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Glossaries - F

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

Failure to Thrive (FAYL-yoor too THRYV)

A condition that occurs when a baby does not grow normally.

Familial Polyposis (fuh-MIL-ee-ul pah-luh-POH-sis)

An inherited disease causing many polyps in the colon. The polyps often cause cancer.

Fasting blood glucose test

A method for finding out how much glucose (sugar) is in the blood. The test can show if a person has diabetes. A blood sample is taken in a lab or doctor's office. The test is usually done in the morning before the person has eaten. The normal, nondiabetic range for blood glucose is from 70 to 110 mg/dl, depending on the type of blood being tested. If the level is over 126 mg/dl, it usually means the person has diabetes (except for newborns and some pregnant women).


One of the three main classes of foods and a source of energy in the body. Fats help the body use some vitamins and keep the skin healthy. They also serve as energy stores for the body. In food, there are two types of fats: saturated and unsaturated.

Saturated fats are solid at room temperature and come chiefly from animal food products. Some examples are butter, lard, meat fat, solid shortening, palm oil, and coconut oil. These fats tend to raise the level of cholesterol, a fat-like substance in the blood.

Unsaturated fats, which include monounsaturated fats and polyunsaturated fats, are liquid at room temperature and come from plant oils such as olive, peanut, corn, cottonseed, sunflower, safflower, and soybean. These fats tend to lower the level of cholesterol in the blood. See also: Carbohydrate; protein.

Fatty acids

A basic unit of fats. When insulin levels are too low or there is not enough glucose (sugar) to use for energy, the body burns fatty acids for energy. The body then makes ketone bodies, waste products that cause the acid level in the blood to become too high. This in turn may lead to ketoacidosis, a serious problem. See also: Diabetic ketoacidosis.

Fatty Liver (FAH-tee LIH-vur)

The buildup of fat in liver cells. The most common cause is alcoholism. Other causes include obesity, diabetes, and pregnancy. Also called steatosis.

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Fecal Fat Test (FEE-kul fat test)

A test to measure the body's ability to break down and absorb fat. The patient eats a fat-free diet for 2 to 3 days before the test and collects stool samples for examination.

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Fecal Incontinence (FEE-kul in-KAN-tuh-nuns)

Being unable to hold stool in the colon and rectum.


Fecal Occult Blood Test (FOBT) (FEE-kul uh-KULT blud test)

A test to see whether there is blood in the stool that is not visible to the naked eye. A sample of stool is placed on a chemical strip that will change color if blood is present. Hidden blood in the stool is a common symptom of colorectal cancer. (Fecal refers to stool. Occult means hidden.)

Feedback Inhibition

mechanism that maintains constant secretion of a product by exerting inhibitory control.

Fermentation (FER-mun-TAY-shun)

The process of bacteria breaking down undigested food and releasing alcohols, acids, and gases.

Fiber (FY-bur)

A substance found in foods that come from plants. Fiber helps in the digestive process and is thought to lower cholesterol and help control blood glucose (sugar). The two types of fiber in food are soluble and insoluble. Soluble fiber, found in beans, fruits, and oat products, dissolves in water and is thought to help lower blood fats and blood glucose (sugar). Insoluble fiber, found in whole-grain products and vegetables, passes directly through the digestive system, helping to rid the body of waste products.


The insoluble protein formed from fibrinogen by the proteolytic action of thrombin during the normal clotting of blood. Fibrin forms the essential portion of the blood clot.

Fibrinogen (fi-BRIN-uh-jen)

A coagulation factor, also known as factor I, that is converted to fibrin by the action of thrombin.

Fibrinolysis (fi-brin-AHL-uh-sis)

The dissolution of fibrin by enzymatic action.

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Fibroblastic (fi-bro-BLAS-tik)

pertaining to fibroblasts, or connective tissue cell.

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A chronic disorder characterized by widespread musculoskeletal pain, fatigue, and multiple tender points.

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Fibrous capsule

A tough wrapping of tendons and ligaments that surrounds the joint.

Fistula (FIST-yoo-luh)

An abnormal passage between two organs or between an organ and the outside of the body. Caused when damaged tissues come into contact with each other and join together while healing.

Flatulence (FLAT-yoo-lunss)

Excessive gas in the stomach or intestine. May cause bloating.


A period of time in which disease symptoms reappear or become worse.

Flatus (FLAH-tus)

Gas passed through the rectum.

Folic acid

a member of the vitamin B complex involved in the formation of red blood cell.

Foodborne Illness (FOOD-born IL-nus)

An acute gastrointestinal infection caused by food that contains harmful bacteria. Symptoms include diarrhea, abdominal pain, fever, and chills. Also called food poisoning.


A type of sugar found in many fruits and vegetables and in honey. Fructose is used to sweeten some diet foods. It is considered a nutritive sweetener because it has calories.

Fulminant Hepatic Failure (FHF) (FOOL-muh-nunt heh-PAT- ik FAYL-yoor)

Liver failure that occurs suddenly in a previously healthy person. The most common causes of FHF are acute hepatitis, acetaminophen overdose, and liver damage from prescription drugs.

Functional antibody

an antibody that binds to an antigen and has an effect that can be demonstrated in laboratory tests. For example, neutralizing antibodies are functional antibodies that inactivate HIV or prevent it from infecting other cells.

Functional Disorders (FUNK-shun-ul dis-or-durz)

Disorders such as irritable bowel syndrome. These conditions result from poor nerve and muscle function. Symptoms such as gas, pain, constipation, and diarrhea come back again and again, but there are no signs of disease or damage. Emotional stress can trigger symptoms. Also called motility disorders.

Functional Medicine

Also called complementary medicine, integrative medicine, or natural medicine, this discipline focuses on using a holistic approach to analyze and treat interdependent systems of the body and to create a dynamic balance integral for good health.

Fungus (FUN-gus)

A mold or yeast such as Candidiasis that may cause infection.

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