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Eclipse - Oral Physiology Biology Dictionary Category: Health and Medicine > Oral Physiology Date & country: 18/09/2007, UK Words: 388

Interferon
a glycoprotein produced by cell s which mobilise the T lymphocytes to inhibit viruses and the growth of cancer cells.

Interleukins
a variety of compounds(about 20) that are produced by lymphocytes, macrophages, and monocytes. They regulate the cell mediated response of the immune system. Interleukin-1 is involved in the triggering of the immune response, starting acute inflammation and maintaining chronic inflammation. Interleukin-2 is produced by helper T cells and induces proliferation of immune cells, both T and B. Interleukin-3 promotes the differentiation and proliferation of stem cells of the leucocyte family.Interleukin -6 produced by various cells including tumour cells and acts as a stimulant of plasma proteins and B and T cells. Interleukin -12 is produced by a range of cells. It activates T cells and natural killer cells. It promotes the response to a range of pathogens including HIV of Interleukin-2. It appears to be one of the most promising Interleukins for the control of viral, bacterial and protozoal infections.

Intermediate filaments
unlike microfilaments and microtubules, they are verystable. Instead of being stacked proteins, as in actin, intermediate filaments are built of interlocking proteins. A dense sheet of intermediate filaments strengthens the nucleus. Skin cells are filled with keratin, which at the last moment, just before they die. they cross link, to provide a really insoluble barrier layer of the skin. The cross linkage is between the sulphur atoms of cysteine, one of keratin's amino acids .

Interproximal wear
loss of enamel on the adjacent surfaces of teeth which is due to continual friction between the two surfaces as teeth move against each other.

Intratubular dentine
dentine formed inside the tubule by the odontoblast process in response to tooth wear, ageing or arrested caries.

Intrinsic fibres
refers to those fibres of cementum which were laid down by cementoblasts. see also extrinsic fibres

Ionised
the loss or gain of an electron from an atom which makes it no longer neutral but an electrically charged ion . If the electron leaves the atom it becomes a positively charged ion, such when calcium or sodium becomes ionised (Ca+,Na+). If the electron is gained, the atom becomes relatively negatively charged such as when chlorine or a phosphate group of atoms lose an electron (Cl-, PO4-). Ionized atoms or groups of atoms are more reactive than when they are neutral.

Ions
an atom or molecules which has a net electrical charge This may be caused by the temporary loss (positive ion) or gain (negative ion) of an electron. A calcium ion is written Ca+.

Ipsilateral
the same side as distinct from contralateral. Often used to refer to the teeth, joint or muscles on the same side as chewing is occurring.

Junctional epithelium
the epithelium which seals the base of the gingival sulcus against the tooth.

Keratan sulphate
a glycosaminoglycan found in cartilage, with chondroitin sulphate.

Keratin
a fibrous polymer which is notas strong as collagen but less soluble. It forms the strong and water-resistant properties of skin, nails, hair, horn and beaks.

Keratinised
an epithelium in which the superficial cells have lost their nuclei and become filled with intermediate filaments ofkeratin.

Keratinocytes
Cells of the epidermis which secrete the protein keratin. They become progressively flattened as they mature and are eventually are off.

Kreb cycle
the end stage of aerobic respiration. Kreb's cycle is a circular series of reactions taking place in the matrix of mitochondria in which acetyl CoA is broken down into carbon dioxide and hydrogen atoms. The hydrogen atoms are used to produce ATP via the electron transport system.

Lamella-bone
- the microscopic structure of cortical bone gives it the appearance of concentric or parallel plates ( from Latin, lamella, the diminutive of lamina, meaning a plate or leaf).

Lamina propria
the layer of loose connective tissue underneath the epithelium of mucosa, which provides physical and nutritional support.

Lamina-dura
the name given to the radiographic appearance of a dense layer of bone around the tooth root. It represents the dense cortical bone lining the tooth socket.

Laminin
an adhesive molecule of connective tissue related to fibronectin andtenascin.

