Glossary

Find definitions for thousands of medical terms, treatments, and tests -- even health-related abbreviations, prefixes, and suffixes.

Filter by First Letter
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

I

Illegal drugs are those that are not prescribed by a doctor or bought at a drugstore. They are sometimes also called "street drugs."

Some examples of illegal drugs include heroin (a narcotic); cocaine (a stimulant); LSD, mescaline, PCP, methamphetamine, and psilocybin (hallucinogens); marijuana and hashish (cannabis); and gamma-hydroxybutyrate (GHB). Although GHB is legal in Europe for anesthetic uses and in the United States for government-approved clinical trials for treating narcolepsy, it has been otherwise illegal in the United States since 1990.

The effects of illegal drugs can be unpredictable because:

  • Most drugs are very addictive.
  • People respond differently to the same drugs.
  • The strength or potency of the drug may be uncertain.
  • They may contain unknown or unexpected substances. There is no quality control for street drugs like that required for prescription drugs.
  • They may interact with other drugs or alcohol in unpredictable ways.

Last Revised: October 13, 2011

Author: Healthwise Staff

Medical Review: William H. Blahd, Jr., MD, FACEP - Emergency Medicine & Peter Monti, PhD - Alcohol and Addiction

The immune system is the body's natural defense system that helps fight infections. The immune system is made up of antibodies, white blood cells, and other chemicals and proteins that attack and destroy substances such as bacteria and viruses that they recognize as foreign and different from the body's normal healthy tissues.

The immune system is also responsible for allergic reactions and allergies, which may occur when the immune system incorrectly identifies a substance (allergen), such as pollen, mold, chemicals, plants, and medicines, as harmful.

Sometimes the immune system also mistakenly attacks the body's own cells, which is known as an autoimmune disease.

Last Revised: April 5, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Peter Shalit, MD, PhD - Internal Medicine

An implantable cardioverter-defibrillator (ICD) is a small device that uses electrical pulses or shocks to help control abnormal heart rhythms, especially ones that can be life-threatening. An ICD is also known as an automatic implantable cardioverter-defibrillator (AICD).

An ICD is implanted under the skin in the chest. A wire threaded through a large vein connects the device to the heart.

An ICD is always checking your heart rate and rhythm. If the ICD detects a life-threatening rapid heart rhythm, it tries to slow the rhythm to get it back to normal. If the dangerous rhythm does not stop, the ICD sends an electric shock to the heart to restore a normal rhythm. The device then goes back to its watchful mode. If your heart is beating too slowly, the ICD acts as a pacemaker, sending mild electrical pulses to bring your heart rate back up to normal.

Last Revised: June 2, 2011

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Rakesh K. Pai, MD, FACC

Infectious disease specialists are medical doctors who specialize in the diagnosis and treatment of complex infections. They also treat people who have long-term (chronic) infections or disorders such as HIV or tuberculosis.

Infectious disease specialists may further specialize in treating people in certain age groups, such as pediatric infectious disease specialists, who only treat children.

Infectious disease specialists are internists or pediatricians who further specialize in infectious diseases. They can be board-certified in infectious disease through the Board of Internal Medicine, which is recognized by the American Board of Medical Specialties.

Last Revised: August 17, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & E. Gregory Thompson, MD - Internal Medicine

Infertility means not being able to make a baby. Your doctor usually won't say you have infertility until you've tried for at least a year to get pregnant.

It can be caused by problems inside the woman's body or the man's body. But sometimes no cause can be found.

Being told that you have this problem doesn't necessarily mean that you will never get pregnant. Often, couples eventually conceive without help. But medical treatments do help many couples.

Last Revised: September 26, 2012

Author: Healthwise Staff

Medical Review: Adam Husney, MD - Family Medicine

Inflammation is the body's response to injury or infection. It may result in pain, swelling, redness, warmth, or loss of function of the affected body part.

In some cases inflammation develops as part of a disease process, such as the inflammation that occurs in rheumatoid arthritis, inflammatory bowel disease, asthma, or an allergic reaction.

Last Revised: November 23, 2012

Author: Healthwise Staff

Medical Review: Kathleen Romito, MD - Family Medicine & Sarah Marshall, MD - Family Medicine

An aortic aneurysm is a bulging section in the wall of the aorta—the large blood vessel delivering blood from the heart to the body—that has become stretched-out and thin. Where the wall of the blood vessel bulges out, it becomes weaker and may burst or rupture, causing bleeding.

