Down Syndrome Glossary of Medical Terms

Abnormal: Not normal. Deviating from the usual structure, position, condition, or behavior. In referring to a growth, abnormal may mean that it is cancerous or premalignant (likely to become cancer ).
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Acute: Of abrupt onset, in reference to a disease. Acute often also connotes an illness that is of short duration, rapidly progressive, and in need of urgent care.
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Advanced maternal age: Usually defined as age 35 or more for the mother at the time of delivery of her baby.
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Aging: The process of becoming older, a process that is genetically determined and environmentally modulated.
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Allele: An alternative form of a gene. One of the different forms of a gene that can exist at a single locus (spot on a chromosome ). Also one of the different forms of any segment of a chromosome.
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Alpha-1: Short for alpha-1 antitrypsin deficiency .
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Alzheimer disease: See: Alzheimer's disease .
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Alzheimer's disease: A progressive neurologic disease of the brain that leads to the irreversible loss of neurons and dementia . The clinical hallmarks of Alzheimer's disease are progressive impairment in memory, judgment, decision making, orientation to physical surroundings, and language. A working diagnosis of Alzheimer disease is usually made on the basis of the neurologic examination. A definitive diagnosis can be made only at autopsy. On a cellular level, Alzheimer's disease is characterized by unusual helical protein filaments in nerve cells (neurons) of the brain. These odd twisted filaments are called neurofibrillary tangles. On a functional level, there is degeneration of the cortical regions, especially the frontal and temporal lobes, of the brain.
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Amniocentesis : Procedure used in prenatal diagnosis to obtain amniotic fluid which can be used for genetic and other diagnostic tests. Informally called an "amnio."
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Analysis: A psychology term for processes used to gain understanding of complex emotional or behavioral issues.
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Arm: 1. In popular usage, the appendage that extends from the shoulder to the hand. However, the medical definition refers to the upper extremity extending from the shoulder only to the elbow, excluding the forearm, which extends from the elbow to the wrist. The arm contains one bone: the humerus. 2. In a randomized clinical trial, any of the treatment groups. Most randomized trials have two "arms," but some have three "arms," or even more.
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Arms: An appendage in anatomy and in clinical trials . See: Arm .
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Atresia: Absence of a normal opening or failure of a structure to be tubular.
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Atrial: Pertaining to the atria , the upper chambers of the heart, as in atrial fibrillation and atrial septal defect .
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Bacterial: Of or pertaining to bacteria . For example, a bacterial lung infection .
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Biopsy: The removal of a sample of tissue for purposes of diagnosis. (Many definitions of "biopsy" stipulate that the sample of tissue is removed for examination under a microscope. This may or may not be the case. The diagnosis may be achieved by other means such as by analysis of chromosomes or genes.)
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Blood: The familiar red fluid in the body that contains white and red blood cells , platelets , proteins , and other elements. The blood is transported throughout the body by the circulatory system . Blood functions in two directions: arterial and venous. Arterial blood is the means by which oxygen and nutrients are transported to tissues while venous blood is the means by which carbon dioxide and metabolic by-products are transported to the lungs and kidneys, respectively, for removal from the body.
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Bowel: Another name for the intestine . The small bowel and the large bowel are the small intestine and large intestine , respectively.
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Cardiac: Having to do with the heart.
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Cell: The basic structural and functional unit in people and all living things. Each cell is a small container of chemicals and water wrapped in a membrane .
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Chorion: The outermost of the two fetal membranes - the amnion is the innermost --. which together surround the embryo. The chorion develops villi (vascular fingers) and gives rise to the placenta. In Greek, the word "chorion" means "skin or leather."
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Chromatin: The nucleoprotein material of chromosomes. Chromatin is essentially the substance of chromosomes . It is made up of DNA attached to a protein structure, together with chromosomal RNA . Chromatin exists in two states, euchromatin and heterochromatin , with different staining and functional properties.
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Chromosome: A visible carrier of the genetic information.
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Chromosomes: The microscopically visible carriers of the genetic material. They are composed of deoxyribonucleic acid (DNA) and proteins and, under a microscope, look like little rods.
