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Glossaries - I

We've defined thousands of terms related to health care. This page discusses glossary terms with the letter I.

Idiopathic (id-ee-oh-PATH-ik)

describing a disease of unknown cause.


Literally, insulin-like growth factor 1, a crucial blood protein produced in the liver in response to stimulation by growth hormone. IGF-1 provides the best indicator of growth hormone levels and optimal levels are linked to healthy bone, heart, thyroid, skin, and nervous system.

Ileal (IL-ee-ul)

Related to the ileum, the lowest end of the small intestine.

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Ileal Pouch (IL-ee-ul powtch)

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Ileitis (il-ee-EYE-tis)

Ileoanal Pull-Through

Ileoanal Pull-Through (il-ee-oh-AY-nul PUL-throo)

An operation to remove the colon and inner lining of the rectum. The outer muscle of the rectum is not touched. The bottom end of the small intestine (ileum) is pulled through the remaining rectum and joined to the anus. Stool can be passed normally. Also called ileoanal anastomosis.

Ileoanal Reservoir (il-ee-oh-AY-nul REZ-uh-vwar)

An operation to remove the colon, upper rectum, and part of the lower rectum. An internal pouch is created from the remaining intestine to hold stool. The operation may be done in two stages. The pouch may also be called a J-pouch or W-pouch.

Ileocecal Valve (il-ee-oh-SEE-kul valv)

A valve that connects the lower part of the small intestine and the upper part of the large intestine (ileum and cecum). Controls the flow of fluid in the intestines and prevents backflow.

Ileocolitis (il-ee-oh-koh-LY-tis)

Irritation of the lower part of the small intestine (ileum) and colon.

Ileostomy (il-ee-AW-stuh-mee)

An operation that makes it possible for stool to leave the body after the colon and rectum are removed. The surgeon makes an opening in the abdomen and attaches the bottom of the small intestine (ileum) to it.

Ileum (il-ee-um)

The lower end of the small intestine.

Immune complex

the result of a reaction between an antigen and a specific antibody. This combination of antigen bound by antibody may or may not cause adverse effects in a person.


natural or acquired resistance provided by the immune system to a specific disease. Immunity may be partial or complete, specific or nonspecific, long-lasting or temporary.


the process of inducing immunity by administering an antigen (vaccine) to allow the immune system to prevent infection or illness when it subsequently encounters the infectious agent.

Immunodeficiency, immune deficiency

a condition resulting from a defective immune system; a breakdown or inability of certain parts of the immune system to function, thus making a person susceptible to diseases that they would not ordinarily develop.


a substance capable of provoking an immune response. Also called an antigen.


capable of developing an immune response; possessing a normal immune system.


the ability of an antigen or vaccine to stimulate immune responses.


a general term for antibodies, which bind to invading organisms, leading to their destruction. There are five classes of immunoglobulins: IgA, IgG, IgM, IgD and IgE. (See also antibody.)

Immunosuppressive Drugs

Drugs that block the body's ability to fight infection or foreign substances that enter the body. A person receiving a kidney or pancreas transplant is given these drugs to stop the body from rejecting the new organ or tissue. Cyclosporin is a commonly used immunosuppressive drug.


a treatment that stimulates or modifies the body's immune response.

Impaction (im-PAK-shun)

The trapping of an object in a body passage. Examples are stones in the bile duct or hardened stool in the colon.

Impaired Glucose Tolerance (IGT)

Blood glucose (sugar) levels higher than normal but not high enough to be called diabetes. People with IGT may or may not develop diabetes. Other names (no longer used) for IGT are "borderline," "subclinical," "chemical," or "latent" diabetes.

Imperforate Anus (im-PUR-fuh-rut AY-nus)

A birth defect in which the anal canal fails to develop. The condition is treated with an operation.


The loss of a man's ability to have an erect penis and to emit semen. Some men may become impotent after having diabetes for a long time because the nerves or blood vessels have become damaged. Sometimes the problem has nothing to do with diabetes and may be treated with counseling.


How often a disease occurs; the number of new cases of a disease among a certain group of people for a certain period of time; the rate of occurrence of some event, such as the number of individuals who get a disease divided by a total given population per unit of time. (Contrast with prevalence.)

Inclusion/exclusion criteria

the medical or social reasons why a person may or may not qualify for participation in a clinical trial. For example, some trials may exclude people with chronic liver disease or with certain drug allergies; others may include only people with a low CD4+ T-cell count.