Most aortic aneurysms are caused by a combination of hardening of the arteries (atherosclerosis), genetics, and aging. But a small number are caused by inflammation or infection. These are called inflammatory aneurysms.

An inflammatory aneurysm can cause complications, such as fever, weight loss, and symptoms of a chronic disease. A massive inflammatory response may affect body parts close to the aneurysm, including part of the small intestine, the ureter, or the veins to the kidney. Any of these structures can become obstructed by the inflammation.

Last Revised: February 22, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & David A. Szalay, MD - Vascular Surgery

Inflammatory bowel disease (IBD) is a condition that causes ongoing inflammation of the intestines. The condition can affect only the large intestine (ulcerative colitis) or any part of the entire digestive tract, from the mouth to the anus (Crohn's disease).

Symptoms of inflammatory bowel disease may include abdominal pain, frequent diarrhea that may contain blood or pus, fever, chills, weight loss, and fatigue. The condition may be mild or severe. The inflammation can also affect other parts of the body, such as the eyes or joints, and may cause a form of arthritis.

Inflammatory bowel disease may recur many times in a person's life. It is treated with medicines and sometimes with diet changes. If the disease is in remission (not causing symptoms), treatment may not be needed, although medicines may help keep the disease in remission. A severe attack may require that the person be hospitalized for treatment. In some cases, surgery may be needed.

Last Revised: October 8, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Arvydas D. Vanagunas, MD - Gastroenterology

Influenza (flu) is an infection, caused by a virus, that makes you feel very sick, often with fever, headache, body aches, and coughing.

People often use the term "flu" to describe a cold or a stomach virus. But influenza isn't a stomach problem, and it usually feels much worse than a cold.

Last Revised: October 9, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Christine Hahn, MD - Epidemiology

Insomnia means not being able to sleep well. Short-term or temporary insomnia is very common and usually isn't a problem. Chronic insomnia lasts a month or longer. It can be caused by other problems, like depression, chronic pain, medicines, or poor sleep habits.

Last Revised: October 9, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Lisa S. Weinstock, MD - Psychiatry

Insulin is a hormone produced in the pancreas that allows sugar (glucose) to enter body cells, where it is used for energy. It also helps the body store extra energy in muscle, fat, and liver cells.

Diabetes develops if the body does not produce enough insulin, does not use insulin properly, or both.

Last Revised: September 20, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Jennifer Hone, MD - Endocrinology, Diabetes and Metabolism

An insulin pen is a device for giving insulin shots. The insulin pen looks like a pen.

Inside the pen is a needle and a cartridge filled with insulin. You can set the dose of insulin with a dial on the outside of the pen. You use the pen to give the insulin shot. Both disposable and reusable insulin pens are available.

Last Revised: December 4, 2012

Author: Healthwise Staff

Medical Review: John Pope, MD - Pediatrics & Stephen LaFranchi, MD - Pediatrics, Pediatric Endocrinology

An insulin pump is a small computerized device that delivers insulin into the body. Using an insulin pump is different from injecting insulin throughout the day using insulin syringes and needles.

Insulin pumps can be programmed to deliver very precise amounts of insulin in a continuous (basal) dose and in carefully planned extra (bolus) doses delivered at specific times throughout the day, usually when eating.

Some pumps connect to the body through a thin tube and needle inserted under the skin, usually in the abdomen. Some pumps attach directly to the body and do not need tubing. Some pump systems use a remote control. Most pumps can hold between 200 and 300 units of insulin, depending on the model used. Some pumps also work as a blood glucose meter or communicate with your meter to adjust your bolus dose of insulin.

Insulin pumps allow flexibility in how a person times his or her meals and snacks. The pumps may help some people to have fewer low blood sugar events (hypoglycemic episodes) than people who inject insulin. The insulin pump is designed to mimic the normal function of the pancreas.

Last Revised: September 20, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Jennifer Hone, MD - Endocrinology, Diabetes and Metabolism

Insulin resistance is a condition in which body cells do not fully respond to the action of insulin, a hormone that controls the amount of sugar (glucose) in the blood. As a result, blood sugar levels become abnormally high.

Over time, insulin resistance can result in consistently high blood sugar levels, which increases a person's risk for type 2 diabetes. Pregnant women who are insulin resistant have an increased risk for gestational diabetes.

