jejunum: The section of the small intestine between the duodenum and the ileum.
jet lag: A feeling of fatigue that occurs as the biological clock resets itself after traveling across time zones, usually by airplane.
joint: A junction in the body where bones are linked together.
julienne: To cut food into thin, matchstick strips.
Kegel: An exercise that helps prevent and treat incontinence by strengthening pelvic floor muscles.
keloid: An unusually hard or thick scar that forms after surgery or an injury.
keratectomy: A procedure in which a laser is used to correct vision problems by reshaping the cornea.
keratin: A protein and the major component of the cuticle and cortex layers of hair; the same protein is found in nails, feathers, claws, and hooves.
keratinocytes: Cells of the epidermis that produce a tough protein called keratin and form a soft, protective sheet for the body.
keratoconjunctivitis sicca: Persistent dryness of the eye.
keratoderma blennorrhagica: A skin rash that sometimes occurs along with an autoimmune condition called Reiter's syndrome.
Keshan disease: Heart disease caused by a lack of selenium, an element that the body needs to function properly.
ketones: Substances produced when the body burns fat for energy or when the body doesn't have enough insulin.
kidney failure: The final stage of chronic kidney disease. At this point, the kidneys can no longer eliminate waste products from the body.
kyphoplasty: A surgical procedure that eases or eliminates the pain of spinal fractures. It also restores vertebrae that have collapsed due to fractures to their normal size.
labile hypertension: Blood pressure that frequently fluctuates between normal and abnormal during the course of a day, often within only a few minutes.
labyrinth: The inner ear. It contains the cochlea, which is responsible for hearing, as well as structures that are needed for balance.
laceration: A tear in the skin.
lacrimal gland: The gland that produces tears.
lactase: An enzyme that breaks down milk sugar (lactose) in the body.
lactic acidosis: A rare but potentially lethal condition in which blood lactic acid levels increase.
lactose: A sugar found in milk and dairy products.
lactose intolerance: The inability of the body to easily digest lactose, a sugar found in milk and dairy products.
lacunar stroke: A small ischemic stroke caused by the blockage of one of the smaller blood vessels in the brain; the most common effect is weakness or disability on one side of the body.
lamellar bone: Hard, dense tissue that forms the outer shell of bones. Also called compact bone.
lamina: One of the two thin, plate-like parts of each vertebra.
laminectomy: An operation in which all or part of one or both laminae is removed.
Langerhans cells: Cells of the immune system that work in the skin to fight infection.
lanugo: Fine, soft hair that grows all over the body of a fetus and is typically shed before birth.
laparoscopy: A surgical procedure carried out with tiny instruments inserted through small openings in the skin.
laser: A concentrated beam of light; lasers are used in certain surgeries and other medical procedures.
laser assisted uvula palatoplasty: A surgical procedure to ease snoring by removing or reshaping some of the tissues in the mouth (usually the uvula and soft palate) that vibrate and cause the noise of snoring.
laser hair removal: Permanent hair removal technique that uses a laser to target and heat melanin in the hair shaft, which damages the hair follicle.
laser photocoagulation: Surgery that uses a laser to seal off blood vessels in the eye; used to treat a number of eye diseases.
laser prostatectomy: A surgical technique for treating an enlarged prostate (benign prostatic hyperplasia). It uses a high-energy laser to remove large amounts of prostate tissue with little bleeding.
latex allergy: An allergic reaction to the proteins found in natural rubber.
laxative: A drug or substance that induces bowel movements or makes the stool softer and looser.
LDL: Abbreviation for low-density lipoprotein. This so-called bad cholesterol can build up on artery walls, narrowing the artery and making a heart attack or stroke more likely.
learned insomnia: When fear of not sleeping develops after a short period of not sleeping well, and this anxiety causes ongoing trouble falling or staying asleep.
LED photomodulation: Use of a panel of light-emitting diodes (LEDs) to stimulate skin cells and improve the look of the skin.
left anterior descending coronary artery: One of the main arteries that supplies blood to the heart; it runs down the front surface of the heart.
left atrium: The left upper chamber of the heart.
left circumflex coronary artery: One of the main arteries that supplies blood to the heart; it curves around the back of the heart.
left ventricle: The left lower chamber of the heart. It pumps blood out of the heart to other organs in the body.
left ventricular hypertrophy: A thickening of the wall of the lower left chamber of the heart, which is responsible for pumping blood to organs throughout the body.
left-ventricular assist device: A surgically implanted pump that augments the pumping action of the left ventricle.
lensometer: A device used to check the prescription of eyeglasses.
leptin: A hormone produced by fat cells that acts on the brain to suppress appetite and burn stored fat.
lesion: An infected, diseased, or wounded area of tissue.
leukotriene blockers: Asthma medications that work by blocking leukotrienes, chemicals made in the body as part of an allergic reaction.
leukotriene modifiers: Asthma medications that work by blocking the production or action of leukotrienes, chemicals made in the body as part of an allergic reaction.
leukotrienes: Chemicals that cause airways to swell when an allergic reaction occurs or in diseases like asthma.
levothyroxine sodium: A man-made version of the thyroid hormone thyroxine.
LH: Abbreviation for luteinizing hormone, a hormone that controls ovulation in women. In men, luteinizing hormone triggers production of testosterone.
libido: Sexual desire.
lice: A blood-sucking parasite known as Pediculus humanus capitis that can cause an itchy scalp; infestations are highly contagious and especially common in school-age children.
ligament: A band of tissue that connects bones.
ligature: Any material that is tied around a blood vessel to stop it from bleeding.
lignans: Antioxidant chemicals found in seeds like flax and sesame, as well as some fruits, vegetables, and grains.
limbic system: A group of structures in the brain that help control memory, emotions, sexual arousal, and motivation.
limbus: The border between the cornea and the white of the eye.
liothyronine sodium: A man-made version of the thyroid hormone triiodothyronine.
lipase: An enzyme secreted by the pancreas that helps the body break down fats.
lipids: Fats, oils, and waxes that serve as building blocks for cells or as energy sources. Lipids are also capable of accumulating in the artery walls to form plaque.
lipoatrophy: Dents or depressions in the skin that are caused by a loss of fatty tissue.
lipohypertrophy: A buildup of fatty tissue.
lipoma: A noncancerous tumor or growth composed of fat cells.
lipoprotein: A combination of fat (lipid) and protein molecules bound together as packages. The combination allows fats and cholesterol to move easily through the blood.
lipoprotein analysis: A test that measures the amount of triglycerides, total cholesterol, HDL (good cholesterol), and LDL (bad cholesterol) in a person's blood.
lipoprotein(a): A molecule made up of fat and protein that is very similar to harmful LDL.
liposuction: A cosmetic procedure that removes fat from an area of the body.
live attenuated vaccines: Vaccines made from a weakened virus or microbe. These weakened viruses and microbes don't cause disease; instead they teach the body to recognize the substance as harmful and destroy it if there is contact with it in the future.
liver: A vital organ that removes waste products from the body and helps with digestion.
living will: A legal document that states what a person would and wouldn't want if he or she is no longer able to make health care decisions.
