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Dead space

the air within the respiratory tract that never reaches the alveoli within the lungs and so does not undergo gaseous exchange


the breakdown of excess amino acids in the liver, whereby the amine group is removed and converted to ammonia and eventually urea before excretion

Deciduous dentition

teeth seen in the young animal soon after birth. These are shed after a few months and are replaced by the permanent teeth.


act of passing feces from the rectum

Definition (radiographic)

the quality of the radiograph which is affected by density, contrast and sharpness


the act of swallowing

Density (radiographic)

the degree of blackening of the radiograph

Dermal papilla

structure situated at the base of the hair follicle containing nerves and blood vessels, which supply nutrients necessary for hair growth


layer of dense connective tissue lying beneath the epidermis


the process of losing moisture or “drying out” when exposed to air


a chemical that disperses and removes soil, organic material and greasy residue from surfaces as well as reducing surface tension and increase the penetrating ability of water. This is a process that is important in allowing disinfectants to penetrate the pathogens underneath. Some disinfectants have their own detergent properties (eg the halogens – bleach and iodine, quaternary ammonium compounds).


a chemical solution which converts exposed silver bromide crystals into silver metal within the emulsion during processing


production of faeces that contain an excess amount of water


a space between teeth. There is a natural space in the jaw of rodents and herbivores where canine teeth would be found in other species.


relaxation stage of the cardiac cycle. The term applies to both atrial and ventricular relaxation.


the net movement, as a result of random motion of its particles, of a substance from an area of high concentration to an area of low concentration


the process by which food materials are broken down into small soluble chemical units

Diploid cells

cells with the full number of chromosomes, each in pairs. These include most cells within the animal’s body.

Diploid number

the number of chromosomes (2n) found in the nucleus of all cells except gametes which are haploid cells


a chemical used to control, prevent and destroy pathogens present on inanimate objects - although it is not usually active against bacterial spores. The process does not necessarily kill all micro-organisms, but reduces then to a level acceptable for a defined purpose, for example a level which is considered not harmful to health. (Note, the difference between “disinfectants” and “antiseptics” which are applied to living tissues.)


the removal or inactivation of pathogenic micro-organisms but not necessarily of bacterial spores


to loose inhibitions and become exited


increased amount of urine produced


drugs used to increase the production of urine by the kidneys and so reduce water retention in the body


deoxyribonucleic acid, the genetic material found inside the nucleus of the cell

DNA gyrase

enzyme that controls coiling and uncoiling of DNA

DNA polymerase

enzyme that catalyses the synthesis of new DNA molecules

Dominant gene

a gene whose characteristics are always present in the phenotype, in homozygous and heterozygous individuals. It is represented with a capital letter, e.g. B.


a device for monitoring exposure to X-rays

Drug schedule

classification of drugs within the Misuse of Drugs Regulations 2001

Dry matter

food residue after being heated to remove all the water


smaller than normal size


abnormal shedding of the skin of reptiles


difficulty swallowing



difficult parturition; difficulty giving birth


difficulty in passing urine

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