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Synaptotagmin
Synaptotagmin (SYT): a family of 17 mammalian vesicle membrane proteins with tandem C2 domains that act as Ca2+ sensors for exocytosis; Syt1/2/9 trigger fast synchronous neurotransmitter release, Syt7 asynchronous release and facilitation.
Synaptotropic hypothesis
Synaptotropic hypothesis: Vaughn's 1989 proposal that synaptic inputs direct dendritic and axonal arbor growth by selectively stabilizing filopodia on which synapses form; tested in Xenopus and zebrafish optic tectum.
Synovial bursa
Synovial bursa (pl. bursae): thin synovial membrane-lined, fluid-filled sacs, about 160 in the adult body, mostly near large joints, that reduce friction between bone, tendon, muscle, and skin; distinct from adventitious bursae.
Synovial fluid
Synovial fluid is the viscous fluid confined within synovial joints, where it lubricates articular cartilage and diffuses nutrients to cartilage, the meniscus, and the labrum, enabling friction coefficients as low as 0.001.
Synovial joint
Synovial joint (diarthrosis): freely movable joint with a fluid-filled joint cavity, articular capsule, synovial membrane, and hyaline cartilage; includes hinge, saddle, planar, pivot, condyloid, and ball-and-socket types such as the knee and shoulder.
Syringe pump
A syringe pump is a motor-driven device that pushes a syringe plunger to deliver fluid at a precisely controlled flow rate, used clinically for drug infusion and in laboratories.
Syringomyelia or syringobulbia
Syringomyelia or syringobulbia (ICD-11 8D66) is a spinal cord or brainstem fluid-filled cavity (syrinx), usually from Chiari I malformation obstructing CSF flow; diagnosed by MRI, treated by decompression or shunting.
Systole
Systole (Greek systolē, contraction): the cardiac cycle phase of heart-muscle contraction and blood ejection, from AV valve closure to semilunar valve closure; includes isovolumetric contraction and ejection; opposite of diastole.
Systolic Blood Pressure Intervention Trial
SPRINT (Systolic Blood Pressure Intervention Trial), NIH-funded RCT of 9361 high-risk adults without diabetes or stroke, showed systolic BP target <120 mm Hg cut cardiovascular events and death versus <140 mm Hg, with more hypotension, syncope, and kidney injury, reshaping 2017 and 2025 ACC/AHA guidelines.
T cell
A T cell, or T lymphocyte, is a white blood cell of the adaptive immune system that develops in the thymus and recognizes antigens through its T cell receptor.
T-FAME-HF trial
T-FAME-HF (NCT04991857) is a University of Hong Kong randomized trial of a 16-week technology-based family-centered empowerment program versus HF education in 270 admitted heart failure patients; completed February 2026, no results posted.
Tachyarrhythmias in pregnancy
Tachyarrhythmias in pregnancy are abnormally rapid heart rhythms, including supraventricular tachycardia, atrial fibrillation or flutter, and ventricular tachycardia, that occur during pregnancy or early postpartum, affecting 0.03% to 0.5% of pregnancies.
Tachycardia-induced cardiomyopathy
Tachycardia-induced cardiomyopathy (tachycardiomyopathy, TIC) is reversible heart failure caused by chronic or recurrent rapid heart rhythms such as atrial fibrillation; systolic function recovers after rate or rhythm control, but recurrence risks rapid decline and sudden death.
Tachykinin family
Tachykinin family, or neurokinins: peptide neurotransmitters sharing the C-terminal Phe-X-Gly-Leu-Met-NH2 motif, including substance P, neurokinin A, and neurokinin B, acting through NK1, NK2, and NK3 GPCRs across vertebrates and invertebrates.
Talus bone
Talus bone (astragalus): the ankle tarsal bone linking tibia and fibula to the foot. No muscle attachments, tenuous blood supply; fractures carry 25-29% avascular necrosis and 43-64% osteoarthritis rates.
Tanner scale
Tanner scale, or Sexual Maturity Rating, is a five-stage system by James Tanner rating breast, genital, and pubic hair development from prepubertal (1) to adult (5), used clinically for puberty timing.
