Use the A-Z list to browse more than 6,000 health-related topics in our library. Clicking on a term opens the definition and, in most cases, links to more information.
An inactive substance given to participants in controlled studies to determine the effectiveness of medications. Another group is given the actual medication to be tested. Neither group knows if their medication is active.
An organ that partially surrounds the fetus during pregnancy and attached to the umbilical cord to nourish the fetus and remove waste. More Information on Placenta: Pregnancy Basics
Also Known As: "Placenta Previa Partialis, Placenta Previa Centraus, Placenta Previa Marginalis"
A potentially serious condition in which the placenta lies very low in the uterus, partially or completely obstructing the opening to the cervix. It is a leading cause of vaginal bleeding. Delivery by Caesarian section may be necessary. More Information on Placenta Previa: Pregnancy Basics
Also Known As: "Placenta Previa Marginalis, Placenta Previa Partialis"
A potentially serious condition in which the placenta lies very low in the uterus, partially or completely obstructing the opening to the cervix. It is a leading cause of vaginal bleeding. Delivery by Caesarian section may be necessary. More Information on Placenta Previa Centraus: Pregnancy Basics
Also Known As: "Placenta Previa Partialis, Placenta Previa Centraus"
A potentially serious condition in which the placenta lies very low in the uterus, partially or completely obstructing the opening to the cervix. It is a leading cause of vaginal bleeding. Delivery by Caesarian section may be necessary. More Information on Placenta Previa Marginalis: Pregnancy Basics
Also Known As: "Placenta Previa Centraus, Placenta Previa Marginalis"
A potentially serious condition in which the placenta lies very low in the uterus, partially or completely obstructing the opening to the cervix. It is a leading cause of vaginal bleeding. Delivery by Caesarian section may be necessary. More Information on Placenta Previa Partialis: Pregnancy Basics
A condition in which there is a flattening of one side of the skull, caused by the premature fusion of the coronal (between the frontal and parietal) or lambdoid (between occipital and parietal) sutures. More Information on Plagiocephaly: Pediatric Brain & Nerve
Also Known As: "Bubonic Plague, Septicemic Plague, Black Plague, Yersinia Pestis, Pneumonic Plague"
A highly infectious and typically fatal epidemic disease. Or, specifically, infection with the Yersinia pestis bacteria from which millions died in the Middle Ages. Today, it is a bioterrorism threat. Types include pneumonic, bubonic or septicemic. More Information on Plague: Bioterror Related Diseases
"Plant Carbohydrate" is more commonly referred to as "Inulin" in the medical community. Inulin
A type of plant carbohydrate that can cause allergic reaction. In processed foods, inulin is used as a fat replacement and fiber enrichment. It is sometimes recommended for diabetics because it is not absorbed and does not affect sugar levels. More Information on Inulin: Food Allergy & Intolerance
Also Known As: "Poison Ivy Dermatitis, Poison Plant Dermatitis, Poison Oak Dermatitis, Poison Sumac Dermatitis"
An itchy, bumpy rash that results from contact with plants containing a certain oil (urushiol). Poison ivy, oak and sumac all contain urushiol and have leaves that cluster in threes. They may form vines or shrubs. More Information on Plant Dermatitis: Dermatitis, Eczema & Hives
"Plant Sterol" is more commonly referred to as "Phytosterol" in the medical community. Phytosterol
A substance found only in plants that is similar in chemical structure to cholesterol. Eating phytosterols may positively impact cholesterol levels. They are found in sesame and sunflower seeds and oils, peanuts, rice bran, green peas, and soybeans. More Information on Phytosterol: Cholesterol
A painful condition in the sole portion of the foot (plantar) caused by excessive wear, inflammation or tearing of the fibrous connective tissue (fascia). Pain is usually felt on the underside of the heel. More Information on Plantar Fasciitis: Arm & Leg Pain