Langherhans
cells are active in the immune response of the skin and mucous membrane. They act as sentries, detecting the presence of foreign antigens on the surface of the epithElium. They do not contain keratin and are thus sometimes called clear cells.

Lectin
- a protein molecule which bindson to a specific sequence of sugars. Bacteria may use lectin attachments to bind onto each other or oral surfaces.

Leucocytes
un pigmented (white) cells of the blood. Those with granular cytoplasm are neutrophils, eosinophils and basophils. The agranulocytes are lymphocytes and monocytes.

Leucotriens
concerned with signalling between cells of the immune system and a member of the eicosanoid family of hormones.

Ligand
a protein molecule which binds to another specific protein molecule. The forces of the bond are week and thus protein-ligand bonds depend on close fit of one molecule to the other, so as to capture as many bonding sites as possible. Ligands are specific for a particular protein. They are found on cell surfaces of microorganisms where they assist in cell adhesion. They are also sights on cell membranes onto which protein messengers attach such ascytokines (see also lectins).

Limbic system
a ring of structures around the thalamus which play a major role in pain as well as other types of behaviour. The limbic system includes the hypothalamus, hippocampus, amygdala, septum and cingulum. The limbic system plays an important role in pain at the level of motivation to avoid it. It thus operates at a slightly higher level than the reticular formation with strong connections to the thalamus and cortex.

Lipid
large molecules containing hydrogen and carbon which are insoluble in water. Simple lipids consist of long chains of fatty acids. Compound lipids contain phosphoric acid, sugars, nitrogenous bases or proteins, and include the phospholipids, glycolipids and lipoproteins. Steroids may also be classified as lipids.

Lubrication
helping two surfaces to slide over each other.

Lycine
one of 20 aminoacids common in proteins. It is a common amino acid of collagen and like proline must be hydroxylated by ascorbic acid in order to allow the formation of bonds which will hold the triple helix together..

Lymphocytes
white cells involved in the immune response. B lymphocytes are so called because they mature in bone while T lymphocytes mature in the thymus. Both cells look alike until they recognise a foreign antigen. The B cell starts to make antibodies while the T lymphocytes accumulate vesicles loaded with cytotoxic agents. On contact with a foreign cell, the lymphocytes changes shape so that all it vesicles are pointed at the enemy. The release of cytotoxic agents need to be carefully controlled. One of the methods by which the enemy cell is killed is by agents which make holes in its cell membrane. Enemy cells maybe bacteria, or the bodies own cells which have ingested viruses or they may be cancer cells, or the cells of transplanted organs .

Lymphokines
a variety of cytokines released by lymphocytes which coordinate the proliferation of T and B lymphocytes. They also regulate the brain's contribution to the immune response via the hypothalamus - adrenal cortex axis.

Lysosomes
small membrane bound vesicles in the cytoplasm of cells which contain toxic enzymes. When a cell dies, these membranes rupture and the enzymes are released. They break down the cells structure, and the debris is removed. The lysosome also contains cytokines which summon inflammatory cells and stimulate inflammation. The contents of lysosomes can be released by macrophages and neutrophils both to kill bacteria and viruses, and to stimulate inflammation.

Macrophages -
cells derived from monocytes which have the ability to phagocytose foreign particles and dead tissue and to move through tissue, or to remain fixed in one place. There are many macrophages in the spleen where they remove dead red blood cells from the circulation.

Major salivary glands
are three large glands on each side of the face; the parotid, submandibular and submaxillary.

Malleus
one of the three bones of the inner ear. The others are the stapes and the incus.

Mastication
the process of preparing food for swallowing and digestion by chewing it.

Matrix
comes from the Latin word 'mater'meaning mother. It is a structure which encloses or holds something within it. Cells are held or enclosed in a matrix of fibres, water and large molecules called the ground substance .

Matrix vesicles
. - small bubble-like structures containing calcium-binding phospholipids and alkaline phosphatase. Crystals of hydroxyapatite from inside the vesicle which ruptures and releasing crystals into the surrounding osteoid or predentine so as to start mineralising it.

