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Eclipse - Oral Physiology Biology Dictionary
Category: Health and Medicine > Oral Physiology
Date & country: 18/09/2007, UK
Words: 391


DNA
Deoxyribosenucleic acid - a complex nucleic acid molecule which is used by cells to store genetic material as genes which control the structure of proteins and hence influencing all enzyme reactions. DNA is coiled in a single closed loop in procaryotes, but coiled round other proteins to form a chromosome, and stored in the nucleus of eucaryotes

Duct
a tube which carries a secretion onto the surface of skin or mucosa.

Ecological balance
astable balance in the numbers of each species in an ecosystem .In the ecosystem of the mouth this balance is brought about by competition and cooperation between the different organism and the hosts defences which tend to control population size.

Ecosystem
a stable environment in which live a large number of different forms of life, each affecting the other. Example are a forest, desert, tidal area, soil, oral cavity, gut.

Ectoderm
the outer of the three cell layers which form, as the clump of early embryonic cells begins to differentiate. The ectoderm will form the epidermis of the skin and the nervous system. The other two layers are the mesoderm and the endoderm.

Ectomesenchyme
a name given to dental MESENCHYME which reflects its partly ectodermal origin.

Eicosanoids
are a class of hormones which are all made from phospholipids. They include prostaglandins, thromboxanes, and leucotriens.

Elastic fibres
are long, thin, ribbons-like fibres, sometimes even sheet-like. They are composed of a central core of elastin, a rubbery protein, surrounded by glycoprotein microfilaments. Elastin is found all over the body but particularly in the walls of blood vessels and in our vocal chords.

Electron
the negatively charged elements of an atom which circle the nucleus. If an electron is lost the atom becomes a relatively positively charged ion. It has been ionised .

Electron Transport System-
Hydrogen ions produced during the 3 preparatory steps of aerobic respiration are carried by nicotinamide adenine dinucleotide (NAD). The hydrogen ion plus one electron form NADH, which is taken to the electron transport system. This transport system is run by a series of 5 molecules. The first, removes the two electrons from NADH,( one comes from the hydrogen atom, leaving behind a hydrogen ion). These two electrons, bounce from the first molecule in the transport system to the second, third, forth and then last one, cytochrome oxidase, which finally places the electrons onto oxygen gas O2. The electron rich oxygen atoms are attractive to the hydrogen ions and they combine to form water. (Oxygen in the process of aerobic respiration acts therefore as an electron acceptor). In the process of bouncing 'downhill' the electrons have released sufficient energy to power up a small battery. This battery has been made by pumping hydrogen ions out of the inner membrane of the mitochondria. The collection of hydrogen ions outside, piles up and their electrical pressure mounts. They want to get back across the membrane, and are allowed, one at a time to pass back through the enzyme ATP synthase. This enzyme sits like a water wheel in the cell membrane, turned by the passage of hydrogen ions. Its turning wheel builds an ATP molecule in every turn. The wheel may be going at about 200 revolutions per second, powering the synthesis of an ATP molecule with each turn. ATP formed in this way takes a while but can be sustained to fuel the body during aerobic exercise. When the demand for power exceeds this rate, the cells have to rely on anaerobic respiration.

Electrostatic
a force generated by differences in electric charge of two particles.

Enamel
the outer layer hard layer which covers the dentine around the crown of a tooth. Enamel consists of closely packed crystals of hydroxyapatite with very little organic material. A recognisable unit of structure in enamel is the enamel prism.

Enamel prisms
rod-like bundles of hydroxyapatie crystals which are orientated at right angles to the tooth surface. Each prism can be traced from the outside of the enamel all the way to the dentine junction.

Enameloid
a type of enamel found in fish and reptiles in which the enamel prisms are haphazardly arranged; in contrast enamel prism are parallel to each other and orientated at right angle to the tooth surface.

Endocrine glands
the secretion passes into the blood stream, like insulin, epinephrine.

