hydrogen atom, and the fourth being free to combine as one bond (monovalent) to something else. Divalent means the atom has a valency of 2 in the compound. Trivalent means the atom has a valency of 3 in the compound.

Glycerol is a pale yellow sweet-tasting syrupy liquid, a sugar alcohol, and sometimes called glycerin or glycerine, formula C3H8O3. Its structure is three Carbon atoms linked as a chain, with a hydroxyl group –OH coming off each Carbon atom. The two end Carbon atoms each have two Hydrogen atoms coming off them. The central Carbon has one Hydrogen off it.

In foods glycerol is a solvent, sweetener, and sugar substitute, and is E422. It does not raise blood sugar levels, does not feed the bacteria that form plaques, and does not cause dental decay.

Glyceryl is derived from glycerol by replacing or removing one or more of its hydroxyl groups.

A ketone is any of a class of compounds with the general chemical formula R’COR where R’ and R are usually alkyl or aryl groups.

An alkyl or alkyl group consists of or contains the monovalent group CnH2n+1. That is a chain of n carbon atoms each having two hydrogen atoms and links to its adjacent carbon atoms; and one end carbon atom has a third hydrogen atom; and the other end has the monovalent bond.

An aryl consists of or contains an aromatic group. An aromatic group has an unsaturated ring containing alternate double and single bonds, especially containing a benzine ring. Aromatic means having a distinctive usually pleasant smell. Compare ketone with acetone.

A peptide is a compound consisting of two or more amino acids linked by chemical bonding between their respective carboxyl and amino groups.

A peptide bond is a chemical linkage written =CHCONHCH= formed by the condensation of the amino group of one amino acid with the carboxyl group of the other. See also polypeptide.

Lipids are any of a group of organic compounds that are esters of fatty acids or closely related substances. Generally they do not dissolve in water. but are soluble in some other organic solvents. See lipids.

An ester is any of a group of compounds produced by a reaction between acids and alcohols and with elimination of water. Fats are solid esters, and a subgroup of the lipids. See under lipids, triglycerides.

Thus we have built up to the following.

A protein is any of a group of organic compounds that contain carbon, oxygen and nitrogen, that are of high molecular weight, and that are essential constituents of all living organisms. They have one or more amino acids linked by peptide bonds and are folded into a specific three-dimensional shape that is held together by further chemical bonding.

Outpatient department, OPD is the hospital area for clinics and treatments where the patients do not stay as inpatients – ie they do not stay overnight in the hospital.


This information was created and edited by Richard Maddison for the BCPA.
Copyright © 1997-2019 The British Cardiac Patients Association, and/or Richard Maddison.
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First published in this form 2002, and updated 2005, 2007, 2008, 2011, 2012, 2013, 2017.
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Authors, sources and acknowledgements

The main sources are BCPA Journal published articles, other information from authors, and publicly available documents and websites. In many cases the journal articles give sources and further information than the Glossary entries.

Parts of the wordings under ECG and Echocardiogram are adapted with permission from BUPA's health information resources, available at

We hope we have thanked everyone.

Richard Maddison

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