Warts that grow on the soles of the feet and tend to be flat and result in callus buildup. They are caused by the human papillomavirus (HPV) type 1 and typically affect teenagers. More Information on Plantar Warts: Skin Related Infections
A material composed of fats (lipids), cholesterol (lipoproteins), calcium and other materials. Its buildup contributes to atherosclerosis and coronary artery disease. More Information on Plaque: Cholesterol
The most common form of psoriasis characterized by well-defined patches of red, raised skin. It can appear on any skin surface but is most commonly found on knees, elbows, scalp, trunk and nails. More Information on Plaque Psoriasis: Psoriasis & Autoimmune Skin
The release of an unstable plaque's contents (e.g., fatty particles) into the bloodstream. This occurs after the thin coating of the unstable plaque has been stripped away. More Information on Plaque Rupture: Cholesterol
A blood test that measures the levels of ammonia present in plasma. Elevated plasma ammonia levels are an indicator of liver damage or disease. It is seldom used today. More Information on Plasma Ammonia Test: Blood Tests
"Plasma Cell Myeloma" is more commonly referred to as "Multiple Myeloma" in the medical community. Multiple Myeloma
Also Known As: "Myeloma Bone Disease, Kahler's Disease, Myelomatosis, Multiple Myeloma Cancer"
A malignant tumor (cancer) of the plasma cells in bone marrow. Soft spots called osteolytic lesions develop in the bone and are seen as "holes" on x-rays. While affecting bone, it is considered a type of blood cancer. More Information on Multiple Myeloma: Leukemia & Bone Cancer
"Plasma Cell Type Castleman's Disease" is more commonly referred to as "Castleman's Disease" in the medical community. Castleman's Disease
Also Known As: "Hyaline Vascular Type Castleman's Disease"
A rare disorder marked by noncancerous (benign) tumor growth in the lymph nodes or tissue, usually in the neck, chest or stomach. These are generally categorized into three types: hyaline vascular, plasma cell or multicentric or generalized. More Information on Castleman's Disease: Lymphoma (Hodgkin's & Non)
A type of white blood cell found in lymphoid tissue that secretes antibodies. They are derived from B cells upon lymphokine stimulation and reaction with a specific antigen. More Information on Plasma Cells: Blood Tests
"Plasma Homocysteine" is more commonly referred to as "Homocysteine" in the medical community. Homocysteine
Homocysteine is a byproduct of the normal metabolic process. There is convincing evidence that high serum homocysteine may contribute to coronary artery disease, stroke, high blood pressure and other heart- and vessel-related conditions. More Information on Homocysteine: Heart Diet & Fitness
A malignant tumor (cancer) that begins in the plasma cells (a type of white blood cell). It can lead to multiple myeloma. More Information on Plasmacytoma: Leukemia & Bone Cancer
A treatment for some autoimmune conditions. Blood is withdrawn from a patient and its components (blood cells, antibodies, immune complexes and other substances) are separated. The remaining plasma is then replaced into the body's circulation. More Information on Plasmapheresis: Autoimmune Basics
"Plasmodium Infection" is more commonly referred to as "Malaria" in the medical community. Malaria
Also Known As: "Paludism, Jungle Fever, Malaria Disease"
A potentially fatal disease caused by a parasite that is marked by high fevers, shaking, chills and flu-like illness. Four types of malaria parasites infect humans - Plasmodium falciparum, P. vivax, P. ovale and P. malariae. More Information on Malaria: Tropical Disease
"Plastic Sheeting" is more commonly referred to as "Membrane Oxygenator" in the medical community. Membrane Oxygenator
Also Known As: "Screen Oxygenator"
A mechanical device that adds oxygen to blood. Blood is passed over a series of screens or membranes that are in an atmosphere filled with oxygen. Oxygen is then exchanged on the thin film of blood that is on the screen.
