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Glossaries - P

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

Pancreas (PAN-kree-ahs)

An organ behind the lower part of the stomach that is about the size of a hand. It makes insulin so that the body can use glucose (sugar) for energy. It also makes enzymes that help the body digest food. Spread all over the pancreas are areas called the islets of Langerhans. The cells in these areas each have a special purpose. The alpha cells make glucagon, which raises the level of glucose in the blood; the beta cells make insulin; the delta cells make somatostatin. There are also the PP cells and the D1 cells, about which little is known.

Pancreatitis (PAN-kree-uh-TY-tis)

Inflammation (pain, tenderness) of the pancreas; it can make the pancreas stop working. It is caused by drinking too much alcohol, by disease in the gallbladder, or by a virus.

Papillary Stenosis (PAH-pih-lair-ee stuh-NOH-sis)

A condition in which the openings of the bile ducts and pancreatic ducts narrow.

Parakeratosis (par-ah-ker-ah-TOE-sis)

persistence of the nuclei in the cells of the stratum corneum of the epidermis, as seen, for example, in psoriasis.


administered intravenously or by injection. For example, medications or vaccines may be administered by injection into the fatty layer immediately below the skin (subcutaneous), or into the muscle (intramuscular). Medications, but not vaccines, can also be administered into a vein (intravenously).

Parenteral Nutrition (puh-REN-tuh-rul noo-TRISH-un)

A way to provide a liquid food mixture through a special tube in the chest. Also called hyperalimentation or total parenteral nutrition.

Parietal Cells (puh-RY-uh-tul selz)

Cells in the stomach wall that make hydrochloric acid.


the origin and development of a disease. More specifically, its the way a microbe (bacteria, virus, etc.) causes disease in its host.

PCR (polymerase chain reaction)

a sensitive laboratory technique used to detect and repeatedly copy small amounts of RNA or DNA. Some PCR tests can also quantify the amount of RNA or DNA. PCR is used to measure viral load in persons infected with viruses such as HIV.

Peak Plasma Drug Concentration

the highest level of drug that can be obtained in the blood usually following multiple dose.

Pediatric Gastroenterologist (pee-dee-AT-trik GAH-stroh-en-tuh-RAW-luh-jist)

A doctor who treats children with digestive diseases.

Pepsin (PEP-sin)

An enzyme in the stomach that breaks down proteins.

Peptic (PEP-tik)

Related to the stomach and the duodenum, where pepsin is present.

Peptic Ulcer (PEP-tik UL-sur)

A sore in the lining of the esophagus, stomach, or duodenum. Usually caused by the bacterium Helicobacter pylori. An ulcer in the stomach is a gastric ulcer; an ulcer in the duodenum is a duodenal ulcer.


a short compound formed by linking two or more amino acids. Proteins are made of multiple peptides.

Percutaneous (PUR-kyoo-TAY-nee-us)

Passing through the skin.

Percutaneous Ercutaneous Transluminal Coronary Angioplasty (PTCA) (per-kue-TAY-nee-us tranz-LOO-min-ul KOR-uh-nair-ee AN-jee-oh-plas-tee)

Dilation of a coronary vessel by means of a balloon catheter inserted through the skin and through the lumen of the vessel to the site of the narrowing, where the balloon is inflated to flatten plaque against the arterial wall.

Perforated Ulcer (PUR-fuh-ray-ted UL-sur)

A hole in the wall of an organ.

Perforation (PUR-fuh-RAY-shun)

An ulcer that breaks through the wall of the stomach or the duodenum. Causes stomach contents to leak into the abdominal cavity.

Perianal (PEH-ree-AY-nul)

The area around the anus.

Perineal (PEH-rih-NEE-ul)

Related to the perineum.

Perineum (PEH-rih-NEE-um)

The area between the anus and the sex organs.

Peripheral neuropathy

Nerve damage, usually affecting the feet and legs; causing pain, numbness, or a tingling feeling. Also called "somatic neuropathy" or "distal sensory polyneuropathy.".

Peripheral vascular disease (PVD)

Disease in the large blood vessels of the arms, legs, and feet. People who have had diabetes for a long time may get this because major blood vessels in their arms, legs, and feet are blocked and these limbs do not receive enough blood. The signs of PVD are aching pains in the arms, legs, and feet (especially when walking) and foot sores that heal slowly. Although people with diabetes cannot always avoid PVD, doctors say they have a better chance of avoiding it if they take good care of their feet, do not smoke, and keep both their blood pressure and diabetes under good control.