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Collagen: Collagen is the principal protein of the skin, tendons, cartilage, bone and connective tissue.
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Condition: The term "condition" has a number of biomedical meanings including the following:

1. An unhealthy state, such as in "this is a progressive condition."
2. A state of fitness, such as "getting into condition."
3. Something that is essential to the occurrence of something else; essentially a "precondition."
4. As a verb: to cause a change in something so that a response that was previously associated with a certain stimulus becomes associated with another stimulus; to condition a person, as in behavioral conditioning.

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Congenital: Present at birth. A condition that is congenital is one that is present at birth. There are numerous uses of "congenital" in medicine. There are, for example, congenital abnormalities. (For more examples, see below.)
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Congenital heart disease: A malformation of the heart or the large blood vessels near the heart. The term "congenital" speaks only to time, not to causation; it means "born with" or "present at birth."
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CVS: 1. Chorionic villus sampling , a procedure for first-trimester prenatal diagnosis . 2. Cyclic vomiting syndrome , also known as abdominal migraine .
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Dementia : Significant loss of intellectual abilities such as memory capacity, severe enough to interfere with social or occupational functioning.
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Developmental delay: Behind schedule in reaching milestones of early childhood development.
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Diagnosis: 1 The nature of a disease ; the identification of an illness. 2 A conclusion or decision reached by diagnosis. The diagnosis is rabies . 3 The identification of any problem. The diagnosis was a plugged IV.
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Dilatation: The process of enlargement or expansion.
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DNA: Deoxyribonucleic acid. One of two types of molecules that encode genetic information. (The other is RNA . In humans DNA is the genetic material; RNA is transcribed from it. In some other organisms, RNA is the genetic material and, in reverse fashion, the DNA is transcribed from it.)
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DNA repair: The body has a series of special enzymes to repair mutations (changes) in the DNA and restore the DNA to its original state.
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Down syndrome : A common chromosome disorder due to an extra chromosome number 21 (trisomy 21). Down syndrome causes mental retardation, a characteristic face, and multiple malformations. Down syndrome is a relatively common birth defect. The chromosome abnormality affects both the physical and intellectual development of the individual.
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Down syndrome critical region: (Abbreviated DSCR) A region on the long (q) arm of chromosome 21 thought to be responsible for some, if not all, of the features of Down syndrome. A number of genes in this region may be involved in the production of the Down syndrome phenotype.
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Duodenal: Pertaining to the duodenum , part of the small intestine. As in duodenal ulcer or duodenal biliary drainage.
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Duodenum: The first part of the small intestine . The duodenum extends from the pylorus at the bottom of the stomach to the jejunum , the second part of the small intestine . The duodenum is a common site for the formation of peptic ulcers . We often live with words without thinking where they come from or what they originally meant. That is the case for me with the duodenum. For decades, this writer knew the duodenum as a short but troubled sector of the small intestine. Only today did I learn that the duodenum began as the dodeka-daktulon, twelve fingers to the Greeks, who astutely observed that the duodenum is about 12 finger-breadths long. In German, the popular term for duodenum is Zwölffingerdarm, the 12-finger intestine.
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Duplication: Part of a chromosome in duplicate, a particular kind of mutation (change) involving the production of one or more copies of any piece of DNA, including a gene or even an entire chromosome.
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Endocardial: Pertaining to the endocardium , the inside lining of the heart.
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Epicanthal fold: A fold of skin that comes down across the inner angle (canthus) of the eye. The epicanthal fold is more common in children with Down syndrome and other birth defects than normal children and so is of value in diagnosis. Although some dictionaries state that this eye fold is found in peoples of Asian origin, this is not true. The normal Asian eyefold is continuous with the lower edge of the upper eyelid and actually appears distinctly different than a true epicanthal fold.
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Esophageal: Pertaining to the esophagus .