lobar hemorrhage: Bleeding that occurs in the white matter of the brain beneath the cerebral cortex.
lobotomy: A surgical procedure to severe one or more branches of nerves into the frontal lobe of the brain.
lobules: Milk-producing glands of the breast.
localized: In reference to cancer, generally means cancer that is limited to a specific gland or other tissue, without any distant spread; an organ-confined cancer.
locus ceruleus: An area of the brain stem that helps control the brain's alertness, responses to certain stimuli, and stress and anxiety levels.
long-term memory: A memory that lasts from a few minutes to decades.
low-calorie diet: A weight-loss plan that limits calories to 800–1,500 a day.
low-density lipoprotein: So-called bad cholesterol. If there is too much LDL in the blood, it can collect on artery walls, narrowing them and making heart attacks and strokes more likely.
lower esophageal sphincter: A ring of muscle where the esophagus and stomach meet. It relaxes to let food into the stomach and closes to prevent stomach acids from backing up and irritating the esophagus.
lumbar puncture: A procedure in which a hollow needle is inserted into the lower part of the spinal canal to withdraw fluid for testing. Also called a spinal tap.
lumbar spine: The lower portion of the spine. It includes the five lowermost bones (vertebrae) of the spine and is the start of the lower back.
lumbar stenosis: Narrowing of the spinal canal in the lower portion of the spine (known as the lumbar spine).
lumen: The hollow part of a tube, like a blood vessel, or the cavity in a hollow organ.
lutein: A natural substance found in green leafy vegetables.
luteinizing hormone: A hormone that controls ovulation in women. In men, luteinizing hormone triggers production of testosterone.
luteinizing hormone-releasing hormone agonist: A drug that slows the production of hormones by the testicles in men or the ovaries in women.
LVAD: Abbreviation for left-ventricular assist device, a surgically implanted pump that augments the pumping action of the left ventricle.
Lyme disease: An infectious disease transmitted by a tick bite.
lymph nodes: Small, bean-shaped organs that filter germs and foreign matter out of the body. Also called lymph glands.
lymphatic system: A system of channels that drains excess clear fluid, called lymph, from tissues and returns it into the bloodstream.
lymphedema: Blockage in or damage to the lymphatic systems, causing lymphatic fluid to build up in tissues, making them swell.
lymphocyte: A type of white blood cell that can recognize foreign substances in the body.
lymphoma: A type of cancer that affects cells in the lymphatic system.
macrocytic anemia: The presence of larger-than-normal red blood cells in circulation—even though there are too few of them—caused by lack of folate and vitamin B12.
macronutrients: Substances that provide energy and that the body needs for growth. The main categories are: fat, carbohydrate, and protein.
macrophage: A type of white blood cell that destroys cell debris, bacteria, and foreign agents.
macula: The area in the center of the retina that produces sharp, clear central vision and allows one to see fine detail.
macular degeneration: An eye disease that slowly destroys sharp, clear central vision.
macular edema: The build-up of fluid in the macula caused by fluid leaking from blood vessels in the eye. It can blur and damage vision.
Magenblase syndrome: Swallowing too much air during a meal, causing excessive gas and discomfort. Also known as stomach bubble syndrome.
magnetic resonance imaging: A scan that creates detailed pictures of internal organs; commonly referred to as MRI. Magnetic resonance imaging uses radio waves, a strong magnetic field, and a computer to produce images of organs and internal tissues.
maintenance of wakefulness test: A test to measure sleepiness during the day. A tester measures how long it takes a person who is sitting up in a chair or bed to fall asleep after he or she has been asked to stay awake.
major depression: Depression that interferes with daily life for an extended period. Episodes of major depression during bereavement can be distinguished from normal sadness by such symptoms as persistent feelings of worthlessness, thoughts about death, feelings of guilt, persistent trouble functioning, and marked mental and physical sluggishness.
major histocompatibility complex molecule: Molecules that help protect the body from foreign substances. These molecules display proteins on the surface of cells so that protective immune system cells can kill the protein if it is harmful to the body.
maladaptive stress response: An unhealthy physiological response to stressors, in which the stress response often does not turn off even when the stressor disappears.
malaise: A general feeling of illness that can be a sign of disease.
malignant hypertension: A dangerous type of high blood pressure marked by an unusually sudden rise in blood pressure to very high levels, often accompanied by headache, blurred vision, and seizures.
malnutrition: Failure to eat or to properly absorb the nutrients needed for good health.
MAOIs: Abbreviation for monoamine oxidase inhibitors, medications used to treat depression. They work by making the chemical messengers serotonin and norepinephrine more available.
mast cell: A cell involved in allergic reactions. When stimulated, it releases chemicals like histamine that signal infection and cause inflammation.
mastoid bone: The bone in the skull behind the ear.
mastopexy: A cosmetic surgery to reshape and lift drooping breasts. Commonly known as a breast lift.
masturbation: Sexual self-stimulation.
maximizer: A person who typically evaluates all options before making a decision, in an effort to identify the perfect choice, and who never settles for second-best.
meal plan: A detailed guide outlining the amounts and types of food a person should eat each day.
Medicaid: A government program that offers health care for low-income Americans of any age.
Medicare: A government program that offers health care for Americans ages 65 and older.
Medigap insurance: Health insurance policies that fill in the holes in Medicare coverage.
medulla: Refers to the middle of something.
megaloblastic anemia: Fewer than normal healthy red blood cells in circulation, caused by a lack of folate or vitamin B12. Red cells become large and deformed, and are unable to carry oxygen efficiently.
meglitinides: A type of medication taken to treat type 2 diabetes.
melanin: A substance that gives the skin, hair, and eyes their natural color.
melanocytes: Cells located deep in the epidermis that produce melanin, the pigment that colors skin.
melanoma: The most dangerous type of skin cancer.
melatonin: A hormone that regulates the body's sleep-wake cycle.
membrane: A thin layer of tissue that surrounds or lines organs or cavities.
memory T cells and B cells: Immune cells that remember harmful agents that have entered the body in the past. When they spot the substance again, they spur the immune system to eliminate the invader.
Ménière's disease: An illness caused by a fluid imbalance in the inner ear.
meninges: The three membranes that cover and protect the brain and spinal cord.
meningitis: Swelling of the membranes that cover and protect the brain and spinal cord.
menopause: The point marking the end of menstruation, officially designated as one year after a woman's final period.
metabolic equivalents: Units used to estimate the oxygen consumption, or metabolic cost, of physical activity, and, hence, its intensity. One metabolic equivalent (MET) is the estimated energy cost of the body at rest.
metabolic syndrome: A cluster of risk factors that accelerate the progression of heart disease.
metabolism: The chemical reactions that occur in all living organisms to maintain life. An example is converting food into energy that the body needs to function.
metastasis: The spread of cancer cells from the primary site to another part of the body.
metered-dose inhaler: A device that delivers a specific dose of an inhaled asthma medication.
Methanobrevibacter smithii: Bacteria in the gut that help with the digestion of complex sugars.
METs: Abbreviation for metabolic equivalents, units used to estimate the oxygen consumption, or metabolic cost, of physical activity, and, hence, its intensity. One MET is the estimated energy cost of the body at rest.