Mechano-receptors
sensory receptors which respond when mechanically deformed by pressure, tension, vibration or touch.

Mesenchyme
dental mesenchyme is tissue derived from the mesoderm of the embryo and which has been infiltrated and highly influenced by migrating cells from theneural crest.

Mesial
towards the midline.

Mesial drift
a gradual movement of all the posterior teeth in a mesial direction. It occurs only if there has been interproximal wear between the teeth. The drift is not a passive one however, as it has been shown that during chewing, the bite force has a a mesial component.

Mesoderm
the middle of the three cell layers which form, as the clump of early embryonic cells begins to differentiate. The mesoderm will form the muscles, blood system, connective tissue, including bone and dentine, the kidneys and the dermis of the skin. The other two layers are the ectoderm and theendoderm.

Messenger RNA
a ribose nucleic acid acid which caries the DNA code in matching nucleotides, from the nucleus to the ribosome of the cell.

Metabolise
to obtain energy by breaking down a molecule into smaller components, as in respiration or to store energy by building a more complex molecule out of smaller components. It always takes place in a number of stages, controlled by enzymes. Each step in the process follows a predictable 'metabolic' pathway for that reaction.

Microbiology
the study of the microscopic forms of life.

Microfilaments
are the smallest filaments of the cytoskeleton. The filaments are made of hundreds of actin molecules, stacked in a line. They can be quickly broken down or extended. Actin filamanents give the cell its shape and help to change it. When cells move, in embryology and repair, or just during the continual patrol of lymphocytes, they must hold on to something in order to crawl. The filaments serve to anchor one part of the cell, via fibronectin to the cell matrix, so the rest of the cell can pull itself towards the anchor. Lymphocytes move and scavenge by sticking out arms and feet to help them crawl and engulf foreign particles. Muscle cells change their shape by using stacks of actin filaments as a ladder on which myosin climbs.

Micron
1000th part of a millimetre.

Microorganisms
single celled animals which may range from the very small viruses, through bacteria and fungi to almost visible protozoa.

Microtubules
are the largest filament in the cytoskeleton. They are the hollow tubes along which cell products are conducted long distances. The system is not unlike a railway network around the cell, sometimes involving long distances. For example, neurones transport out neurotransmitter substances along the axons to distant synapses, inside microtubules.

Minor salivary glands
are microscopic glands under the surface of the oral mucosa. They are found throughout the lining mucosa of the mouth including the tongue.

Mitochondria
a cell organelle found in eucaryotic cells which produces ATP as a product of the kreb cycle and the electron transport system Cells requiring large amounts of energy, such as secreting odontoblasts, have large numbers of mitochondria. Mitochondria are self replicating and contain their own DNA for this purpose.

Mitosis-
the division of a cell into two daughter cells, each of which is identical.

Mitotic activity
the rate of mitosis, and hence cell division. The mitotic activity of basal cells in an epithelium must match the rate of desquamation.

Molecules
a combination of atoms joined together in fixed proportions.

Monocytes
remain in the blood only a short time before they migrate into the tissues particularly where dead tissue must be removed, where they are calledmacrophages.

Morphogenesis
the process in which tissue shapes and organ structures are developed during embryology.

Morphogenic fieled
an environment in which the shape or pattern of a developing organ is determined.

Motoneurone
nerve cells with their cell bodies in the brain stem or spinal cord, which transmit impulses along their axons to effector organs, including endocrine, exocrine glands and muscles fibres. The axons of most motoneurones have many branches, each of which ends at a neuromuscular junction. The group of muscle cells innervated by one motoneurone is called a motor unit .

Mucoperiosteum
a type of oral mucosa which has a fibrous lamina propria , no submucosa, and is attached to the underlying periosteum of bone. The attached gingiva is a mucoperiosteum.

Mucous
a secretion which is viscous and slimy due to the presence ofglycoproteins .