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Esophagus: The tube that connects the pharynx (throat) with the stomach. The esophagus lies between the trachea (windpipe) and the spine. It passes down the neck, pierces the diaphragm just to the left of the midline, and joins the cardiac (upper) end of the stomach. In an adult, the esophagus is about 25 centimeters (10 inches) long. When a person swallows, the muscular walls of the esophagus contract to push food down into the stomach. Glands in the lining of the esophagus produce mucus, which keeps the passageway moist and facilitates swallowing. Also known as the gullet or swallowing tube. From the Greek oisophagos, from oisein meaning to bear or carry + phagein, to eat.
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Eye color: The color of the iris. The genetics of eye color are complicated. Eye color is polygenic. It is determined by multiple genes. The eye color genes include EYCL1 (a green/blue eye color gene located on chromosome 19), EYCL2 (a brown eye color gene) and EYCL3 (a brown/blue eye color gene located on chromosome 15). There are clearly other genes that influence eye color. The once-held view that blue eye color is a simple recessive trait has been shown to be wrong. The genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.
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Father: (1) The male parent. (2) One who originates. For example, " Wilhelm Roentgen is considered the father of radiology ." (3) To produce offspring as a male. (4) To provide paternal protection and guidance to children.
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Femur: The femur is the bone in the leg that extends from the hip to the knee.
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Fertile: Able to conceive and bear offspring.
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Gastrointestinal: Adjective referring collectively to the stomach and small and large intestines.
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Gastrointestinal tract: The tube that extends from the mouth to the anus in which the movement of muscles and release of hormones and enzymes digest food. The gastrointestinal tract starts with the mouth and proceeds to the esophagus, stomach, duodenum, small intestine, large intestine (colon), rectum and, finally, the anus. Also called the alimentary canal, digestive tract and, perhaps most often in conversation, the GI tract.
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Gene: The basic biological unit of heredity . A segment of deoxyribonucleic acid (DNA) needed to contribute to a function.
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Genes: The basic biological units of heredity . Segments of deoxyribonucleic acid (DNA) needed to contribute to a function.
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Genetic: Having to do with genes and genetic information.
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Genetic counseling: An educational counseling process for individuals and families who have a genetic disease or who are at risk for such a disease. Genetic counseling is designed to provide patients and their families with information about their condition and help them make informed decisions.
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Genetics: The scientific study of heredity . Genetics pertains to humans and all other organisms. So, for example, there is human genetics, mouse genetics, fruitfly genetics, etc.
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Gestation: Period of time from conception to birth.
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Gonadotropin: Hormones that are secreted by the pituitary gland, and that affect the function of the male or female gonads.
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hCG: Human chorionic gonadotropin, a human hormone made by chorionic cells in the fetal part of the placenta . Human chorionic gonadotropin (hCG) is directed at the gonads and stimulates them. Hence, the name "gonadotropin."
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Heart: The muscle that pumps blood received from veins into arteries throughout the body. It is positioned in the chest behind the sternum (breastbone; in front of the trachea, esophagus, and aorta; and above the diaphragm muscle that separates the chest and abdominal cavities. The normal heart is about the size of a closed fist, and weighs about 10.5 ounces. It is cone-shaped, with the point of the cone pointing down to the left. Two-thirds of the heart lies in the left side of the chest with the balance in the right chest.
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Heart disease: Any disorder that affects the heart. Sometimes the term "heart disease" is used narrowly and incorrectly as a synonym for coronary artery disease . Heart disease is synonymous with cardiac disease but not with cardiovascular disease which is any disease of the heart or blood vessels. Among the many types of heart disease, see, for example: Angina ; Arrhythmia ; Congenital heart disease ; Coronary artery disease ( CAD ); Dilated cardiomyopathy ; Heart attack ( myocardial infarction ); Heart failure ; Hypertrophic cardiomyopathy ; Mitral regurgitation ; Mitral valve prolapse ; and Pulmonary stenosis .
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Hormone: A chemical substance produced in the body that controls and regulates the activity of certain cells or organs.
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Hospital: It may seem unnecessary to define a "hospital" since everyone knows the nature of a hospital. A hospital began as a charitable institution for the needy, aged, infirm, or young.
