P
pacemaker the region of the heart that initiates atrial contraction and thus controls heart rate. The natural pacemaker is the sinus node which is situated at the junction of the superior vena cava and the right atrium; the wave of contraction begins here, then spreads over the heart. See also cardiac pacemaker.
PACS (Picture Archiving and Communications Systems) a system which enables digital images to be stored electronically and then viewed on computer screens, and therefore allowing the transfer of images and data across the intranet.
PACS broker enables two computer systems to talk to each other by changing (translating) information into a common language.
paediatric advanced life support (PALS) the special techniques, drug doses and equipment appropriate to the body weight and surface area of the child being resuscitated.
paediatric dentistry the diagnosis, prevention and treatment of dental and related diseases in children.
Paget’s disease (osteitis deformans) a chronic disease of bone where overactivity of the osteoblasts and osteoclasts leads to dense bone formation and areas or rarefaction. Sufferers are particularly susceptible to sarcoma of bone, if the vestibulocochlear (auditory) nerve is involved, there is impairment of hearing. Erosion of the nipple caused by invasion of the dermis by intraduct carcinoma of the breast.
pain unpleasant sensation experienced when specialist nerve endings (nociceptors) are stimulated. It is individual and subjective with a physiological and emotional component. Pain ranges from mild to agonizing, but individual responses are influenced by factors which include: information about cause, age, whether acute or chronic and pain tolerance.
pain management involves a holistic multidisciplinary approach, and in some healthcare settings there is a designated pain team or nurse specialist.
pain threshold the lowest intensity at which a stimulus is felt as pain. There is very little difference between people.
pain tolerance the greatest intensity of pain that the individual is prepared to put up with. There is substantial variation between people.
pair production when a photon with energy greater than 1.02 MeV collides with the nucleus of an atom sometimes giving up all its energy in the production of an electron and a positron.
palate the roof of the mouth. See also hard palate, soft palate.
palatine associated with the palate.
palatine arches the bilateral double pillars or arch-like folds formed by the descent of the soft palate as it meets the pharynx.
palatine bones irregular bones that lie on the posterior aspect of the nasal and orbital cavities.
palliate relieve symptoms. Often refers to option where a patient is not curable and is fit only for treatment to prevent distress from symptoms. It may involve surgery, chemotherapy, radiotherapy, nerve block, and/or drugs (typically opioids).
palliative (describes) anything that serves to alleviate but cannot cure a disease.
palliative care the specialty of symptom relief.
palliative treatment aims to relieve the symptoms of cancer or restrain the temporary growth of a tumour.
palm the anterior or flexor surface of the hand.
palmar associated with the palm of the hand.
palmar arches superficial and deep, are formed by the anastomosis of the radial and ulnar arteries.
panarthritis inflammation of all the structures of a joint.
panchromatic emulsions are film emulsions that are sensitive to all wavelengths of the visible spectrum.
pancreas a tongue-shaped glandular organ lying below and behind the stomach. Its head is encircled by the duodenum and its tail touches the spleen. It is about 18cm long and weighs about 100g. It secretes the hormones insulin and glucagon, and also alkaline pancreatic juice which contains digestive enzymes involved in the digestion of fats, carbohydrates and proteins in the small intestine.
pancreatitis inflammation of the pancreas which may be acute or chronic. Most commonly caused by gallstones or alcohol.
pancreozymin intestinal hormone identical to cholecystokinin (CCK). Previously both names were used.
panosteitis inflammation of all constituents of a bone, the medulla, bony tissue and periosteum.
Papanicolaou test (Pap) a smear of epithelial cells taken from the cervix is stained and examined under the microscope for detection of the early stages of cancer.
papilla a minute nipple-shaped eminence.
papillary carcinoma a malignant tumour of the thyroid caused by irradiating the neck in childhood, it is characterized microscopically by having delicate finger-like cores of stroma lined by tumour cells.
papilloedema swelling of the optic disc, the white patch on the retina where the optic nerve emerges.
papilloma a benign tumour of epithelial cells characterized by being branching or lobular, generally viral warts.
papillomatosis the growth of benign papillomata on the skin or a mucous membrane. Removal by laser means fewer recurrences.
paracentesis usually applied to the surgical puncture of the abdominal cavity for the aspiration of fluid.
paradigm an example, model, or set of ideas or assumptions.
paradigm shift the changes that occur as the build-up of evidence causes a paradigm to be questioned and eventually replaced by a new set of ideas.
paradoxical respiration associated with injuries that result in the ribs on one side being fractured in two places, such as in flail chest. The injured side of the chest moves in (deflates) on inspiration and vice versa.
paraesthesia any abnormality of sensation such as tingling.
parallel-hole collimator gamma camera collimator made of a thick lead plate with several thousand parallel sided holes perpendicular to the plane of the plate, gives a 1:1 relationship between the object being recorded and the image produced.
parallel pair used in radiotherapy to describe two directly opposing treatment fields.
paralysis complete or incomplete loss of nervous function to a part of the body. This may be sensory or motor or both.
paralytic associated with paralysis.
paralytic ileus paralysis of the intestinal muscle so that the bowel content cannot pass onwards even though there is no mechanical obstruction. See also aperistalsis.
paramagnetic a substance that increases the strength of a magnetic field in which it is placed by aligning with the static magnetic field and therefore affecting the relaxation times of the tissues containing them. See also diamagnetic, superparamagnetic, ferromagnetic.
paramagnetism the influence of an applied magnetic field on the electrons orbiting the nuclei within the substance which results in the formation of an elementary bar magnet.
parametric tests statistical tests that presuppose the data are from a sample from a population that has a normal distribution curve, the data are interval and therefore the test is powerful. See also non-parametric tests.
parametrium the connective tissues immediately surrounding the uterus.
paranasal near the nasal cavities, as the various sinuses.
paraneoplastic describes symptoms or signs associated with the presence of a malignant neoplasm but not directly from the situation of the primary or the metastases.
paraoesophageal near the oesophagus.
paraparesis loss of power in the legs.
paraplegia paralysis of the lower limbs, usually including the bladder and rectum below the level of the spinal cord abnormality. See also hemiplegia, monoplegia, tetraplegia.
paraplegic a person with paralysis of the lower limbs.
parasympathetic describes the part of the autonomic nervous system having craniosacral outflow. It is concerned with the normal at rest body processes and opposes the action of the sympathetic nervous system.
parathormone parathyroid hormone. See also parathyroid glands.
parathyroid glands four small endocrine glands lying close to or embedded in the posterior surface of the thyroid gland. They secrete parathyroid hormone (PTH) a protein hormone that regulates calcium and phosphate homeostasis. It is released when serum calcium level is decreased.
paraurethral near the urethra.
paravertebral near the spinal column.
paravertebral block anaesthesia (more correctly, analgesia) is induced by infiltration of local anaesthetic around the spinal nerve roots as they emerge from the intervertebral foramina.
paravertebral injection introduction of a local anaesthetic into sympathetic chain can be used as a test in ischaemic limbs to see if sympathectomy is indicated.
parenchyma the essential, active cells of an organ as distinguished from its vascular and connective tissue.
pareneoplastic syndrome a collection of general effects associated with cancer, for example, infection, fever, cachexia, anaemia.
parent radionuclide a nucleus before it has decayed. See also radioactive decay.
parenteral not via the alimentary tract. Therapy such as fluid, drugs, or nutrition administered by a route other than the alimentary tract.
paresis partial or slight paralysis; weakness of a limb.
parietal associated with a wall.
parietal bones the two bones which form the sides and vault of the skull.