MHC molecule: Abbreviation for major histocompatibility complex molecule, molecules that help protect the body from foreign substances. These molecules display proteins on the surface of cells so that protective immune system cells can kill the protein if it is harmful to the body.
microalbuminuria: Leakage of small amounts of a protein called albumin into the urine caused by kidney disease or damage.
microaneurysm: A tiny bulge that develops in the wall of a blood vessel.
microbe: A microorganism.
microdermabrasion: A cosmetic procedure in which tiny crystals under high pressure are sprayed on the face. This buffs away the outer layer of skin, eliminates fine lines, and improves the look of the skin.
microgram: A unit of mass, equal to one-thousandth of a milligram. Abbreviated as mcg.
micronized: Reducing a substance to very small particles.
micronutrients: Vitamins and minerals needed to maintain normal body functions and prevent certain illnesses.
microvascular disease: A condition in which the smallest blood vessels in the walls of the heart are narrowed or inelastic.
microvasculature: The body's small blood vessels.
micturition: Emptying the bladder. Also called urination or voiding.
middle ear: The air-filled cavity behind the eardrum that contains the three small bones that transmit sound vibrations to the inner ear.
migraine headache: A severe headache with pain that usually begins on one side of the head. Symptoms may include visual disturbances (called aura), nausea, vomiting, and sensitivity to light or noise.
migraine with aura: A severe headache preceded by visual disturbances such as flashing lights, seeing lines, or a blind spot.
migraine without aura: A severe headache that is not preceded by visual disturbances such as flashing lights. Also known as common migraine.
mild cognitive impairment: The loss of some brain functions, such as memory, thinking, or language, that is noticeable, but doesn't interfere with ability to carry out daily tasks.
milligram: A metric unit of weight equivalent to one-thousandth of a gram. Abbreviated as mg.
mindfulness: A practice with its roots in Buddhism that encourages people to be more fully aware of the present moment. Often achieved through meditation.
mindfulness meditation: A form of meditation with roots in ancient Buddhist practice through which a person has a calm awareness of his or her body and feelings and is fully engaged in the present; also called insight meditation.
mindfulness-based cognitive behavioral therapy: A well-established acceptance-based therapy, used principally in treatment of depression and anxiety.
mindlessness: Acting without full attention to one's surroundings, behavior, or internal experience.
miotic: An eye drop that constricts the pupil; used to treat glaucoma.
mitochondria: Small structures within cells that create break down nutrients and create energy for cells. Known as the power producers or energy factories of cells.
mitral valve: The valve that controls the one-way flow of blood from the left atrium to the left ventricle.
mitral valve prolapse: A valve problem in which one or both of the mitral valve flaps collapse backward into the left atrium. This may allow a small amount of blood to leak backward (regurgitate) through the valve.
mitral valve stenosis: A narrowing of the mitral valve opening that limits blood flow from the left atrium to the left ventricle.
monoamine oxidase inhibitors: Medications used to treat depression. They work by making the chemical messengers serotonin and norepinephrine more available.
monoclonal antibody: An antibody is a protein molecule that can bind to a virus and mark it for destruction by the immune system. A monoclonal antibody is a man-made substance used to treat some viral and other diseases.
monocytes: White blood cells that protect the body from disease by attacking and consuming foreign particles.
monounsaturated fat: A type of fat abundant in vegetable oils such as olive, peanut, sesame, and canola oils. Monounsaturated fats don't raise levels of unhealthy LDL cholesterol, and may even lower it.
Morton's neuroma: A thickening of nerve tissue between the toes that causes irritation, tingling, or a burning pain in the ball of the foot.
motilin: A hormone that helps the small intestine contract and move food through the digestive tract.
motility: The ability of the digestive tract to move its contents.
motor neuron: A nerve cell that directs activity in a specific group of muscle fibers.
motor unit: The pairing of a nerve cell and the group of muscle fibers it commands.
MRI: Abbreviation for magnetic resonance imaging--a scan that creates detailed pictures of internal organs. MRIs use radio waves, a strong magnetic field, and a computer to produce images of organs and internal tissues.
mucosa: Tissue that lines the tube-like structures of the body such as the respiratory and gastrointestinal tracts.
mucous cysts: Small cysts that form between the nail bed and the top joint of the finger.
mucous membrane: A thin layer that lines many cavities and structures in the body that are exposed to air in the environment, such as the nose, mouth, and lungs.
multi-infarct dementia: Memory loss and impaired thinking caused by tiny strokes that are often too small to notice until a sizable area of the brain is affected.
multinodular goiter: An enlargement of the thyroid gland with more than one lump or nodule appearing on the neck.
multiple sclerosis: An autoimmune disease in which the body's immune system mistakenly attacks myelin, the substance that covers nerve fibers.
multiple sleep latency test: A sleep test to measure daytime sleepiness. It times how quickly a person falls asleep when asked to rest in a quiet, darkened room during the day.
murmur: An sound heard during an examination of the heart caused by abnormal flow of blood through heart chambers or valves. Many heart murmurs do not indicate heart problems; others do.
muscle fatigue: Weakness felt in muscles when they have been tired out.
muscle fibers: Cells bundled together to make up muscle tissue. Also known as muscle cells.
muscle-contraction headache: A headache characterized by constant pressure, mild to moderate pain, and the feeling that a tight band is squeezing the head. Also known as a tension headache.
muscular endurance: The ability of muscle to continue to perform without stopping because of fatigue.
muscularis: The thin layer of smooth muscle lining of the colon or rectum.
musculoskeletal: Related to the muscles and the skeleton.
MUSE: Abbreviation for medicated urethral system for erection. In this therapy, a small drug pellet is inserted into the tip of the penis to produce an erection.
mutation: The process by which a change occurs in genetic material and is inherited by the next generation.
myalgia: Pain or tenderness in a muscle.
myasthenia: An abnormal weakness in a muscle or group of muscles.
mydriatic: A type of drug that widens the pupil.
myelin: A fatty material that surrounds and protects some nerve fibers.
myelography: A test that uses a special dye and X-rays to detect spinal cord problems. The dye is injected into the space surrounding the spinal cord, making the spinal cord, spinal canal, and nerve roots appear in detail on the X-ray.
myelopathy: A disorder in which the spinal cord is compressed, diseased, or damaged.
myocardial infarction: Medical term for heart attack, the sudden death of part of the heart muscle from lack of oxygen.
myocardial rupture: Tearing of one of the walls of the heart. It usually occurs immediately after a heart attack.
myocarditis: Inflammation of the heart muscle (myocardium).
myocardium: The middle layer of heart tissue. The muscular myocardium is sandwiched between the outer layer (epicardium) and the inner layer (endocardium).
myocyte: A muscle cell.
myofibrils: Long interlocking strands that make up muscle fibers.
myofilaments: The fundamental muscle proteins that form myofibrils. Myofilaments slide over one another, bunching up and generating force, when a muscle contracts.
myopia: Nearsightedness. An optical error in which light rays meet and focus before reaching the retina, making objects that are far away appear blurry.
myosin: A protein that helps muscle contract and relax.
