2,701 articles
Paraneoplastic cerebellar degeneration
Paraneoplastic cerebellar degeneration (PCD), or paraneoplastic cerebellar ataxia, is tumor-induced autoimmune Purkinje cell loss causing subacute ataxia, mainly anti-Yo antibody with breast and gynecologic cancers, with poor prognosis.
Paraplegia
Paraplegia is paralysis of the lower body and both legs with preserved arm function, usually from spinal cord injury below the neck; also called paraplegic paralysis, distinct from quadriplegia or tetraplegia.
Parasympathetic nervous system
Parasympathetic nervous system, the craniosacral division of the autonomic nervous system coined by Langley. Outflow via cranial nerves III, VII, IX, X and S2–S4; long preganglionic fibers, acetylcholine, ganglia near target organs, rest-and-digest function.
Parasympathetic neuron
Parasympathetic neuron: cholinergic motor neuron of the parasympathetic (craniosacral) autonomic division; preganglionic cells in brainstem nuclei and S2–S4, postganglionic cells in ganglia near target organs, vagus carrying 75% of fibers.
Parathyroid gland
Parathyroid glands: four (3–8) pea-sized endocrine glands on the thyroid that secrete parathyroid hormone (PTH) to regulate blood calcium; discovered by Sandström 1880; disorders include hyperparathyroidism, hypoparathyroidism, rare parathyroid cancer.
Parathyroid hormone
Parathyroid hormone (PTH), an 84-amino acid peptide from the parathyroid chief cells, regulates calcium and phosphate homeostasis via PTH1R; intermittent dosing (teriparatide, abaloparatide) treats osteoporosis, unlike continuous hyperparathyroid resorption.
Parenchyma
Parenchyma is the essential functional tissue of an organ, distinct from its stroma; coined by Erasistratus for coagulated blood around vessels, now used in liver, lung, kidney, and plant histology.
Parenteral nutrition
Parenteral nutrition (PN), formerly total parenteral nutrition (TPN), is intravenous feeding via central or peripheral catheter for patients whose GI tract cannot meet nutritional needs; developed clinically by Stanley Dudrick in 1968, with home PN for chronic intestinal failure.
Parietal lobe
The parietal lobe, bounded by the central and parieto-occipital sulci, contains primary somatosensory cortex and posterior association areas for spatial attention, reaching, language, and number; damage causes neglect, apraxia, Gerstmann and Bálint syndromes.
Parinaud's syndrome
Parinaud's syndrome, also called dorsal midbrain or Sylvian aqueduct syndrome, is a neuro-ophthalmologic disorder caused by dorsal midbrain lesions, classically pineal tumors, producing upward gaze palsy and convergence-retraction nystagmus.
Parkes Weber syndrome
Parkes Weber syndrome (PKWS), a rare congenital vascular malformation disorder with limb overgrowth, port-wine stain capillary malformations, and high-flow arteriovenous fistulas; caused by RASA1 or EPHB4 variants, distinct from Klippel-Trenaunay syndrome.
Parkinson's disease
Parkinson's disease, also called shaking palsy, is the second-most common neurodegenerative disorder, defined by substantia nigra dopaminergic neuron loss and α-synuclein Lewy bodies, causing tremor, rigidity, and bradykinesia, treated with levodopa and deep brain stimulation.
Parkinsonism
Parkinsonism, also called parkinsonian syndrome or Parkinson-plus when atypical, is a clinical syndrome of bradykinesia with rigidity, resting tremor, or postural instability; Parkinson's disease is its most common cause.
Parotid gland
Parotid gland: largest of the three paired major salivary glands, in the retromandibular fossa; serous saliva via Stensen duct; facial nerve traverses it; site of 80% of salivary tumors.
Paroxysmal supraventricular tachycardia
Paroxysmal supraventricular tachycardia (PSVT) is a regular, rapid heart rhythm of abrupt onset and termination, mostly AVNRT or AVRT; treated acutely with vagal maneuvers and adenosine, and cured by catheter ablation in 94-98% of cases.