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Human chorionic gonadotropin: (hCG) A human hormone made by chorionic cells in the fetal part of the placenta . Human chorionic gonadotropin (hCG) is directed at the gonads and stimulates them. Hence, the name "gonadotropin."
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Humerus: The long bone in the arm which extends from the shoulder to the elbow.
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Hypothyroid: Deficiency of thyroid hormone which is normally made by the thyroid gland which is located in the front of the neck:

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Immune: Protected against infection. The Latin immunis means free, exempt.
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Immune system: A complex system that is responsible for distinguishing us from everything foreign to us, and for protecting us against infections and foreign substances. The immune system works to seek and kill invaders.
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In situ: In the normal location. An "in situ" tumor is one that is confined to its site of origin and has not invaded neighboring tissue or gone elsewhere in the body.
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In situ hybridization: The use of a DNA or RNA probe to detect the complementary sequence .
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Infection: The growth of a parasitic organism within the body. (A parasitic organism is one that lives on or in another organism and draws its nourishment therefrom.) A person with an infection has another organism (a "germ") growing within him, drawing its nourishment from the person.
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Interferon : A naturally occurring substance that interferes with the ability of viruses to reproduce. Interferon also boosts the immune system.
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Interphase: The interval in the cell cycle between two cell divisions when the individual chromosomes cannot be distinguished, interphase was once thought to be in resting phase but it is far from a time of rest for the cell. It is the time when DNA is replicated in the cell nucleus.
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Intervention: The act of intervening, interfering or interceding with the intent of modifying the outcome. In medicine, an intervention is usually undertaken to help treat or cure a condition. For example, early intervention may help children with autism to speak. "Acupuncture as a therapeutic intervention is widely practiced in the United States," according to the National Institutes of Health. From the Latin intervenire, to come between.
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Isochromosome: An abnormal chromosome with two identical arms due to duplication of one arm and loss of the other arm. Isochromosomes are found in some girls with Turner syndrome , patients with the Pallister-Killian syndrome , and some tumors.
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Kidney: One of a pair of organs located in the right and left side of the abdomen which clear "poisons" from the blood, regulate acid concentration and maintain water balance in the body by excreting urine. The kidneys are part of the urinary tract. The urine then passes through connecting tubes called "ureters" into the bladder. The bladder stores the urine until it is released during urination.

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Leg: In popular usage, the leg extends from the top of the thigh down to the foot. However, in medical terminology, the leg refers to the portion of the lower extremity from the knee to the ankle.
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Leukemia : Cancer of the blood cells. The growth and development of the blood cells are abnormal. Strictly speaking, leukemia should refer only to cancer of the white blood cells (the leukocytes) but in practice it can apply to malignancy of any cellular element in the blood or bone marrow, as in red cell leukemia (erythroleukemia).
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Lymphocytic: Referring to lymphocytes, a type of white blood cell.
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Maternal: 1. Pertaining to the mother as, for example, the maternal mortality rate. 2. Related through the mother as, for example, the maternal grandparents. 3. Inherited from the mother as, for example, the maternal X chromosome.
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Maternal age: The age of the mother at the time of delivery. Advanced maternal age is usually defined as age 35 or more at delivery.
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Mental retardation: A term used when a person has certain limitations in mental functioning and in skills such as communicating, taking care of him or herself, and social skills. These limitations will cause a child to learn and develop more slowly than a typical child. Children with mental retardation may take longer to learn to speak, walk, and take care of their personal needs such as dressing or eating. They are likely to have trouble learning in school. They will learn, but it will take them longer. There may be some things they cannot learn. As many as 3 out of every 100 people have mental retardation. In fact, 1 out of every 10 children who need special education has some form of mental retardation.
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Metabolism: The whole range of biochemical processes that occur within us (or any living organism). Metabolism consists both of anabolism and catabolism (the buildup and breakdown of substances, respectively). The term is commonly used to refer specifically to the breakdown of food and its transformation into energy.