Parinaud’s syndrome conjunctivitis that is usually unilateral, follicular and followed by enlargement of the preauricular lymph nodes and tenderness.
Paris system a method of introducing radioactive sources during brachytherapy using Iridium:-192
Parkinson’s disease an incurable neurodegenerative condition in which there is a relatively selective loss of dopamine nerve cells in the brain causing a resting tremor, bradykinesia (slowness of movement) and rigidity in the limbs. Some people differentiate between Parkinson’s disease and parkinsonism, the causes of which are multiple and include repeated brain trauma (as in boxing), stroke, atherosclerosis, various toxic agents, viral encephalitis and neuroleptic drugs (typical).
parotid gland the salivary gland situated in front of and below the ear on either side.
parous having borne a child or children.
Parrot’s nodes bossing of frontal bones in congenital syphilis.
pars interarticularis the area between the superior and inferior articular processes in the spinal column, deficient in spondylolisthesis.
particle range the distance from its point of origin that a charged particle no longer reacts with the material it is travelling through.
particle theory the basic concept of quantum physics and considers that electromagnetic radiation of short wavelength and high velocity consists of particles or quanta or photons each having a discrete amount of energy.
PASCAL a high-level language for computers.
passwords entry is forbidden into many computer-controlled systems unless a particular password has been entered. Passwords are frequently graded, so that limited access to the system is allowed by some passwords but unlimited access is provided by other passwords.
patella a triangular, sesamoid bone; the kneecap.
patent open; not closed or occluded.
patent ductus arteriosus failure of ductus arteriosus to close soon after birth, so that an abnormal shunt between the pulmonary artery and the aorta is preserved. patent interventricular septum a congenital defect in the dividing wall between the right and left ventricle of the heart.
Paterson-Parker system a method of introducing radioactive sources during brachytherapy for gynaecological applications using 137caesium needles and tubes.
pathogen an agent capable of producing disease.
pathological fracture a fracture caused by underlying disease.
patient advice and liaison service (PALS) an advice service to patients in NHS and Primary Care Trusts, representing their concerns and complaints to the relevant department within the trust.
patient contour the shape of a cross-section of a patient when they are initially positioned prior to radiotherapy treatment. See also contouring device.
patient dosimetry the measure of dose delivered to the clinical target volume.
patient immobilization equipment to enable a patient to remain still during treatment or examination including, patient shells, effervescent materials, vacuum bags, bite blocks, breast boards, foam pads, sandbags.
patients’ forum a statutory and independent body comprising patients who will represent the views of patients about how their local NHS services are run.
patient shell a clear plastic structure which is worn by the patient to enable accurate localization, patient position, patient contour, beam exit and entry points and a base for additional build-up material and shielding.
pattern of distribution in statistics looks at the frequency that a qualitative result occurs.
peak bone density (PBD) or mass (PBM) the greatest bone density achieved by an individual, usually achieved in the 30s.
peak sensitivity the range of wavelengths that a film emulsion is the most sensitive to.
peak value the maximum value of either positive or negative current or voltage that occurs on an alternating current waveform.
peau d’orange appearance of (usually) the breast when a cancer results in lymphatic obstruction and dimpling at the hair follicles causing the breast to look (literally) like orange skin; usually a sign of locally advanced disease.
pectoral associated with the breast.
pectus carinatum see pigeon chest.
pectus excavatum see funnel chest.
pedal associated with the foot.
pedal pulse the dorsalis pedis artery palpated on the dorsum of the foot.
pedicle a stalk, for example, the narrow part by which a tumour is attached to the surrounding structures.
peduncle a stalk-like structure.
peer support support from other members of a group to which one belongs. For example, new patients perceive established patients as providing support. Likewise, health professionals use their peer groups to gain and provide support, particularly in stressful circumstances.
Pel–Ebstein fever a recurrent high temperature having a cycle of 15–21 days, which occurs in cases of lymphadenoma.
pellagra a syndrome caused by a diet deficient in niacin and in patients suffering from alcoholism and drug addiction.
pelvic relating to the pelvis.
pelvic cavity that formed by the pelvic bones, more particularly the part below the iliopectineal line.
pelvic floor a mainly muscular partition with the pelvic cavity above and the perineum below. In the female, weakening of these muscles can contribute to urinary incontinence and uterine prolapse.
pelvic girdle the bony pelvis comprising two innominate bones, the sacrum and coccyx.
pelvimetry the measurement of the dimensions of the pelvis.
pelvis a basin-shaped cavity, for example, pelvis of the kidney. The large bony basin-shaped cavity formed by the innominate bones and sacrum, containing and protecting the bladder, rectum and, in the female, the organs of generation. contracted pelvis one in which one or more diameters are smaller than normal; this may result in difficulties in childbirth. false pelvis the wide expanded part of the pelvis above the brim. true pelvis that part of the pelvis below the brim.
penis the male organ of copulation.
penumbra the area at the edge of a beam of radiation that receives some but not all of the main beam because it is not practically possible to produce an X-ray beam from a point source. See also geometric unsharpness.
pepsin a proteolytic enzyme secreted by the stomach, as the precursor pepsinogen, which hydrolyses proteins to polypeptides. It has an optimum pH of 1.5–2.0.
pepsinogen a proenzyme secreted mainly by the chief cells in the gastric mucosa and converted to pepsin by hydrochloric acid or existing pepsin.
peptic associated with pepsin or to digestion generally. peptic ulcer a non-malignant ulcer in those parts of the digestive tract that are exposed to the gastric secretions; hence usually in the stomach or duodenum but sometimes in the lower oesophagus or with a Meckel’s diverticulum.
peptidase an enzyme that breaks down proteins into amino acids. See also aminopeptidases, dipeptidases.
peptides organic compounds that yield two or more amino acids on hydrolysis; for example, dipeptides and polypeptides. peptide bond a chemical bond formed during a dehydration reaction when two amino acids form peptides.
percentage depth dose in radiotherapy, the ratio of the absorbed dose at any given point to the absorbed dose on the beam axis at the depth of maximum dose expressed as a percentage.
perceptibility the point at which an image can be clearly seen, when contrast is equal to, or greater than the contrast threshold.
perceptibility curve a curve produced from measurable data after a phantom has been radiographed and a number of people have recorded the contrast observed at various exposure levels.
percutaneous through the skin.
percutaneous endoscopic gastrostomy (PEG) gastrostomy tube inserted endoscopically through the abdominal wall to allow feeding and the passage of drugs.
percutaneous myocardial revascularization a treatment for angina. A catheter with laser energy source is introduced into the heart via the femoral artery. The laser is used to produce channels through to the myocardium, thus allowing more oxygenated blood to reach the myocardium.
percutaneous nephrolithotomy see nephrolithotomy.
percutaneous transhepatic cholangiography (PTC) see cholangiography.
percutaneous transluminal angioplasty a balloon is passed into a stenosed artery (for example, coronary artery) and inflated with contrast agent; it presses the atheroma against the vessel wall, thereby increasing the diameter of the lumen.
percutaneous transluminal coronary angioplasty (PTCA) a procedure used in the treatment of angina. A balloon-tipped catheter is used to dilate a stenosed coronary artery.
perforation a hole in a previously intact sheet of tissue. Used in reference to perforation of the tympanic membrane, or the wall of the stomach or gut, constituting a surgical emergency.
performance indicators (PIs) quantitative measures of the activities and resources used in healthcare delivery. High-level performance indicators, for example, deaths from all causes (people aged 15–64), early detection of cancer, day case rate, cancelled operations, and clinical indicators, for example, deaths in hospital after surgery, a heart attack or hip fracture, are used to assess the six areas of the National Framework for Assessing Performance.