Mutation
a change in the order of nucleotide bases on a gene, which alters the configuration of the protein produced, and thus may alter the behaviour of the cell. A mutation may cause a cell to die, or become cancerous. Mutations in bacteria and viruses help them to evade detection by their hosts.

Myelin
the fatty covering of myelinated nerves which appears white to the naked eye. The parts of the brain and spinal cord, in which myelinated nerves run, has therefore been called the 'white' matter as distinct from the 'grey' matter composed of nerve cells. Myelin also contains about 20 % of proteins whose prime role is to mediate adhesion between adjacent Schwann cells. These cell membrane glycoproteins are also members of the immunoglobulin family of cell surface proteins. Defects in the these surface proteins may cause them to act as antigens to the immune system. The disease multiple sclerosis is caused by antibodies to the myelin proteins, which results in inflammation and loss of myelin.

Myelinated
nerves axons which are completely wrapped in a sheath of myelin by schwann cells. One cell wraps about a millimetre of nerve axon. Myelinated nerve axons carry impulses faster then unmeyelinated nerves as the impulse jumps across the myelin sheath of each adjacent Schwann cell to that of the next

Nerve growth factor-
a cytokine that promotes the growth and repair of sensory nerves and maintenance of sympathetic nerves.

Neural crest cell
s - cells derived from the ectoderm layer in the embryo. This layer folds to form a neural tube which will later become the spinal cord of the animal. Cells from the crest of this fold, leave the ectoderm and migrate into the mesoderm layer. These neural crest cells are thus of ectomesenchymal origin. They migrate to form the dental mesenchyme, supportive cells of the nervous system, the adrenal cortex and melanocytes of the skin.

Neuromuscular junction
the synapse between the axon terminal of a motoneurone and a skeletal muscle fibre. The release at this synapse of the neurotransmitter substance, acetyl choline causes the muscle to contract.

Neuropeptides
compounds which have extremely potent affect to excite or depress nerve cells, in very low concentration . In this regard they are distinctly different from neurotransmitters. They include substances such as prostaglandins, substance P , endorphins and enkephalins. Neuropeptides also have receptors on lymphocytes and thus influence the immune response.

Neurotransmitters
chemicals which are secreted into a synapse in order to transmit an electrical nerve impulse from a nerve axon of one cell to the cell body of another nerve cell. They bind to receptors on nerve cells and are produced rapidly in high concentrations at nerve synapses. In these respects they differ from neuropeptides. There are many different neurotransmitter substances. They include acetyl choline, epinephrine, histamine, serotonin GABA and glutamate.

Niche
an opportunity which can be exploited in order to make a living or survive in an ecosystem.

Noma
a highly destructive and usually fatal infection of the teeth and jaws which is a progression of ANUG Only found in malnourished children. - also called cancrum oris.

Nucleic acids
occur as chains of nucleotides, either asDNA (two chains) or RNA(one chain) and make up the genetic material of a cell.

Nucleotides
are made up of three components, a pentose sugar (ribose or deoxyribose), a phosphate group and an organic base which may either be a purine ( adenine or guanine) or a pyrimidine ( cytosine thymine or uracil).This basic structure is found in many important cell molecules such as in ADP, ATP and coenzymes. Nucleotides also form the subunits from which nucleic acids (DNA and RNA)are built.

Nucleus
a cell organelle which contains the chromosomes whose genes control the structure of proteins within the cell. The nucleus is also a term used to refer to the mass of nerve cell bodies connected by tracts of nerve fibres, which occur in the brain.

Occlusal interference
contact between opposing teeth during chewing, which prevents the other teeth touching. In extreme lateral and protrusive positions of the jaw, this would happen in most dentitions and be of no concern. When occlusal interference occurs close to the area of maximum tooth contact, it may be troublesome.

Occlusal wear
loss of enamel on the biting surface of the teeth due to the abrasive action of chewing natural unprocessed food.

Odontoblast process
the extension of the cytoplasm of an odontoblast which remains surrounded by dentine during tooth formation. The process is still an active part of the cell and contributes to the production of intratubular dentine in response to ageing, tooth wear or arrested caries.

