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Splenic injury
Splenic injury: trauma to the spleen, the most commonly injured organ in blunt abdominal trauma. Also called splenic trauma; treated by nonoperative management, embolization, or splenectomy, with NOM failure under 10% overall.
Splenic lymph nodes
Splenic lymph nodes (nodi splenici) lie at the splenic hilum, drain the spleen, pancreas body/tail, and stomach, and form gastric cancer station 10; key regional nodes in pancreatic and gastric cancer surgery.
Splenic vein
Splenic vein: large abdominal vein formed at the splenic hilum, draining spleen, pancreas, and stomach; joins the superior mesenteric vein behind the pancreatic neck to form the portal vein; key diseases are splenic vein thrombosis and left-sided portal hypertension.
Splenomegaly
Splenomegaly, an enlarged spleen (over 12 cm length or 400 g), arises from portal hypertension, infections like EBV and malaria, infiltration, or hematopoiesis; massive splenomegaly exceeds 20 cm or 1000 g and risks rupture.
Splenosis
Splenosis, also called splenic autotransplantation, is benign ectopic splenic tissue implanted after splenic trauma or splenectomy; diagnosed by Tc-99m heat-damaged RBC scintigraphy, it mimics malignancy and occurs in up to 65% of splenic ruptures.
Split S2
Split S2: auscultated separation of the second heart sound into aortic (A2) and pulmonic (P2) components. Normally split on inspiration, single on expiration; fixed split suggests atrial septal defect, reverse split LBBB or aortic stenosis.
Split-brain
Split-brain: condition after corpus callosotomy, severing the corpus callosum to treat drug-resistant epilepsy. Studied by Sperry, Bogen, and Gazzaniga from the 1960s; classic left-hand/left-visual-field findings; debate over split versus unified consciousness.
Sporadic adult-onset ataxia of unknown etiology
Sporadic adult-onset ataxia of unknown etiology (SAOA, idiopathic late-onset cerebellar ataxia) is a rare non-hereditary degenerative ataxia beginning around age 50, with progressive gait ataxia, dysmetria, and dysarthria, differentiated from MSA-C and increasingly reclassified genetically (FGF14, RFC1).
Sporadic Creutzfeldt-Jakob disease
Sporadic Creutzfeldt-Jakob disease (sCJD, sporadic CJD) is the most common human prion disease, about 85-90% of CJD cases, a rapidly fatal dementia with myoclonus, median onset age 65, incidence roughly 0.5-2 per million per year, no treatment.
Sporadic lymphangioleiomyomatosis
Sporadic lymphangioleiomyomatosis (S-LAM) is a rare cystic lung neoplasm of women without tuberous sclerosis, caused by somatic TSC2/TSC1 mutations activating mTOR; treated with sirolimus.
Squamous cell carcinoma of conjunctiva
Squamous cell carcinoma of conjunctiva (CSCC, ICD-11 2D00.2) is the invasive malignant end of ocular surface squamous neoplasia, driven by UV exposure, HIV immunosuppression, and possibly HPV, commonest in Africa, treated by excision, topical chemotherapy, or radiotherapy.
Squatting position
Squatting position: a resting, working, toileting, and exercise posture with deeply flexed knees and hips; used by at least a fourth of humanity, defined by knee flexion angles, and reviewed for knee safety.
Squid giant synapse
Squid giant synapse: large glutamatergic synapse in the squid stellate ganglion's giant fiber system (escape circuit), classical preparation that established calcium-triggered, quantal, nanodomain-coupled neurotransmitter release.
Standing Position
Standing position: the upright, orthostatic human posture supported only by the feet (MeSH D000078783, 2019). Covers its anatomy, evolutionary origin, and health effects of prolonged occupational standing.
Stapes
Stapes: smallest bone of the human body, the third middle-ear ossicle, footplate seated in the oval window; discovered by Ingrassia in 1546 and central to otosclerosis surgery.