perfusion the passage of fluid through tissue, a specific organ or body part.
perianal surrounding the anus.
periapical film a small radiographic film in a waterproof envelope that is placed inside the mouth to radiograph individual teeth.
periarterial surrounding an artery.
periarthritis inflammation of the structures surrounding a joint. Sometimes applied to frozen shoulder.
periarticular surrounding a joint.
peribulbar around the eyeball inside the orbit.
pericardial effusion a collection of pericardial fluid in the heart restricting cardiac movement, producing signs and symptoms of heart failure.
pericarditis inflammation of the pericardium of the heart.
pericardium the double serous membranous sac which envelops the heart. The layer in contact with the heart is called visceral (or epicardium); that reflected to form the sac is called parietal. Between the two is the pericardial cavity, which normally contains a small amount of serous fluid.
perichondrium the membranous covering of cartilage.
pericranium the periosteal covering of the cranium.
perifollicular around a follicle.
perilymph the fluid contained in the internal ear, between the membranous and bony labyrinth.
perimetrium the peritoneal covering of the uterus.
perinephric surrounding the kidney.
perineum the wedge-shaped structure situated between the rectum and the external genitalia.
perineurium connective tissue enclosing a bundle of nerve fibres.
period the number of seconds taken to complete one cycle of alternating current. In ultrasound the length of time required for one oscillation to occur.
periodic table a list of the 103 elements with the number of electron shells shown horizontally and the chemical properties, that is the number of electrons in the outer shell grouped vertically.
periodontal disease gum disease. In the early stages it presents as gingivitis and later causes loosening of the teeth.
periodontal membrane a membrane that attaches a tooth to the socket in the maxilla or mandible.
periodontics branch of dentistry concerned with prevention and treatment of diseases of the supporting tissues of the teeth.
periodontitis inflammatory disease of the periodontium, resulting in destruction of the periodontal ligament.
periodontium collective name given to the tissues supporting a tooth and comprising the gingiva, periodontal ligament, cementum and surrounding alveolar bone.
periosteum the membrane which covers a bone. In long bones only the shaft as far as the epiphysis is covered. It protects and allows regeneration.
periostitis inflammation of the periosteum. See also diffuse periostitis, haemorrhagic periostitis.
peripheral relating to the outer parts of any structure. Any device attached to a computer, e.g. a printer or modem.
peripheral nervous system (PNS) describes that part of the nervous system outside the brain or spinal cord. Usually applied to those nerves which supply the musculoskeletal system and surrounding tissues to differentiate from the autonomic nervous system.
peripheral resistance (PR) the force exerted by the arteriolar walls which is an important factor in the control of normal blood pressure.
peripheral vascular disease (PVD) any abnormal condition arising in the blood vessels outside the heart, the main one being atherosclerosis, which can lead to thrombosis and occlusion of the vessel, resulting in gangrene.
peripheral venography the radiographic investigation of the venous system of a limb following the direct injection of contrast agent into a vein.
peripheral vision that surrounding the central field of vision.
periportal surrounding the hepatic portal vein.
peristalsis a rhythmic wave-like contraction and dilatation occurring in a hollow structure, for example, ureter, gastrointestinal tract. In the intestine it is the movement by which the contents (food and waste) are propelled along the lumen. It consists of a wave of contraction preceded by a wave of relaxation.
peritoneal cavity a potential space between the parietal and visceral layers of the peritoneum.
peritoneal effusion a collection of serous fluid in the peritoneal cavity.
peritoneum the delicate serous membrane which lines the abdominal and pelvic cavities (parietal layer) and also covers some of the organs (visceral layer) contained in them.
peritonitis inflammation of the peritoneum, usually secondary to disease of one of the abdominal organs.
periumbilical surrounding the umbilicus.
perivascular around a blood vessel.
permanent teeth adult teeth, 32 in number, which are numbered 12345678 in each quadrant of the mouth.
permeability the measure of the response of a material to a magnetic field. It is the ratio of the magnetic flux induced in the material to the strength of the applied magnetic field. In physiology, the extent to which sub-stances dissolved in the body fluids are able to move through cell membranes or layers of cells (for example, the walls of capillaries or absorptive tissues).
permittivity absolute permittivity is the ratio of the electrical displacement to the electrical field at the same point. relative permittivity (or dielectric constant) of a capacitor is the ratio of its capacitance with the spe-cific dielectric between the plates to its capacitance with air between the plates.
pernicious anaemia results from the inability of the bone marrow to produce normal red cells because of the lack of a protein, released by gastric parietal cells, called the intrinsic factor, which is necessary for the absorption of vitamin B12 from food. An autoimmune mechanism may be responsible.
peromelia a teratogenic malformation of a limb.
persistent (patent) ductus arteriosus a congenital heart defect.
perspiration the excretion from the sweat glands through the skin pores. See also insensible perspiration, sensible perspiration.
Perthes’ disease (pseudocoxalgia) avascular degeneration of the upper femoral epiphysis occurs in children; revascularization occurs, but residual deformity of the femoral head may subsequently lead to arthritic changes.
pes a foot or foot-like structure.
pes cavus (high-arched foot, claw-foot) a pathological elevation of the longitudinal arch caused by plantar flexion of the forefoot relative to the rearfoot. The medial longitudinal arch is most affected but the lateral longitudinal arch can also be elevated. There is dorsal humping of the midfoot and associated forefoot and rearfoot deformities. These may include clawing or retraction of the lesser toes, a trigger first toe, and a depressed first metatarsal with either heel varus or equinus. It may be acquired or congenital.
pes planus (flat-foot) a generic term for a foot with an abnormally low arch. The medial longitudinal arch is depressed or absent, and the foot has an increased contact area with the ground. During weightbearing the foot appears to have no longitudinal arch. It may be congenital or acquired. When young children first stand the feet appear to be flat, as adipose tissue under the medial longitudinal arch is pressed close to the ground. Older children very frequently have flattening of the medial longitudinal arch on standing but the arch reappears on standing on tiptoe (a mobile flat foot). flexible pes planus is generally asymptomatic in children but may become a semi-rigid condition in adulthood. It has been linked with excess laxity of the joint capsule and the ligaments supporting the arch, which allows it to collapse when weight is applied. rigid pes planus in adults may be a progression from flexible to semi-rigid to rigid as part of the ageing process. Structural changes due to the existing abnormal position become fixed, as soft and osseous tissues adapt. Rigidity is increased where there are significant osteoarthritic changes or inflammatory arthritic destruction.
petit mal a form of epilepsy where there is a brief alteration in consciousness.