Endoderm
the inner of the three cell layers which form, as the clump of early embryonic cells begins to differentiate. The endoderm will form the gut system and its associated organs. The other two layers are the mesoderm and the ectoderm.

Endoplasmic reticulum
a system of inner cell membranes which is continuous with the nuclear membrane. It transports products of cell synthesis to the golgi apparatus. Described as rough endoplasmic reticulum when there are many ribosomes attached.

Endorphins
a neuropeptide which has specific binding sites on nerve cells called opiate receptors. When the receptor is activated by endorphins or morphine it reduces the excitability of the post synaptic cell. Peptide receptors are also found on lymphocytes which suggest an association between neuropeptides and the regulation of the immune response.

Endosteum
a layer of bone forming cells, osteoblasts which covers the entire surface of the internal aspect of cortical and spongy bone, separating it from the surrounding connective tissue. see also bone membrane.

Endothelial cells
the epithelial cells of the endothelium which lines blood vessels. The cells are flattened into a pavement stone shape and are usually two or three layers thick.

Endotoxins
the contents and cell wallsof dead bacteria which may be toxic to the host.

Enkephalins
similar in structure and action to endorphins.

Environment
describes the surroundings in which organisms live. Some physical features of an environment are fairly stable, like trees, rivers, mountains, houses, soil, teeth. Some physical features are changeable, like wind, water, light, pH, food supply. Others features are less predictable, such as the balance in the community of collaborators, competitors and parasites. All forms of life including bacteria in the mouth, have an environment, which has an important influence on their survival. Successful organisms manage to exploit their environment to the best advantage or to adapt to it, perhaps only after several generations, if it becomes a serious challenge to the species.

Enzyme
a protein that controls and helps a chemical reaction to take place, but is not used up in the process. Usually each enzyme is specific for a particular step in a reaction. Enzymes are sensitive to their environment, especially to excessive temperature or pH.

Epidermal growth factor
a cytokine that stimulates epithelial cell proliferation.

Epinephrin
e - a neurotransmitter substance found at all adrenergic synapses (nor epinephrine or epinephrine). It is the most common neurotransmitter in the nervous system, in particular at ganglion cells of the sympathetic nervous system.

Epitaxy
the initiation of crystalformation in a saturated solution by providing a template against which crystal can form. There are specific sites on collagen molecules which appear to function as templates against which hydroxyapatite crystals form.

Epithelial attachment
the cuff of junctional epithelium which joins the gingival sulcus epithelium to the enamel of the tooth. Apical migration of the epithelium down onto the cementum may occur due to ageing or periodontal disease. Loss of attachment produces a periodontal pocket and a new habitat for anaerobic oral bacteria.

Epithelium
a layer of cells which forms alining for a tube or the covering for an organ or the whole body.

Eucaryote
a cell in which the genetic material is confined to the nucleus, in distinction to a procaryote in which the genetic material is dispersed throughout the cell. Other distinctions of eucarytoic cells are the presence of organelles such as the golgi apparatus, endoplasmic reticulum, lysosomes and mitochondria

Exocrine glands
the secretion passes intoa duct like sweat, saliva and mucous.

Extinct
a plant or animal species may entirely cease to exist. Recent examples are the dodo, a large flightless bird which used to live as recently as two hundred years ago, on the island of Mauritius. There are today many species of birds, flowers, fish, insects, large mammals, including certain types of whale, which are threatened with extinction, most as a result of human activity. Happily, the smallpox virus is about to become extinct

Extra cellular matrix
the supporting surrounding material of a cell including ground substance and fibres.

Extrinsic fibres
refers to those fibres of cementum which are continuous with periodontal ligament fibres. Extrinsic fibres have been trapped in cementum during its formation in order to anchor them. see also intrinsic fibres, and sharpey's fibres.

