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Hydrogen sulfide
Hydrogen sulfide (H2S, sulfane hydrogen) is a colorless, rotten-egg-smelling toxic gas, the third gasotransmitter after NO and CO, produced enzymatically in mammals by CBS, CSE, and 3MST and studied for signaling and therapy.
Hydrogen therapy
Hydrogen therapy is a medical treatment administering molecular hydrogen by inhalation, hydrogen-rich water, or saline, aiming to reduce oxidative stress and inflammation in a range of diseases.
Hydrogen water
Hydrogen water (hydrogen-rich water) is water with dissolved molecular hydrogen gas, made by pressurized infusion, electrolysis, or magnesium tablets; FDA GRN 520 covers beverage use, and clinical evidence remains small-scale and mixed.
Hydrogen–deuterium exchange mass spectrometry
Hydrogen–deuterium exchange mass spectrometry (HDX-MS) measures the exchange of protein backbone amide hydrogens with deuterium from solvent, using the resulting mass shifts to map protein structure, dynamics, and interactions.
Hydrogen–deuterium exchange measurement
Hydrogen–deuterium exchange measurement (HDX) is a biophysical technique that monitors exchange of protein backbone amide hydrogens with solvent deuterium, most often by mass spectrometry, to characterize protein structure and dynamics.
Hydrogenase
Hydrogenase, also called H2ase, is a metalloenzyme catalyzing H2 ⇌ 2H+ + 2e−. Three classes exist, [NiFe], [FeFe], and [Fe], distinguished by active-site metals, catalytic bias, and oxygen tolerance.
Hydrogenated soy lecithin
Hydrogenated soy lecithin, or hydrogenated soy phosphatidylcholine (HSPC), is soybean lecithin with unsaturated fatty acids saturated by catalytic hydrogenation, giving higher oxidative stability; used in cosmetics, foods (GRN 534), and liposome drug carriers.
Hydrogenotrophic methanogenesis
Hydrogenotrophic methanogenesis is the methanogenic pathway in which archaea reduce carbon dioxide to methane using hydrogen or formate, the route most methanogens use in anoxic habitats.
Hydrolethalus
Hydrolethalus syndrome (HLS, OMIM 236680/614120), a lethal autosomal recessive Finnish-enriched ciliopathy from HYLS1 or KIF7 mutations, causing hydrocephalus, keyhole occipital defect, polydactyly, cleft palate, and heart defects.
Hydrolycus scomberoides
Hydrolycus scomberoides, the payara (basionym Hydrocyon scomberoides Cuvier 1819), is a fanged piscivorous characiform fish of the Amazon basin, family Cynodontidae, IUCN Least Concern, max 117 cm TL and 17.8 kg.
Hydrolysed proteins
Hydrolysed proteins (protein hydrolysates) are peptide and amino acid mixtures from hydrolysed animal or plant proteins, used as an EU low-risk pesticide active substance (insect attractant), as plant biostimulants, and in infant formula and sports nutrition.
Hydrolyzed pork cartilage
Hydrolyzed pork cartilage (hydrolyzed porcine trachea cartilage, Peptan II) is a type II collagen and chondroitin sulfate food ingredient, GRAS under FDA GRN 713 by Rousselot, used at 1.2–2 g per serving.
Hydrolyzed yeast
Hydrolyzed yeast, including enzymatically hydrolyzed and autolyzed Saccharomyces cerevisiae products such as DNF-10, is yeast broken into peptides and amino acids for flavoring, nutrition, feed, and cosmetics; FDA issued no-questions letter GRN 1033 in 2023.
Hydromantes
Hydromantes (web-toed salamanders), genus of lungless plethodontid salamanders; five species in northern California, closely allied to the eight European cave salamanders (Speleomantes); known for a ballistic tongue, webbed climbing feet, and Miocene fossils from Slovakia.
Hydromedusa
Hydromedusa: a genus of two South American snake-necked side-necked turtles (H. maximiliani, H. tectifera) in Chelidae; also hydromedusae, the medusa stage of hydrozoan cnidarians, over 3,600 planktonic species.
