facet joints: Paired joints that link a vertebra to its neighboring vertebrae. They allow the spine to move as a unit.

facet rhizotomy: Surgical destruction of certain nerves and nerve roots to relieve pain.

false negative: Test results that show that a disease or substance isn't present, even though it is.

familial combined hyperlipidemia: An inherited disorder in which the liver overproduces very low-density lipoprotein, causing high levels of cholesterol or triglycerides, or both.

familial hypercholesterolemia: An inherited disorder in which the liver cannot properly remove low-density lipoprotein particles from the blood, causing a very high cholesterol level.

fasting lipid profile: A laboratory test to determine the relative levels of high-density lipoprotein, low-density lipoprotein, and total cholesterol in the blood. Also referred to as a lipoprotein analysis, full lipid profile, or cholesterol profile.

fasting plasma glucose test: A blood test that determines the amount of sugar (glucose) in the blood after an overnight fast of at least eight hours.

fast-twitch fiber: One of two main types of skeletal muscle fibers. Fast-twitch fibers are recruited most heavily when bursts of power are needed, as in sprinting. See also slow-twitch fiber.

fat: One of the three major nutrients, along with carbohydrates and proteins.

fatigue: A lack of energy. A decrease over time in the ability to perform a physical or mental task.

fatty acids: Components of fats that can be used for energy by cells.

fatty streak: The first stage of atherosclerosis, a build-up of fatty materials in the wall of a blood vessel.

febrile: Feverish; having a high body temperature.

fecal impaction: A mass of dry, hard stool that gets lodged in the rectum.

fecal occult blood test: A test that checks for colorectal cancer by detecting blood in the stool.

femur: Thigh bone.

ferritin: A protein that captures and stores iron.

fetal alcohol syndrome: A collection of birth defects resulting from exposure of the fetus to alcohol during pregnancy.

fiber: A substance found in plant foods that the body can't digest.

fibrillation: Rapid and uncoordinated contractions of heart muscle fibers. When this occurs, the heart can't properly contract or pump blood.

fibrin: A stringy protein that is the primary component of a blood clot.

fibrinogen: A protein that helps stop bleeding by aiding in forming blood clots.

fibroadenoma: A tumor that is not cancer; usually found in the breast.

fibroblast: A cell that helps form the collagen and elastic fibers of connective tissue.

fibroid: A tumor that is not cancer, which is found in the uterus.

fibromyalgia: A condition causing pain and tender spots throughout the body.

fibrous plaque: A buildup of fat on the inside of a blood vessel that interferes with blood flow.

fibula: The calf bone.

filtering procedure: A procedure to treat glaucoma in which a surgeon creates a drainage hole in the eye to relieve pressure.

finasteride: A medication for treating benign prostatic hyperplasia (enlargement of the prostate gland).

fixed joint: An area where two bones meet that is fixed, or doesn't move.

flaccid: Soft, not erect.

flare: Reappearance or worsening of symptoms.

flat feet: A condition in which the arch is flat all the time or flattens when bearing weight.

flatulence: Excess gas in the stomach or intestines that is expelled from the anus.

flatus: Gas expelled through the anus.

flavonoids: Chemicals found in fruits, vegetables, wine, and tea that may protect cells from damage and have health benefits.

flex: Bend a joint (for example, flexing the knees).

flexibility: A component of physical fitness that refers to the range of motion available at a joint.

flight-or-fight response: Changes that occur in the body, such as rapid breathing and heartbeat, when a person is confronted with a perceived physical or emotional threat. Also called the stress response.

floaters: Tiny spots or lines that appear in a person's field of vision when the jelly-like fluid of the eye breaks down with age. They are usually harmless, but can signal serious eye problems.

flow: A term coined by positive psychology pioneer Mihaly Csikszentmihalyi to describe an effortless, active state of being during which one loses awareness of time, self, and distractions. Flow hinges on balancing the size of a challenge and the level of skill a person brings to it.

fluorescein angiography: A test that uses special dye and a camera to examine blood flow in the retina.

fluoride: A mineral that protects teeth from decay and cavities.

fluoroscopy: A test that gives moving images of the inside of the body; could be likened to an x-ray movie.

foam cells: Lipid-laden cells, named for their foamy appearance under the microscope. As foam cells build up on the inside of blood vessel walls, they form a plaque that can block blood flow.

focal neuropathy: Damage to a specific nerve, causing pain or numbness.

focus words: Peaceful, relaxing words or phrases used during stress relief exercises.

follicle: A group of cells that form a small sac.

follicle-stimulating hormone: A hormone released by the pituitary gland that stimulates the production of eggs in women and sperm in men.

follicular unit: A small bundle that includes one to four follicles, oil glands, a tiny muscle, and other tissue.

follicular unit transplantation: Transplantation of follicular units, which mimic natural hair growth.

folliculitis: An inflammation of the hair follicle.

food allergies: Sensitivities to certain foods that can cause symptoms ranging from the mild (like hives) to the life threatening (such as anaphylaxis).

forehead lift: Cosmetic surgery to minimize creases on the forehead and between the eyebrows, and to lift sagging eyebrows.

fovea: A small dimple in the middle of the retina that provides sharp central vision.

fracture: A break in a bone.

FRAX tool: An algorithm for estimating the probability of breaking a bone because of low bone mass over a period of 10 years.

free fragment: Part of a disk in the back that has broken off from the main portion of the disk.

free radical: An unstable molecule in the body that plays a role in aging and can damage tissue; antioxidants help prevent free radical damage.

frequency: The pitch of a sound; measured by the speed at which sound waves vibrate.

frequency range: How much amplification a hearing aid produces in both high and low frequencies.

frequency response: The amplification that a hearing aid produces across different sound frequencies.

frontal lobe: Part of the brain that plays a role in determining consequences and choosing behaviors.

frontotemporal lobar degeneration: A brain disorder that can cause dementia, aphasia, neurotic behavior, and gradual changes in personality and emotional control.

frozen shoulder: Inflammation of various tissues of the shoulder, along with growth of abnormal bands of tissue that cause the shoulder to become so stiff that movement is severely limited.

fructose: A simple sugar found in corn syrup, honey, and many sweet fruits.

FSH: Abbreviation for follicle-stimulating hormone, a hormone released by the pituitary gland that stimulates the production of eggs in women and sperm in men.

functional gastrointestinal disorders: Gut problems that aren't caused by an infection or structural problem with the gastrointestinal system.

functional incontinence: Recognition of the need to urinate but being unable to get to the bathroom in time due to mental or physical problems, such as limited mobility.

fundoplication: Surgery that restructures the stomach to prevent acid reflux.

fundus photography: Imaging test that provides multi-dimensional pictures of the back of the eyeball.

fungus: Organisms and microorganisms, such as yeasts and molds, that can live as a parasite on plants and animals.