2,701 articles
Pigmentary open-angle glaucoma
Pigmentary open-angle glaucoma (pigmentary glaucoma, PG): secondary open-angle glaucoma from pigment dispersion syndrome, affecting young myopic men, with higher surgery rates and LTP/MIGS failure than POAG.
Pigmentation
Pigmentation: coloration or discoloration of tissue by a pigment, chiefly melanin in human skin, hair, and eyes. Covers melanin biology, hyper- and hypopigmentation disorders, measurement scales, and device accuracy effects.
Pikachurin
Pikachurin (EGFLAM) is an extracellular matrix protein of the photoreceptor ribbon synapse cleft, identified in 2008, that binds alpha-dystroglycan via LG2-LG3 domains and GPR179, aligning bipolar dendrites; its loss disrupts retinal signaling.
Pilocarpine
Pilocarpine, a plant-derived muscarinic cholinergic agonist introduced to ophthalmology in 1876, lowers intraocular pressure in glaucoma and, in low concentrations (Vuity 1.25%, Qlosi 0.4%), treats presbyopia; limited today by miosis, blurred vision, and frequent dosing.
Pilocytic astrocytoma
Pilocytic astrocytoma, also known as juvenile pilocytic astrocytoma, is a slow-growing grade 1 glioma, the most common brain tumor in children, with 90% ten-year survival.
Pinch Strength
Pinch strength: force exerted by the index finger and thumb, measured by pinch gauge as maximum voluntary contraction. Types are tip, three-jaw chuck, and lateral pinch; reliability ICC > 0.75-0.90, correlated with grip strength (r 0.72-0.92).
Pineal gland
Pineal gland (epiphysis, conarium): a 100-150 mg midline neuroendocrine organ in the brain that secretes melatonin at night under sympathetic control from the SCN, timing circadian and seasonal physiology.
Pinguecula
Pinguecula: a common benign yellow-white raised growth on the conjunctiva near the limbus, caused by UV, wind, and dust; unlike pterygium it never invades the cornea and is usually asymptomatic.
Piriformis muscle
Piriformis muscle: pear-shaped hip external rotator from the sacrum (S2–S4) to the greater trochanter, innervated by S1–S2; landmark for the sciatic nerve and namesake of piriformis syndrome.
Piriformis syndrome
Piriformis syndrome, also called deep gluteal syndrome, is sciatic nerve compression by the piriformis muscle causing buttock pain radiating down the leg; treated first with stretching, NSAIDs, injections, and rarely surgery.
Pitch and loudness coding in the auditory system
Pitch and loudness coding in the auditory system is how frequency and intensity are represented via cochlear place codes and phase-locked spike timing, which fails above a few kHz.
Pituitary abscess
Pituitary abscess: a rare pus collection in the pituitary gland or sella turcica, under 1% of pituitary lesions; primary or secondary; headache and visual loss; treated by transsphenoidal drainage plus antibiotics.
Pituitary gland
Pituitary gland (hypophysis cerebri), the pea-sized master endocrine gland below the hypothalamus in the sella turcica; anterior lobe makes TSH, ACTH, FSH, LH, GH, prolactin; posterior lobe stores oxytocin and ADH.
Placentophagy
Placentophagy, or placentophagia, is the eating of a human placenta after childbirth, most often as capsules, a practice that grew since the 1970s despite controlled research finding no evidence of its claimed benefits.
Plagiocephaly
Plagiocephaly, or flat head syndrome, is asymmetric infant skull flattening. Deformational (positional) plagiocephaly affects 5-48% of newborns; synostotic plagiocephaly from premature suture fusion is rare. Treatment ranges from repositioning to helmet therapy.
Plakoglobin
Plakoglobin (junction plakoglobin, gamma-catenin), encoded by JUP on chromosome 17, is an armadillo-family protein in desmosomes and adherens junctions of heart and skin; JUP mutations cause Naxos disease, arrhythmogenic cardiomyopathy, and lethal congenital epidermolysis bullosa.
Plantar fascia
Plantar fascia (plantar aponeurosis): dense fibrous tissue from heel to toes supporting the foot arch via the windlass mechanism; central, lateral, medial bands; source of plantar fasciitis, seen in about 10% of people.
Plantar reflex
Plantar reflex: sole-of-foot reflex; normal adults flex the big toe, while upgoing toe (Babinski sign, described 1896) indicates corticospinal tract dysfunction; insensitive but highly specific.
Plasma Volume
Plasma volume is the cell-free intravascular portion of blood, part of the extracellular fluid compartment. Measured by indicator dilution with Evans blue, indocyanine green, or radio-iodinated albumin; hematocrit-based estimates are unreliable.
Plastic bronchitis
Plastic bronchitis (PB), also called cast bronchitis or Hoffman bronchitis, is a rare disorder in which branching bronchial casts obstruct airways. Subtypes are lymphatic (post-Fontan) and eosinophilic; treatment includes lymphatic embolization.
Pleural cavity
Pleural cavity: potential space between visceral and parietal pleura around each lung, holding serous fluid under negative pressure; filters fluid from parietal capillaries, drains via lymphatic stomata; disorders include pneumothorax and pleural effusion.
Polyphasic sleep
Polyphasic sleep: distributing sleep into 3+ episodes per 24 h (Uberman, Everyman, Dymaxion schedules) to cut total sleep. Controlled studies show impaired vigilance, reduced deep sleep, and adverse health effects versus monophasic sleep.
Polysomnography
Polysomnography (PSG), the overnight sleep study, records EEG, EOG, EMG, breathing, oxygen, and heart activity to diagnose sleep apnea, narcolepsy, and parasomnias; term coined 1974.
Polyvagal theory
Polyvagal theory, proposed by Stephen Porges in 1995, links vagal brainstem nuclei to social behavior and autonomic states; its physiological and evolutionary premises are contested by Grossman and other experts.
Popliteal artery
Popliteal artery: continuation of the superficial femoral artery behind the knee, supplying the distal leg; branches into genicular and sural arteries, divides into tibial arteries, with ~10% branching variation and common aneurysm site.
Popliteal artery aneurysm
Popliteal artery aneurysm (PAA), popliteal aneurysm: dilation of the artery behind the knee; the most common peripheral aneurysm, mainly in men over 65, treated by open vein bypass or stent graft when over 2 cm or symptomatic.
Port-wine stain
Port-wine stain (nevus flammeus, capillary malformation) is a congenital pink-to-purple vascular birthmark present in 0.3–0.5% of infants, caused by somatic GNAQ R183Q mutations, often facial, sometimes linked to Sturge-Weber syndrome, treated with pulsed dye laser.
Portal vein
Portal vein (hepatic portal vein): large vein formed by the splenic and superior mesenteric veins, carrying about 75% of liver blood flow; divides into right and left branches, with variants in 20–35% of people, and prone to portal vein thrombosis.
Portal vein thrombosis
Portal vein thrombosis (PVT) is clot formation in the portal vein, affecting about 1% of the population and up to 25% of decompensated cirrhosis patients; classified as recent or chronic, treated with anticoagulation, DOACs, or TIPS.
Post anoxic brain damage
Post anoxic brain damage (ICD-11 8E44) is encephalopathy from circulatory arrest, hypotension, or asphyxia, also called hypoxic-ischemic brain injury; marked by coma after cardiac arrest, multimodal prognostication at 72 hours, and slow rehabilitation recovery.