Odontoblasts-
cells lining the dental pulp, derived from the dental papilla wich form the dentine of the tooth crown and root. New odontoblasts may become differentiated from less specialised pericytes in the pulp.

Oncogenes
genes which have the capacity if expressed to cause tumour formation.

Organelle
a structures within a cell which has a specific structure or function, such as thenucleus, endoplasmic reticulum, golgi apparatus, lysosomes and mitochondria.. Cell organelles are a feature of eucaryotic cells.

Osmotic pressure
Water tends to move towards dense concentrations of ions. Sugar solutions on the surface of exposed dentine cause water to be drawn out of the dentinal tubules causing which distorts the odontoblast causing pain.

Osseous integration
a term used to describe the desired adhesion between an implant and the bone which holds it in place.

Osteoblasts
cells which differentiate from pericytes and secrete both the matrix and mineral of bone.

Osteocalcin
a calcium binding protein, synthesised by the osteoblast and secreted into the matrix at the time of bone mineralisation. Mice bread without the osteocalcin gene develop heavy bones suggesting that osteocalcin is a negative regulator of bone formation

Osteoclast
a multi-nucleate cellcapable of removing both the organic and mineral component of bone. Osteoclasts activity is controlled by nearby osteoblasts.

Osteoid
the extracellular matrix inwhich bone forms. It is high in collagen and other bone proteins but lacks any crystal formation.

Osteonectin
a bone glycoprotein which has the property of binding to both collagen fibres and the hydroxyapatite crystals, and thus may be important in initiating bone mineralisation by acting as a template for nucleation. Osteonectin is also produced by endothelial cells and plateletes and is able to bindfibrinogen.

Osteopontin
an adhesive glycoprotein related to sialoproteins, which is secreted by osteoclasts to assist in their adhesion to the bone surface. After bone resorption it may then act as a signal to stimulate osteoblast activity

Osteoporosis
a reduction in bone mass which occurs commonly in post menopausal females, but also in older men. It is due to a reduction in the activity of the ovaries and a decreased secretion of oestrogen. Bone formation and bone healing are not affected but more bone is resorbed by osteoclasts than is replaced. Lack of exercise is also a factor in bone loss.

Oxytalin fibres
are related to elastic fibres, though they have a smaller core of elastin. They are found in the periodontal ligament and in the epidermis of thin skin, but not in the oral mucosa.

Paracrine
cell messengers also called cytokines which are locally acting, produced by neighbouring cells or the extracellular matrix, as distinct from as distinct from endochrine or hormonal messengers.

Parakeratinised
an epithelium in which the superficial cells have not lost their nuclei , but have become filled with keratin. see also keratinised

Parasympathetic
part of the autonomic nervous system concerned with maintaining routine functions. Always acts as a balance to activity of the sympathetic nervous system.

Pathogenic
able to cause disease.

Pellicle
a thin layer of salivary proteins which forms on the surface of enamel.

Peptide bonds
a covalent bond made between the carbon atom of the carboxyl group of one amino acid and the nitrogen atom from the amine group of another. In the process a molecule of water is removed. Peptide bonds allow chains of amino acids to form polypeptides and proteins When peptide bonds are broken apart they need water to reform the amino acids. This process is known as hydrolysis, and occurs during cooking and in digestion. .

Periaquaductal grey
is an integrative centre for inputs form the autonomic nervous system, the limbic system and from sensory and motor pathways. It has an inhibitory affect on pain transmission due to descending connections through the raphe nucleus along the corticospinal tract to the cells of the dorsal horn.

Pericytes
small cells lying next to the endothelial cells of capillaries which have the capacity to differentiate into osteoblasts.

Periodontal pocket
loss of epithelial attachment to the tooth, producing an increase in gingival sulcus depth beyond the normal 1-2 mm.

Periosteum
a connective tissue layer containing osteoblasts on the external aspect of all bones. see alsoendosteum.

Peritubular dentine
see intratubular dentine