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Microcephaly: An abnormally small head due to failure of brain growth. In precise terms, microcephaly is a head circumference that is more than 2 standard deviations below the normal mean for age, sex, race, and gestation . (Some authorities define microcephaly as more than 3 standard deviations below the mean.)
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Microscopic: So small it cannot be seen without the aid of microscope. As opposed to macroscopic (large enough to be seen with naked eye). A tiny tumor is microscopic while a big tumor is macroscopic.
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Mongolism: Obsolete name for Down syndrome .
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Neck: The part of the body joining the head to the shoulders. Also, any narrow or constricted part of a bone or organ that joins its parts as, for example, the neck of the femur bone.
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Neurology: The medical specialty concerned with the diagnosis and treatment of disorders of the nervous system -- the brain, the spinal cord, and the nerves.
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Nose: The external midline projection from the face.
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Nuchal: Referring to the back of the neck (nape). For example, nuchal rigidity is a stiff neck, sometimes a symptom of meningitis.
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Obstruction: Blockage of a passageway. See, for example: Airway obstruction ; Intestinal obstruction .
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Oncogene: 1. A gene that played a normal role in the cell as a proto-oncogene and that has been altered by mutation and now may contribute to the growth of a tumor.
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Organ: A relatively independent part of the body that carries out one or more special functions. The organs of the human body include the eye , ear , heart , lungs , and liver .
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Ovum: An egg in the ovary of the female. This egg is called the female "gamete" or sex cell. It combines with the male gamete, called a sperm, to form a zygote. This formation process is called "fertilization." (see sperm, zygote).
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Palm: The grasping side of the hand; the flexor surface of the hand. In contrast to the back of the hand, the extensor surface of the hand.
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Parkinson disease : A slowly progressive neurologic disease characterized by a fixed inexpressive face, a tremor at rest, slowing of voluntary movements, a gait with short accelerating steps, peculiar posture and muscle weakness, caused by degeneration of an area of the brain called the basal ganglia , and by low production of the neurotransmitter dopamine . Most patients are over 50, but at least 10 percent are under 40. Also known as paralysis agitans and shaking palsy.
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Parkinson's disease: See: Parkinson disease .
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Pediatrics: "Pediatrics is concerned with the health of infants, children and adolescents, their growth and development, and their opportunity to achieve full potential as adults." (Richard E.Behrman in Nelson's Textbook of Pediatrics)
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Pelvis: The lower part of the abdomen located between the hip bones.
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Penetrance: The likelihood a given gene will result in disease. For example, if half (50%) of the people with the neurofibromatosis (NF) gene have the disease NF, the penetrance of the NF gene is 0.5.
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Perinatal: Pertaining to the period immediately before and after birth. The perinatal period is defined in diverse ways. Depending on the definition, it starts at the 20th to 28th week of gestation and ends 1 to 4 weeks after birth. The word "perinatal" is a hybrid of the Greek "peri-" meaning "around or about" and "natal" from the Latin "natus" meaning "born."
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Pharmacy: A location where prescription drugs are sold. A pharmacy is, by law, constantly supervised by a licensed pharmacist.
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Physical therapy: A branch of rehabilitative health that uses specially designed exercises and equipment to help patients regain or improve their physical abilities. Physical therapists work with many types of patients, from infants born with musculoskeletal birth defects, to adults suffering from sciatica or the after- effects of injury, to elderly post-stroke patients.
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Pregnancy : The state of carrying a developing embryo or fetus within the female body. This condition can be indicated by positive results on an over-the-counter urine test, and confirmed through a blood test, ultrasound, detection of fetal heartbeat, or an X-ray. Pregnancy lasts for about nine months, measured from the date of the woman's last menstrual period (LMP). It is conventionally divided into three trimesters, each roughly three months long.
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Pregnant: The state of carrying a developing fetus within the body.
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Prenatal: Occurring or existing before birth.
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Prognosis: 1. The expected course of a disease .
2. The patient's chance of recovery.
The prognosis predicts the outcome of a disease and therefore the future for the patient . His prognosis is grim, for example, while hers is good.