Exudate
the fluid plasma which leaks out of blood vessels due to an increase in capillary permeability. The increased permeability, is caused by histamine, and bradykinin, which are released in response to tissue damage. The formation of an exudate is the first step in the process of inflammation.

Fatty acids
long straight chains of carbon and hydrogen ending with an acid group at one end. Saturated fatty acids have no capacity to absorb more hydrogen atoms. Animal fats are mostly of this type and are considered less healthy as they end to accumulate in the linings of arteries.

Feedback
a system of control, where work being done is modified by the product. For example the blood pressure is maintained by the strength of the heart beat and the muscle tone of the arterioles. In the walls of the large arteries are receptors sensitive to the degree of stretch in the muscle wall. As the blood pressure increases, the wall are stretched, and the receptor sends signals via the brain to the sympathetic nervous system back to the heart and blood vessels, causing decreased pumping effort and more relaxed muscle tone in the arteries. In chemical reactions the accumulated product slows down the rate of production. For example if the oxygen level of the body falls, the rate of respiration.increases to restore the levels to normal. These control system are thus circular; what is produced returns to control the further production. They are examples of negative feedback, and are common in maintaining stability or homeostasis. Positive feedback is less common as it tends to be unstable. An example is the release by platelets of thrompotaxin. When the levels of thrombotaxin are high, they do not inhibit further production as occurs in a negative feedback system but actually stimulate more platelets to produce more thrombotaxin and so on until there is an explosive increase in the number of sticky platelets. This is useful in an emergency to stop bleeding, but very dangerous when a clot forms inside a blood vessel.

Fibre
a long thin string-like structure constructed of smaller fibrils and even smaller microfibrils. Examples are collagen, elastic and keratin fibres. Collagen fibres are arranged parallel to each other in a tendon, to give it great resistance to tension (pulling).

Fibrinogen
a large soluble protein found in blood which is converted into fibrin during blood clotting.

Fibroblasts
cell of connective tissue which form both the intercellular matrix and fibres.

Fibronectin
a glycoprotein which is found in the extracellular matrix and is important for the attachments, and therefore the movement of cells.

Filamentous
long, thin, hair-like.

Fluorapatite-
an apatite crystal in which fluoride has replaced hydroxyl ions.

Fluorosis
mottling of the teeth caused by an excess of fluoride in the drinking water. A fluorosis index recognises 4 stages of severity.

Foramina
the plural of foramen, which is a hole, for example Foramen Ovale.

Fossils
dead plant or animal remains whichhave become infused with minerals over many millions of years and are now hard and rock -like. The original shape of the animal or plant may be very well preserved.

Fractal dimension
a dimension which is some fraction in between a line(1) and a plane(2), or a plane and a solid (3). These fractal dimensions are useful in describing the quality of natural lines and surfaces, such as coastlines, trees, vascular branching and the patterns of trabecula bone

Freeway space
the space between the teeth when the jaw is in a rest position .

Ganglion
a collection of nerve cells usually found outside the central nervous system, from which axons arrive from the periphery and proceed to the spinal cord or brain.

Gangrene
the death of tissue on a large scale. May be caused by certain bacteria which spread rapidly through tissues, or by an inadequate blood supply.

Gene cloning
a technique which uses recombinant DNA , inserted into a host cell as a plasmid which reproduces copies of itself, and hence the inserted gene, many times

Generic
belonging to the same main group. For example generic medicines are identified by the main group they fall into rather than by their trade names.

Genes
the unit of inheritance that transmits information from one cell to its daughters and hence to the next generation. A gene consists of a specific series of DNA nucleotides. Each three nucleotides is the code for an amino acid. Humans have about 200,000 genes which collectively are know as the genome.

Genetic engineering
see recombinant DNA.

Genome
the complete complement ofgenetic material in a species.

Gingival crevice fluid
a secretion found in the gingival sulcus, formed by the cells attaching the gingival epithelium to the tooth.

