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Otorrhoea
Otorrhoea (otorrhea) is ear discharge, usually from otitis media, otitis externa, or a perforated eardrum; types include purulent, serous, bloody, mucoid, and clear, with CSF leak after head trauma a serious cause.
Otosclerosis
Otosclerosis: abnormal bone remodeling fixing the stapes in the middle ear, causing progressive conductive hearing loss, tinnitus, and sometimes vertigo; treated with hearing aids or stapes surgery (stapedectomy, stapedotomy).
Ototoxicity
Ototoxicity is drug- or chemical-induced inner ear damage causing hearing or balance loss, chiefly from aminoglycoside antibiotics and platinum chemotherapy such as cisplatin, with pooled prevalence near 43%.
Ovary
Ovary: paired female gonad producing oocytes and the hormones estrogen and progesterone; almond-sized organs beside the uterus; follicles, ovulation, corpus luteum, menopause, and disorders such as PCOS and ovarian cancer.
Overwhelming post-splenectomy infection
Overwhelming post-splenectomy infection (OPSI), or post-splenectomy sepsis, is fulminant sepsis in asplenic or hyposplenic people, mainly from Streptococcus pneumoniae and other encapsulated bacteria, progressing within 24-48 hours with 50-70% mortality if untreated.
Ovulation
Ovulation, release of an egg from the dominant ovarian follicle after the LH surge, around day 12-14 of a 28-day cycle; detected by urinary LH kits (97% accuracy), midluteal progesterone, or ultrasound; BBT charting is inaccurate.
OWBLM trial
OWBLM (NCT04425681) is a phase II single-arm trial of osimertinib 80 mg daily plus bevacizumab 7.5 mg/kg for leptomeningeal metastasis from EGFR-mutant NSCLC; 14 patients, median LM PFS 9.3 months, ORR 50%, LM OS 12.6 months.
Oxygen Consumption
Oxygen consumption (VO2) is the rate at which tissues or the whole body use oxygen, measured by indirect calorimetry; key units are mL O2/kg/min and METs (1 MET = 3.5 mL O2/kg/min), with VO2max as the main fitness metric.
Oxygen–hemoglobin dissociation curve
Oxygen–hemoglobin dissociation curve (oxyhemoglobin dissociation curve, ODC): sigmoid plot of hemoglobin oxygen saturation versus oxygen partial pressure; P50 about 26 mmHg for adult blood, shifted right by low pH, high CO2, heat, and 2,3-DPG, left by fetal hemoglobin and carbon monoxide.
Oxytocin
Oxytocin, a cyclic nonapeptide hormone of the posterior pituitary, drives labor contractions and milk ejection; first synthesized by Vincent du Vigneaud (1953, Nobel 1955), it is a standard obstetric drug and a debated social-behavior research target.
Pacemaker failure
Pacemaker failure is the malfunction of an implanted cardiac pacemaker, its leads, or its programming so that it fails to keep an adequate heart rate.
Pacemaker neuron
A pacemaker neuron is a neuron that generates rhythmic bursts of action potentials independently of synaptic input, driving circadian rhythms in the suprachiasmatic nucleus and respiration in the preBötzinger complex.
Pacemaker syndrome
Pacemaker syndrome: iatrogenic symptoms from ventricular pacing causing AV dyssynchrony, first described 1969; incidence 2-80%; treated by reprogramming or dual-chamber upgrade.
Pain Threshold
Pain threshold: the minimum stimulus intensity perceived as painful (IASP definition); distinct from pain tolerance. Measured psychophysically via QST methods of limits or levels, with pressure, thermal, and electrical stimuli; reliability varies by modality.
Palate
The palate (palatum) is the roof of the mouth and floor of the nasal cavities, divided into bony hard palate and muscular soft palate (velum); key facts include trigeminal sensory innervation, greater palatine artery supply, and week 6 to 12 human palatogenesis.
