P: Chemical symbol for phosphorus. 32P radioactive phosphorus.
pabulum (pab′ū-lum): Food or nourishment.
Pacchioni’s bodies (pak-ā-ō′nāz): Projections of the arachnoid membrane through the dura mater into the superior sagittal sinus. Also called arachnoid granulations.
pacemaker: The sinoatrial node of specialized nervous tissue located at the junction of the superior vena cava and the right atrium. It originates the contractions of the atria, which transmit the impulse on to the atrioventricular node, thereby inhibiting the contraction of the ventricles. ARTIFICIAL P. an electrical device used to re-establish the muscular contractions of an arrested heart or to steady the heartbeat; consists of an electrode introduced into the right atrium or ventricle and attached to an electrical source that is either implanted within the body or located externally; it initiates an increase in the rate of contraction of the ventricle resulting in output adequate to allow the patient to participate in his or her usual activities; ASYNCHRONOUS P. a device that paces the heartbeat when the heartbeats too slowly or not at all without help; also called fixed-rate P.; ATRIAL P. used to stimulate atrial contraction when the conduction system between the atria and the ventricles is intact; DEMAND P. a P. that will provide or withhold stimulation depending on how the heart is functioning on its own; EXTERNAL P. a temporary P. placed outside the body until a permanent P. can be implanted; TEMPORARY P. used in certain emergency situations to correct severe cardiac arrhythmias; usually inserted into the subclavian, jugular, basilic, or femoral vein; WANDERING P. a condition in which the origin of the heartbeat is shifted from the head of the sinoatrial node to the lower or other part of the atrium.
pachy-: Combining form denoting thick.
pachydermoperiostosis (pak-i-der′mō-per′i-os-tō′sis): A condition characterized by thickening of the skin over bones, especially those of the face and distal parts of the extremities, with clubbing of the fingers; may be hereditary or due to underlying pulmonary disease.
pachymeter (pa-kim′i-ter): An instrument for measuring thickness, especially of thin objects or tissues, e.g., a membrane.
pachyonychia (pak′ -i-ō-nik′i-a): Abnormal thickening of the fingernails or toenails, often congenital.
pachypleuritis (pak-i-ploo-rī′tis): Inflammation of the pleura accompanied by thickening of the membrane. Also called productive pleurisy.
pachysomia (pak-i-sō′mi-a): Abnormal thickening of parts of the body, especially of the soft parts, as seen in acromegaly.
pacifier (pas′i-fi-er): 1. A rubber nipple-shaped device for babies to suck, also known as a ‘comforter’ or ‘dummy’. 2. A tranquillizer.
pacing (pās′ing): The application of an electric stimulus to the heart to initiate contractions.
Pacini’s corpuscles (pa-chā′nāz): Oval bodies in the deep parts of the corium of the skin that act as end organs for the sense of pressure; found especially in the skin of the hands and feet, but also in tendon and some internal structures. [Filippo Pacini, Italian anatomist, 1812–1883.]
pack: 1. A collection of instruments or equipment needed for a certain medical or surgical procedure. 2. To fill a cavity or tubular structure. 3. A hot or cold, wet or dry dressing applied to the body or part of it.
packed cells: Refers to whole blood from which the plasma has been removed by centrifugation or sedimentation; the cells then have a haematocrit of about 80% and are used in certain blood transfusions; also called packed red cells. P. CELL VOLUME the volume of cells in 100 ml of a blood sample after it has been centrifuged.
paederasty: See PEDERASTY.
paediatrician (pā-di-a-trish′un): A medical practitioner who specializes in the health supervision and treatment of children.
paediatrics (pā-di-at′riks): The branch of medicine that deals with the development and care of the child and with the diseases of children and their treatment.
paedodontics (pā′ -dō-don′tiks): The branch of dentistry that deals with the diagnosis and treatment of conditions of the teeth and surrounding tissues in children.
paedophilia (pā-dō-fil′i-a): Abnormal fondness for children. P. EROTICA sexual perversion in which children are the preferred objects.
paedophobia (pā-dō-fō′bi-a): An abnormal fear or dread of children.
PAF: Abbreviation for performance assessment framework (q.v.).
Paget’s disease: 1. Osteitis deformans. A chronic disease of the bone that resembles arthritis; of unknown cause. Characterized by softening and thickening of the bones of the spine, skull, pelvis, thigh, and lower legs, and by degeneration of the joints, with consequent distortion and bowing deformity of the long bones. Occurs most often in people of Western European descent, particularly those from the British Isles, France and Germany and who are in the 60 or 70 year age group. 2. A progressive, inflammatory, eczematous dermatosis of the nipple and surrounding area, seen most often in older women. There is itching, soreness, ulceration and retraction of the nipple. May be precancerous or associated with cancer of the breast. 3. Paget’s disease of the vulva, a rare condition seen mostly in postmenopausal women; usually malignant and occurring in association with carcinoma in some other part of the vulvorectal area; symptoms include pain, pruritus, and burning; treatment is usually vulvectomy. [Sir James Paget, English surgeon, 1811–1899.]
pagophagia (pā-gō-fā′ji-a): Ice eating; thought to be a sign of iron deficiency.
pagoplexia (pā′gō-plek′si-a): Frostbite.
pain: Physical or mental suffering. A state of localized or generalized discomfort that ranges from mild distress to acute agony; usually caused by injury to a part or disturbance of the normal condition or functioning of a part of the body. In the plural it usually refers to the pains experienced during childbirth. AFTERPAINS those due to contraction of the uterus following the birth of a child; FALSE P.S occur late in pregnancy and resemble labour pains but do not result in labour; GROWING P.S. those that sometimes occur in muscles and joints...