Gingival sulcus
a potential space between the gingival margin and the tooth, lined by non-keratinised epithelium. The depth of the sulcus is normally between 1 and 2 mm in health.

Gingivitis
an inflammation of the gingival mucosa, due to the increase in the virulence or mass of bacteria in the gingival sulcus, or to reduced resistance of the host.

Glands
a collection of cells secreting a specific product such as insulin or sweat.

Glucocorticoids
one of the two major hormones secreted by the adrenal medulla. The most common glucocorticoid is cortisol (hydrocortisone) but they all share the common effect of increasing blood glucose concentration. They may achieve this at the cost of body protein stores, by converting amino acids into glucose. Cortisol also converts fatty acids into glucose. Any type of stress, including trauma, infection, fear, anxiety or malnutrition causes an increase in cortisol secretion. Cortisol stabilises the membrane of lysosomes, which are then unlikely to rupture, a process which stimulates inflammation. Cortisol therfore inhibits inflammation. Cells like neutrophils, are less able to protect the body from foreign proteins. Stress therefore reduces the bodies ability to cope with infection. Malnutrition not only stunts mental and physical development but also allows viral, bacterial and parasitic infections to flourish.

Glucosamine
a glucose or galactose molecule with an amine group attached. see also glucuronic acid.

Glucose
a molecule of great importance to life as it provides a ready source of energy for both plant and animal cells. Glucose can only be formed in plants with the aid of sunlight. This process of photosynthesis sustains all animal life on earth. The glucose molecule is formed by a ring of a six carbon atoms. It is progressively broken down in a process called glycolysis during both aerobic and anaerobic respiration into ATP

Glucuronic acid
a glucose molecule with an acid carboxyl group. One of the two molecules which makes up the repeating disaccharide unit of glycosaminoglycans other molecule is a glucosamine.

Glycine
one of 20 amino acids commonly found in proteins.

Glycogen
a polysaccharide made up of repeated glucose units. Animals make glycogen and store it in liver and muscles.

Glycolysis
the breakdown of glucose in series of metabolic steps. Energy in the form of ATP is released even if there is no oxygen available as in anaerobic respiration . In the presence of oxygen as in aerobic respiration the breakdown is more complete and yields more energy.

Glycoproteins
are proteins which have many sugar molecules attached to them. They are an important component of saliva where they provide lubrication for the teeth. They also have a wide range of other functions in connective tissues. Examples are fibronectin, osteonectin, osteopontin and interferon. Glycoproteins are also found in cell membranes where they define part of the cells identity. The four major blood groups are defined by glycoproteins on the cell membranes of red blood cells.

Glycosaminoglycans
(GAGs) - large to huge molecules of the connective tissue matrix, made up of repeating disaccharide units linked to a protein core. The disaccharide units are made of glucosamine and glucuronic acid. The position of a sulphate molecule on the glucosamine determines the type of GAG.

Golgi apparatus
a cell organelle which is part of the inner cell membrane. It collects and stores the products from the endoplasmic reticulum. It is prominent in actively secreting cells.

Gomphosis
a form of tooth attachment in which the root is help in a bony socket by a fibrous ligament.

Gonial angle
the angle made by the posterior part of the ramus and the lower border of the mandible.

Ground substance
a jelly-like substance which surrounds cells and provides, with fibre, a supportive matrix around each cell. It consists of water and huge molecules which helps transport nutrients to cells and carries away cell products.

Habitat
a location which has a suitable environment for an organism to live in. Caves are natural habitats for bats, trees for birds; oral surfaces and crevices, for some bacteria.

Haemostasis
the prevention of blood loss through a damaged vessel wall. There are three main mechanisms, vasoconstriction, formation of a platelet plug and blood clotting.

Heparin sulphate
a glycosaminoglycan which is unusual in that it is stored inside the cell (mast cells) surrounding the liver. Heparin prevents blood clotting.

