446 age spots Also known as liver spots, sun spots, or lentigines. Brown spots on the skin

Glossary that resemble freckles and that are caused by long-term exposure to sunlight.

agnosia The inability to recognize familiar faces, locations, or objects. Agnosia may result from brain damage due to head injury or stroke.

AIDS See acquired immunodeficiency syndrome.

allergen Any substance—such as pollen, animal dander, or a particular food—that produces an allergic reaction in some people.

allergic contact dermatitis A skin condition that occurs when the skin comes into contact with an allergen, causing a rash that is characterized by redness, swelling, and blisters. Allergic contact dermatitis may be difficult to distinguish from other skin conditions (see eczema, atopic).

allergic reaction An inappropriate immune system response that occurs when an allergen enters the body.

allergic rhinitis Also known as hay fever. An inflammation of the mucous membrane lining the nose and caused by an allergic reaction. Symptoms include coughing, stuffy nose, and sneezing.

allergy An abnormal sensitivity to an allergen.

alpha-blocker A medication used to treat heart and circulation disorders such as high blood pressure and peripheral vascular disease.

ALS See amyotrophic lateral sclerosis.

Alzheimer's disease A progressive, incurable condition that destroys brain cells, gradually causing loss of intellectual abilities (such as memory) and extreme changes in personality and behavior.

amino acids Chemical compounds that are the basic components of all proteins.

amnesia Loss of the ability to store information in memory or to recall information already stored in memory. Amnesia can be caused by brain damage or disease and is a common symptom of various neurological disorders.

amyotrophic lateral sclerosis Also known as Lou Gehrig's disease. This most common motor neuron disease is characterized by a progressive loss of muscle function, leading to paralysis.

anabolic steroids Synthetic drugs that imitate the effects of testosterone.

anaphylactic shock A severe, life-threatening allergic reaction that requires immediate medical treatment. Symptoms include a sudden, severe drop in blood pressure and difficulty breathing.

androgens Male sex hormones.

anemia A blood disorder caused by a deficiency of red blood cells or hemoglobin; 447

anemia reduces the ability of the blood to supply oxygen to the tissues and to remove Gl°ssary carbon dioxide from the body.

aneurysm An abnormal ballooning of a weakened area in an artery wall. An aneurysm in the brain may rupture, causing a hemorrhagic stroke.

angina A tight, heavy, squeezing pain sensation deep beneath the breastbone or in a band across the chest that results from a reduced supply of oxygen to the heart muscle, indicating coronary artery disease. The pain also may radiate to the left arm, shoulder, neck, jaw, or middle of the back and may be accompanied by nausea, sweating, or shortness of breath.

angiography A diagnostic procedure for examining the inside of an artery. A contrast medium is injected through a catheter into the artery, and a rapid-sequence series of X rays is taken.

angioplasty A surgical procedure used to clear a narrowed or blocked artery.

angiotensin-converting enzyme (ACE) inhibitor An antihypertensive used to treat high blood pressure and heart failure.

ankylosing spondylitis A form of rheumatoid arthritis that primarily affects the spine, shoulders, hips, and knees.

anorexia A potentially life-threatening eating disorder (most frequently occurring in young women) that is characterized by an abnormal fear of being fat, prolonged avoidance of food, excessive weight loss, and obsession with exercise.

antibiotic A medication used to treat bacterial infections.

antibodies Also known as immunoglobulins. Proteins found in the blood and tissue fluids that protect the body from infectious organisms.

anticoagulant A medication used to treat abnormal blood clotting.

antidepressant A medication used to treat depression. Three commonly prescribed types of antidepressants are tricyclic antidepressants, monoamine oxidase inhibitors, and selective serotonin reuptake inhibitors.

antigens Proteins such as microorganisms or toxins that trigger the immune system to produce antibodies.

antihistamine A medication that blocks the effects of histamine.

antihypertensive A medication used to treat high blood pressure. See also alpha-blocker, angiotensin-converting enzyme (ACE) inhibitor, beta-blocker, calcium channel blocker, and diuretic.

anti-inflammatory A medication such as aspirin or ibuprofen that relieves the symptoms of inflammation.