Peyer’s patches aggregates of lymphatic tissue situated in the ileum. Function to prevent microorganisms entering the blood. Site of infection in typhoid fever.
pH hydrogen ion concentration, expressed as a negative logarithm and a quantitative method of measuring the acidity or alkalinity of a solution, on a log scale of 0 to 14, where pure water is 7. Below 7 is acid, and higher than 7 is alkaline. Developer has a pH of 9.6–10.6, and fixer a pH of 4.2–4.9.
pH meter a calibrated, electric meter used to take accurate pH readings of processor chemicals.
phaeochromocytoma (paraganglioma) a condition in which there is a tumour of the adrenal medulla, or of the structurally similar tissues associated with the sympathetic chain. It secretes adrenaline (epinephrine) and allied hormones and the symptoms are due to the excess of these substances. Results in hypertensive crises, with associated headache, flushing and tachycardia.
phagocyte a cell capable of engulfing bacteria and other particulate material.
phagocytosis the process by which phagocytes engulf particles such as bacteria.
phalanges the small bones of the fingers and toes.
phantom limb the sensation that a limb is still attached to the body after it has been amputated. Pain may seem to come from the amputated limb.
pharmacy medicines drugs which can only be sold if a pharmacist is present.
pharyngeal pouch pathological dilatation of the lower part of the pharynx.
pharyngolaryngeal associated with the pharynx and larynx.
pharyngotympanic tube (eustachian tube) a canal, partly bony, partly cartilaginous, connecting the pharynx with the tympanic cavity. It allows air to pass into the middle ear, so that the air pressure is kept even on both sides of the eardrum.
pharynx the cavity at the back of the mouth. It is cone-shaped and is lined with mucous membrane; at the lower end it opens into the oesophagus. The pharyngotympanic (eustachian) tubes pierce its lateral walls and the posterior nares pierce its anterior wall. The larynx lies immediately below it and in front of the oesophagus.
phase contrast angiography a two-dimensional or three-dimensional magnetic resonance imaging technique to distinguish flowing blood from static tissue. The magnitude image shows the blood vessels and the phase image shows the direction of flow.
phase encoding a technique used to locate a magnetic resonance signal by applying a series of varying phase-encoded, gradient pulses so that the phase of spin is altered prior to the signal readout. The spins retain the memory of the separate phase-encoded pulses.
phased array in ultrasound a sector field of view with multiple transducer elements, formed in precise sequence and under electronic control. This gives a wide field of view using a small transducer, for example, cardiac or paediatric head scans.
pheromones chemicals with a specific odour. They are present in the sweat produced by the apocrine sweat glands. They may influence sexual behaviour.
Philadelphia chromosome (Ph) an anomaly of chromosome number 22. It is found in the blood cells of most people with chronic myeloid leukaemia.
phimosis constriction of the prepuce so that it cannot be drawn back over the glans penis.
phlebography (venography) radiological examination of the venous system involving injection of an opaque medium. Mostly replaced by ultrasound.
phlegm (sputum) mucus expectorated (coughed up) from the bronchi.
phocomelia teratogenic malformation. Arms and feet attached directly to trunk giving a seal-like appearance. Many cases in the 1960s were associated with the use of thalidomide during pregnancy.
phonation the production of speech sounds.
phosphates salts of phosphoric acid.
phosphor a substance that has a characteristic light emission when stimulated by an electron beam.
phosphorescence is when a medium is irradiated and light is emitted, when the irradiation stops light continues to be emitted.
phosphor layer the suspension of phosphor crystals in a binder to form the layer of an intensifying screen that converts radiation to light.
phosphor storage plate see imaging plate.
phosphor type the higher the total efficiency of a phosphor the more light is produced and therefore the thinner the phosphor, rare earth phosphors are more efficient than calcium tungstate phosphors.
phosphorus (P) a poisonous element. Forms an important constituent (as phosphates) of nucleic acids, bone and all cells. radioactive phosphorus (32P) is used in the treatment of thrombocythaemia.
phosphorylation the process of attaching a phosphate group to a protein, sugar or other compound.
photocathode a structure made of zinc cadmium which produces elec-trons in proportion to the amount of light falling on it. See also image intensifier.
photodynamic therapy the administration of a tumour-localizing, photosensitizing drug which is activated by a laser light of a specific wavelength to damage tumour cells.
photoelectric absorption when a photon collides with an orbiting electron and gives all its energy to the electron which is then ejected from the atom.
photofluorography the recording of the image on the output phosphor of an image intensifier.
photographic dosimeter a device containing a photographic film and several different filters that is worn over a period of time. The film is processed and the density on the film is measured. The density is proportional to the amount of radiation received by the wearer.
photographic unsharpness blurring of a radiographic image due to the recording medium. See also unsharpness.
photomultiplier tube equipment that produces an amplified current when exposed to electromagnetic radiation, photons hitting the cathode produce electrons which in turn hit other surfaces thus producing more electrons. Used in earlier CT scanner units.
photons a quantum of electromagnetic radiation having an energy of hf, h equals Planck’s constant and f is the frequency of the radiation.
photoscan the image from a linear scanner recorded on radiographic film.
photo-thermographic printing uses a film containing chemicals which are activated when an image is scanned by a laser onto the film, the film is then heated to produce the image, the chemicals remain in the film. See also thermographic printing.
physical abuse see abuse, non-accidental injury.
physical half-life is the time required for the activity of a radioactive sample to decay to half its original value.
physiological often used to describe a normal process or structure, to distinguish it from an abnormal or pathological feature (for example, the physiological level of glucose in the blood).
physiological advantage a muscle’s ability to shorten. Its greatest physiological advantage is when a muscle is at rest.
physiological saline see isotonic.
physiological solution a fluid isotonic with the body fluids and containing similar salts.
physiology the science dealing with normal functioning of the body.
pia mater the innermost of the meninges; the vascular membrane which lies in close contact with the brain and spinal cord.
picture archiving communications system (PACS) in radiography, a networked system of viewing monitors connected to a central image database that allows integration of image and demographic information.
pie chart in statistics, a circle divided into segments, each segment represents a number of results as a proportion of the whole.
pie lines marks on a processed film which have been caused by chemicals drying on the surface of the automatic processor rollers.
piezoelectric crystal a crystal which converts electrical impulses into sound waves and vice versa by deforming when a voltage is applied across it, for example, ceramic or quartz crystals.
piezoelectric effect when an electric current is produced by certain materials when pressure is applied to their surface. See also inverse piezoelectric effect.
pigeon chest (pectus carinatum) a narrow chest, bulging anteriorly in the breast bone region.
pilomotor nerves tiny nerves that innervate the hair follicle, causing the hair to become erect and give the appearance of ‘goose flesh’.
pilosebaceous associated with the hair follicle and the sebaceous gland opening into it.
pilot study an early smaller-scale study carried out before the main research project to evaluate viability and to identify problems with the research methodology.
pineal body (pineal gland) a small reddish-grey conical structure on the dorsal surface of the midbrain. It secretes various substances which include 5-hydroxytryptamine and melatonin. The release of melatonin is connected to the amount of light entering the eye. Melatonin levels fluctuate during the 24 hours and appear to influence gonadotrophin secretion, diurnal rhythms such as sleep, and mood. See also depression.
pin-hole collimator gamma camera collimator with a small hole, a few millimetres in diameter at the end of a lead cone which, due to the divergence of the gamma rays, give an enlarged image of a small object.
pinna the auricle. That part of the ear which is external to the head.
pisiform one of the eight bones of the wrist.
pitch in CT scanning, is the ratio of table movement, during one 360° rotation.
pituitary fossa a depression in the spenoid bone for the pituitary gland; if the gland becomes enlarged, the fossa becomes enlarged.
pituitary gland (hypophysis cerebri) a small oval endocrine gland lying in the pituitary fossa of the sphenoid bone. The anterior lobe (adenohypophysis) produces and secretes several hormones; growth hormone, adrenocorticotrophic hormone, thyroid-stimulating hormone, luteinizing hormone, follicle stimulating hormone, prolactin and melanocyte stimulating hormone. The posterior lobe (neurohypophysis) stores and secretes oxytocin and vasopressin (antidiuretic hormone). These hormones are made by nerve fibres in the hypothalamus.
pivot joint a synovial joint which allows rotation only, for example, the superior radio-ulnar joint.
pixel picture cell, the dots which can be used by a character on a digital image display screen, the smaller the pixel the greater the image quality.
placebo a harmless substance given as medicine. In a randomized placebo-controlled trial, an inert substance, identical in appearance with the material being tested. When neither the researcher nor the subject knows which is which, the trial is said to be double blind.
placebo effect a therapeutic effect is observed after the administration of a placebo.
placenta the afterbirth, a hormone-secreting vascular structure developed and functioning about the third month of pregnancy and attached to the inner wall of the uterus. Through it the fetus is supplied with nourishment and oxygen and through it the fetus gets rid of its waste products. In normal labour it is expelled, with the fetal membranes, during the third stage of labour. When this does not occur it is termed a retained placenta and may be an adherent placenta. The placenta is usually attached to the upper segment of the uterus; where it lies in the lower uterine segment it is called a placenta praevia and usually causes placental abruption with painless antepartum bleeding.
placenta accreta when the placenta invades the uterine muscles which makes separation from the placenta difficult and can result in bleeding during birth.
placenta praevia when the placenta is attached to the lower part of the uterine wall and may cause antepartum haemorrhage.
placentography radiographic examination of the placenta, now superseded by ultrasound.
planar implants an interstitial implant to treat a volume of tissue of the same area to a thickness of 5mm on either side.