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Progressive: Increasing in scope or severity. Advancing. Going forward. In medicine, a disease that is progressive is going from bad to worse.
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Prophylaxis: A measure taken for the prevention of a disease or condition.
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Receptor: 1. In cell biology, a structure on the surface of a cell (or inside a cell) that selectively receives and binds a specific substance. There are many receptors. There is a receptor for ( insulin ; there is a receptor for low-density lipoproteins ( LDL ); etc. To take an example, the receptor for substance P, a molecule that acts as a messenger for the sensation of pain , is a unique harbor on the cell surface where substance P docks. Without this receptor, substance P cannot dock and cannot deliver its message of pain. Variant forms of nuclear hormone receptors mediate processes such as cholesterol metabolism and fatty acid production. Some hormone receptors are implicated in diseases such as diabetes and certain types of cancer. A receptor called PXR appears to jump-start the body's response to unfamiliar chemicals and may be involved in drug-drug interactions.
2. In neurology, a terminal of a sensory nerve that receives and responds to stimuli.
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Recurrence: The return of a sign, symptom or disease after a remission. The reappearance of cancer cells at the same site or in another location is, unfortunately, a familiar form of recurrence.
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Recurrence risk: In medical genetics, the recurrence risk is the chance that a genetic (inherited) disease present in the family will recur in that family and affect another person (or persons). It is the chance of "lightning striking twice" (or thrice, etc.).
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Red blood cells: The blood cells that carry oxygen. Red cells contain hemoglobin and it is the hemoglobin which permits them to transport oxygen (and carbon dioxide). Hemoglobin, aside from being a transport molecule, is a pigment. It gives the cells their red color (and their name).
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Renal: Having to do with the kidney. From the Latin renes (the kidneys), which gave the French les reins which mean both the kidneys and the lower back.
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Risk factor: Something that increases a person's chances of developing a disease.
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Robertsonian translocation: A common and significant type of chromosome rearrangement that is formed by fusion of the whole long arms of two acrocentric chromosomes (chromosomes with the centromere near the very end). One in about 900 babies is born with a Robertsonian translocation making it the most common kind of chromosome rearrangement known in people. All five of the acrocentric chromosomes in people -- chromosome numbers 13, 14, 15, 21 and 22 -- have been found to engage in Robertsonian translocations. However, the formation of Robertsonian translocations was discovered by Hecht and coworkers to be highly nonrandom. Far and away the most frequent forms of Robertsonian translocations are between chromosomes 13 and 14, between 13 and 21, and between 21 and 22.
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Serum: The clear liquid that can be separated from clotted blood. Serum differs from plasma, the liquid portion of normal unclotted blood containing the red and white cells and platelets. It is the clot that makes the difference between serum and plasma.
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Sign: Any objective evidence of disease. Gross blood in the stool is a sign of disease. It can be recognized by the patient, doctor, nurse, or others. In contrast, a symptom is, by its nature, subjective. Abdominal pain is a symptom. It is something only the patient can know.
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Skeletal: Pertaining to the skeleton, the bones of the body which collectively provide the framework for the body.
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Skin: The skin is the body's outer covering. It protects us against heat and light, injury, and infection. It regulates body temperature and stores water, fat, and vitamin D. Weighing about 6 pounds, the skin is the body's largest organ. It is made up of two main layers; the outer epidermis and the inner dermis.

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Speech therapy: The treatment of speech and communication disorders. The approach used depends on the disorder. It may include physical exercises to strengthen the muscles used in speech (oral-motor work), speech drills to improve clarity, or sound production practice to improve articulation.
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Sperm: A sperm is the male "gamete" or sex cell. It combines with the female "gamete," called an ovum, to form a zygote. The formation process is called "fertilization." (see ovum, zygote).
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Stenosis: A narrowing, as in:

• aortic stenosis (narrowing of the aortic valve of the heart),
• pulmonary stenosis (narrowing of the pulmonary valve of the heart),
• pyloric stenosis (narrowing of the outlet of the stomach), and
• spinal stenosis (narrowing of the vertebral canal).

