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
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