platelet count The calculated number of platelets in a volume of blood, usually expressed as platelets per cubic millimeter (cmm) of whole blood. Platelets are the smallest cell-like structures in the blood and are important for blood clotting and plugging damaged blood vessels. Platelet counts are usually done by laboratory machines that also count other…
pleiotropic Producing or having multiple effects from a single gene. For example, the Marfan gene is pleiotropic, potentially causing such diverse effects as long fingers and toes (arachnodactyly), dislocation of the lens of the eye, and dissecting aneurysm of the aorta.
pleomorphic Many-formed. For example, a pleomorphic tumor would be a growth that is composed of different types of tissues. Also known as protean.
plethoric Florid, red-faced. Persons with polycythemia vera commonly have a plethoric facial appearance.
pleura One of the two membranes around the lungs. These two membranes are called the visceral and parietal pleurae. The visceral pleura envelops the lung, and the parietal pleura lines the inner chest wall. There is normally a small quantity (about 3 to 4 teaspoons) of fluid that is spread thinly between the visceral and…
pleural space The tiny area between the two pleurae, which is normally filled with a small amount of fluid. See also effusion, pleural.
pleurisy Inflammation of the pleurae, the membranes surrounding the lungs. Symptoms include pain in the chest, chest tenderness, cough, and shortness of breath. The chest pain is sharp and aggravated by breathing. A physician can often hear with a stethoscope the friction generated by the rubbing of the two inflamed layers of pleurae with each…
pleuritis See pleurisy.
pleurodesis A procedure that causes the membranes around the lungs to stick together and prevents the buildup of fluid in the space between the membranes (pleural space). Pleurodesis is done in cases of severe recurrent pleural effusions (outpourings of fluid around the lungs) to prevent the reaccumulation of the fluid. During pleurodesis, an irritant is…
pleurodynia See Bornholm disease.
plumbism See lead poisoning.
placebo A sugar pill or any other inactive substance that is given instead of medication. In a controlled clinical trial, one group may be given a medication and another group a placebo, to learn whether a difference in treatment response is due to the medication, the power of suggestion, or other factors. See also placebo…