nanograms per milliliter: A small quantity of a substance; equivalent to one-billionth of a gram (454 grams make 1 pound) in one-thousandth of a liter (1 liter is approximately 1 quart). Abbreviated as ng/ml.
narcolepsy: A sleep disorder that causes extreme sleepiness and uncontrollable sleep attacks, making a person fall asleep at inappropriate times during the day.
nasolabial folds: Lines in the skin leading from the nose to the outer corners of the mouth. Also known as smile or laugh lines.
natural killer cells: A type of white blood cell of the immune system. These cells destroy other cells that fail to display the right chemical flags signaling that they are normal cells.
natural recoverers: People who overcome addiction without treatment or formal self-help programs.
nebulizer: A device that converts a liquid medicine into a mist that can be breathed in.
necrosis: The premature death of living cells or tissues.
needle biopsy: Use of a hollow needle to remove a small sample of tissue for examination.
neoadjuvant therapy: A helper treatment given before a primary treatment is started, such as when chemotherapy is done before surgery in order to shrink a tumor.
neonatal: Relating to an infant younger than 4 weeks of age.
neoplasm: An abnormal growth of tissue, either cancerous or benign.
nephritis: Inflammation of the kidneys.
nephropathy: Kidney disease.
nerve block: Injection of a medication into one or more nerves to relieve pain.
nerve growth factor: A molecule in the body that promotes the growth and repair of nerve cells.
nerve sparing: When referring to prostatectomy, the surgical procedure that preserves the nerves needed to allow the penis to become erect.
neuralgia: A burning or stabbing pain that follows the path of a nerve.
neuritic plaques: Clumps of sticky proteins found in the brains of people with Alzheimer's disease.
neurofibrillary tangles: Twisted strands of proteins that are found inside the dead or dying nerve cells of people with Alzheimer's disease.
neuroleptic agents: Powerful tranquilizing drugs used to treat schizophrenia.
neurologist: A physician trained to diagnose and treat disorders of the nervous system, including the brain and spinal cord.
neuromuscular junction: The tiny space between the end of a nerve and the surface of a muscle.
neuron: A nerve cell.
neuropathy: Nerve damage and resulting loss of sensation, movement, or other function.
neuropeptides: Small proteins that aid in transmitting signals between nerve cells.
neurosyphilis: A rare infection of the brain or spinal cord that occurs when syphilis goes untreated for many years.
neurotransmitter: A chemical messenger released by nerve cells that transmits messages to nearby other nerve cells.
neurotransmitter receptors: Cell structures (usually proteins) that recognize specific neurotransmitters and bind to them. Once bound, a receptor often changes shape, causing a cascade of chemical events within the cell. These events can alter which genes are turned on or off and can make the cell more or less likely to release its neurotransmitters.
neutral alignment: Keeping the body in a straight line from head to toe except for the slight natural curves of the spine.
neutral posture: A standing or seated position in which the chin is parallel to the floor; the shoulders, hips, and knees are at even heights; and the knees and feet point straight ahead.
neutral spine: A position in which the back is straight except for the slight natural curves of the spine.
neutropenia: An abnormally low number of white blood cells.
neutrophils: White blood cells that seek out and engulf foreign cells.
nitrates: Medications that widen blood vessels; usually used to treat chest pain from angina and other heart problems.
nitric oxide: A compound produced by the endothelium (the lining of the interior walls of arteries) that helps widen blood vessels and counteract high blood pressure. Also called endothelium-derived relaxing factor.
nitroglycerin: A drug that relaxes blood vessels and increases the supply of blood and oxygen to the heart while reducing its workload. It is commonly used to treat angina.
NK: Abbreviation for natural killer cells, a type of white blood cell of the immune system. These cells destroy other cells that fail to display the right chemical flags signaling that they are normal cells.
NMDA receptor: Abbreviation for the N-methyl-D-aspartame receptor, a molecule on the surface of a brain cell that admits calcium when activated by the chemical messenger glutamate.
N-methyl-D-aspartame receptor: A molecule on the surface of a brain cell that admits calcium when activated by the chemical messenger glutamate.
NO: Abbreviation for nitric oxide, a compound produced by the endothelium (the lining of the interior walls of arteries) that helps widen blood vessels and counteract high blood pressure. Also called endothelium-derived relaxing factor.
nociceptors: Nerve endings that detect pain and transmit pain information to the brain and spinal cord.
nocturia: Waking up more than once during the night to urinate.
nodule: A small rounded bump or knot of tissue.
nomogram: A chart or graph of mathematical calculations of risk; used in making treatment recommendations and predicting outcomes.
non-HDL cholesterol: The sum of all cholesterol types other than high-density lipoprotein (HDL). These include very-low-density lipoprotein, low-density lipoprotein, and intermediate-density lipoprotein.
non-insulin-dependent diabetes: Now called type 2 diabetes. A disease in which levels of blood sugar (glucose) are too high initially because cells can't properly use insulin (a hormone that helps cells absorb glucose from the bloodstream). Over time the production of insulin may decline.
noninvasive test: A test that does not require any medical instruments to break the skin or enter the body.
nonketotic hyperglycemic hyperosmolar syndrome: A rare and very serious condition associated with type 2 diabetes. Symptoms include extremely high (more than 800 mg/dl) blood sugar levels, severe dehydration, and changes in mental status, ultimately resulting in coma.
nonproliferative retinopathy: A condition in which the walls of the small blood vessels in the retina leak serum and tiny pockets of swelling form in the walls of blood vessels. Also called background retinopathy.
non-REM sleep: The sleep phase that includes deep sleep, the type considered most important for preventing daytime sleepiness.
nonsteroidal anti-inflammatory drug: A drug that reduces swelling and pain.
noradrenaline: A hormone produced by adrenal glands that puts the body on heightened alert when a threat is perceived (the fight-or-flight response). Also known as norepinephrine.
norepinephrine: A hormone produced by adrenal glands that puts the body on heightened alert when a threat is perceived (the fight-or-flight response). Also known as noradrenaline.
normal-pressure hydrocephalus: A buildup of fluid in the brain that causes the brain to swell, and leads to slowing of mental function, trouble walking, and a loss of bladder control.
NSAID: Abbreviation for nonsteroidal anti-inflammatory drug, a drug that reduce swelling and pain.
nuclear tests: Tests that use tiny amounts of short-lived radioactive substances that can target particular organs or cell receptors to diagnose disease.
nucleus accumbens: Part of the brain's reward pathway that is most tightly and consistently responsive to pleasure. Also known as the pleasure center.
nucleus pulposus: The gel-like shock-absorbing central portion of each spinal disc.
nutraceutical: Dietary supplement containing concentrated forms of a presumed bioactive substance originally derived from food and used to enhance health in dosages exceeding those normally obtainable from food.
nutrients: Substances in foods that the body needs to survive.
obesity: A body weight that is much higher than is healthy. Defined as having a body mass index of 30 or more. Obesity puts a person at greater risk of developing numerous chronic diseases.
object of addiction: The psychoactive drug or rewarding behavior with which a person with addiction has a pathological relationship.
obstructive sleep apnea: A disorder marked by heavy snoring and interrupted breathing during sleep. It increases the risk of developing high blood pressure and having a stroke and is more common in people who are obese.
occipital lobe: The region in the back of the brain responsible for visual processing.
occlusion: The closing or blocking of a hollow organ or body part.
occult: Something not visible to the naked eye but seen under a microscope or through lab tests.
omega-3 fatty acids: Beneficial fats, also known as n-3 fatty acids. These are polyunsaturated fat found in fatty fish, such as salmon.
omega-6 fatty acids: Fatty acids found in certain foods that the body needs for good health but can't make on its own. Also known as n-6 fatty acids.
oncogene: A gene that, under certain conditions, can cause cancer.
oncologist: A physician who deals with the diagnosis and treatment of cancer. There are three types—medical oncologists, radiation oncologists, and surgical oncologists.
