All articles starting with R

Retrograde and prograde motion

Retrograde and prograde motion, also called direct motion, describe the two directions of orbital or apparent motion: prograde matches the central body's rotation, retrograde opposes it.

Retrograde ejaculation

Retrograde ejaculation (dry climax): semen travels backward into the bladder during orgasm because the bladder neck fails to close. Causes include diabetes, TURP, RPLND, and alpha-blockers; treated with pseudoephedrine, imipramine, or sperm retrieval from urine.

Retrograde intrarenal surgery

Retrograde intrarenal surgery (RIRS) is a minimally invasive urological procedure in which a flexible ureteroscope passed through the urethra and bladder reaches the kidney to treat stones with laser.

Oct 15, 2026

Retrograde metamorphism

Retrograde metamorphism is the stage of a metamorphic rock's history in which pressure and temperature decrease during exhumation toward the surface, partially overprinting minerals formed at peak conditions.

Oct 20, 2026

Retrograde Obturation

Retrograde obturation is the placement of a filling into a prepared cavity at a tooth's root end during apical surgery, sealing the canal system when root canal treatment has failed.

Retrograde perfusion

Retrograde perfusion is a cardiac surgery technique that delivers cardioplegia backward through the coronary sinus to arrest and protect the heart during valve and bypass operations.

Oct 15, 2026

Retrograde rotation

Retrograde rotation is the rotation of a body opposite to its orbital direction, seen in Venus, which spins backward every 243.690 days, and Uranus, tilted 97.77 degrees.

Retrograde tracing

Retrograde tracing is a neuroanatomical method that identifies which neurons send their axons to a chosen brain region by transporting a tracer back to the cell bodies.

Retrograde urethrogram

A retrograde urethrogram (RUG) is a fluoroscopic exam in which iodinated contrast is injected backward into the urethra, the gold standard for diagnosing and staging urethral strictures.

Retrogressive thaw slump

A retrogressive thaw slump, also known as a megaslump, is a slope failure in ice-rich permafrost in which a steep headwall retreats upslope as the ground thaws.

Retrolisthesis

Retrolisthesis: posterior slippage of a vertebra on the one below, opposite of anterolisthesis. Usually 2-3 mm, Grade I, common at L3/4, prevalence about 17%, often a compensatory sagittal-balance mechanism.

Sep 19, 2026

Retromigration

Retromigration is the stage name of Malik Kassim, a German-born, Amsterdam-based house producer and DJ with Nigerian and Ghanaian roots, known for a jazz-inflected take on house music.

Retronym

Retronym: a new word coined for an older thing after a newer version appears, e.g. acoustic guitar, analog watch, snail mail. Coined by Frank Mankiewicz (1980) and popularized by William Safire; paired term: neonym.

Retroperitoneal arteriovenous malformation

Retroperitoneal arteriovenous malformation (retroperitoneal AVM): a rare fast-flow vascular malformation with a dysplastic artery-vein nidus behind the abdominal cavity, causing heart failure, pulmonary hypertension, or bleeding; treated mainly by transcatheter embolization.

Retroperitoneal fibrosis

Retroperitoneal fibrosis (Ormond's disease) is a rare fibroinflammatory disorder in which fibrous tissue forms around the abdominal aorta and encases the ureters, causing obstructive uropathy; most cases are idiopathic, many linked to IgG4-related disease, and corticosteroids are first-line treatment.

Retroperitoneal lymph node dissection

Retroperitoneal lymph node dissection (RPLND) is a urologic operation that removes lymph nodes behind the abdominal organs around the aorta, used to stage and often cure testicular cancer.

Retroperitoneal space

Retroperitoneal space (retroperitoneum): abdominal space behind the parietal peritoneum, from diaphragm to pelvis, holding kidneys, aorta, IVC, pancreas, duodenum, and colon, divided into three fascial compartments and interfascial planes.

Retropharyngeal or parapharyngeal abscess

Retropharyngeal and parapharyngeal abscesses are deep neck space pus collections, usually from upper respiratory infection or foreign body trauma, causing odynophagia, neck pain, and fever; treated with antibiotics and drainage.

Retrophyllum

Retrophyllum is a genus of six (or five) dioecious podocarp conifers with twisted, comb-like flattened leaves and red drupe-like seed cones, disjunctly distributed in South America and Australasia, with fossils from the Late Cretaceous to Miocene.

Retroreflector

A retroreflector, also known as a cataphote, is a device or surface that sends incoming light back toward its source, making road signs glow at night and enabling laser ranging to the Moon.

Oct 15, 2026

Retroreflector free-space optical communication

Retroreflector free-space optical communication uses a modulating retroreflector that returns laser light with data, so only the interrogator end needs a laser and pointing system.

Retrospect (Mya album)

Retrospect is Mýa's tenth (some sources say ninth) studio album, released May 15, 2026 on her label Planet 9 after eight years. A 16-track, sample-free throwback to 1970s and 1980s funk and soul, produced with MyGuyMars, featuring D-Nice, Snoop Dogg, Too $hort, and others.

Retrospective cohort study

A retrospective cohort study, also called a historical cohort study, is an observational study that uses existing records to identify past exposures and trace outcomes forward to the present.

Retrospective think-aloud

Retrospective think-aloud, also called retrospective protocol, is a verbal protocol method in which a participant works silently, then verbalizes thoughts while reviewing a replay of the session.

Retrosynthetic analysis

Retrosynthetic analysis is a planning method in organic chemistry that works backward from a target molecule to simpler precursors, formalized by E. J. Corey in 1967.

Retrotransposon

Retrotransposon (class I transposable element): a DNA element that copies itself via an RNA intermediate and reverse transcriptase, inserting new copies genome-wide. Includes LTR retrotransposons and LINEs/SINEs; L1 and Alu make up about a third of the human genome.

Retrotransposon hot spot protein,C-terminal

Retrotransposon hot spot protein,C-terminal (IPR046836) is the highly variable C-terminal domain of RHS proteins: a toxin module in bacteria and a nuclear protein region in Trypanosoma, diversified by recombination.

Retroverted uterus

Retroverted uterus (tilted or tipped uterus): a uterus tilted backward toward the sacrum instead of forward, a normal variant in roughly 16–25% of women, usually asymptomatic, occasionally linked to dyspareunia, prolapse, and rare pregnancy incarceration.

Retroviral integration

Retroviral integration: insertion of viral DNA into host DNA by integrase, forming a provirus. HIV-1 uses LEDGF/p75 and nuclear pores; MLV uses BET proteins; site selection is nonrandom and clinically consequential.