IND (investigational new drug)

the status of an experimental drug after the FDA agrees that it can be tested in people.

Indigestion (in-duh-JES-tchun)

Poor digestion. Symptoms include heartburn, nausea, bloating, and gas. Also called dyspepsia.

Indirect thrombin inhibitor

An agent that inactivates thrombin by catalyzing the activation of naturally occurring thrombin inhibitors such as antithrombin III and heparin cofactor II.

Informed consent

An agreement signed by prospective volunteers for a clinical research trial that indicates their understanding of:

  1. why the research is being done,

  2. what researchers want to accomplish,

  3. what will be done during the trial and for how long,

  4. what risks are involved,

  5. what, if any, benefits can be expected from the trial,

  6. what other interventions are available, and

  7. the participants right to leave the trial at any time.

Infarct (IN-farkt)

An area of necrosis in a tissue due to local ischemia resulting from obstruction of circulation to the area, most commonly caused by a thrombus or embolus.

Infarction (in-FARK-shun)

The formation of an infarct.

Infectious Diarrhea (in-FEK-shus dy-uh-REE-uh)

Diarrhea caused by infection from bacteria, viruses, or parasites. See also Travelers' Diarrhea and Gastroenteritis.

Infectious Gastroenteritis (in-FEK-shus gah-stroh-en-tuh-RY-tis)

Infiltrate (in-FILL-trait)

material deposited as a result of filtration.

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A typical reaction of tissues to injury or disease. It is marked by four signs: swelling, redness, heat, and pain.

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Inflammatory Bowel Disease (IBD) (in-FLAM-uh-toh-ree BAH-wul duh-zeez)

Long-lasting problems that cause irritation and ulcers in the GI tract. The most common disorders are ulcerative colitis and Crohn's disease.

Inguinal Hernia

Inguinal Hernia (IN-gwuh-nul HUR-nee-uh)

A small part of the large or small intestine or bladder that pushes into the groin. May cause pain and feelings of pressure or burning in the groin. Often requires surgery.


A hormone that helps the body use glucose (sugar) for energy. Imbalances of insulin are common in diabetes, gastrointestinal disorders, and obesity. The beta cells of the pancreas (in areas called the Islets of Langerhans) make the insulin. When the body cannot make enough insulin on its own, a person with diabetes must inject insulin made from other sources, i.e., beef, pork, human insulin (recombinant DNA origin), or human insulin (pork-derived, semisynthetic).

Insulin Allergy

When a person's body has an allergic or bad reaction to taking insulin made from pork or beef or from bacteria, or because the insulin is not exactly the same as human insulin or because it has impurities.

The allergy can be of two forms. Sometimes an area of skin becomes red and itchy around the place where the insulin is injected. This is called a local allergy.

In another form, a person's whole body can have a bad reaction This is called a systemic allergy. The person can have hives or red patches all over the body or may feel changes in the heart rate and in the rate of breathing. A doctor may treat this allergy by prescribing purified insulins or by desensitization. See also: Desensitization.

Insulin Antagonist

Something that opposes or fights the action of insulin. Insulin lowers the level of glucose (sugar) in the blood, whereas glucagon raises it; therefore, glucagon is an antagonist of insulin.

Insulin Binding

When insulin attaches itself to something else. This can occur in two ways. First, when a cell needs energy, insulin can bind with the outer part of the cell. The cell then can bring glucose (sugar) inside and use it for energy. With the help of insulin, the cell can do its work very well and very quickly. But sometimes the body acts against itself. In this second case, the insulin binds with the proteins that are supposed to protect the body from outside substances (antibodies). If the insulin is an injected form of insulin and not made by the body, the body sees the insulin as an outside or "foreign" substance. When the injected insulin binds with the antibodies, it does not work as well as when it binds directly to the cell.

Insulin-Dependent Diabetes Mellitus (IDDM)

A chronic condition in which the pancreas makes little or no insulin because the beta cells have been destroyed. The body is then not able to use the glucose (blood sugar) for energy. IDDM usually comes on abruptly, although the damage to the beta cells may begin much earlier. The signs of IDDM are a great thirst, hunger, a need to urinate often, and loss of weight. To treat the disease, the person must inject insulin, follow a diet plan, exercise daily, and test blood glucose several times a day. IDDM usually occurs in children and adults who are under age 30. This type of diabetes used to be known as "juvenile diabetes," "juvenile-onset diabetes," and "ketosis-prone diabetes." It is also called type I diabetes mellitus.