Hydromethylthionine
Hydromethylthionine (leucomethylene blue, LMTM, TRx0237) is the reduced form of methylene blue, an oral tau aggregation inhibitor developed by TauRx for Alzheimer's disease and frontotemporal dementia; investigational, MHRA review expected 2026.
Hydromorphone
Hydromorphone (Dilaudid), a semisynthetic Schedule II opioid agonist derived from morphine, two to eight times morphine's potency, no active metabolites, used for moderate to severe postoperative and cancer pain.
Hydronephrosis
Hydronephrosis is swelling of the kidney from urine build-up, dilating the renal pelvis and calices. Causes include stones, pregnancy, and prostate enlargement; it does not always mean obstruction, and treatment ranges from drainage to surgery.
Hydronephrosis with ureteropelvic junction obstruction
Hydronephrosis with ureteropelvic junction obstruction (ICD-11 GB56.0): urine outflow blocked where the renal pelvis joins the ureter, dilating the kidney. Incidence 1:1,500, male predominance, treated by pyeloplasty with about 95% success.
Hydrophilic Contact Lenses
Hydrophilic (soft) contact lenses: water-containing HEMA or silicone hydrogel polymer lenses worn on the eye; FDA Class II under 21 CFR 886.5925; hydrogels date to Wichterle's 1961 spin-cast patent, silicone hydrogels to 1999.
Hydrophilidae
Hydrophilidae (water scavenger beetles), family Latreille 1802 of Hydrophiloidea; over 3,000 species worldwide except Antarctica; six subfamilies per Short & Fikáček 2013; aquatic larvae predatory, adults herbivorous or scavenging.
Hydrophis
Hydrophis (Latreille 1801) is the largest sea snake genus, Elapidae, with 49 Indo-West Pacific viviparous species that radiated rapidly around 1 million years ago; includes H. platurus, H. cyanocinctus, H. schistosus.
Hydrophobic tagging
Hydrophobic tagging (HyT) is a targeted protein degradation strategy in which a hydrophobic tag makes a protein appear misfolded, recruiting chaperones like HSP70; unlike PROTACs, it needs no specific E3 ligase.
Hydrophyllaceae
Hydrophyllaceae R.Br., the waterleaf family, is a Boraginales family of about 12 genera and 250 species centered in western North America; APG IV merges it into Boraginaceae, while Luebert et al. 2016 recognize it.
Hydroponics
Hydroponics is a method of growing plants without soil, with roots in an aerated nutrient solution, first used on a large scale during World War II.
Hydrops
Hydrops (Wagler, 1830) is a South American genus of aquatic dipsadine water snakes with three species, H. caesurus, H. martii, and H. triangularis, in the tribe Hydropsini with Helicops and Pseudoeryx; oviparous fish-eaters.
Hydrops fetalis
Hydrops fetalis, including non-immune hydrops fetalis (NIHF), is abnormal fluid accumulation in two or more fetal compartments. Causes include aneuploidy, RASopathies, cardiac anomalies, and infection; survival often under 50%.
Hydrops of gallbladder
Hydrops of gallbladder (gallbladder mucocele, hydropic gallbladder), ICD-11 DC10.1: cystic duct obstruction, usually by an impacted gallstone, replacing bile with clear mucus-like "white bile"; treated by laparoscopic cholecystectomy.
Hydropsychidae
Hydropsychidae, the net-spinning caddisflies (Curtis, 1835), a Trichoptera family of about 1,500-1,982 species whose larvae spin silk filter nets in fixed stream retreats, serve as water-quality bioindicators and streambed ecosystem engineers.
Hydroptilidae
Hydroptilidae, the micro-caddisflies (family, Trichoptera), largest caddisfly family with over 2,600 species in six subfamilies and 76 genera; tiny adults (forewing 2–5 mm) whose larvae build purse cases only in the final instar.