2,701 articles
Serratus anterior muscle
Serratus anterior (musculus serratus anterior), the fan-shaped "boxer's muscle" on the lateral thoracic wall; originates from ribs 1-8/9, inserts on the scapula, innervated by the long thoracic nerve (C5-C7), protracts and rotates the scapula; paralysis causes winged scapula.
Sertoli cell
Sertoli cell (nurse cell of the testis): somatic support cell of seminiferous tubules discovered by Enrico Sertoli in 1865; nourishes germ cells, forms the blood-testis barrier, secretes AMH, androgen-binding protein, and GDNF, and is the testis's most age-sensitive cell type.
Sesamoid bone
Sesamoid bone: a small bone embedded in a tendon or muscle near a joint, acting as a pulley; includes the patella and hallucal sesamoids; variable prevalence, prone to sesamoiditis and avascular necrosis.
Sex differences in human physiology
Sex differences in human physiology: biological differences between males and females in chromosomes, hormones, anatomy, brain, and drug response; most traits overlap, NIH SABV policy (2016) requires studying both sexes.
Sex differences in humans
Sex differences in humans: average male-female differences in biology, psychology, and behavior. Meta-analyses show mostly overlapping distributions (average d < 0.22), larger gaps in mental rotation, and NIH/FDA rules requiring sex-specific clinical research.
Sexuality after spinal cord injury
Sexuality after spinal cord injury (SCI): how lesion level and completeness change arousal, erection, ejaculation, lubrication, orgasm, and fertility, plus assessment tools (IIEF, FSFI) and rehabilitation approaches.
SF268
SF268 (SF-268, CVCL_1689) is a human glioblastoma/astrocytoma cell line from the right parietal lobe, established in 1987, an NCI-60 CNS drug-screen line with homozygous TP53 p.Arg273His and a flagged Y-chromosome identity issue.
SF295
SF295 (SF-295, CVCL_1690) is a human glioblastoma cell line established at UCSF from a 67-year-old woman's left temporal lobe tumor; an NCI-60 CNS panel line with PTEN, TP53, and TERT promoter mutations.
Shaken baby syndrome
Shaken baby syndrome (SBS), renamed abusive head trauma (AHT) by the AAP in 2009, is a diagnosis attributing the infant triad of subdural hemorrhage, retinal hemorrhage, and encephalopathy to violent shaking; incidence 25–35 per 100,000 under age 1, fatal in about one quarter of cases, and scientifically contested.
Sharad Panday
Sharad Panday (1934–2004), Indian cardiothoracic surgeon at KEM Hospital, Mumbai; with P.K. Sen performed India's first heart transplant (16 February 1968, sixth worldwide); devised the Panday shunt for mitral valve replacement; father of actor Chunky Panday.
Shepard tone
Shepard tone: auditory illusion by Roger Shepard (1964) of octave-spaced components under a fixed bell-shaped envelope, heard as endlessly rising or falling pitch; basis of the Risset glissando, tritone paradox, and film and game sound design.
Shock (circulatory)
Circulatory shock: life-threatening acute circulatory failure with inadequate cellular oxygen utilization and dysoxia, not synonymous with hypotension. Four types (hypovolemic, cardiogenic, obstructive, distributive); septic shock most common; ICU mortality about 38%.
Shoulder
The shoulder is the body region connecting the arm to the trunk, built from three bones and four joints, the most mobile joint system in the body.
Shoulder girdle
Shoulder girdle (pectoral girdle): the clavicle and scapula linking the upper limb to the axial skeleton, with three joints and two gliding zones, a 2:1 scapulohumeral rhythm, and a defined trauma and clinical-testing literature.
Shoulder joint
Shoulder joint (glenohumeral joint): the ball-and-socket articulation between the humeral head and the scapula's glenoid cavity, the body's most mobile joint, stabilized by the glenohumeral ligaments, labrum, capsule, and rotator cuff.
Sigmoid colon
Sigmoid colon: S-shaped terminal segment of the large intestine, 25-40 cm, joining descending colon to rectum at S3; intraperitoneal via sigmoid mesocolon, supplied by IMA sigmoidal branches, prone to diverticulitis.
Simple columnar epithelium
Simple columnar epithelium (Epithelium simplex columnare) is a single layer of tall cells with basal oval nuclei, ciliated in the female genital tract and nonciliated with microvilli in the gastrointestinal and biliary tracts, serving secretion and absorption.
Single transverse palmar crease
Single transverse palmar crease, also called single palmar crease or formerly simian crease, is a fusion of the two transverse palm creases into one line, seen in about 1 in 30 people, twice as often in males, and associated with Down syndrome and other conditions.
Single-ventricle physiology
Single-ventricle physiology: one functional ventricle pumps to both lungs and body with mixing of blood. Treated by staged Norwood, Glenn, and Fontan palliation; Fontan circulation causes venous hypertension, liver disease, and transplant-dependent failure.
Sinoatrial node
The sinoatrial node, also called the SA node, is a cluster of cells in the right atrium that generates the heartbeat's electrical rhythm as the heart's natural pacemaker.
Sinus (anatomy)
In anatomy, a sinus is an air-filled cavity within a bone or tissue, most often one of the four paired paranasal sinuses around the nose, which all drain into it.
Sinus node dysfunction
Sinus node dysfunction, formerly sick sinus syndrome, is impaired sinoatrial node impulse generation or conduction causing bradycardia, pauses, or chronotropic incompetence; treated with dual-chamber pacemakers per DANPACE and MOST trial evidence.
Sinus rhythm
Sinus rhythm is the normal heart rhythm initiated by the sinoatrial node, the heart's natural pacemaker, at a rate of 60 to 100 beats per minute.
Sinus tachycardia
Sinus tachycardia: a regular heart rhythm from the sinoatrial node at over 100 bpm, usually an appropriate response to exercise, fever, or stress; also covers inappropriate sinus tachycardia (IST), a diagnosis of exclusion defined by resting HR >100 bpm.
Sitting
Sitting, the supported resting posture of humans, spans chair history from Song dynasty China to modern ergonomics; prolonged sitting raises spinal load, reduces vascular function, and is best countered by posture variation rather than standing alone.
Sixth nerve palsy
Sixth nerve palsy (abducens palsy, CN VI palsy): paralysis of the sixth cranial nerve causing esotropia and horizontal double vision worse at distance and toward the affected side; usually microvascular, about 80% recover.
Skeletal muscle
Skeletal muscle: voluntary striated muscle tissue, over 600 muscles of multinucleated fibers; sarcomeres with actin-myosin sliding filaments, type I/II fiber types, myokine endocrine role, sarcopenia and muscular dystrophies.
Skeletal muscle fiber
Skeletal muscle fiber (myofiber, muscle fiber): a large multinucleate muscle cell formed by myoblast fusion, containing myofibrils and sarcolemma. Types I, IIA, IIX (formerly IIB) classified by myosin heavy chain or mATPase; highly plastic, sex- and age-dependent.
Skene's gland
Skene's glands (paraurethral glands, female prostate) are two glands beside the female urethra that secrete lubricating, antimicrobial fluid, may source female ejaculation, and can develop skenitis, cysts, abscesses, or rare PSA-expressing cancers.
Skull
Skull (cranium): the 22-bone structure of the head, divided into neurocranium and viscerocranium, joined by sutures; protects the brain, forms the face, and anchors clinical topics like fracture, craniosynostosis, and skull lesions.