口腔生理学术语(B)

    basal lamina - a term used to describe the different layers which make up the basement membrane. these different layers of the basement membrane, the lamina lucida and lamina densa are only visible with electron microscopy. into the lamina dense collagen fibres of the lamina propria are anchored. and on the epithelial side are anchored bundles of tonofilaments from the hemi-desmosomes which anchor the basal epithelial cells to the basement membrane.

    basement membrane - a thin sheet of proteins held together by type iv collagen. on this sheet epithelial cells attach with hemi-desmosomes. all epithelia, whether simple cuboidal cells such as found in the salivary glands, or endothelial cells lining capillaries or thick stratified squamous epithelia of the skin, are all anchored to a basement membrane.

    benign- not harmful. in the sense of tumours, not malignant. when referring to parasites, quite harmless.

    biofilm - a layer of microorganisms on a surface which is kept constantly wet. dental plaque is an oral biofilm

    biosurfactants - products of bacteria which increase the hydrophilic nature of a surface so as to allow for better adhesion.

    blood clotting - one of three key processes in haemostasis, the prevention of blood loss. after three minutes of rupture of a small blood vessel, the entire cut is filled with a blood clot. after an hour, the clot has retracted inside the vessel making the plug even more effective. within a few more hours, fibroblasts have moved into the clot, followed by capillary -forming endothelial cells. within 10 days the clot is replaced by fibrous scar tissue. clotting takes place in three steps. 1. in response to damage to the blood vessel prothrombin activator is formed. 2 this activator converts prothrombin into thrombin. 3.the thrombin acts as an enzyme converting fibrinogen into fibrin threads which adhere to the damaged walls of the blood vessel, trap platelets, blood cells and plasma to form a clot.

    blood groups - blood cells from different people do not always have the same cell surface antigens. a transfusions of blood whose antigens do not match the recipient evokes an immune response and the donor cells are broken down. two of the common blood groups are the a,b,o group and the rh group. the blood group antigens are glycoproteins or glycolipids.

    bolus - a piece of food which is being chewed to break it down into small pieces.

    bone membrane - a theoretical membrane separating the fluid surrounding bone crystals from the fluid of the surrounding connective tissue. the membrane would be formed by the endosteum.

    bone morphogenic proteins (bmp) - part of the cytokine family of transforming growth factors. bmp have a powerful ability to cause differentiation of stem cells into osteoblasts and to initiate bone formation.

    bradykinin - one of several substances, all known as kinins, which cause vasodilation and increased capillary permeability, both events associated with inflammation.

    buffers - chemical which are able to keep the ph of a solution within a normal range, neither acid nor alkali. salivary buffers are important in reducing the progress of caries by neutralising plaque acids.

    buttress- an arch shaped support, used by builders of bridges and churches in the days before steel.