Staphylococcus capitis
Staphylococcus capitis, a coagulase-negative staphylococcus and skin commensal first described in 1975, causes neonatal late-onset sepsis in NICUs; its multidrug-resistant NRCS-A clone, first reported in France in 2012, has spread worldwide.
Stargardt disease
Stargardt disease (STGD1, fundus flavimaculatus), also called Stargardt macular degeneration or juvenile macular degeneration, is an inherited ABCA4-related retinal dystrophy causing childhood-onset central vision loss from lipofuscin buildup in the macula, with no approved treatment.
Starling equation
Starling equation: Jv = LpS[(Pc−Pi) − σ(πc−πi)], Ernest Starling's 1896 law of capillary fluid exchange balancing hydrostatic and oncotic pressures; revised with the glycocalyx model and lymphatic return.
Startle Reflex
The startle reflex is an automatic whole-body reaction to a sudden intense stimulus, causing muscle contraction, limb flexion, eye blinking, and autonomic changes like accelerated heart rate.
Steatopygia
Steatopygia: pronounced accumulation of fat on the buttocks and thighs, described among Khoisan peoples, depicted in Paleolithic and Jomon figurines, and causing imaging artifacts in obese patients.
Stellate neuron
Stellate neuron (Cell Ontology CL:0000122, stellate cell): a neuron with star-shaped radiating dendrites. Distinct populations exist in cerebellar molecular layer (GABAergic), neocortical layer 4 (excitatory spiny stellate), and entorhinal cortex layer II (grid-cell related).
STEMI equivalents and occlusion patterns
STEMI equivalents are ECG patterns indicating acute coronary artery occlusion when standard ST-elevation criteria are absent, including de Winter pattern, posterior MI, Wellens syndrome, and modified Sgarbossa-positive LBBB; missing them delays reperfusion.
Stent-electrode recording array
Stent-electrode recording array (Stentrode, Synchron): a nitinol stent with 16 platinum electrodes implanted via the jugular vein into the superior sagittal sinus to record vascular ECoG for brain-computer interfaces in paralysis; first-in-human SWITCH trial showed no serious adverse events over 12 months.
STEP trial (NCT03015311)
STEP (NCT03015311), Strategy of Blood Pressure Intervention in the Elderly Hypertensive Patients: Chinese randomized trial of 8,511 patients aged 60-80 testing intensive systolic target 110-<130 mm Hg versus 130-<150 mm Hg; intensive treatment cut cardiovascular events (HR 0.74; 6-year HR 0.82).
Stereotactic surgery
Stereotactic surgery: 3D coordinate-guided minimally invasive brain surgery, also called stereotaxis. Frame-based or frameless targeting for biopsy, functional neurosurgery, and radiosurgery; pioneered by Horsley-Clarke (1908) and Spiegel-Wycis (1947).
Sternocleidomastoid muscle
Sternocleidomastoid (SCM), sternomastoid: paired superficial neck muscle from sternum and clavicle to mastoid process; rotates and flexes the head, innervated by CN XI, divides neck into triangles.
Sternum
Sternum (breastbone): flat midline chest bone of manubrium, body, and xiphoid process; protects the mediastinum, anchors ribs 1-7 via costal cartilage, and marks the sternal angle at the 2nd rib.
Stewart–Treves syndrome
Stewart–Treves syndrome is angiosarcoma arising in chronically lymphedematous tissue, classically the arm after mastectomy; first described 1948, it appears about 15 years after lymphedema with poor survival.
Stimulus (physiology)
Stimulus (physiology): a detectable environmental or internal change (light, sound, chemical, temperature, pressure) that activates sensory receptors. Key facts: transduction into graded receptor potentials, coding of modality, location, intensity, duration, and receptor adaptation.
Stomach
Stomach: hollow muscular digestive organ mixing food with acid and enzymes and releasing chyme into the duodenum; also an endocrine and defensive organ. Varies from simple acid sac in humans to fermenting chambers in ruminants; H. pylori causes most gastric cancer.