Glossary

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A laser is a highly focused beam of light that can be used during surgery to cut or destroy tissue. Laser light cleans (sterilizes) and seals as it cuts tissue, which reduces bleeding, pain, and healing time.

Lasers are used for many different types of surgery, including dental surgery, eye surgery, surgery on the female reproductive organs, hemorrhoid surgery, and plastic surgery.

Last Revised: June 21, 2012

Author: Healthwise Staff

Medical Review: Sarah Marshall, MD - Family Medicine & Kirtly Jones, MD - Obstetrics and Gynecology

LDL (low-density lipoprotein) cholesterol is "bad" cholesterol, which carries mostly fat and only a small amount of protein from the liver to other parts of the body. A high LDL cholesterol level is considered a risk factor for coronary artery disease (CAD) because, under certain conditions, it can cause hardening of the arteries (atherosclerosis).

Cholesterol is measured either in milligrams per deciliter of blood (mg/dL) or in millimoles per liter of blood (mmol/L).

  • An LDL cholesterol level of less than 100 mg/dL (less than 2.6 mmol/L) is considered optimal.
  • 100 to 129 (2.6 to 3.35) is considered near optimal.
  • 130 to 159 (3.35 to 4.10) is considered borderline high.
  • 160 to 189 (4.12 to 4.88) is considered high.
  • 190 and above (4.90 and above) is considered very high.

People who have at least a moderate risk for developing heart disease (especially those who have diabetes) may benefit from lowering their LDL cholesterol levels. The specific target LDL level depends on a person's number and type of risk factors.

Last Revised: June 29, 2012

Author: Healthwise Staff

Medical Review: Kathleen Romito, MD - Family Medicine & Robert A. Kloner, MD, PhD - Cardiology & Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology

Oxygen-rich blood flows from the lungs through the left upper chamber (atrium) of the heart into the left lower chamber (ventricle) of the heart. The left ventricle muscle contracts to pump blood out through the aorta—a large blood vessel carrying blood out of the heart—to the rest of the body.

Last Revised: September 12, 2012

Author: Healthwise Staff

Medical Review: Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology & Stephen Fort, MD, MRCP, FRCPC - Interventional Cardiology

Leukemia is a type of cancer that happens when cells in your bone marrow grow abnormally and out of control. These cells can spread to other parts of your body.

There are four main types of leukemia: acute lymphoblastic (ALL), acute myelogenous (AML), chronic lymphocytic (CLL), and chronic myelogenous (CML). The acute types can get worse quickly and need to be treated right away. The chronic types get worse slowly and may not need to be treated until you have symptoms.

Last Revised: December 14, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Brian Leber, MDCM, FRCPC - Hematology

Leukoplakia is a condition in which thick, hard, white patches form inside the mouth and cannot be wiped off. Leukoplakia is commonly caused by irritation, such as from the rubbing of a rough tooth or a poorly fitting denture, or from smoking or using smokeless tobacco.

Leukoplakia may clear up if the source of the irritation is removed, by fixing the tooth or denture, or by stopping tobacco use. It may take several weeks or even months for the leukoplakia to go away completely.

In some cases, leukoplakia can be an early sign of cancer of the mouth.

Last Revised: December 21, 2012

Author: Healthwise Staff

Medical Review: Adam Husney, MD - Family Medicine & Arden Christen, DDS, MSD, MA, FACD - Dentistry

Mental health counselors—often social workers or marriage and family therapists—provide counseling services for individuals, couples, families, teens, and children.

Mental health counselors must earn a master's degree in counseling or a closely related mental health field and complete a certain amount of clinical work after earning their degree.

Most mental health counselors are licensed by the states in which they practice and have passed a state-developed or national licensure or certification exam.

Last Revised: August 17, 2012

Author: Healthwise Staff

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

Ligaments are strong, tough, ropy connective fibers. They connect bones to each other, connect cartilage to joints, and support internal organs, such as the kidneys.

Last Revised: April 5, 2012

Author: Healthwise Staff

Medical Review: William H. Blahd, Jr., MD, FACEP - Emergency Medicine & Freddie H. Fu, MD - Orthopedic Surgery

Lightheadedness makes a person feel that he or she is about to faint or pass out. It is caused by a momentary drop in blood pressure and blood flow to the head.

Nausea or vomiting sometimes accompanies lightheadedness. Symptoms usually improve or go away after lying down.

It is common to feel lightheaded occasionally. Lightheadedness often occurs when a person gets up too quickly from a seated or lying position (orthostatic hypotension).

Unlike vertigo, lightheadedness does not produce a sensation of movement. Vertigo causes a spinning or whirling sensation that may lead to nausea or vomiting, loss of balance, trouble walking or standing, and falling.