Paroxysmal tachycardia
Paroxysmal tachycardia: abnormally rapid heartbeats with sudden onset and cessation (ICD-11 MC81.3, ICD-10 I47). Covers PSVT, mainly AVNRT; treated with vagal maneuvers, adenosine, and newly approved intranasal etripamil.
Patch-sequencing
Patch-seq (Patch-sequencing) is a multimodal neuroscience technique combining patch-clamp electrophysiology, single-cell RNA sequencing, and morphology in the same neuron, first implemented reliably in 2016 and central to brain cell type atlases.
Patella
Patella (kneecap), largest sesamoid bone, embedded in the quadriceps tendon at the knee; increases quadriceps leverage (31% of extension torque at full extension), ossifies at age 5-6, prone to dislocation and fracture.
Patellar reflex
Patellar reflex (knee jerk, Patellarsehnenreflex): monosynaptic L2-L4 stretch reflex elicited by tapping the patellar tendon, causing quadriceps contraction; described by Erb and Westphal in 1875 and increasingly quantified with EMG and motion analysis.
Patent ductus arteriosus
Patent ductus arteriosus (PDA), persistent ductus arteriosus: a congenital heart defect in which the fetal vessel joining aorta and pulmonary artery stays open after birth. Common in preterm infants; treated with indomethacin, ibuprofen, acetaminophen, or catheter/surgical closure; first surgically repaired by Robert Gross in 1938.
Patent foramen ovale
A patent foramen ovale is a flap-like opening between the heart's right and left atria that fails to seal after birth, present in about 25% of adults.
Pathophysiology of heart failure
Pathophysiology of heart failure: mechanisms of HFrEF (cardiomyocyte death, DAMP-driven inflammation, remodeling) versus HFpEF (comorbidity-driven microvascular endothelial inflammation, low nitric oxide, stiff ventricle), with biomarker and treatment contrasts.
Patulous Eustachian tube
Patulous Eustachian tube (tuba aperta, ICD-10 H69.0): an abnormally open Eustachian tube causing autophony and eardrum movement with breathing; linked to weight loss, treated by plug or shim surgery.
Pediatric tachyarrhythmias
Pediatric tachyarrhythmias are abnormally fast heart rhythms in fetuses, infants, children, and adolescents. Supraventricular tachycardia is the most common, often from accessory pathways that frequently resolve with age.
PEGASUS trial
PEGASUS trial: name shared by several clinical trials, chiefly PEGASUS-TIMI 54 (NCT01225562), a 21,162-patient AstraZeneca/TIMI trial of ticagrelor 60 or 90 mg twice daily plus aspirin after myocardial infarction, and a phase 3 pegcetacoplan-versus-eculizumab trial in paroxysmal nocturnal hemoglobinuria.
Pellucid marginal degeneration
Pellucid marginal degeneration, also called pellucid marginal corneal degeneration (PMCD), is a rare, usually bilateral disorder in which a crescent-shaped band of the peripheral cornea thins progressively.
Pelvic arteriovenous malformation
Pelvic arteriovenous malformation (pelvic AVM), a rare congenital high-flow vascular anomaly with internal iliac artery feeders and a dominant outflow vein; treated mainly by coil embolization of the draining vein, with recurrence up to 15%.
Pelvic splanchnic nerves
Pelvic splanchnic nerves (nervi erigentes) are preganglionic parasympathetic nerves from S2-S4 anterior rami supplying the bladder, hindgut, ureter, prostate, urethra, and erectile tissue via the inferior hypogastric plexus.
Pelvis
The pelvis, or pelvic girdle, is the bony structure at the base of the trunk that connects the spine to the legs and supports the upper body.
Penetrating atherosclerotic ulcer
A penetrating atherosclerotic ulcer is an ulcerated aortic atherosclerotic plaque that breaks through the internal elastic lamina into the aortic wall's media, one of three acute aortic syndromes.