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Subacute: Rather recent onset or somewhat rapid change. The term "subacute" is used in contrast to acute which indicates very sudden onset or rapid change and chronic which indicates indefinite duration or virtually no change. A chronic condition is one lasting 3 months or more, by the definition of the U.S. National Center for Health Statistics. In ancient Greece, the "father of medicine" Hippocrates distinguished diseases that were acute (abrupt, sharp and brief) from those that were chronic. This is still a very useful distinction. Subacute has been coined to designate the mid-ground between acute and chronic.
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Surgery: The word "surgery" has multiple meanings. It is the branch of medicine concerned with diseases and conditions which require or are amenable to operative procedures. Surgery is the work done by a surgeon. By analogy, the work of an editor wielding his pen as a scalpel is s form of surgery. A surgery in England (and some other countries) is a physician's or dentist's office.
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Syndrome: A set of signs and symptoms that tend to occur together and which reflect the presence of a particular disease or an increased chance of developing a particular disease.
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Synthesis: Putting together different entities to make a whole which is new and different. In biochemistry , synthesis refers specifically to the process of building compounds from more elementary substances by means of one or more chemical reactions.
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Therapeutics: In medicine, the branch that deals specifically with the treatment of disease and the art and science of healing.
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Therapy: The treatment of disease .
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Thyroid: 1. The thyroid gland . Also, pertaining to the thyroid gland. 2. A preparation of the thyroid gland used to treat hypothyroidism . 3. Shaped like a shield. (The thyroid gland was so-named by Thomas Wharton in 1656 because it was shaped like an ancient Greek shield.)
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Thyroid hormone: A chemical substance made by the thyroid gland for export into the bloodstream. The thyroid gland needs iodine to make thyroid hormones. The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3).
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Tissue: A tissue in medicine is not like a piece of tissue paper. It is a broad term that is applied to any group of cells that perform specific functions. A tissue in medicine need not form a layer. Thus,

• The bone marrow is a tissue;
• Connective tissue consists of cells that make up fibers in the framework supporting other body tissues; and
• Lymphoid tissue is the part of the body's immune system that helps protect it from bacteria and other foreign entities.

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Tongue: The tongue is a strong muscle anchored to the floor of the mouth. It is covered by the lingual membrane which has special areas to detect tastes.
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Trimester: The nine months of pregnancy is traditionally divided into three trimesters: distinct periods of roughly three months in which different phases of fetal development take place.
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Trisomy: The presence of three copies of a chromosome rather than the normal two. The most common trisomies in newborns are trisomy 13 ( Patau syndrome ), trisomy 18 syndrome ( Edwards syndrome ) and trisomy 21 ( Down syndrome ). The most common trisomy among spontaneous abortions is trisomy 16.
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Tyrosine: An amino acid , one of the 20 building blocks of protein . A nonessential amino acid, tyrosine is produced from another amino acid, phenylalanine. Deficiency of the enzyme phenylalanine hydroxylase that catalyzes this reaction causes the genetic disease called phenylketonuria (PKU). Tyrosine is a precursor of thyroid hormones, catecholamines, and melanin. Symbol: Tyr.
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Ultrasound : High-frequency sound waves. Ultrasound waves can be bounced off of tissues using special devices. The echoes are then converted into a picture called a sonogram. Ultrasound imaging, referred to as ultrasonography, allows physicians and patients to get an inside view of soft tissues and body cavities, without using invasive techniques. Ultrasound is often used to examine a fetus during pregnancy . There is no convincing evidence for any danger from ultrasound during pregnancy.
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Vein: A blood vessel that carries blood low in oxygen content from the body back to the heart. The deoxygenated form of hemoglobin (deoxyhemoglobin) in venous blood makes it appear dark. Veins are part of the afferent wing of the circulatory system which returns blood to the heart.
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Ventricular: Pertaining to the ventricles, the lower chambers of the heart , as in ventricular fibrillation and ventricular septal defect .
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Villi: Plural of villus , a tiny finger-like or vascular projection.
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