Ondine's curse: A rare and potentially fatal disorder in which a person may stop breathing, especially at night. Also called congenital central hypoventilation syndrome.
onychomycosis: Toenail fungus.
open prostatectomy: A surgical procedure in which an enlarged prostate is removed through an incision in the abdomen.
ophthalmologist: A physician who specializes in treating the eye and eye disease.
ophthalmoscope: An instrument with a light and mirrors for examining the deep interior of the eye.
opiate: Any painkilling drug such as morphine or codeine derived from the opium poppy.
opioid: Any narcotic, natural or synthetic, that behaves in the body like an opium-derived drug.
optic disk: The front surface of the optic nerve, where all the retinal nerve fibers come together to carry an image to the brain.
optic nerve: A cable of specialized nerve fibers that transmit visual impulses from the eye to the brain.
optician: A technician who helps select and fit eyeglasses or contact lenses for people with vision problems.
optimism: A characteristic frame of mind that leads a person to expect positive outcomes and to view the world as a positive place.
optometrist: A health care professional licensed to examine the eye, and diagnose and treat some eye diseases.
oral glucose tolerance test: A test to check for diabetes. It involves fasting overnight and having blood sugar levels checked before and after drinking a sugary solution.
oral mucosa: The layer of soft pinkish tissue that lines the interior of the mouth.
orbit: The bony socket that holds the eyeball.
orbital irradiation: X-ray treatment to the eye; sometimes used in more serious cases of Graves' eye disease.
orchiectomy: Surgery to remove the testicles. Usually done to remove a cancerous testicle or to lower testosterone levels and slow or halt the growth of prostate cancer.
organic matrix: The protein framework of bone tissue.
organonitrile: A chemical found in cruciferous vegetables that may have anti-cancer properties.
orgasm: The series of pleasurable, rhythmic muscle contractions that mark the peak of sexual arousal and the release of muscle tension.
orthopedist: A medical doctor who specializes in correcting disorders of the bones, joints, muscles, and tendons.
orthosis: A custom shoe insert that helps cushion or realign the foot.
orthostatic hypotension: A sudden drop in blood pressure upon standing or getting out of bed, causing dizziness.
osseointegration: A process in which bone heals around an implant to create a stable anchor.
ossicles: Three bones in the middle ear that move in response to sound vibrations.
ossification: The process by which bone is formed.
osteoarthritis: A joint disease in which the cartilage that lines the joints slowly deteriorates. Also called degenerative joint disease.
osteoblasts: Cells that build bone tissue.
osteoclasts: Cells that remove bone tissue.
osteocytes: A cell that is embedded in fully formed bone.
osteomalacia: A condition in which bones are soft and weak, usually due to a lack of vitamin D or an inability of the body to use vitamin D properly.
osteomyelitis: A bone infection caused by bacteria or fungi.
osteons: The building blocks of compact bone, the hard, tightly-packed tissue that forms the outer shell of bones.
osteopath: A doctor licensed to practice medicine, perform surgery, and prescribe drugs. The training is similar to that of a regular M.D., but more emphasis is placed on the importance of the musculoskeletal system and the body's ability to heal itself.
osteopenia: Mild thinning and weakening of the bones; bone density is lower than normal but not low enough to be classified as osteoporosis.
osteophyte: An outgrowth of bone on a joint or spinal disk; commonly called a bone spur.
osteoporosis: Significant thinning and weakening of bones over time, making them vulnerable to breaks.
osteotomy: An operation in which bone is cut to change its alignment or shorten or lengthen it.
otic capsule: The bony shell that surrounds the inner ear.
otitis externa: An infection of the skin lining the ear canal of the outer ear. Also called swimmer's ear.
otitis media: An infection of the middle ear.
otosclerosis: An abnormal bony growth in the middle ear that causes hearing loss.
outbreak: Synonymous with epidemic. Sometimes used to refer to a local epidemic as compared to a larger, general epidemic.
outer ear: The external part of the ear, as well as the external ear canal and the eardrum.
outpatient: A person who receives treatment at a hospital or other medical facility but does not stay overnight.
output: The loudest sound that a hearing aid can produce.
ovariectomy: Surgical removal of one or both ovaries.
overactive bladder: Frequent urination and urges to urinate.
overt proteinuria: A condition of declining kidney function. It is part of the progression of kidney disease, developing after microalbuminuria (when a damaged kidney begins to leak small amounts of a protein called albumin into urine) and before chronic kidney disease.
overweight: A body weight above the healthy range but not obese. Usually defined as a body mass index of 25 to 29.9.
ovulation: The release of a mature egg from the ovary, at which time it is available to be fertilized by sperm.
oxidant: An unstable molecule in the body that plays a role in aging and can damage tissue. Also known as a free radical.
oxidation: A process in which oxygen combines with a substance, altering its structure and changing or destroying its normal function.
oxygenated blood: Blood that has moved through the lungs where it has absorbed oxygen; oxygenated blood moves from the lungs into the heart, from which it is then pumped throughout the body.
pacemaker, artificial: A small electronic device generally placed in the chest to correct an irregular heartbeat. It generates small electrical pulses that prompt the heart to beat at a normal pace.
pacemaker, natural: A specialized cluster of cells called the sinoatrial node in the top of the right atrium. The pacemaker produces a steady flow of beat now signals that flash across the atria and then pass through the atrioventricular node to the ventricles.
PAD: Abbreviation for peripheral artery disease, a condition caused by atherosclerosis in the arteries in the legs or leading to them.
painkillers: Drugs that relieve pain.
palate: The tissues that make up the roof of the mouth.
palliative care: Treatment that relieves the symptoms of a serious illness, but does not cure the disease itself.
palpate: To examine a part of the body by touching it carefully.
palpitation: Sensation that the heart is beating rapidly or irregularly.
palsy: Paralysis in part of the body, often with loss of sensation and uncontrolled body movements.
pancreas: A gland in the abdomen that produces digestive enzymes and hormones.
pandemic: A disease outbreak affecting large populations or a whole region, country, or continent.
pannus: An abnormal layer of tissue that forms over joints or the cornea of the eye.
papillary muscles: Threads of muscle that pull the heart valves between the upper and lower chambers of the heart closed during heart contractions.
paraplegia: Paralysis of the legs and lower part of the body.
parasomnias: Sleep disorders, such as night terrors or sleep walking, that periodically interfere with sleep.
parasympathetic nervous system: Part of the nervous system that calms body systems excited by the stress hormones.
parathyroid glands: Glands responsible for releasing a hormone that controls calcium levels and influences bone loss and growth.
parathyroid hormone: A hormone that controls levels of calcium and phosphorous in the blood and influences bone loss and growth.
parietal lobe: Part of the brain. It plays a role in sensory processes, like pain and touch, and language.