Peristalsis (PEH-ree-STAWL-sis)

A wavelike movement of muscles in the gastrointestinal tract. Peristalsis moves food and liquid through the gastrointestinal tract. For detailed information about the gastrointestinal tract click here.

Peritoneum (PEH-rih-toh-NEE-um)

The lining of the abdominal cavity.

Peritonitis (PEH-rih-toh-NY-tis)

Infection of the peritoneum.

Pernicious Anemia (pur-NIH-shus uh-NEE-mee-uh)

Anemia caused by a lack of vitamin B12. The body needs B12 to make red blood cells.

Peutz-Jeghers Syndrome (POYTS-YAY-gurz sin-drohm)

An inherited condition. Many polyps grow in the intestine. There is little risk of cancer.

Pharynx (FAR-ingks)

The space behind the mouth. Serves as a passage for food from the mouth to the esophagus and for air from the nose and mouth to the larynx.

Phase 1 clinical trial

a closely monitored clinical trial of a drug or vaccine conducted in a small number of healthy volunteers. A Phase 1 is designed to determine the drugs safety in humans, its metabolism and pharmacologic actions, and side effects associated with increasing doses.

Phase 2 clinical trial

controlled clinical study of a drug or vaccine to identify common short-term side effects and risks associated with the drug or vaccine and to collect information on its immunogenicity. Phase 2 trials enroll some volunteers who have the same characteristics as persons who would be enrolled in an efficacy (Phase 3) trial of a drug or vaccine. Phase 2 trials enroll up to several hundred participants and have more than one arm.

Phase 3 clinical trial

large controlled study to determine the ability of a vaccine to produce a desired clinical effect on the risk of a given infection, disease, or other clinical condition at an optimally selected dose and schedule. These trials also gather additional information about safety needed to evaluate the overall benefit-risk relationship of the drug or vaccine and to provide adequate basis for labeling. Phase 3 trials usually include several hundred to several thousand volunteers.


the processes of absorption, distribution, metabolism and excretion of a drug or vaccine.


A doctor who specializes in the diagnosis and management of injuries and diseases causing pain, loss of function, and disability. Treatment plans often include the use of exercise, massage, heat, electricity (TENS), relaxation techniques, splints and braces, and local injections to relieve pain.


the process of adding phosphate (a unique combination of phosphorous and oxygen atoms) molecular groups to a compound.

Pituitary, pituitary gland

a pea-sized structure, which secretes many important hormones, located behind the hypothalamus. Often called "the master gland," the pituitary serves the body in many ways-in growth, in food use, and in reproduction.


an inactive compound having no physiological effect; an inert substance identical in appearance to the treatment drug used in clinical studies; an inactive substance administered to some study participants while others receive the agent under evaluation, to provide a basis for comparison of effects.

Plaque (plak)

Any patch or flat area. Atheromatous plaque is a swelling on the inner surface of an artery produced by lipid deposit.


an extra-chromosomal ring of DNA, especially of bacterial origin, that replicates autonomously.

Plasmin (PLAZ-min)

A serine protease that solubilizes fibrin clots and also degrades various coagulation factors, including fibrinogen and factors V and VII. Derived from plasminogen.

Plasminogen (plaz-MIN-oh-jen)

The inactive precursor of plasmin, cleaved by plasminogen activators to form plasmin.

Plasminogen Activator

A general term for a group of substances that have the ability to cleave plasminogen and convert it into plasmin. Includes prourokinase, u-plasminogen activator (urokinase), and tissue plasminogen activator (tPA). Plasminogen is activated for therapeutic thrombolysis by recombinant forms of physiologic activators and by streptokinase, a bacterial enzyme.


inflammation of the lung.


inflammation of several joints at the same time.


A great thirst that lasts for long periods of time; a sign of diabetes.

Polymer (POL-eh-mer)

a molecule formed by the joining of many smaller molecules; a protein, for example, is a polymer of amino acids.


an enzyme that forms long chain polymers from simple molecular components; DNA polymerase, for example, forms DNA strands from nucleosides.


A rheumatic disease that causes weakness and inflammation of muscles.

Polyp (PAH-lip)

Tissue bulging from the surface of an organ. Although these growths are not normal, they often are not cause for concern. However, people who have polyps in the colon may have an increased risk of colorectal cancer.


A linear chain of amino acids connected end-to-end. Proteins are complex polypeptides.


Great hunger; a sign of diabetes. People with this great hunger often lose weight.

