A

Acidosis
Too much acid in the body, a distinctly abnormal condition resulting from the accumulation of acid or from the depletion of alkaline reserves. In acidosis, the pH of the blood is abnormally low. Acidosis is associated with diabetic ketoacidosis, lung disease, and severe kidney disease. The opposite of acidosis is alkalosis.

Alactasia
Lack of the enzyme lactase which is needed to digest the milk sugar lactose.
AAlbumin
The main protein in human blood and the key to the regulation of the osmotic pressure of blood. Chemically, albumin is soluble in water, precipitated by acid, and coagulated by heat.

Alkalosis
A dangerous decrease in the normal acidity of the blood. There is too much base in the blood and body. This is a distinctly abnormal condition. It results from the accumulation of base or from the depletion of acid. The pH of the alkalotic body is above normal. Alkalosis can be caused by high altitudes, hyperventilation, and excessive vomiting. The opposite of alkalosis is acidosis.

Allergen
A substance that is foreign to the body and can cause an allergic reaction in certain people. For examples, pollen, dander, mold.
Allergy
A misguided reaction to foreign substances by the immune system, the body system of defense against foreign invaders, particularly pathogens (the agents of infection). The allergic reaction is misguided in that these foreign substances are usually harmless. The substances that trigger allergy are called allergen.
Anaphylactic shock
A widespread and very serious allergic reaction. Symptoms include dizziness, loss of consciousness, labored breathing, swelling of the tongue and breathing tubes, blueness of the skin, low blood pressure, heart failure, and death. Immediate emergency treatment is required.
Antibody
An immunoglobulin, a specialized immune protein, produced because of the introduction of an antigen into the body, and which possesses the remarkable ability to combine with the very antigen that triggered its production. The production of antibodies is a major function of the immune system and is carried out by a type of white blood cell called a B cell (B lymphocyte). Antibodies can be triggered by and directed at foreign proteins, microorganisms, or toxins. Some antibodies are autoantibodies and home in against our own tissues.
Anus
The opening of the rectum to the outside of the body.
Appendix
A small outpouching from the beginning of the large intestine (the ascending colon).
Autoantibody
An antibody directed against the patient's own body tissue.

Autoimmunity
The immune system fights infections and illnesses. It prevents you from getting sick, or, if you do, it helps you get better. It's called the immune system because it's not just one body part. It's a system of different organs, cells, and proteins known as antibodies. Together, they identify, attack, and destroy germs and other foreign substances.But sometimes the immune system makes a mistake and attacks part of the body. This is called autoimmunity. One example of an autoimmune disease is type 1 diabetes, in which the immune system destroys the cells in the pancreas that produce insulin.

Autosomal recessive
A genetic condition that appears only in individuals who have received two copies of an autosomal gene, one copy from each parent. The gene is on an autosome, a nonsex chromosome. The parents are carriers who have only one copy of the gene and do not exhibit the trait because the gene is recessive to its normal counterpart gene.