Angiogenesis - the development of blood vessels - a key event in embryology and healing.

Ankylosis - bony fusion of the two surfaces of a joint to each other, which prevents movement. Ankylosis of the tooth root to its bony socket may causes root resorption.

Antibacterial - inhibiting the growth of bacteria.

Antibodies -are proteins called immunoglobulins which circulate in the blood and body fluids. They bind specifically to antigens that have induced them. Antibodies are able to inactivate bacterial toxins, viruses and help phagocytes to engulf whole bacteria. They have a vital role to play in the bodies immune response to foreign proteins.

Antigens - proteins, usually foreign, which cause the bodies defense system to produce an antibody. Antigens may be food proteins, bacteria ,viruses or protozoa or cells from another individual(transplant).

Antrum - a hollow cave or SINUS, inside the maxillary bone which is lined by respiratory epithelium.

Apatites- a family of calcium1 phosphate salts which are found in hard tissues like bone, teeth and shells.

Apoptosis - death of a cell which is programmed by a set of specific genes. Apoptosis of chondrocytes allows osteoblasts to attach to their calcified3 matrix, and the epithelial cells forming webs between the fingers to die.

Articular - one of the bones which together with the quadrate bones and the dentary, made/make up a reptile's jaw. In mammals the quadrate bone is incorporated into the middle ear as the malleus.

Artificial mouth - a laboratory device for keeping bacteria growing in a controlled environment It allows for observing bacteria and their growth under different experimental conditions.

Ascorbic acid - or Vitamin C is a dietary requirement for the proper formation of collagen. Deficiency causes scurvy.

ATP - adenosine triphosphate - ATP is a convenient packet of energy used by both animals and plant cells. The energy in ATP is stored in its three negatively charged phosphate groups which are held close together, in spite of their repulsion for each other. This energy, multiplied many hundreds of thousand of times, for each cell is able to move our muscles, transport molecules across membranes and power all the cells other energy requirements. Once the energy has been used the ATP molecule6 now only has two phosphate groups. It needs energy now from either aerobic or anaerobic10 respiration to charge it up again, a process known as phosphorylation. Large stores of ATP are not kept as it is highly reactive. The long term storage of energy in animals is in carbon rich molecules, such as glycogen or fatty acids. In plants energy is stored as starch.

Attachment, see epithelial-attachment

Autocrine; cell messengers which are produced by the cell itself and regulate the expression of genes .

Autonomic nervous system - controls routine body functions such as gut14 activity, respiration, blood pressure and heart rate. There are two main divisions the sympathetic nervous system and the parasympathetic system.

Axon - the extension of a nerve cell, as a thin tube which may be as long a metre or a few short microns in length. The axon, like the cell body is able to depolarise and carry impulses along its length. The impulses from one axon to another nerve cell are transmitted at a synapse15. Axons may be myelinated or unmeyelinated, and they may vary in diameter. Thicker, myelinated axons transmit impulses faster than thins unmeyelinated axons.