One of several coagulation tests used to measure the time it takes for an individual's blood to clot. More Information on Platelet Aggregation: Blood Tests
"Platelet Count" is more commonly referred to as "CBC" in the medical community. CBC
Also Known As: "Red Blood Cell Count, Blood Count, Complete Blood Count, Hematocrit Calculation, White Blood Cell Count, Hemoglobin Count, Differential Blood Count"
A routine blood test that measures the composition of blood cells within the blood. This usually includes counts of all blood cells (red, white and platelets), each type of cell, levels of hemoglobin and calculations based on those measurements. More Information on CBC: Blood Tests
Factors in the blood that affect coagulation, clotting and hemostasis (stoppage of bleeding). In response to injury, platelets begin to stick to each other and to the sides of the injured tissue to form a plug, blocking further blood loss. More Information on Platelets: Heart Basics
A brand of antiplatelets, medications that block the formation of blood clots by decreasing the ability of the body's natural blood-clotters (platelets) to bind together (aggregate). More Information on Plavix: Heart Drug & Medication
Many childhood injuries occur on playground equipment such as climbing devices and swings. It is important that all equipment within a playground is safe and that children are supervised by an adult. More Information on Playground Safety: Pediatric First Aid & Safety
Also Known As: "Impedance Plethysmogram, Oculoplethysmogram, Body Plethysmogram"
A noninvasive test widely used to measure the blood flow in the veins of the arms or legs, in order to detect and assess the presence of any blockages. More Information on Plethysmogram: Vascular Disease
Thin layers of tissue that cover the outer lungs and the inner lining of the chest cavity. The two layers are separated by fluid that acts as a lubricant, allowing the lungs to inflate and deflate smoothly during breathing. More Information on Pleura: Breathing & Lung
Fluid buildup in the space between the lungs and chest wall. There are many reasons why this condition may occur, including heart failure, chest injury or rheumatoid arthritis. More Information on Pleural Effusion: Heart Signs & Symptoms
"PLIF" is more commonly referred to as "Posterior Lumbar Interbody Fusion" in the medical community. Posterior Lumbar Interbody Fusion
Surgical procedure during which bone graft is added to an area of the spine to set up a biological response that causes the bone to grow between the two vertebral elements. More Information on Posterior Lumbar Interbody Fusion: Back, Neck & Shoulder Pain
"PLMD" is more commonly referred to as "Periodic Limb Movement Disorder" in the medical community. Periodic Limb Movement Disorder
A sleep disorder where the patient moves involuntarily during sleep. Symptoms range from a small amount of movement in the ankles and toes to severe flailing of all four limbs. More Information on Periodic Limb Movement Disorder: Sleep
"Plummer Vinson Syndrome" is more commonly referred to as "Sideropenic Dysphagia" in the medical community. Sideropenic Dysphagia
Also Known As: "Paterson Kelly Syndrome"
A disorder that increases the risk of esophageal cancer. It involves iron deficiency and web-like growths in the throat that make it difficult to swallow. More Information on Sideropenic Dysphagia: Head, Neck & Mouth Cancer
"PMDD" is more commonly referred to as "Premenstrual Dysphoric Disorder" in the medical community. Premenstrual Dysphoric Disorder
An extreme variation of premenstrual syndrome that involves severe physical, emotional and quality-of-life problems. Estimated to occur in up to 10 percent of women. More Information on Premenstrual Dysphoric Disorder: Menstruation
"PMLE" is more commonly referred to as "Polymorphous Light Eruption" in the medical community. Polymorphous Light Eruption
Also Known As: "Polymorphic Light Eruption"
Small red blisters and/or pimples that appear on the skin within one to four days of sunlight exposure. It is an allergic reaction to ultraviolet (UV light) that occurs in some photosensitive people. It may spread to unexposed skin areas. More Information on Polymorphous Light Eruption: Skin & Hair Basics
"PMR" is more commonly referred to as "Polymyalgia Rheumatica" in the medical community. Polymyalgia Rheumatica
Also Known As: "Arthritic Rheumatoid Disease, Anarthritic Syndrome"
A rheumatic disease that involves tendons, muscles, ligaments and tissues around the joints, often in people over 50. Pain, aching and morning stiffness in the neck, shoulders, lower back and hips characterize the disease. More Information on Polymyalgia Rheumatica: Fibromyalgia & Pain Disorders
"PMS" is more commonly referred to as "Premenstrual Syndrome" in the medical community. Premenstrual Syndrome
Also Known As: "Premenstrual Tension Syndrome"
Irritability, mood changes, breast tenderness, water retention and other symptoms starting several days before and usually ending shortly after onset of menstruation. More Information on Premenstrual Syndrome: Menstruation
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