Herbivorous
an animal whose diet consists of grass, leaves, roots or other plant matter.

Heterodont-
a dentition in which some of the teeth have different shapes and special functions. Form 'hetero' = different) see also homodont.

Hierarchy
an order of power between individuals. A ranking of most dominant to least dominant.

Hippocampus
part of the limbic system, it seems to provide a spatial map, useful in the event of a sudden need to escape from an unpleasant sensory experience.

Histamine
is a product of the amino acid, histidene and is released by damaged cells. Histamine causes an increase in capillary permeability and vasodilation, two vascular events which are the first stages of inflammation. Histamine is also a neurotransmitters substance, released at nerve synapses mostly in the hypothalamus.

Homeostasis
control of an organism`s internal environment. Water content, temperature, acid-base balance, level of oxygen and carbon dioxide, adequate supply of energy are some of the many factors in the organism which require monitoring and control. A common form of control is feedback.

Homodont
a dentition in which all the teeth are the same shape (from 'home' = same) see also heterodont.

Hyaluronic acid
the largest glycosaminoglycan known, it plays an important role of restricting the flow of water in tissues, particularly in synovial fluid where it acts as a lubricant..

Hydrogen bonds
a weak force holding two molecules containing hydrogen together, each of which has a covalent bond with another atom. For example, water is a molecule made up of two hydrogen atoms attached covalently to an oxygen atom. The hydrogen proton is however not completely balanced and is still attracted to the oxygen atom of a neighbouring molecule. Molecules of water are thus held together by hydrogen bonds, which accounts for the unusually high boiling point of water considering its low molecular weight. Hydrogen bonds hold protein molecules in shape by linking up various sections. When proteins are heated, these bonds collapse and the protein is physically altered, even though its chemical composition remains unchanged. When an egg is heated the white part rapidly gels, indicating a change in the shape of the protein. The process is not reversible.. so an egg cannot be uncooked.

Hydroxyapatite
one of the apatites which is the main salt of bone and teeth.

Hydroxyl ion
a negatively charged ion of hydrogen and oxygen written as OH-.

Hyperplasia
an increase in the size of an organ due to an increase in the numbers of cells. The developing embryo increases in size due to cell division. The cells of some tissues retain the ability to divide throughout life, like the epithelium and connective tissues but muscle and nerve cells lose their ability to divide soon after birth. When hyperplasia is uncontrolled it produces a tumour which may be benign if it is well contained, not destructive and does not spread. But it may be malignant, destroys normal tissue, and spread all over the body.

Hypertrophy
an increase in the size of an organ due to an increase in the size of each cell. Muscles increase in size due to hypertrophy.

Hypoplasia
reduced formation of a tissue during development. Enamel hypoplasia may be recognised as pits and depressions in the enamel and may be cause by fluorosis.

Hypothalamus
this small body of nerve cells controls the activity of the pituitary gland, the source of several hormones which control the activity of other hormones, including ACTH which in turn controls the level of glucocorticoid secretion. The hypothalamus also has powerful connections with the other members of the limbic system, from which nerve pathways descend to control nerves in the spinal cord. The influence of the limbic system on the hypothalamus explains the raised levels of glucocorticoids in response to emotional stress. This bridge with the peripheral nervous system, provides a link between the emotional state of a person, as influenced by the activity of the limbic system, and the excitability of neurones in the spinal cord, to in-coming pain impulses.

Hypotonic
a comparison between two solutions, indicating that one has a lower osmotic pressure, or is less salty than the other.

