Medical Dictionary Definitions A-Z List
Medical Dictionary Definitions A - Z - «P»:
Porphyria: A diverse group of diseases in which the production of heme is disrupted. Porphyria is derived from the Greek word "porphyra", which means purple. When heme production is faulty, porphyrins are overproduced and lend a reddish-purple color to urine.
All forms of porphyrias are inherited. T...
Porphyria cutanea tarda
Porphyria cutanea tarda: Literally, the late skin form of porphyria, a genetic photosensitive (light-sensitive) skin disease with onset in adult life with substances called uroporphyrins in the urine due to a deficiency of uroporphyrinogen decarboxylase (UROD), an enzyme required for the synthesis o...
Port wine stain
Port wine stain: A mark on the skin that resembles port wine
(porto) in its rich ruby red color. Due to an abnormal aggregation of capillaries, a port wine stain is a type of hemangioma. A port wine stain on the face is a sign of the Sturge-Weber syndrome....
Portable generator safety
Portable generator safety: Safety, an essential matter in using a portable residential or recreational generator. Portable residential generators may be used to supply essential home power needs during power-outages, for powering cabin appliances, or for power tools needed during projects. Recreatio...
Portal vein: A large vein that carries blood from
the stomach and the intestines to the liver.
The portal vein is
formed by the union of the splenic and superior mesenteric veins. It
conveys venous blood to the liver for detoxification before the blood
is returned to the circulation via the h...
Position, anatomical: See: Anatomical position....
Positional cloning: Cloning a gene based simply on knowing its
position in the genome without any idea of the function of that gene. Because this is the
reverse of how things have been traditionally done, it has also been called reverse
Positive clinical trial
Positive clinical trial: A clinical trial that shows that the new treatment has a large beneficial effect and is superior to standard treatment. See: Clinical trials. See also:
Inconclusive clinical trial;
Negative clinical trial;
Non-inferior clinical trial....
Positive end-expiratory pressure
Positive end-expiratory pressure: Better known as PEEP. See: PEEP....
Positive pressure ventilation
ventilation: The provision of oxygen under pressure by a mechanical
respirator, a machine designed to improve the exchange of air between the lungs
and the atmosphere. The device is basically designed for administering artificial respiration, especially
for a prolonged period,...
Positive, false: A result that is erroneously positive when a
situation is normal. An example of a false positive: a particular test designed to detect
cancer of the toenail is positive but the person does not have toenail cancer....
Positive-strand RNA virus
Positive-strand RNA virus: Also known as a sense-strand RNA virus, a virus whose genetic information consists of a single strand of RNA that is the positive (or sense) strand which encodes mRNA (messenger RNA) and protein. Replication in positive-strand RNA viruses is via a negative-strand intermedi...
Positron emission tomography
Positron emission tomography: PET. A highly specialized imaging technique that uses short-lived radioactive substances to produce three-dimensional colored images of those substances functioning within the body. These images are called PET scans and the technique is termed PET scanning.
Post: Short for postmortem examination (an autopsy)....
Post-exposure prophylaxis: A treatment administered following exposure to a harmful agent which attempts to block or reduce injury or infection. Prophylaxis means a defense or protection.
Post-exposure prophylaxis (PEP), for example, might concern the treatment of a health care worker exposed by a n...