Palatine tonsil
Palatine tonsil (faucial tonsil), paired oropharyngeal lymphoid tissue of Waldeyer ring between the palatoglossal and palatopharyngeal arches; M-cell antigen sampling, 10-30 crypts, five-artery supply, and Paradise tonsillectomy criteria.
Palinopsia
Palinopsia, or visual perseveration, is the abnormal persistence or recurrence of an image after its stimulus is gone. Distinct from normal afterimages, it divides into hallucinatory (lesions, seizures) and illusory (migraine, drugs) types.
Pallor mortis
Pallor mortis is the paleness of skin appearing 15-30 minutes after death, the earliest of the four classical postmortem signs with algor, rigor, and livor mortis; distinct from contact pallor, the pressure-induced absence of lividity.
Palmar arches
The palmar arches are two arterial loops in the palm that join the ulnar and radial arteries into one circuit, so either forearm artery can supply the whole hand.
Palmaris longus muscle
Palmaris longus, a slender superficial forearm flexor muscle (musculus palmaris longus) running from the medial humeral epicondyle to the palmar aponeurosis; absent in about 20% of people and widely used as a tendon graft donor.
Palpitations
Palpitations: awareness of an abnormal, rapid, or irregular heartbeat, felt as fluttering or pounding in the chest or neck. A symptom, not a diagnosis; causes include arrhythmias, anxiety, thyroid disease, and drugs; evaluated with 12-lead ECG and ambulatory monitoring.
Pancreatic islets
Pancreatic islets (islets of Langerhans) are endocrine cell clusters in the pancreas; beta cells make insulin. About one million per pancreas; FDA-approved donor-islet therapy (Lantidra) treats type 1 diabetes since 2023.
Pancreatic juice
Pancreatic juice: alkaline exocrine secretion of the pancreas (1–4 L/day) carrying about 20 digestive enzymes and bicarbonate to the duodenum; regulated by secretin and cholecystokinin; lipolytic action discovered by Claude Bernard in 1848; now used as a biomarker fluid for pancreatic cancer detection.
Pancreatic polypeptide
Pancreatic polypeptide (PP) is a 36-amino-acid peptide hormone secreted by pancreatic F cells that inhibits exocrine pancreatic secretion, regulates gastrointestinal function, and reduces food intake.
Pantothenate kinase-associated neurodegeneration
PKAN (pantothenate kinase-associated neurodegeneration, formerly Hallervorden-Spatz syndrome, NBIA1) is a rare autosomal recessive PANK2 disorder causing dystonia, brain iron accumulation, and the eye-of-the-tiger MRI sign.
Paolo Macchiarini
Paolo Macchiarini, Italian thoracic surgeon, performed the first synthetic stem-cell-seeded trachea transplants at Karolinska (2011–2014); patients died, he was found guilty of research misconduct, and in 2023 received a 2.5-year Swedish prison sentence.
Papillary intralymphatic angioendothelioma
Papillary intralymphatic angioendothelioma (PILA, Dabska tumor), a rare low-grade lymphatic vascular tumor of skin and subcutis in children and young adults, first described 1969, treated by wide excision, rarely metastasizing.
Papilledema
Papilledema is optic disc swelling caused by elevated intracranial pressure, usually bilateral. Most common cause is idiopathic intracranial hypertension; diagnosed with MRI/MRV, lumbar puncture, and OCT; treated with acetazolamide, weight loss, or shunting.
PARADIGM-HF trial
PARADIGM-HF was a randomized trial of 8,442 patients comparing sacubitril/valsartan with enalapril in chronic heart failure with reduced ejection fraction, stopped early in 2014 for a 20% reduction in cardiovascular death.
Paranasal sinuses
Paranasal sinuses: air-filled mucosa-lined cavities in the frontal, ethmoid, maxillary, and sphenoid bones communicating with the nasal cavity; function debated, distribution ecologically shaped, prone to sinusitis.