Insulin Pump

A device that delivers a continuous supply of insulin into the body. The insulin flows from the pump through a plastic tube that is connected to a needle inserted into the body and taped in place. Insulin is delivered at two rates: a low, steady rate (called the basal rate) for continuous day-long coverage, and extra boosts of insulin (called bolus doses) to cover meals or when extra insulin is needed. The pump runs on batteries and can be worn clipped to a belt or carried in a pocket. It is used by people with insulin- dependent diabetes.

Insulin Receptor

Areas on the outer part of a cell that allow the cell to join or bind with insulin that is in the blood. When the cell and insulin bind together, the cell can take glucose (sugar) from the blood and use it for energy.

Insulin Resistance

Many people with noninsulin-dependent diabetes produce enough insulin, but their bodies do not respond to the action of insulin. This may happen because the person is overweight and has too many fat cells, which do not respond well to insulin. Also, as people age, their body cells lose some of the ability to respond to insulin. Insulin resistance is also linked to high blood pressure and high levels of fat in the blood. Another kind of insulin resistance may happen in some people who take insulin injections. They may have to take very high doses of insulin every day (200 units or more) to bring their blood glucose (sugar) down to the normal range. This is also called "insulin insensitivity".

Insulin Shock

A severe condition that occurs when the level of blood glucose (sugar) drops quickly. The signs are shaking, sweating, dizziness, double vision, convulsions, and collapse. Insulin shock may occur when an insulin reaction is not treated quickly enough. See also: Hypoglycemia.


Refers to the status of insulin levels within the blood; often used to indicate elevated levels of insulin.


A doctor who specializes in internal medicine (not requiring surgery).

Intestines (in-TES-tinz)

See Large Intestine and Small Intestine. Also called gut.

Intestinal Flora (in-TES-tuh-nul FLOR-uh)

The bacteria, yeasts, and fungi that grow normally in the intestines.

Intestinal Mucosa (in-TES-tuh-nul myoo-KOH-zuh)

The surface lining of the intestines where the cells absorb nutrients.

Intestinal Pseudo-Obstruction (in-TES-tuh-nul SOO-doh ub-STRUK-shun)

A disorder that causes symptoms of blockage, but no actual blockage. Causes constipation, vomiting, and pain. See also Obstruction.

Intolerance (in-TAH-luh-runs)

Allergy to a food, drug, or other substance.

Intramuscular Injection

Putting a fluid into a muscle with a needle and syringe.

Intravenous Injection

Putting a fluid into a vein with a needle and syringe.

Intrinsic Factor

A protein normally secreted by the epithelium (lining) of the stomach that binds vitamin B12, the intrinsic factor/B12 complex is selectively absorbed by the distal ileum (large intestine), though only the vitamin is taken into the cell.

Intussusception (IN-tuh-suh-SEP-shun)

A rare disorder. A part of the intestines folds into another part of the intestines, causing blockage. Most common in infants. Can be treated with an operation.

In vitro (in VEE-troh)

from the Latin meaning in glass; in an artificial environment such as a test tube or the equivalent laboratory apparatus; an artificial environment created outside a living organism (e.g., in a test tube or culture plate) used in experimental research to study a disease or biologic process.

In vivo (in VEE-voh)

testing within a living organism, e.g., human or animal studies.

IRB (Institutional Review Board)

a committee of physicians, statisticians, community advocates and others that reviews clinical trial protocols before they can be initiated. IRBs ensure that the trial is ethical and that the rights of participants are adequately protected.

Irritable Bowel Syndrome (IBS) (EER-uh-tuh-bul BAH-wul sin-drohm)

A disorder that comes and goes. Nerves that control the muscles in the GI tract are too active. The GI tract becomes sensitive to food, stool, gas, and stress. Causes abdominal pain, bloating, and constipation or diarrhea. Also called spastic colon or mucous colitis.

Ischemic Colitis (is-KEE-mik koh-LY-tis)

Decreased blood flow to the colon. Causes fever, pain, and bloody diarrhea.

Islets of Langerhans

Special groups of cells in the pancreas. They make and secrete hormones that help the body break down and use food. Named after Paul Langerhans, the German scientist who discovered them in 1869, these cells sit in clusters in the pancreas. There are five types of cells in an islet: beta cells, which make insulin; alpha cells, which make glucagon; delta cells, which make somatostaton; and PP cells and D1 cells, about which little is known.

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