Polyunsaturated fats

A type of fat that comes from vegetables.


Having to urinate often; a common sign of diabetes.

Porphyria (por-FEER-ee-uh)

A group of rare, inherited blood disorders. When a person has porphyria, cells fail to change chemicals (porphyrins) to the substance (heme) that gives blood its color. Porphyrins then build up in the body. They show up in large amounts in stool and urine, causing the urine to be colored blue. They cause a number of problems, including strange behavior.

Portal Hypertension (POR-tul hy-pur-TEN-shun)

High blood pressure in the portal vein. This vein carries blood into the liver. Portal hypertension is caused by a blood clot. This is a common complication of cirrhosis.

Portal Vein (POR-tul vayn)

The large vein that carries blood from the intestines and spleen to the liver.

Portosystemic Shunt (POR-toh-sih-STEM-ik shunt)

An operation to create an opening between the portal vein and other veins around the liver.

Postcholecystectomy Syndrome (POST-koh-luh-sis-TEK-tuh-mee sin-drohm)

A condition that occurs after gallbladder removal. The muscle between the gallbladder and the small intestine does not work properly, causing pain, nausea, and indigestion. Also called biliary dyskinesia.

Postgastrectomy Syndrome (POST-gah-STREK-tuh-mee sin-drohm)

A condition that occurs after an operation to remove the stomach (gastrectomy). See also Dumping Syndrome.

Postvagotomy Stasis (POST-vay-GAW-tuh-mee STAY-sis)

Delayed stomach emptying. Occurs after surgery on the vagus nerve.

Preeclampsia (pree-ee-KLAMP-see-ah)

development of hypertension (high blood pressure), accompanied by edema, proteinuria, or both, due to pregnancy.


the number of people in a given population affected with a particular disease or condition at a given time. Prevalence can be thought of as a snapshot of all existing cases at a specified time. (Contrast with incidence).

Primary Biliary Cirrhosis (PRY-muh-ree BILL-ee-air-ee suh-ROH-sis)

A chronic liver disease. Slowly destroys the bile ducts in the liver. This prevents release of bile. Long-term irritation of the liver may cause scarring and cirrhosis in later stages of the disease.

Primary Sclerosing Cholangitis (PRY-muh-ree skluh-ROH-sing KOH-lun-JY-tis)

Irritation, scarring, and narrowing of the bile ducts inside and outside the liver. Bile builds up in the liver and may damage its cells. Many people with this condition also have ulcerative colitis.

Proctalgia Fugax (prahk-TAL-jee-uh FYOO-gaks)

Intense pain in the rectum that occasionally happens at night. Caused by muscle spasms around the anus.

Proctectomy (prahk-TEK-tuh-mee)

An operation to remove the rectum.

Proctitis (prahk-TY-tis)

Irritation of the rectum.

Proctocolectomy (PRAHK-toh-koh-LEK-tuh-mee)

An operation to remove the colon and rectum. Also called coloproctectomy.

Proctocolitis (PRAHK-toh-koh-LY-tis)

Irritation of the colon and rectum.

Proctologist (prahk-TAW-luh-jist)

A doctor who specializes in disorders of the anus and rectum.

Proctoscope (PRAHK-tuh-skohp)

A short, rigid metal tube used to look into the rectum and anus.

Proctoscopy (prahk-TAW-skuh-pee)

Looking into the rectum and anus with a proctoscope.

Proctosigmoidoscopy (PRAHK-toh-SIG-moy-DAW-skuh-pee)

An endoscopic examination of the rectum and sigmoid colon. See also Endoscopy.


Prolactin is a hormone produced by the anterior pituitary gland in both men and women. It is known as a gonadotrophic hormone as it affects the gonads (testes and ovaries). It also has an effect on other organs in the body. However, only the effects on the reproductive organs will be discussed here.

In males, prolactin influences the production of testosterone and affects sperm production. In conditions where prolactin secretion is increased (hyperprolactinaemia), testosterone levels drop and sperm production is reduced or absent, resulting in male infertility.

The main action of prolactin in females is the induction and maintenance of lactation (breastfeeding). Prolactin levels build up during pregnancy but milk secretion does not begin until after birth. As an infant suckles, prolactin is released into the mother's blood stream, causing the milk glands to produce more milk. Prolactin and other hormones are responsible for the development of mammary glands during pregnancy. Prolactin also affects the ovaries. The main target area is the corpus luteum, the secretory organ formed from the ruptured ovarian follicle after ovulation. High prolactin levels lead to reduced progesterone function. The result of hyperprolactinaemia (excess production of prolactin) can be the non-appearance of menarche (beginning of menstruation at puberty), amenorrhoea (absence of menstruation in a woman after puberty) and anovulatory menstrual cycles (absence of ovulation i.e. no mature eggs produced). These effects can be the basis of female infertility.