Planck’s constant a constant that relates the quantum of energy (E) of a photon to the frequency (f) of the corresponding electromagnetic radiation. E=hf where h is Planck’s constant.
plane joint a synovial joint that allows a gliding movement only, for example, the sacro-iliac joints.
planning target volume (PTV) a tissue volume used to aid the selection of the appropriate beam sizes and arrangements to ensure that the prescribed dose of radiation is delivered to the clinical target volume during radiotherapy treatment.
plantar associated with the sole of the foot.
plantar arch the union of the plantar and dorsalis pedis arteries in the sole of the foot.
plantar flexion downward movement of the big toe.
plaque an elevated area of skin. In dentistry a soft deposit of bacteria and cellular debris formed when oral hygiene is poor. See also dental plaque.
plasma the fluid part of blood.
plasma cell an immune cell that produces antibodies. It is derived from B lymphocytes/cells.
plasmacytoma a rare condition where a myeloma is confined to one or two bones only.
plasmin proteolytic enzyme produced when plasminogen is activated. It breaks down fibrin clots when healing is complete. Also called fibrinolysin.
plasminogen precursor of plasmin. Release of activators, for example, tissue plasminogen activator (t-PA), from damaged tissue promotes the conversion of plasminogen into plasmin.
plasticizer an addition to the radiographic film emulsion to prevent it from becoming too brittle.
platelets (thrombocytes) cellular fragments concerned with blood coagulation.
platelet plug one of the four overlapping stages of haemostasis. Platelets aggregate and adhere to form a temporary plug at the site of blood vessel damage.
pleomorphism differences between individual daughter cells or subclones.
pleura the serous membrane covering the surface of the lung (visceral pleura), the diaphragm, the mediastinum and the chest wall (parietal pleura).
pleural cavity is the potential space between the visceral and parietal pleurae which in health are in contact in all phases of respiration.
pleural effusion inflammation of the pleura of the lungs with secretion of serous fluid into the pleural cavity.
pleurisy, pleuritis inflammation of the pleura. May be fibrinous (dry), be associated with an effusion (wet), or be complicated by empyema.
pleuropulmonary relating to the pleura and lung.
plexopathy decreased movement or sensation in a joint caused by impaired function of the nerves that cause sensation and movement.
plexus a network of vessels or nerves.
Plummer–Vinson syndrome a rare disorder caused by oesophageal webs at the level of the cricoid cartilage.
PN junction is formed by fusing together a P-type semiconductor and an N-type semiconductor.
pneumoconiosis (dust disease) fibrosis of the lung caused by long-continued inhalation of dust in industrial occupations. The most important com-plication is the occasional superinfection with tuberculosis. See also anthracosis, asbestosis, byssinosis, rheumatoid pneumoconiosis, siderosis, silicosis.
pneumocytes cells lining the alveolar walls in the lungs. Type I are flat. Type II are cuboidal and secrete surfactant.
pneumoencephalography radiographic examination of cerebral ventricles after injection of air by means of a lumbar or cisternal puncture.
pneumonia acute infection of the lung by an invading organism associated with new pulmonary shadowing on a radiograph. Can be subdivided into community-acquired, hospital-acquired, and pneumonia associated with profound immunosuppression.
pneumonitis inflammation of lung tissue.
pneumoperitoneum air or gas in the peritoneal cavity. Can be introduced for diagnostic or therapeutic purposes.
pneumothorax air or gas in the pleural cavity separating the visceral from the parietal pleura so that lung tissue is compressed. Occurs spontaneously when an over-dilated pulmonary air sac ruptures, permitting communication of respiratory passages with the pleural cavity. Associated with many lung diseases, including asthma, bronchial cancer, COPD, congenital cysts, tuberculosis, trauma, and positive pressure ventilation. tension pneumothorax a valve-like wound or tear in the lung allows air to enter the pleural cavity with each inspiration, but not to escape on expiration, thus progressively increasing intrathoracic pressure and constituting an acute medical emergency. Signs are of hyperinflation, midline shift and increasing respiratory distress.
point defects the loss of an atom from a structure. Frenkel defect forming an interstitial ion or atom. Schottky defect removing the atom completely.
polar graph paper paper with a series of circular lines around a central point, intersected with radial lines from the same point forming 15° divisions, used in treatment planning.
polarized describes the resting state of the plasma membrane of an excitable cell where there is no impulse transmission. The inside of the membrane is electrically negative relative to the outside. See also depolarization.
polar molecules when an atom contains molecules that are not coincident to the nucleus resulting in a positive and a negative end to the atom.
polyarthralgia pain in several joints.
polyarthritis inflammation of several joints.
polycystic composed of many cysts.
polycystic kidney diseases a number of conditions which have variable effects on kidney function. Many lead to end-stage renal failure and the need for dialysis. Often associated with cystic disease of other organs, especially the liver and meninges.
polycythaemia (rubra vera) an uncommon disease of the bone marrow, characterized by increased production of red blood cells, leucocytes and platelets.
polydactyly (polydactylism) having more than the normal number of fingers or toes. On the foot the extra digits may develop from one metatarsal or there may be duplication of metatarsal segments. Sometimes selective amputation at an early age is indicated. This ensures optimum foot function, thus facilitating shoe fitting in childhood and adult life.
polymorphonuclear having a many-shaped or lobulated nucleus, usually applied to the phagocytic leucocytes (granulocytes), neutrophils, basophils and eosinophils.
polyp (polypus) a pedunculated tumour arising from any epithelial surface, for example, cervical, uterine, nasal, intestinal. Usually benign but may be malignant. adenomatous polyps are premalignant. Tissue overgrowth underlying the epithelium may also be the cause of polyp formation.
polyposis a condition in which there are numerous intestinal polyps.
polyuria excess urine production, the urine contains sugar and is a sign of diabetes mellitus.
pons a bridge; a process of tissue joining two sections of an organ.
pons varolii part of the brainstem which serves to connect the various lobes of the brain.