Parkinson's disease: A brain disorder that causes movement problems, including shaking, difficulty walking, and rigidity in muscles.
paroxysm: A sudden, violent attack or convulsion; or the worsening of symptoms or recurrence of disease.
paroxysmal hemicrania: A rare form of headache. Sufferers experience a severe throbbing, drilling pain on one side of the face or behind the eye.
passive immunity: Immunity that is conferred by another, such as a mother's antibodies protecting her baby during gestation and shortly after birth.
patch test: A test used to diagnose whether a rash was caused by a reaction to certain allergens, such as poison ivy or a cosmetic ingredient, or an irritant such as soap.
patella: The thick bone that protects the knee joint; also known as the kneecap.
pathogen: A tiny organism such as a virus, bacterium, or parasite that can invade the body and produce disease.
pathology: The underlying abnormalities that contribute to or are characteristic of a disease.
patient-controlled analgesia: A method that allows a person to control, within limits, the amount and timing of pain medication he or she receives. It is usually done by pressing a button to release the medication from a computerized pump into an IV.
pattern-recognition receptors: Proteins that recognize classes of pathogens and stimulate the innate immune system to signal the adaptive immune system.
PCOS: Abbreviation for polycystic ovary syndrome, an inherited disorder characterized by the formation of abnormal cysts in enlarged ovaries; a leading cause of female infertility and a common cause of excess facial or body hair (hirsutism).
PDE5 inhibitors: Abbreviation for phosphodiesterase type 5 inhibitors, drugs that can help a man achieve and maintain an erection.
peak bone mass: The greatest amount of bone tissue that a person has during his or her life.
peak flow: A measure of how fast a person can blow air out of the lungs.
peak flow meter: A device to assess lung function, often used to diagnose and monitor asthma.
Pediculus humanus capitis: A blood-sucking parasite commonly known as the louse (plural, lice) that can cause an itchy scalp; infestations are highly contagious and especially common in school-age children.
pellagra: A rare disease brought on by severe niacin deficiency that causes diarrhea, dermatitis, and dementia.
pelvic floor: The sling of muscles that support the intestines and bladder, as well as the uterus in women. Weak or damaged pelvic floor muscles can cause incontinence or diminished sexual pleasure, among other problems.
penile prosthesis: An inflatable or bendable device that is implanted in the penis to allow a man with erectile dysfunction to have erections when he wishes.
pepsin: Enzymes secreted by the stomach to break down protein.
peptic ulcer: A raw, crater-like sore in the lining of the stomach or duodenum that causes burning stomach pain.
percutaneous diskectomy: Surgical removal of part of a spinal disk that is bulging out abnormally and pressing on a nerve root or the spinal column.
percutaneous electrical nerve stimulation: A pain relief therapy that uses needles to deliver low-voltage electrical current under the skin to stop pain signals from reaching the brain.
percutaneous transluminal coronary angioplasty: A procedure used to open blocked coronary arteries. A small, thin tube with a tiny balloon at its tip is inserted into a narrowed coronary artery. The balloon is then inflated to widen the narrowed area. A stent may be put in place to hold the artery open. Percutaneous transluminal coronary angioplasty is also known as balloon angioplasty.
perforation: A hole, such as an ulcer, in an organ or tissue.
performance anxiety: Concern about sexual performance that is so severe that it leads to sexual dysfunction.
perfusion: Passage of a fluid through a specific organ or an area of the body.
perfusion defect: A test result that indicates abnormal blood flow or areas of damaged or dead heart muscle.
pericarditis: Inflammation of the pericardium, the heart's sac-like covering.
pericardium: The fibrous sac that surrounds the heart and the roots of the major blood vessels.
perimenopause: The transition time in a woman's life that begins when ovaries produce less estrogen and menstruation becomes less frequent, and ends when the ovaries no longer produce eggs and menstruation stops.
perineum: The area of skin between the vagina and anus in women, and between the scrotum and anus in men.
periodic limb movement disorder: A sleep disorder in which the legs jerk or cramp repeatedly during the sleep.
periodization: An exercise strategy that varies reps, sets, and resistance to alternate heavier and lighter workouts over a period of time.
periodontal disease: Diseases, including gingivitis and periodontitis, that attack the gum tissue and the structures supporting the teeth. Also called gum disease.
periodontitis: An advanced stage of gum disease that attacks the teeth's supporting structures.
peripheral artery disease: A condition caused by atherosclerosis in the arteries in the legs or leading to them.
peripheral nervous system: The parts of the nervous system outside of the brain, brain stem, and spinal cord.
peripheral neuropathy: Damage to the long nerves radiating from the spine to the arms and legs.
peripheral vascular disease: Narrowing of blood vessels that supply blood to the legs, arms, stomach, or kidneys.
peripheral vision: Side vision, or what the eye perceives outside the direct line of vision.
peristalsis: Wavelike movement of intestinal muscles that propels food through the digestive tract.
peritoneal dialysis: Treatment for kidney failure that uses a machine to remove toxins from the bloodstream.
peritonitis: Inflammation of the membrane that line the abdominal cavity and surrounds most abdominal organs.
pernicious anemia: A form of anemia in which red blood cells enlarge and decrease in size due to an inability to properly absorb vitamin B12.
personal emergency response system: A device worn around the neck or wrist that allows a person to call for help by pressing a button.
pessary: A device placed in the vagina to support or correct the position of the uterus, rectum, or bladder.
pessimism: A characteristic frame of mind that leads a person to expect negative outcomes and to view the world as a negative or fearful place.
petechiae: Pinpoint-sized red or purple spots that appear in clusters on the skin, caused by bleeding under the skin.
PET scan: Abbreviation for positron emission tomography, a medical imaging test that uses a radioactive substance to assess organ and tissue function in the body and to look for disease.
