In medicine, absorption is defined as the process through which substances (for example drugs and nutrients) reach blood circulation.
Aerosol is a colloidal suspension (see also “colloid”) composed of liquid or solid particles dispersed in gas
Amino acids are organic molecules consisting of a basic amino group (―NH2), an acidic carboxyl group (―COOH), and a side chain (which is unique to each amino acid) attached to a central carbon atom. Few linked amino acids form peptides, while large chains of amino acids (>50) form proteins.
A unit of length equal to 10−10 meters. In natural sciences, the Ångstrom is often used to indicate the dimensions of atoms, the lengths of chemical bonds, and to measure the wavelength of radiations.
An antibiotic is an antimicrobial substance designed to kill bacteria or inhibit their growth. Antibiotics cannot kill viruses. Hence, antibiotics have no therapeutic effect in case of viral infections.
Antimicrobial resistance occurs when pathogens (mostly bacteria and fungi), develop molecular mechanisms that allow them to become resistant to those drugs designed to kill them.
An antibody (or Immunoglobulin) is a glycoprotein produced by specialized immune cells (named plasma cells) against a specific antigen. Once secreted in the extracellular space, the antibody recognizes the antigen and binds to it. The antigen-antibody binding activates other components of the immune system, thus leading to the neutralization and destruction of the organism expressing that particular antigen.
An antigen is a molecule that induce the production of antibodies against it. “Foreign antigens” are fragments of pathogens (such as bacteria, viruses, parasites), chemicals, pollens, and toxins. “Self-antigens” are those peptides, carbohydrates, and nucleic acid sequences produced by our body and presented to the immune cells. In normal conditions, the immune system is able to differentiate self- from non self-antigens. However, in autoimmune disorders, immune cells secrete antibodies against self-antigens.
Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals and other molecules that may damage the cells of an organisms. Examples of antioxidants are ascorbic acid (vitamin C), vitamin A, Vitamin E, beta-carotene, and turmeric (curcumin). See also “oxidative stress”.
Apoptosis is the programmed sequence of molecular events within a cell leading to its death.
Aptamers are single-stranded DNA or RNA molecules able to bind specific target molecules (such as proteins and carbohydrates).
An atom is the smallest particle of matter that possess all the physio-chemical properties of a specific chemical element.
An axon is a long projection of a neuron that conducts electrical impulses and carries nutrients from the center to the periphery of the neuronal cell. The axon has the central function of transmitting the impulse from one neuron to another one. According to their function and position within the nervous system, axons can measure from few millimeters to more than one meter in length.