TAPCAP trial
TAPCAP (Application of Transesophageal Echocardiography in Pre-hospital Cardiac Arrest Patients, NCT06672315) is an ongoing cluster-randomized Taiwan trial led by Jen-Tang Sun testing TEE-guided mechanical chest compression positioning versus standard landmark placement in adults with non-traumatic out-of-hospital cardiac arrest, started December 2024, completing August 2027.
Tapetum lucidum
Tapetum lucidum: reflective layer behind the retina of many vertebrates and some invertebrates that boosts dim-light vision and causes eye-shine; types include retinal, guanine, cellulosum, and fibrosum tapeta; absent in primates, birds, and pigs.
Targeted temperature management
Targeted temperature management (TTM), formerly therapeutic hypothermia, is protocolized temperature control after cardiac arrest. Current guidance targets 32–37.5 °C for at least 36 hours; TTM2 (2021) found no benefit of cooling to 33 °C over fever prevention.
Tarlov cyst
Tarlov cyst (perineural cyst): CSF-filled sac around sacral spinal nerve roots containing nerve fibers, first described by Isadore Tarlov in 1938; prevalence 1.5–13.2%, symptomatic in 10–20%, treated by surgery or fibrin-sealant aspiration.
Tarsal tunnel syndrome
Tarsal tunnel syndrome, also called posterior tibial neuralgia or tibial nerve entrapment, is compression of the posterior tibial nerve in the tarsal tunnel at the ankle, defined by Keck and Lam in 1962, causing foot pain and numbness, treated conservatively or by flexor retinaculum release.
Tarsus (skeleton)
Tarsus (skeleton): the seven tarsal bones of the human foot (calcaneus, talus, cuboid, navicular, three cuneiforms), their joints, gait biomechanics, historical names, and accessory ossicles.
Taste
Taste (gustation) is the chemical sense detecting sweet, sour, salty, bitter, and umami via taste bud receptor cells; also covers transduction, TAS2R38 genetics, PROP/PTC heritability, oleogustus, taste disorders, and penguin taste loss.
Taste bud
Taste bud: cluster of 50-100 neuroepithelial cells in tongue, palate, and throat papillae that transduces sweet, sour, salty, bitter, and umami stimuli; 2,000-5,000 per human oral cavity, continually renewed.
Taste receptor
Taste receptor: receptor proteins on taste receptor cells detecting bitter, sweet, umami, salty, and sour tastants. T1R and T2R GPCR families; TAS1R2+TAS1R3 sweet receptor; TAS2R14 structure solved 2024; also expressed in gut, lungs, heart, brain.
Tay–Sachs disease
Tay–Sachs disease, a fatal autosomal recessive GM2-gangliosidosis caused by HEXA gene variants on chromosome 15 lacking hexosaminidase-A; infantile form kills by age five, carriers common in Ashkenazi Jews, no cure, gene therapy in trials.
TBIDFTECWCTC trial
TBIDFTECWCTC is a registered clinical trial (NCT07451678) testing eyelid cleansing with topical chlorhexidine wipes twice daily for four weeks against Demodex folliculorum blepharitis, assessing collarettes, erythema, and dry eye.
Tbx18 transduction
Tbx18 transduction delivers the T-box transcription factor 18 gene or mRNA to heart muscle to create a biological pacemaker, converting cardiomyocytes into sinoatrial-node-like cells; large-animal results exist but a 2026 AAV study found no genuine TBX18 pacemaker activity.
Tears
Tears (lacrimal fluid) are secretions of the lacrimal, Meibomian, and conjunctival glands forming the tear film that lubricates, protects, and optically smooths the eye; types are basal, reflex, and emotional, and deficiency causes dry eye disease.
Teething
Teething is the normal eruption of deciduous (baby) teeth through the gums, starting around 4 to 10 months and complete by about 2.5 to 3 years. Evidence links it only to mild local symptoms; fever and diarrhoea suggest other illness. Covers biology, timeline, safe care, and regulation.