POP (Post Office Protocol) an email system.
popliteal associated with the area behind the knee.
popliteal space the diamond-shaped depression behind the knee, bounded by muscles and containing the popliteal nerve and vessels (artery and vein).
popliteus a muscle in the popliteal space which flexes the leg and aids rotation.
population the pool of information from which statistics are drawn.
population inversion when half the atoms in a structure are in an excited state.
pore a minute surface opening. One of the mouths of the ducts (leading from the sweat glands) on the skin surface; they are controlled by fine papillary muscles, closing in the cold and opening in the presence of heat.
porphyrins group of organic compounds that form the basis of respiratory pigments, including haemoglobin. Naturally occurring porphyrins are uroporphyrin and coproporphyrin.
port a connection point on a computer for input or output hardware.
porta the depression (hilum) of an organ at which the vessels enter and leave.
porta hepatis the transverse fissure through which the hepatic portal vein, hepatic artery and bile ducts pass on the under surface of the liver.
portacaval, portocaval relating to the hepatic portal vein and inferior vena cava.
portacaval anastomosis the hepatic portal vein is joined to the inferior vena cava with the object of reducing the pressure within the hepatic portal vein in cases of hepatic portal hypertension.
portal circulation see hepatic portal circulation.
portal hypertension more properly called hepatic portal hypertension. Increased pressure in the hepatic portal vein. Usually caused by cirrhosis of the liver; results in splenomegaly, with hypersplenism and alimentary bleeding. See also oesophageal varices.
portal imaging methods of verifying the radiotherapy treatment area, using either radiographic film or digital imaging methods. The portal image of the treatment area is compared to the image taken at simulation. See also therapy verification film, electronic portal imaging.
portal vein more properly called hepatic portal vein. That conveying blood into the liver; it is about 75mm long and is formed by the union of the superior mesenteric and splenic veins.
portal venography the radiographic investigation of the portal system following a direct injection of contrast agent into the spleen.
positive correlation in statistics, when information is linked and an increase in one item will result in an increase in the other and a decrease in one item will result in a decrease in the other.
positron emission tomography (PET) uses cyclotron-produced isotopes of extremely short half-life that emit positrons which are introduced into the patient. A specialist gamma camera is used that has multiple detectors lying in a circular gantry that surrounds the patient. The detectors detect the isotopes that decay through positron emission as this produces two photons of 511 keV which are emitted at 180° to each other. Only if two detectors are opposite each other, each registering a photon within nanoseconds of each other, are the photons recorded. PET scanning is used to evaluate physiological function of organs, for example, the brain.
positrons positively charged particles that combine with electrons (negative charge), causing gamma rays to be emitted.
post anaesthesia after anaesthetic and before full recovery.
posterior situated at the back. See also anterior.
posterior chamber of the eye situated between the anterior surface of the lens and the posterior surface of the iris. See also aqueous.
posteroanterior radiograph from the back to the front of the body.
postganglionic situated distal to a collection of nerve cells (ganglion), as a postganglionic nerve fibre.
postnasal behind the nose and in the nasopharynx.
postpartum occurring after labour.
potassium bromide a developer restrainer.
potassium hydroxide a developer accelerator.
potassium metabisulphite a developer preservative.
potassium sulphite a fixing solution preservative.
Posteroanterior radiograph (PA).
From Pocketbook of radiographic positioning, 2nd edn, Ruth Sutherland, 2003, Churchill Livingstone, Edinburgh, with permission.
potential difference a measure of electrical work on a unit positive charge in moving it from one point to another in volts.
potential energy represents the work done in raising a body to a height h. Work which can be performed due to the position or state of a system; unit: joule.
Pott’s disease spondylitis; spinal caries; spinal tuberculosis. The resultant necrosis of the vertebrae causes kyphosis.
Pott’s fracture a fracture-dislocation of the ankle joint. A fracture of the lower end of the tibia and fibula, 75mm above the ankle joint, and a fracture of the medial malleolus of the tibia.
pouch a pocket or recess. pouch of Douglas the rectouterine pouch.
power is the rate at which work is done in joules per second. SI unit watt. In ultrasound the power of the ultrasound beam is the energy flow rate of the whole beam which must be kept to a minimum value due to the harmful effects of ultrasound.
power calculation a measure of statistical power. The likelihood of the research study to generate statistically significant results.
Power Doppler a measure of the amplitude of the Doppler signal when scanning very slow moving structures, for example, small blood vessels in the body, it will not show the velocity or direction of flow.
PR (per rectum) describes the route used for examination of the rectum, or introduction of drugs or fluids into the body.
precancerous pertaining to a stage of abnormal tissue growth that is likely to develop into a malignant tumour. See also carcinoma in situ.
precordial (praecordial) relating to the area of the chest immediately over the heart.
pre-exposed step wedges produced by film manufacturers that when processed, have a series of increased density steps which can be used to determine the consistency of the film processor.
prefrontal situated in the anterior portion of the frontal lobe of the cerebrum.
preganglionic proximal to a collection of nerve cells (ganglion), as a preganglionic nerve fibre.
preload the degree of stretch present in the myocardial muscle fibres at the end of diastole. See also afterload, stroke volume.
premature occurring before the proper time.
premature beat see extrasystole.
premature birth in English law, the birth of a baby after 24 weeks but before 37 weeks’ gestation.
premedication drugs given before the administration of another drug, for example, those given before a general anaesthesia to reduce anxiety.
premenstrual preceding menstruation. premenstrual (cyclical) syndrome (PMS) a group of physical and mental changes occurring any time between 2 and 14 days before menstruation. They are relieved almost immediately when menstruation starts.
premolar tooth permanent tooth with two cusps (bicuspid), placed fourth and fifth from the midline. They succeed the primary molars. They have either a single grooved root or two roots.
prenatal associated with the period between the last menstrual period and birth of the child, normally 40 weeks or 280 days.
prepatellar in front of the patella, as applied to a large bursa. See also bursitis.
prepuce the foreskin of the penis.
prescription only medicines drugs which must have a written prescription signed by a doctor, dentist or specialist nurse prescriber.
presenile dementia occurring in people between 50 and 60 years of age. See also Alzheimer’s disease.
preservative in developer, a chemical, potassium metabisulphite that discourages oxidation and slows down the formation of discolouration products, in fixing solutions, for example, sodium sulphite or potassium sulphite is used to prevent the breakdown of the fixing agent into sulphur particles.
pressure force applied per unit area; unit pascal.
pressure areas any body area subjected to pressure sufficient to compress the capillaries and disrupt the microcirculation. Usually occurs where tissues are compressed between a bone and a hard surface, for example, theatre table, trolley, bed, chair, splint, or where two skin surfaces are in contact such as under the breasts. Pressure areas include: head, spine, sacrum, shoulders, elbows, hips, buttocks, heels, ankles. See also pressure ulcer.
pressure point a place at which an artery passes over a bone, against which it can be compressed, to stop bleeding.
pressure ulcer (decubitus ulcer, pressure sore) previously called a bedsore. Defined as an area of localized damage to the skin and underlying tissue caused by pressure, shear, friction, or a combination of these factors. Pressure ulcers develop when any area of the body is subjected to unrelieved pressure that leads to local hypoxia, ischaemia and necrosis with inflammation and ulcer formation. Shearing forces also disrupt the microcirculation when they cause the skin layers to move against one another. Shearing damages the deeper tissues and can lead to an extensive pressure ulcer. Friction from continual rubbing leads to blisters, abrasions and superficial pressure ulcers, and is made worse by moisture such as urine or sweat. Factors that increase the risk of pressure ulcer formation include: poor oxygenation, incontinence, age over 65–70, immobility, altered consciousness, dehydration and malnutrition.
presystole the period preceding the systole or contraction of the heart muscle.
prevalence total number of cases of a disease existing in a population at a single point in time.
prevalence rate the number of cases of a particular disease which exist at a given point in time.
prevalence ratio the prevalence of a disease, expressed as a ratio of population size.
preventive dentistry the prevention of, and preventive treatment for, dental disease and the promotion of good oral health.
prima facie ‘at first sight’, or sufficient evidence brought by one party to require the other party to provide a defence.