Usually, insulin resistance develops in people who are overweight and not physically active. These characteristics are often associated with having high cholesterol and high blood pressure. People who are insulin resistant have an increased risk of heart disease and stroke, especially if other risk factors, such as being a smoker or having high cholesterol levels, are present.

Last Revised: November 3, 2011

Author: Healthwise Staff

Medical Review: Sarah Marshall, MD - Family Medicine & Alan C. Dalkin, MD - Endocrinology

Intermittent claudication is a tight, aching, or squeezing pain in the calf, foot, thigh, or buttock that occurs during exercise, such as walking up a steep hill or a flight of stairs. This pain usually occurs after the same amount of exercise, intensifies until exercise becomes impossible, and is relieved by rest.

Intermittent claudication is the main symptom of peripheral arterial disease. As the condition gets worse, leg pain may occur even at rest (rest pain or rest claudication). Medicines and procedures are available to treat this condition.

Last Revised: October 14, 2011

Author: Healthwise Staff

Medical Review: Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology & David A. Szalay, MD - Vascular Surgery

An internist is a medical doctor who specializes in the care of adults. People might choose an internist as their primary doctor for regular checkups and for treating illness.

Internists can further specialize in areas such as:

  • Adolescent medicine (conditions and diseases common to teenagers).
  • Allergy, or immunology (immune system diseases).
  • Cardiology (diseases and conditions of the heart and blood vessels).
  • Endocrinology (diseases of the endocrine glands, which regulate hormones).
  • Gastroenterology (diseases of the digestive system).
  • Geriatric medicine (conditions and diseases in older adults).
  • Hematology (diseases of the blood and blood system).
  • Infectious disease (complex infections).
  • Nephrology (diseases of the kidney and urinary system).
  • Oncology (cancer).
  • Pulmonology (lung diseases such as asthma, emphysema, and pneumonia).
  • Rheumatology (immune system diseases and diseases of the joints).
  • Sports medicine (the treatment of injuries to the bones, muscles, joints, tendons, or ligaments that result from physical activity).

Internists can be board-certified by the American Board of Internal Medicine, which is recognized by the American Board of Medical Specialties.

Last Revised: August 17, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & E. Gregory Thompson, MD - Internal Medicine

Interventional cardiologists are medical doctors who specialize in performing surgical or invasive procedures—such as cardiac catheterization, angioplasty, and stenting—to diagnose and treat heart disease.

Interventional cardiologists can be board-certified as internists or interventional cardiologists through the Board of Internal Medicine, which is recognized by the American Board of Medical Specialties.

Last Revised: August 17, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & E. Gregory Thompson, MD - Internal Medicine

An intrauterine device (IUD) is a method of birth control that is placed inside the uterus to prevent pregnancy. It is not clearly understood how the IUD prevents pregnancy, and different types of IUDs may prevent pregnancy in different ways.

All IUDs have a plastic string that extends through the opening of the cervix into the vagina. The string allows a woman to check that the IUD is in place. It also allows a health professional to remove the device at the woman's request or at the end of its effectiveness (usually anywhere from 5 to 10 years, depending on the type).

The IUD is very effective at preventing pregnancy.

Last Revised: May 4, 2012

Author: Healthwise Staff

Medical Review: Sarah Marshall, MD - Family Medicine & Femi Olatunbosun, MB, FRCSC - Obstetrics and Gynecology

Intravenous means occurring within or by way of a vein. Medicines or fluids may be given by inserting an intravenous (IV) needle into a vein, usually in the back of the hand or on the forearm.

When the IV needle is in place, medicines or fluids can go quickly into the bloodstream and into the rest of the body.

Last Revised: September 30, 2011

Author: Healthwise Staff

Medical Review: Adam Husney, MD, MD - Family Medicine & John M. Freedman, MD, MD - Anesthesiology

The iris is the colored part of the eye. A circular muscle in the iris controls the amount of light that enters the eye through the pupil.

Pigment cells (melanin) in the iris produce its color. Each person's irises have a distinct color, texture, and pattern.

Last Revised: June 9, 2011

Author: Healthwise Staff

Medical Review: Kathleen Romito, MD - Family Medicine & Christopher J. Rudnisky, MD, MPH, FRCSC - Ophthalmology