Peyronie's disease: Scarring of some of the tissue inside the penis, causing the penis to bend at an angle during an erection.
pH monitoring: A test to determine whether stomach acid is backing up into the esophagus. For this test, a sensing probe is inserted through the nose and positioned above the lower esophageal sphincter.
phacoemulsification: A method of cataract removal. It uses ultrasound waves to break up the clouded lens of the eye so it can be suctioned out with a needle.
phagocytes: Cells that can ingest other cells, bacteria, and foreign particles.
phase shift disorder: Sleep problem that results when a person's internal clock becomes out of sync with external time. This can be a problem for people who work the night shift.
phase-2 enzyme: A helpful enzyme that seems to clear toxins and help prevent cancer-causing substances from binding to DNA.
phenothiazines: Powerful tranquilizing drugs used to treat schizophrenia and, sometimes, severe nausea.
phenylpropanolamine: A decongestant drug used to treat nasal congestion and sometimes mild incontinence.
pheochromocytoma: A rare adrenal gland tumor that secretes hormones that narrow blood vessels and increase blood pressure.
phlegm: Thick, sticky mucus secreted by mucous membranes, such as the sinuses.
phonophobia: Sensitivity to noise, often experienced during a migraine attack.
phosphodiesterase type 5: An enzyme that breaks down substances that help the penis become erect and maintain an erection.
photocoagulation: Use of a laser to seal off blood vessels.
photodynamic therapy: A medical treatment that uses a light source to activate a photosensitizing drug (one that becomes activated by light exposure). Often used in oncology, dermatology, and cosmetic surgery.
photophobia: Sensitivity to light, often experienced during a migraine attack.
photopsia: A sensation of sparks or flashes of light across the visual field.
photorefractive keratectomy: Laser surgery used to reshape the cornea in order to correct vision problems.
photorejuvenation: A cosmetic procedure that uses intense pulsed light to remove wrinkles and improve skin tone and texture.
physiatrist: A physician who specializes in physical medicine, pain, and rehabilitation. These doctors diagnose and treat sports injuries and degenerative conditions like arthritis or low back pain, and oversee rehab for patients with severe impairments resulting from trauma, stroke, and other conditions.
physical activity: Any voluntary body movements that burn calories, including walking up stairs, vacuuming a floor, going for a brisk stroll, or engaging in a structured program of exercise.
physical dependence: The process through which the body becomes accustomed to a psychoactive drug or rewarding behavior and misses it if it's taken away. People with physical dependence who stop or cut down on their substance or activity of choice might develop uncomfortable withdrawal symptoms.
physical fitness: A state of being physically sound and healthy; having the ability to perform physical activity well.
phytochemicals: Substances made by plants that have biological effects in the human body. Examples include isoflavones, lycopene, lutein, and zeaxanthin.
phytoestrogen: A plant component that mimics the effects of estrogen hormones in the body.
Pick's disease: A brain disorder that causes dementia, neurotic behavior, and gradual changes in personality and emotional control.
pineal gland: A gland located in the middle of the brain, between the brain's two hemispheres, that produces melatonin in response to declining light.
Pittsburgh Compound B: A substance that binds to amyloid proteins in the brain (markers for Alzheimer's disease), making them visible under positron emission tomography (PET) scanning.
pituitary gland: The so-called master gland, located at the base of the brain. It controls and regulates the thyroid and other glands throughout the endocrine system.
placebo: A false or inactive medication or treatment that may still offer relief despite being ineffective. In clinical trials, the effectiveness of a new drug is often tested against a placebo.
placebo effect: A change or improvement in symptoms that is due to a dummy medication or treatment (placebo) rather than a real drug or treatment.
plantar fascia: Connective tissue in the foot which joins the heel bone to the ball of the foot.
plantar fasciitis: An inflammation of the plantar fascia; the leading cause of heel pain.
plantar wart: A wart on the sole of the foot, caused by a virus.
plaque: 1) A layer of bacteria that forms on the surface of a tooth and can cause dental disease. 2) A fatty deposit in or on the walls of an artery, as part of atherosclerosis.
plasma: The fluid in which blood cells are suspended.
plasma cells: White blood cells that produce large quantities of antibodies as part of an immune system response.
plasmin: An enzyme that breaks down the protein involved in clotting blood (fibrin), dissolving the clot.
platelet: A colorless, disk-shaped cell in the blood that is necessary for clotting.
podiatrist: A physician who specializes in the medical, surgical, and orthopedic management of foot and ankle disorders.
poliosis: A localized patch of gray or white hair on the scalp, eyebrows, or eyelashes.
polycystic ovary syndrome: An inherited disorder characterized by the formation of abnormal cysts in enlarged ovaries; a leading cause of female infertility and a common cause of hirsutism.
polydipsia: Excessive thirst.
polymyositis: A rare disease in which the muscles become inflamed and weak.
polyp: An abnormal, noncancerous growth that protrudes from mucous membranes, like those found in the sinuses and colon lining.
polysomnography: A sleep study that examines brain waves and other measures of physiological functioning.
polyunsaturated fat: A type of fat that is abundant in soybean, corn, cottonseed, safflower, and sunflower oils, as well as in fatty fish. One type, omega-3 fats, are especially important for cardiovascular health.
polyuria: Excessive urination.
positive psychology: A branch of psychology that studies mental health rather than illness, focusing on how life can be more happy and fulfilling.
positron emission tomography: A medical imaging test that uses a radioactive substance to assess organ and tissue function in the body and to look for disease. Commonly called a PET scan.
posterior chamber: The part of the eye behind the iris and in front of the lens that is filled with aqueous humor.
posterior heel bursitis: An inflammation of the bursa sac surrounding the joint in the heel of the foot, causing swelling and pain.
posterior keyhole foraminotomy: A minimally invasive surgical procedure that is sometimes an option for repairing a herniated disk.
posterior myocardial infarction: Heart attack involving the rear wall of the heart muscle.
postherpetic neuralgia: Nerve pain caused by the herpes zoster virus, also known as shingles.
postmenopausal osteoporosis: Bone loss caused by lower estrogen levels associated with menopause. Sometimes called type I osteoporosis.
postmenopause: The period in a woman's life lasting from the end of perimenopause until the end of life.
postpartum: Pertaining to the period after giving birth.
post-traumatic headache: A persistent headache resulting from a head or neck injury, sometimes lasting for a year or more.
post-traumatic stress disorder: A prolonged reaction to a traumatic event. Post-traumatic stress disorder can cause crippling anxiety and leading to other problems, such as sleep disturbances, depression, and substance abuse. Often referred to as PTSD.
post-void residual: The amount of urine left in the bladder after urinating.
power: Force times speed of movement. It reflects how quickly a given force is exerted.
power training: An emerging field of physical medicine aimed at boosting the ability to exert strength quickly, especially in relation to practical, day-to-day tasks.
prazosin: A member of a class of drugs called alpha blockers. Prazosin eases the symptoms of benign prostatic hyperplasia by relaxing smooth muscle tissue in the capsule that surrounds the prostate.
precursor: A substance that the body can convert into the active form of a vitamin. One example is beta carotene, which the body can convert into vitamin A as needed.
prediabetes: A fasting blood sugar level above a healthy level, but still below the level used to diagnose diabetes. An individual with prediabetes is at increased risk for developing diabetes.
preeclampsia: High blood pressure during pregnancy accompanied by such signs as protein in the urine and swelling of the hands and feet; can progress to eclampsia, characterized by seizures.
prehypertension: Blood pressure that is above normal but not high enough to qualify as hypertension. An individual with prehypertension is at increased risk for developing hypertension.
preload reduction: A method of reducing cardiac workload by decreasing the pressure of blood entering the heart.
premature atrial contraction: An early beat in an atria that feels like the heart skipped a beat.
premature ejaculation: Ejaculation that occurs before or immediately after penetration; this can interfere with a couple having a mutually satisfying sexual experience.
premature ventricular contraction: An early beat in a ventricle that feels like the heart skipped a beat.
presbycusis: Age-related hearing loss caused by the death of hair cells in the inner ear.