Primary Care Trust (PCT) in England a body that works with Social Services and other local government departments and other relevant bodies, for example, voluntary sector, to assess local health needs, plan, develop and provide community and primary healthcare services, and commission secondary services for the local population, in order to improve health, and reduce inequalities in health and improve access. They employ staff, run community hospitals, own property, and are responsible for public health. See also Strategic Health Authority.
primary collimation indicates the maximum field size of an X-ray beam at a specific distance.
primary haemorrhage bleeding that occurs at the time of the injury.
primary radiation the main beam of radiation from a source which has not interacted with an object.
primary radiation barrier the floor, walls and ceiling of a room which may be exposed directly to the primary beam of radiation from X-ray equipment.
primary site the initial position of tumour growth.
primary solute the main solute used in liquid scintillation counting as it fluoresces when electrons drop to their original low-energy state. See also fluorescence.
primary tumour the neoplasm at the site of origin.
primigravida a woman who is pregnant for the first time.
primipara a woman who has given birth to a child for the first time.
Private Finance Initiative (PFI) a joint venture between private and public sector to build a facility, for example, a hospital, using private finance. The NHS then leases the building. Some non-clinical services may also be provided under the lease agreement.
probability the likelihood that something is going to occur.
probe (transducer) a hand-held instrument composed of multiple elements of piezo-electric material each with its own electrodes, used in ultrasound imaging.
process a prominence or outgrowth of any part.
proctitis inflammation of the anus or rectum.
proctocolitis inflammation of the anus, rectum and colon.
proctoscope an endoscope with a light source used to visually inspect the rectum.
professional self-regulation the professional quality and continuing professional development standards set by various professional regulatory bodies for health professionals, for example, General Medical Council (GMC), for professional practice, discipline and conduct.
profile the image captured by the detector in CT scanning.
progesterone a steroid hormone secreted by the corpus luteum, placenta and, in limited amounts, by the adrenal glands. Progesterone acts on the endometrium, myometrium, cervical mucus and breasts. It is important in the preparation for and maintenance of pregnancy.
progestogen any natural or synthetic progestational hormone including progesterone.
progestogen-only pill an oral contraceptive that is taken continuously and at regular time intervals to provide effective contraception.
prognosis a forecast of the probable course and termination of a disease.
program a set of written instructions for the computer.
prolactin (PRL) a hormone secreted by the anterior pituitary, concerned with lactation and reproduction.
prolactinoma prolactin-secreting pituitary adenoma of the pituitary gland. See also hyperprolactinaemia.
prolapse descent; the falling of a structure.
prolapse of an intervertebral disc (PID) protrusion of the disc nucleus into the spinal canal. Most common in the lumbar region where it causes low back pain and/or sciatica. prolapse of the iris iridocele. prolapse of the rectum the lower portion of the intestinal tract descends outside the external anal sphincter. prolapse of the uterus the uterus descends into the vagina and may be visible at the vaginal orifice.
proliferate increase by cell division.
PROM (Programmable Read Only Memory) a specially prepared computer chip which can be programmed.
promontory a projection; a prominent part.
pronate to place ventral surface downward, for example, on the face; to turn (the palm of the hand) downwards. See also supinate.
pronator that which pronates, usually applied to a muscle. See also supinator.
prone lying on the anterior surface of the body with the face turned to the side. Of the hand, with the palm downwards. See also supine.
Pronosco X-posure SystemTM specialist equipment for assessing bone mineral density.
propagate in ultrasound to move forward through a medium, at an initial velocity and direction.
propagation speed the speed at which a wave moves through a medium in metres per second.
prophylactic an agent which prevents the development of a disease.
proprioception appreciation of balance and the position of the body and individual body parts in relation to each other, especially as they change during movement.
proprioceptor a sensory receptor located in a muscle, tendon, ligament or vestibular apparatus of the ears whose reflex function is locomotor or postural.
proptosis protrusion or bulging of an organ – commonly describes forward displacement of the eyeball.
prospective study research that deals with future data, moving forward in time. See also retrospective study.
prostacyclin a substance formed by endothelial cells lining blood vessels. It inhibits platelet aggregation and is concerned with preventing intravascular clotting.
prostaglandins a large group of regulatory lipids. Found in most body tissues where they regulate physiological functions including: smooth muscle contraction, inflammation, gastric secretion and blood clotting. Used pharmaceutically to terminate pregnancy, induce labour and for asthma and gastric hyperacidity.
prostate a small conical gland at the base of the male bladder and surrounding the first part of the urethra. Adds alkaline fluid containing enzymes into the semen.
prostate specific antigen (PSA) protein secreted by prostatic tissue. Acts as a tumour marker for prostate cancer, and its detection in the blood forms the basis for a screening test. Conditions other than prostate cancer can cause an increase in PSA level.
prostatic relating to the prostate. benign prostatic hyperplasia (BPH) benign enlargement of the prostate gland occurring mainly in older men. Leads to urinary problems such as poor stream and retention. prostatic acid phosphatase. See also acid phosphatase.
prostatitis inflammation of the prostate gland.
prosthesis an artificial substitute for a missing part, a device designed to improve function such as a pacemaker.
prosthetic dentistry the restoration of the function and aesthetics of missing teeth using artificial dentures.
prosthetic services provide prostheses, for example replacement breast, eye, nose, or wigs.
protease an enzyme which digests protein (proteolytic).
protective barriers methods of protecting the patients, staff and general public from unnecessary exposure to radiation using lead panelling and/or concrete.
protective isolation (reverse barrier nursing) involves separating patients who are immunocompromised and susceptible to infection, either by disease or treatment. The type of patients needing protection from infection include those with leukaemia, those having immunosuppressant treatment for organ transplantation, chemotherapy or radiation or neutropenic patients. See also containment isolation, source isolation.
proteins highly complex nitrogenous compounds found in all animal and vegetable tissues. They are built up of amino acids and are essential for growth and repair of the body. Those from animal sources are of high biological value because they contain the essential amino acids. Those from vegetable sources contain not all, but some of the essential amino acids. Proteins are hydrolysed in the body to produce amino acids, which are then used to build up new body proteins.
proteolysis the hydrolysis of the peptide bonds of proteins with the formation of smaller polypeptides.
proteolytic enzymes enzymes that promote proteolysis; they are used in the management of leg ulcers to remove slough.
prothrombin inactive precursor of the enzyme thrombin produced in the liver. Factor II in blood coagulation.
prothrombin time assesses the activity of the extrinsic coagulation pathway. It is the time taken for plasma to clot in vitro following the introduction of thromboplastin in the presence of calcium. It is inversely proportional to the amount of prothrombin present, a normal person’s plasma being used as a standard of comparison. The prothrombin time is extended in people taking anticoagulant drugs and in some haemorrhagic conditions.
protocol written standards for a way of working or the transfer of information, for example, between different computers.
proton a positively charged particle found in the nucleus of an atom.
proton density weighted image a magnetic resonance image showing contrast related to the number of mobile protons in the structure and requires scanning parameters that minimize the effects of relaxation time (T1 and T2) to obtain the appropriate weighting.
proto-oncogene a gene with the potential to become a cancer-causing oncogene if stimulated by mutagenic carcinogens. See also oncogene.
protopathic the term applied to the somatic sensations of fast localized pain; slow, poorly localized pain; and temperature. See also epicritic.
protraction a forward movement such as thrusting out the jaw. See also retraction.
proximal nearest to the head or source. See also distal.
prune belly syndrome a condition when the muscles of the lower abdomen are defective and the recti muscles are absent. It is associated with undescended testes and dilated ureters and bladder, the skin on the abdominal wall appears wrinkled.
pseudoarthrosis a false joint, for example, due to ununited fracture; also congenital, for example, in tibia.
pseudocoxalgia see Perthes’ disease.
pseudocyesis see phantom pregnancy.
pseudofractures (Looser’s zones) narrow bands of decalcification indicating osteomalacia.
pseudogout an arthritis (usually monoarthritis) caused by crystals of calcium pyrophosphate dihydrate within the joint.
pseudohermaphrodite a person in whom the gonads of one sex are present, while the external genitalia comprise those of the opposite sex.