Immunity
The body`s response to a foreign antigen, either ingested as food, or as part of a foreign organism. There are two major ways the body defends itself; one is by antibody, production, the so called humeral response, as the antibodies circulate in the blood and the fluid between cells. The other is the cellular response, as it involves the cells of the immune system, the family of leucocytes. The particular leucocyte responsible for immune specificity is the lymphocyte . In total cell mass there are as many lymphocytes as there are liver or brain cells. During development there are millions of B (from the Bone marrow) lymphocytes made, each with a different cell membrane ligand, specific for any one of millions of antigens. The lymphocytes are circulating all the time so that they can have the chance to meet up with a foreign antigen. As soon as an antigen has been recognised by one of these cells, and bound to the cell ligand, it stimulates the cell to reproduce millions of copies of itself. All the daughter cells are clones of the original cell. These B lymphocyte daughters, migrate to the site where the antibody is needed. Instead of making an antigen for the membrane these cells make large amounts of soluble antibody. They are now recognisable as plasma cells. T lymphocytes ( having spent time in the Thymus) comprises the cell mediated response to an antigen. They are of two types, Killer T cells and Helper T Cells. Most T lymphocytes are helpers and they regulate the response of the B lymphocytes . The killer T cells are however capable of recognising the foreign antigen on the surface of a cell, and then killing the entire cell. The immune response is part of a less specific defense and healing response of the body known as inflammation.

In Vitro
experiments which are carried out in a laboratory as distinct from in vivo experiments

In Vivo
experiments which are carried out in live animals as distinct from in vitro experiments

Indirect pulp cap
a dressing, usually calcium hydroxide, placed against the pulpal wall of a deep cavity, in order to encourage affected dentine to remineralise. The cavity is closed with a temporary filling material and re-opened after 6 weeks to assess the state of the pulp.

Induction
cell differentiation which is brought about by the influence of cytokines released by cells of another type.

Infected dentine
dentine which has been damaged beyond repair by caries and is infected by large numbers of caries bacteria.

Inflammation
is a whole complex of events which occur in sequence, in response to injury. Tissue damaged by bacteria, chemicals, heat, trauma etc, release histamine and bradykinin and serotonin which cause an increase in capillary permeability and vasodilation. Both these factors contribute to the formation of a fluid exudate in the damaged tissue, which includes fibrinogen and therefore soon clots into a firm gel. This process has the effect of walling off the bacteria or toxic substances causing the damage, or at least it slows down their spread into surrounding tissues. Local macrophages, begin their phagocytic activity but their numbers are small. Damaged tissues also release interleukin, messengers which are transported all the way to the bone marrow, where millions of leucocytes are stored.. These stores now release leucocytes, mostly neutrophils into the blood. The neutrophils gather at the site of damage because the endothelial cells of the local capillary walls have become sticky to leucocytes. This stickiness is specific for leucocytes and is the work of selectins expressed on the cell membrane of the endothelial cell. The leucocytes begin to catch and roll along the endothelium until they are brought to a standstill. The increased permeability of the endothelial cells allows leucocytes to wriggle out of the capillary and migrate into the damaged area. This migration is also dependent on a process know as chemotaxis, in which cytokine messages from the damaged cells attract the leucocytes to come to their aid. After several days the battle zone is filled with dead bacteria, dead tissue cells, dead neutrophils and macrophages. This dead mass of tissue is called pus. The end of the event may be the gradual resorption of pus by fresh macrophages, or the pus, now under some pressure, may force its way somewhere else. Pus from the apex of a tooth may escape laterally through the alveolar bone and mucosa, where it is recognisable as a 'gum boil'.Ten days after a foreign protein is detected for the first time, the bodies immune system has mounted a more specific defense. Antibodies are produced by B lymphocytes and T lymphocytes have been alerted to the invasion.

Insulin
an endochrine hormone produced in the spleen which controls the amount of sugar in the blood by a) transporting it into cells and promoting glycolysis b) converting it into glycogen for storage in the liver and muscles, and c) converting it into fats . Without sufficient insulin, glucose accumulates in the blood and urine and the cells of the body are starved, a condition known as diabetes. The control of insulin production is another example of a feedback system.

Insulin-like growth facto
r (IGF) - a cytokine that influences growth hormone activity.