There are many causes of increased prolactin secretion.


The substance made first in the pancreas that is then made into insulin. When insulin is purified from the pancreas of pork or beef, all the proinsulin is not fully removed. When some people use these insulins, the proinsulin can cause the body to react with a rash, to resist the insulin, or even to make dents or lumps in the skin at the place where the insulin is injected. The purified insulins have less proinsulin and other impurities than the other types of insulins.

Prokinetic Drugs (PROH-kih-NET-ik drugz)

Medicines that cause muscles in the GI tract to move food. An example is cisapride (SIS-uh-pryd) (Propulsid).

Prolapse (PROH-laps)

A condition that occurs when a body part slips from its normal position.

Proliferative Retinopathy

A disease of the small blood vessels of the retina of the eye.


prevention of disease.

Prospective, randomized, double-blind trial

a clinical trial in which the method for analyzing data has been specified in the protocol before the study has begun (prospective), the patients have been randomly assigned to receive either the study drug or alternative treatment, and in which neither the patient nor the physician(s) conducting the study know which treatment is being given to the patient.

Protease (PRO-tee-aze)

Any enzyme that catalyzes the cleavage of internal peptide bonds in a polypeptide or protein.

Protease inhibitor

one of a class of anti-HIV drugs designed to inhibit the enzyme protease and interfere with virus replication. Protease inhibitors prevent the cleavage of HIV precursor proteins into active proteins, a process that normally occurs when HIV replicates.

Protein (PROH-teen)

One of the three main classes of food. Proteins are made of amino acids, which are called the building blocks of the cells. The cells need proteins to grow and to mend themselves. Protein is found in many foods such as meat, fish, poultry, brown rice and eggs. See also: carbohydrate; fats.


Prostaglandins are natural chemicals which are involved in body inflammation. By inhibiting the body's production of certain chemical messengers (prostaglandins), NSAIDs (Nonsteroidal anti-inflammatory drugs) decrease inflammation. However, certain prostaglandins are also important in protecting the stomach lining from the corrosive effects of stomach acid as well as playing a role in maintaining the natural healthy condition of the stomach lining. By disrupting the production of prostaglandins in the stomach, NSAIDs can cause ulcers and bleeding. Some NSAIDs have less effect on the stomach prostaglandins than others, and, therefore, a lower risk of ulcer formation.


Too much protein in the urine. This may be a sign of kidney damage.

Prothrombin (PRO-throm-bin)

A coagulation factor, also known as factor II, converted to thrombin by extrinsic prothrombin converting principle.

Prothrombin Time

The rate at which prothrombin is converted to thrombin in citrated blood with added calcium; used to assess the extrinsic coagulation system of the blood. The test is often used to monitor administration of Coumarin.


the detailed plan for a clinical trial that states the trial's rationale, purpose, vaccine dosages, routes of administration, length of study, eligibility criteria and other aspects of trial design.

Proton Pump Inhibitors (PROH-tawn pump in-HIH-bih-turz)

Medicines that stop the stomach's acid pump.

Prune Belly Syndrome (PROON bel-ee sin-drohm)

A condition of newborn babies. The baby has no abdominal muscles, so the stomach looks like a shriveled prune. Also called Eagle-Barrett syndrome.

Pruritus (proo-RY-tus)

Itching skin; may be a symptom of diabetes.

Pruritus Ani (proo-RY-tus AY-ny)

Itching around the anus.

Psoriatic arthritis

Joint inflammation that occurs in about 5 to 10 percent of people with psoriasis (a common skin disorder).

Pulmonary Embolism (PE)

The occlusion of the pulmonary artery or one of its branches by an embolus, sometimes associated with lung infarction.

Pyloric Sphincter (py-LOR-ik SFEENK-tur)

The muscle between the stomach and the small intestine.

Pyloric Stenosis (py-LOR-ik stuh-NOH-sis)

A narrowing of the opening between the stomach and the small intestine.

Pyloroplasty (py-LOR-oh-plah-stee)

An operation to widen the opening between the stomach and the small intestine. This allows stomach contents to pass more freely from the stomach.

Pylorus (py-LOR-us)

The opening from the stomach into the top of the small intestine (duodenum).

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