Pseudomonas a Gram-negative motile bacillus commonly found in decaying organic matter.
pseudopolyposis widely scattered polypi, usually the result of previous inflammation – sometimes ulcerative colitis.
psoas abscess a cold abscess in the psoas muscle, resulting from tuberculosis of the vertebrae. The abscess appears as a firm smooth swelling which does not show signs of inflammation – hence the adjective ‘cold’.
psoriasis inflammation of the skin, redden areas with white scales.
psoriatic arthritis arthritis occurring in association with psoriasis.
psychoactive substances and drugs that may alter mental processes.
psychometry the science involved with mental testing.
pterygium a triangular patch of fibrous tissue on the cornea that extends medially from the nasal border of the cornea to the outer canthus of the eye.
ptosis prolapse of an organ. Drooping of the upper eyelid due to paralysis of the third cranial nerve.
P-type semiconductor a device where the majority carriers of electrons are the positive holes in the valence band and the minority carriers are the electrons which have sufficient energy to rise to the conduction band. See also N-type semiconductors.
puberty the period during which the reproductive organs become functionally active and the secondary sexual characteristics develop.
pubes the hair-covered area over the pubic bone.
pubis the pubic bone or os pubis. The two bones that meet at the symphysis pubis.
pudendum the external reproductive organs, especially of the female.
pulley a hand hold placed over a bed to enable patient’s on traction to lift themselves up to give themselves exercise and make bedmaking easier.
pulmonary associated with the lungs.
pulmonary artery flotation catheter (PAFC) specialized balloon-tipped catheter which is ‘floated’ from the central veins, through the heart and into the pulmonary artery. Allows measurement of pulmonary artery pressure, pulmonary artery occlusion pressure and cardiac output.
pulmonary artery occlusion pressure (PAOP) pressure in the left atrium measured by inflating a balloon on the tip of a pulmonary artery catheter thereby temporarily occluding the pulmonary artery; also known as wedge pressure.
pulmonary artery pressure blood pressure in the pulmonary artery usually measured using a pulmonary artery catheter.
pulmonary circulation deoxygenated blood leaves the right ventricle to the pulmonary artery, flows through the lungs where it loses carbon dioxide, becomes oxygenated and returns to the left atrium of the heart.
pulmonary embolus (PE) a blockage which occurs in the pulmonary arterial system in the lungs; most commonly as a result of deep vein thrombosis in the leg or pelvic veins. Prophylaxis includes deep breathing and foot exercises, early mobilization, antithromboembolic stockings with the administration of heparin in at-risk groups.
pulmonary emphysema overdistension and subsequent destruction of alveoli and reduced gas exchange in the lungs. Associated with tobacco smoking, it is a form of chronic obstructive pulmonary disease (COPD). See also bronchitis.
pulmonary hypertension raised blood pressure within the pulmonary circulation, due to increased resistance to blood flow within the pulmonary vessels. It may be primary (genetic), or secondary due to chronic lung disease or chronic pulmonary embolism.
pulmonary infarction obstruction of a branch of the pulmonary artery resulting in death of lung tissue.
pulmonary oedema fluid within the alveoli. The lungs are ‘waterlogged’ and gas exchange is reduced, such as in left ventricular failure, mitral stenosis, or fluid excess in renal failure.
pulmonary stenosis narrowing of the pulmonary valve.
pulmonary tuberculosis see tuberculosis.
pulmonary valve semilunar valve situated between the pulmonary artery and right cardiac ventricle.
pulmonary ventilation (minute volume) the amount of air moved in and out of the lungs in one minute.
pulp the soft, interior part of some organs and structures. digital pulp the tissue pad of the finger tip.
pulp cavity the central canal(s) of the tooth. See also dental pulp.
pulsation beating or throbbing, as of the arteries or heart.
pulsativity index a method of numerically determining the low diastolic blood flow (impedance) through a vessel using the equation systolic – diastolic/mean.
pulse height analyser a device which can be adjusted to record input pulses within a specific range and then produce an electrical output, therefore can be used to detect different radionuclides.
pulse modulator supplies high-voltage negative pulses to the magnetron or klystron in a linear accelerator.
pulse rate the number of cardiac contractions per minute.
pulse repetition frequency in ultrasound the number of pulses occurring in one second expressed in kilohertz (kHz).
pulsed dose-rate technique the radiotherapy method of using high-dose-rate equipment to deliver a low-dose-rate treatment by repeating a programmed cycle at predetermined intervals such as 1 hour.
pulsed-wave Doppler an ultrasound system which transmits bursts of ultrasound and then, after a preselected time, receives for a very short period of time, enabling a specific point within the beam to be examined.
pulser the part of an ultrasound machine that generates electrical pulses which stimulate the transducer to produce ultrasound.
punctum entrance to lacrimal drainage system on eyelid margin.
pupil the opening in the iris of the eye, which allows the passage of light.
pupillary relating to the pupil.
pupillary reflex the reflex dilatation and constriction of the pupil in response to the amount of light entering the eye. Controlled by the oculomotor nerves (third cranial).
purgative a strong drug to encourage complete bowel evacuation.
purines nitrogenous bases needed as constituents of nucleoproteins. Uric acid is produced when purines are broken down. Increased uric acid in the blood is associated with disorders of metabolism and excretion of uric acid, and leads to the development of gout.
PV (per vaginam) describes the route used for examination of the vagina, or the administration of drugs.
P value in research, the symbol used to denote the probability of the results of a test occurring by chance. A P value is given in all inferential statistics. This is the probability that the results found have occurred by chance alone. The P value is measured on a scale of 0–1, so, for example, a P value of P =0.05 means 5%, or a 1 in 20 chance. A lower-case p is used for proportions.
pyarthrosis pus in a joint cavity.
pyelonephritis infection within the substance of the kidney, often derived either from the urine or from the blood.
pyloric stenosis narrowing of the pylorus due to scar tissue formed during the healing of a peptic ulcer. Congenital hypertrophic pyloric stenosis due to a thickened pyloric sphincter muscle. See also pyloromyotomy.
pyloroduodenal associated with the pylorus and the duodenum.
pylorus region containing the opening of the stomach into the duodenum, controlled by a sphincter muscle.
pyopneumothorax pus and gas or air within the pleural sac.
pyothorax pus in the pleural cavity.
pyramidal applied to some conical eminences in the body.
pyramidal cells (Betz cells) nerve cells in the precentral motor area of the cerebral cortex, from which originate impulses to voluntary muscles.
pyramidal tracts main motor tracts in the brain and spinal cord, which transmit impulses arising from the pyramidal cells. Most decussate (cross over) in the medulla.
pyrexia body temperature above normal, usually between 37°C and 40/41°C. pyrexia of unknown origin where the reason for the raised body temperature is not known. See also fever, hyperpyrexia.
pyrimidines nitrogenous bases needed as constituents of nucleic acids.
pyrogens foreign proteins arising from previous bacteriological activity producing fever.
pyruvic acid an important metabolic molecule. Converted to acetyl CoA which is used in the Krebs cycle, or forms lactic acid during anaerobic glucose metabolism.
