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Home >>Biology Dictionary >> Dental Formula - Diageotropism

Demography. Numerical study of human populations.

Dendrite. A slender branching process of the cell body of a neurone. It forms connections (see synapse) with the axons of other neurons and transmits nerve impulses from these to the cell body.

Dental formula. Formula indicating for a given species of mammal, the number of each kind of its teeth. The number in the upper jaw of one side is written above that in the lower jaw of one side; and the categories are given in the order; incisors, canines, premolars, molars.

2 1 2 3

man
(32 teeth)
1 1 2 3
3 1 4 2 bear
(42 teeth)
3 1 4 3
2 0 3 3 rabbit
(28 teeth)
1 0 2 3

Dentary. The only bone of the lower jaw of mammals, only on each side; one of several lower bones in other vertebrates. A dermal bone.

Dentine. Main constituent of teeth. Like bone in structure, but contains no cells, though cell-processes penetrate it from cells in pulp cavity of tooth. Formed from mesoderm or neural crest of embryo. Ivory is dentine.

Dermis (corium; cutis).
The thicker and innermost layer of the skin of vertebrates, the other layer being the epidermis.

The dermis consists of fibrous connective tissue in which are embedded blood vessels, sensory nerve endings, and (in mammals) hair follicles, sebaceous glands, and sweat ducts. Beneath the dermis lies the subcutaneous tissue.

Desmoplera. The order of insectivorous mammals containing the flying lemurs that have a membrane stretching between wrist, ankle and tail.

Description. The formal statement of the character of a taxon with particular emphasis on those distinguishing it form other closely related forms.

Desmosomes.
Attachments between adjacent cells a few tenths of a micrometer in diameter, consisting of a number of intracellular filaments attached to a dense patch inside the plasma membrane, corresponding to a similar arrangement in the adjacent cell.

Detergent. A substance that when dissolved in water acts as a cleansing agent for the removal of grease by altering the inter facial tension of matter with other liquids or solids.

Determinant. (Antigenic). The part of an antigen molecule that forms a specific attachment to the combining site of a corresponding antibody. (Genetic) A factor that transmits inheritance, either a gene or a plasm gene.

Determination.
The process by which embryonic tissues become able to produce only one particular sort of adult organs or tissue.

Determined. Describing embryonic tissue at a stage when it can develop only as a certain kind of tissue (rather than as any kind).

Detritus. Organic debris from decomposing plants and animals.

Deutoplasm. Yolk

Dextrose. Glucose.

Diadelphous. (of staments) united by their filaments to form two groups, or having one salitary and the others united, e.g. pea.

Diageotropism. Orientation of plant part by growth curvature in response to stimulus of gravity so that its axis is at right-angles to direction of gravitational force, i.e. horizontal; exhibited by rhizomes of many plants.

Diagnosis.
Statements that distinguishes the particular Taxon in question from other similar taxa, internus of the most important haractrs.

Dialysis.
A method by which large molecules (such as starch or portein) and small molecules (such as glucose amino acids) in solution may be separated by selective diffusion through a semipermeable membrane. For example, if a mixed solution of starch and glucose is placed in a closed container made of a semipermeable substance (such as Cellophane), which is then immersed in a breaker of water, the smaller glucose molecules will pass through the membrane into the water while the starch molecules remain behind. The cell membranes of living organisms are semipermeable, and dialysis take place naturally in the kidney for the excretion of nitrogenous waste. An artifical kidney (dialyser) utilizes the principle of dialysis by taking over the functions of diseased kidneys.
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