Last Revised: January 2, 2013

Author: Healthwise Staff

Medical Review: William H. Blahd, Jr., MD, FACEP - Emergency Medicine & David Messenger, MD

Lipid disorders are problems that affect the way cholesterol is produced, used, carried in the blood, or disposed of by the body. People who have lipid disorders develop very high total cholesterol levels, very low HDL (or "good") cholesterol levels, and/or high triglyceride levels.

Lipid disorders are often inherited. People who have lipid disorders are usually at risk for coronary artery disease, often at an early age.

If a person is known to have a lipid disorder, treatment can be started early to lower the person's cholesterol. And family members can be made aware that they may also be at risk.

Examples of inherited lipid disorders include familial combined hyperlipidemia and familial hypercholesterolemia.

Last Revised: June 29, 2012

Author: Healthwise Staff

Medical Review: Kathleen Romito, MD - Family Medicine & Robert A. Kloner, MD, PhD - Cardiology & Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology

Lipids, such as cholesterol, triglycerides, and fatty acids, are fat and substances like fat used as a source of fuel by the body. Lipid levels can be an important measure of health. For example, a person who has high cholesterol has an increased risk of heart disease and stroke.

Lipids are found in the bloodstream or stored in tissues. They are an important part of cell structure and other biological functions in the body.

Last Revised: June 29, 2012

Author: Healthwise Staff

Medical Review: Kathleen Romito, MD - Family Medicine & Robert A. Kloner, MD, PhD - Cardiology & Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology

The liver is a large organ in the right upper part of the abdomen. It performs a range of complex and important functions that affect all body systems.

Some of the specific functions of the liver include:

  • Controlling the amounts of sugar (glucose), protein, and fat entering the bloodstream.
  • Removing bilirubin, ammonia, and other toxins from the blood. (Bilirubin is a by-product of the breakdown of hemoglobin from red blood cells.)
  • Processing most of the nutrients absorbed by the intestines during digestion and converting those nutrients into forms that can be used by the body. The liver also stores some nutrients, such as vitamin A, iron, and other minerals.
  • Producing cholesterol, substances that help blood clot, bile, and certain important proteins, such as albumin.
  • Breaking down (metabolizing) alcohol and many drugs.

Last Revised: January 17, 2012

Author: Healthwise Staff

Medical Review: Adam Husney, MD - Family Medicine & W. Thomas London, MD - Hepatology

A living will, also called a treatment directive, is a type of advance directive that documents personal wishes about end-of-life medical treatment in case decision-making or communication abilities are lost. A living will specifies the conditions under which certain kinds of treatment or life-support measures would or would not be wanted.

A living will can be changed or revoked at any time and will not take effect until a person is no longer able to make or communicate decisions. Copies of living wills should be given to and discussed with a person's health professional and family members.

Although living wills can be written without the help of an attorney, legal advice may be useful. This is especially true for people who live in states where living wills are not recognized or the laws governing them are unclear. Many hospitals and nursing homes provide living will forms that comply with state-specific requirements.

Last Revised: December 29, 2011

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Shelly R. Garone, MD, FACP - Palliative Medicine

Local anesthesia is a method to deliver pain control medicine to a specific area. It can be injected or applied to the skin or mucous membranes to numb an area and its surrounding tissues.

Local anesthesia does not make the person sleepy or relieve other pains. But it may be used along with other medicines that have properties to relax the person or provide stronger pain relief.

Last Revised: September 30, 2011

Author: Healthwise Staff

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

Low back pain is pain in your back anywhere below the ribs and above the legs. It can be dull or sharp. You might feel it in only one spot or over a broad area. Some people also have numbness, tingling, or weakness in one or both legs from a pinched nerve in the back.

Most back pain gets better within 4 to 6 weeks with home treatment like exercises and taking over-the-counter pain medicine. But in some people the pain lasts longer.

Most people who have low back pain get it again at least once.

Last Revised: October 9, 2012

Author: Healthwise Staff

Medical Review: William H. Blahd, Jr., MD, FACEP - Emergency Medicine & Robert B. Keller, MD - Orthopedics

The lower esophageal sphincter (LES) is a ring of muscle that forms a valve at the lower end of the esophagus where it joins the stomach.

The LES stays closed except during swallowing, when it allows food to pass from the esophagus into the stomach. When the LES is closed, it prevents the backflow (reflux) of stomach acid into the esophagus. If the LES does not close tightly enough, stomach acid backs up into the esophagus, causing heartburn. A weak lower esophageal sphincter is a major cause of gastroesophageal reflux disease (GERD).

Last Revised: March 6, 2012

Author: Healthwise Staff

Medical Review: Adam Husney, MD - Family Medicine & Peter J. Kahrilas, MD - Gastroenterology

Lung cancer means that cells in your lungs are growing abnormally and out of control. The cancer cells can spread to other parts of your body. Most lung cancer is caused by tobacco smoke.

Last Revised: October 9, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Michael Seth Rabin, MD - Medical Oncology

Lupus is a long-term autoimmune disease. This means that your immune system attacks your body's healthy tissues. Lupus may cause problems with your skin, kidneys, heart, lungs, nerves, or blood cells.