presbyopia: Age-related difficulty focusing the eyes at close range, as the flexible lens of the eye becomes less elastic.
priapism: An erection that lasts longer than three hours. Emergency medical treatment is required to prevent permanent damage to the penis.
prick test: A commonly used skin test to confirm hypersensitivity to a broad range of allergens.
primary angioplasty: Use of angioplasty as the first treatment to open a blocked artery that is causing a heart attack, rather than using clot-busting (thrombolytic) drugs.
primary hypertension: High blood pressure with no known cause. Also known as essential hypertension.
primary osteoporosis: Bone loss that results from a normal physiological process, such as menopause or aging.
prion: The smallest known infectious agent; unlike a virus or bacterium it is made entirely of protein and contains no nucleic acid or chromosomes.
probate: A public, legal process supervised by the courts after a person dies that helps ensure debts are paid and assets are properly owned and correctly distributed.
probiotic: Live microorganisms used to benefit health, such as the L. acidophilus bacteria found in yogurt.
procedural memory: The long-term memory of skills and procedures, or how-to knowledge. Also called implicit memory.
processes: Bony projections that extend in several directions from each vertebra bone in the spine.
prodrome: A group of early symptoms preceding a given disease or condition. For example, a migraine prodrome (fatigue, hunger, nervousness) may occur hours or days before the headache strikes.
progesterone: A female steroid hormone produced by the ovaries that prepares the uterine lining for pregnancy.
progestin: A synthetic compound that produces effects similar to those of the hormone progesterone.
progestogen: Any hormone having the same effect as progesterone in the body; refers to both natural progesterone and synthetic progestin.
prognosis: A prediction on how a person's disease will progress in the future.
progressive muscle relaxation: A mind/body technique for inducing the relaxation response that involves isolating, tensing, and relaxing specific sets of muscles in sequence.
prolapse: A condition in which an organ or other body part drops from its normal position.
prolapsed disk: When part of a spinal disk bulges out of a tear or weak spot in the disk's tough outer shell. Also known as herniated disk.
proliferative retinopathy: An advanced stage of diabetic eye disease characterized by the development of new blood vessels that grow into the vitreous cavity; they are fragile and may bleed and cause loss of vision.
prophylaxis: Steps taken to prevent a particular disease or condition, such as taking nitroglycerin to prevent angina.
proprioception: The ability to sense the position of one's body in space, in relation to other objects.
proptosis: Forward bulging or displacement of an organ, especially of an eye. See exophthalmos.
prospective study: A type of research method that collects data on a group of people at the start of the study and then follows them into the future, gathering data over time.
prostaglandins: A group of chemicals that have hormone-like actions; prostaglandins help regulate blood pressure and contraction of smooth-muscle cells (for example, those in the lining of the blood vessels).
prostate cancer: Cancer of the prostate gland.
prostate gland: A walnut-shaped gland at the base of the male bladder. It produces a fluid that forms part of semen.
prostate-specific antigen: A protein produced by the prostate. Elevated levels may indicate the presence of cancer, benign prostatic hyperplasia, or prostatitis. Often referred to as PSA.
prostatic carcinoma: Another name for prostate cancer.
prostatic urethral stent: A small, springlike cylinder, designed to relieve pressure from an enlarged prostate and improve urine flow by widening a narrowed urethra.
prostatism: A blockage at the base of the bladder that reduces or prevents the flow of urine into the urethra, the tube that carries urine out of the body (also known as bladder outlet obstruction). Typical symptoms include feeling the need to urinate right away yet having to strain to do so, having a weak urinary stream, dribbling after urinating, feeling as though the bladder has not been emptied completely, needing to urinate frequently, or experiencing urinary incontinence.
prostatitis: An inflammation of the prostate gland, sometimes caused by a bacterial infection, which may result in painful or difficult urination.
prosthesis: An artificial device such as a hearing aid, artificial joint, or dentures that substitutes for a missing body part.
protease inhibitor: A class of drugs that help fight retrovirus infections; commonly prescribed to treat human immunodeficiency virus (HIV).
protein: One of the three major nutrients (along with carbohydrates and fats). It is used by the body for building and repairing tissues. Protein is derived primarily from animal sources but can be obtained from nuts and seed, some grains, and other plant sources.
protocol: A plan that lays out the procedures that will be followed in conducting a physical examination, a research study, or the treatment of a disease.
PSA: Abbreviation for prostate-specific antigen, a protein produced by the prostate. Elevated levels may indicate the presence of cancer, benign prostatic hyperplasia, or prostatitis.
PSA velocity: The rate at which a man's PSA level increases over time.
pseudoephedrine: A decongestant drug that may also relieve mild incontinence.
pseudogout: Arthritis caused by crystals of calcium pyrophosphate dihydrate in the joints. Also known as calcium pyrophosphate dihydrate disease.
psoriasis: A common skin disease characterized by thickened patches of inflamed red skin; sometimes accompanied by painful joint swelling and stiffness.
psychodynamic therapy: A form of therapy that focuses on how life events, desires, and close relationships lead to conflict, symptoms such as anxiety or depression, and difficulty in managing life's tasks.
psychogenic: Symptoms and illnesses that have a psychological cause, rather than a physical one.
psychogenic erectile dysfunction: Difficulty in getting or maintaining erections because of a psychological cause, such as stress or depression.
psychosomatic: Symptoms and illnesses that involve both the mind and the body, in which psychological stress may result in physical illness.
PTCA: Abbreviation for percutaneous transluminal coronary angioplasty, a procedure used to open blocked coronary arteries.
ptosis: A drooping of the eyelid attributed to weakened muscles.
PTSD: Abbreviation for post-traumatic stress disorder, a prolonged reaction to a traumatic event. PTSD can cause crippling anxiety and leading to other problems, such as sleep disturbances, depression, and substance abuse.
puborectalis muscle: A pelvic floor muscle that forms a sling around the rectum and helps maintain fecal continence.
pudendal arteries: Arteries supplying blood to the genital area.
pudendal nerve: The nerve that carries sensation from the genital area to the central nervous system.
pulmonary: Pertaining to the lungs.
pulmonary edema: A condition caused by excess fluid accumulating in the lungs, making breathing difficult.
pulmonary embolism: Blockage of one or more arteries in the lungs by a blood clot that formed elsewhere, often in the legs. Typically accompanied by sudden shortness of breath, chest pain, and cough.
pulmonary veins: The veins that carry blood from the lungs to the left atrium.
pulp: Tissue containing nerves and blood vessels that fills the chamber at the center of the tooth.
pulse pressure: The difference between systolic blood pressure and diastolic blood pressure (systolic pressure minus diastolic pressure = pulse pressure). Pulse pressure may help predict heart disease risk.
pump failure: When the heart muscle becomes so weak that it can no longer pump enough blood to the rest of the body.
pupil: The dark, circular opening in the middle of the iris of the eye.
purulent: Formed of or containing pus.
pus: A thick, yellow or green liquid that is composed of dead cells and bacteria, most often found at the site of a bacterial infection.
pyloric sphincter: A muscular valve at the lower end of the stomach that opens to the duodenum.
pyridoxine: A form of vitamin B6.