448 antioxidant A compound that protects against cell damage caused by oxygen free

Glossary radicals.

anus The opening at the rectum through which feces pass to the outside of the body.

aorta The body's main artery.

aortic stenosis The most common heart valve disorder. Aortic stenosis causes narrowing or stiffening of the aortic valve and can lead to angina and heart failure.

aortic valve The valve between the aorta and the left ventricle of the heart.

aphasia Loss of language skills (comprehension, expression, or both) due to a brain injury.

apraxia The inability to perform tasks, such as dressing or tying one's shoes, because of loss of the ability to recall the sequence of necessary steps.

arrhythmia An abnormally fast or slow heartbeat or an irregular heartbeat.

arteriole A tiny branch of an artery.

arteriosclerosis A term used to describe a group of disorders characterized by thickening and scarring of artery walls. See also atherosclerosis.

arteriovenous malformation A congenital disorder in which there is a fragile, tangled web of arteries and veins in a particular part of the body, such as the brain, spinal cord, or digestive tract.

artery A blood vessel that carries oxygen-filled blood away from the heart to the organs and tissues.

arthritis A general term used to describe inflammation of a joint accompanied by swelling, stiffness, and pain. See also osteoarthritis and rheumatoid arthritis.

arthroplasty A surgical procedure in which a damaged joint is replaced with an artificial joint made of metal and plastic. Arthroplasty is most often used on the knee and hip, but it is also performed on the ankles, hands, wrists, and toes.

arthroscopy Examination of or surgery on a joint using a viewing tube called an arthroscope inserted through a small incision.

artificial crown See crown, artificial.

asthma A respiratory disorder characterized by reversible narrowing of the airways, causing wheezing, shortness of breath, chest tightness, and coughing.

asymptomatic Without signs or symptoms of disease.

atheroma Fatty deposits on the inner lining of an artery that can lead to atherosclerosis.

atherosclerosis The buildup of fatty material called arterial plaque in the inner lining 449

of an artery; atherosclerosis can narrow the blood vessels and reduce blood flow to the Gl°ssary organs and tissues, increasing the risk of myocardial infarction (MI) or stroke.

athlete's foot Also known as tinea pedis. A common contagious fungal infection of the foot that affects the skin between the toes or of the soles or sides of the feet. Athlete's foot causes the skin to itch, peel, crack, and, occasionally, form blisters.

atopic eczema See eczema, atopic.

atria See atrium.

atrial fibrillation An abnormal heartbeat in which the atria beat rapidly and irregularly, and independently of the ventricles.

atrium Singular of atria. One of the two small upper chambers of the heart.

audiogram A graphic record of a person's hearing ability that is obtained during audiometry.

audiologist A health professional trained to evaluate hearing loss and to fit hearing aids.

audiometry Hearing tests performed to measure a person's hearing ability.

auditory nerve Also known as the acoustic nerve. The part of the vestibulocochlear nerve (eighth cranial nerve) that carries sensory impulses from the cochlea in the inner ear to the hearing center in the brain, where the impulses are interpreted as sound.

autoimmune disease A disease in which the immune system mistakenly attacks the body's own cells and tissues.

autologous blood donation Donation of a person's own blood before scheduled elective surgery to make the blood available in case a transfusion is necessary during or after surgery.

"bad" cholesterol See low-density lipoprotein (LDL) cholesterol. balanitis Inflammation of the head and foreskin of the penis.

basal cell carcinoma A slow-growing form of skin cancer, found in the outer layer of skin, that rarely spreads to other parts of the body. Basal cell carcinoma accounts for about 90 percent of all skin cancers.

B cell See lymphocyte.

Bell's palsy A peripheral nerve disorder that causes one-sided weakness, twitching, or paralysis of the facial muscles.

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