When you have lupus symptoms, you are having flares or relapses. When your symptoms get better, you are in remission. Lupus can't be cured, but home treatment and medicine can help control the symptoms.

Last Revised: October 9, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Nancy Ann Shadick, MD, MPH - Internal Medicine, Rheumatology

Luteinizing hormone (LH) is produced by the pituitary gland. In women, LH helps regulate the menstrual cycle and egg production (ovulation); in men, LH stimulates the production of testosterone, which plays a role in sperm production.

Women's LH levels normally vary with the phase of the menstrual cycle, rapidly increasing just before ovulation occurs. This "LH surge" is a dependable sign that a woman is in a fertile time of her cycle. Men's LH levels normally remain constant.

Abnormally high or low LH levels can be a sign of an inability to produce eggs or sperm.

Last Revised: June 8, 2012

Author: Healthwise Staff

Medical Review: Sarah Marshall, MD - Family Medicine & Kirtly Jones, MD - Obstetrics and Gynecology

Lyme disease is an illness from getting bitten by a tick infected with a certain type of bacteria. It can cause fatigue, headache, stiff neck, fever, sore muscles and joints, and sometimes a red rash that looks like a bull's-eye.

Antibiotics usually work. If you don't get treated right away, Lyme disease can cause serious problems with the joints, nervous system, and heart.

Last Revised: October 9, 2012

Author: Healthwise Staff

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

Lymph nodes are part of the lymphatic system, which carries lymph fluid, nutrients, and waste material between the body tissues and the bloodstream. The lymphatic system is also an important part of the immune system, the body's defense system against disease.

The lymph nodes (sometimes called lymph glands) filter lymph fluid as it flows through them, trapping bacteria, viruses, and other foreign substances, which are then destroyed by special white blood cells called lymphocytes. Lymph nodes may be found singly or in groups; they may be as small as the head of a pin or as large as an olive. Groups of lymph nodes can be felt in the neck, groin, and underarms. Many lymph nodes in the body can't be felt.

When a part of the body is infected, the nearby lymph nodes become swollen as they collect and destroy the infecting organisms. For example, if a person has a throat infection, the lymph nodes in the neck may swell and become tender.

Cancer can spread through the lymphatic system.

Last Revised: March 29, 2011

Author: Healthwise Staff

Medical Review: Sarah Marshall, MD - Family Medicine & C. Dale Mercer, MD, FRCSC, FACS - General Surgery

The lymph system is a network of vessels and organs throughout the body. This network carries a fluid that contains special white blood cells called lymphocytes between the body tissues and the blood.

The lymph system includes the lymph nodes, tonsils, thymus, spleen, and bone marrow. The lymph nodes filter lymph fluid as it flows through them, trapping bacteria, viruses, and other foreign substances, which are then destroyed by the lymphocytes.

The lymph system is also an important part of the immune system, the body's defense against disease. When a part of the body is infected, the nearby lymph nodes become swollen as they collect and destroy the infecting organisms. For example, if a person has a throat infection, lymph nodes in the neck may swell and become tender.

Sometimes diseases, like cancer, can begin and spread through the lymph system.

Last Revised: March 29, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Douglas A. Stewart, MD - Medical Oncology

Lymphedema is a collection of fluid that causes swelling (edema) in the arms or legs. This type of edema occurs when the amount of lymph fluid in a person's arm or leg exceeds the body's ability to remove it, and the fluid then collects in the tissues of the limb.

One of the causes of lymphedema is surgery to remove lymph nodes, usually during cancer treatment. Lymphedema causes the blood vessels and lymph channels in the limb to increase in size and number. It also reduces oxygen delivery to the tissues, interferes with wound healing, and can lead to infection. Lymphedema is often a permanent condition and may not completely go away, even with treatment. The amount of swelling may fluctuate at different times.

Lymphedema is often managed with physical therapy and compression sleeves or stockings.

Last Revised: June 28, 2011

Author: Healthwise Staff

Medical Review: Sarah Marshall, MD - Family Medicine & Douglas A. Stewart, MD - Medical Oncology

A lymphoma is a type of cancer that affects the lymph system, which is part of the body's immune system. The two main types of lymphoma are Hodgkin's lymphoma and non-Hodgkin's lymphoma.

Lymphomas are more common in men than in women. In most cases the cause is not known. Symptoms of lymphoma include swelling in one or more groups of lymph nodes, weakness, fever, weight loss, and an enlarged liver and spleen.

Depending on the type of lymphoma and whether it is confined to a single group of lymph nodes or affects many lymph nodes, treatment may include radiation therapy, chemotherapy, or, in serious cases, a stem cell transplant. Because the disease and its treatment impair the immune system, a person who has lymphoma has an increased risk of dying from infection.

Last Revised: March 29, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Douglas A. Stewart, MD - Medical Oncology