All articles starting with H
20,046 articles
Hypophosphorous acid
Hypophosphorous acid, systematically named phosphinic acid (H3PO2), is a monoprotic phosphorus oxyacid and strong reducing agent, used mainly as a 50% aqueous solution for electroless nickel plating and hypophosphite production.
Hypophthalmichthys nobilis
Hypophthalmichthys nobilis, the bighead carp, a large East Asian filter-feeding cyprinid farmed worldwide and invasive in the Mississippi River basin; introduced to the US in 1973, listed injurious in 2011.
Hypophysectomy
Hypophysectomy is the surgical removal of the pituitary gland, evolved from open craniotomy to endoscopic endonasal surgery, most often to treat pituitary adenomas; the first transsphenoidal resection was by Hermann Schloffer in 1907.
Hypopigmentation-punctate palmoplantar keratoderma syndrome
Hypopigmentation-punctate palmoplantar keratoderma syndrome, or Cole disease (OMIM 615522), is a rare autosomal dominant ENPP1-related skin disorder with punctate palmoplantar keratoderma, extremity hypopigmentation, and occasional ectopic calcification.
Hypopituitarism
Hypopituitarism: deficiency of one or more pituitary hormones, also called Simmonds' disease; causes include pituitary adenoma, surgery, radiation, and Sheehan's syndrome; treated with hormone replacement.
Hypoplasia of pancreas
Hypoplasia of pancreas (ICD-11 LB21.5), also called partial pancreatic agenesis, is congenital underdevelopment of the pancreas, usually of the dorsal anlage. It causes exocrine insufficiency and neonatal diabetes, most often from GATA6, PDX1, PTF1A, or HNF1B mutations.
Hypoplasminogenemia
Hypoplasminogenemia (plasminogen deficiency type 1) is a rare autosomal recessive PLG disorder causing ligneous fibrin-rich mucosal lesions, chiefly ligneous conjunctivitis; treated with plasma-derived plasminogen concentrate Ryplazim, FDA approved 2021.
Hypoplastic left heart syndrome
Hypoplastic left heart syndrome (HLHS) is a critical congenital heart defect with underdeveloped left ventricle, mitral and aortic valves, and ascending aorta; treated with Norwood, Glenn, and Fontan staged surgery.
Hypoplastic model
A hypoplastic model is a constitutive equation of geotechnical engineering that predicts the nonlinear, path-dependent stress–strain behavior of granular soils from a single rate equation, without a yield surface.
Hypoplastic right heart syndrome
Hypoplastic right heart syndrome (HRHS) is a rare cyanotic congenital defect with underdeveloped tricuspid valve, right ventricle, pulmonary valve, and pulmonary artery, treated with prostaglandin, shunts, and Glenn/Fontan palliation.
Hypopnea
Hypopnea: a sleep-related breathing event of reduced (not absent) airflow lasting at least 10 seconds, scored by AASM rules (30% airflow drop with 3% desaturation or arousal) and counted in the apnea-hypopnea index for obstructive sleep apnea diagnosis.
Hypopyon
Hypopyon (anterior chamber pus level, ICD-11 MC20.2) is a gravity-dependent layer of white blood cells in the eye's anterior chamber, signaling severe intraocular inflammation from causes such as HLA-B27 uveitis, Behçet disease, endophthalmitis, and keratitis.
Hyporheic zone
The hyporheic zone is the porous region of a stream bed and banks where surface water and shallow groundwater mix, a subsurface environment distinct from both.
Hyposmia-nasal and ocular hypoplasia-hypogonadotropic hypogonadism syndrome
Hyposmia-nasal and ocular hypoplasia-hypogonadotropic hypogonadism syndrome, also called Bosma arhinia microphthalmia syndrome (BAMS, OMIM 603457), is an extremely rare autosomal dominant disorder caused by SMCHD1 missense mutations, combining arhinia, microphthalmia, hyposmia, and hypogonadotropic hypogonadism with normal intelligence.
Hypospadias
Hypospadias: congenital male urethral malformation with a ventrally displaced urethral opening, also called distal, penile, or penoscrotal hypospadias; repaired surgically, usually at 6-18 months, with fistula and stenosis as main complications.
Hypospadias repair
Hypospadias repair is the pediatric urological operation that moves the urethral opening to the tip of the penis and straightens curvature, usually done at 6 to 18 months of age.
Hypospadias, penile
Hypospadias, penile (ICD-11 LB53.1): hypospadias with the urethral meatus on the penile shaft, the middle severity class; occurs in 1 of 150-300 male births, repaired surgically at 6-18 months.
Hypospadias, penoscrotal
Penoscrotal hypospadias (ICD-11 LB53.2) is a severe proximal hypospadias with the urethral meatus at the penoscrotal junction, usually with ventral curvature, requiring staged repair in 20-25% of hypospadias cases.
Hypostasis (philosophy and religion)
Hypostasis, Greek for "that which is placed under," is a term of philosophy and Christian theology meaning a distinct subsisting reality within the one divine essence.
Hypostatic union
The hypostatic union, or unio hypostatica, is the Christian doctrine that Jesus Christ is one person with both divine and human natures, defined at Chalcedon in 451.
Hypostomus plecostomus
Hypostomus plecostomus, also known as the common pleco, is an armored suckermouth catfish native to the Guianas in northern South America, a popular algae-eating aquarium fish.
Hypotelorism
Hypotelorism (hipotelorismo) is an abnormally decreased distance between the eyes, classified as ICD-11 LB71.0. It signals midline defects, chiefly holoprosencephaly and trigonocephaly, and is linked to trisomy 13 and Sonic hedgehog pathway alterations.
Hypotension
Hypotension is abnormally low blood pressure, generally below 90/60 mm Hg in adults. Key forms include orthostatic, postprandial, and neurally mediated hypotension and shock; treatment targets symptoms, with midodrine and droxidopa FDA-approved for orthostatic hypotension.
Hypotensive peristalsis
Hypotensive peristalsis (ICD-11 DA21.21), also called ineffective esophageal motility, is abnormally weak (<30 mmHg) esophageal peristaltic contractions seen in GERD, scleroderma, and lung disease.
Hypotenuse
The hypotenuse is the side of a right triangle opposite the right angle, and the longest side, given by the Pythagorean theorem and central to sine and cosine.
Hypothalamic gonadotropin-releasing hormone neuron
Hypothalamic GnRH neuron, also called GnRH-1 neuron, a neuroendocrine cell born in the nasal placode that migrates into the forebrain and secretes pulsatile GnRH controlling LH/FSH release; its failure causes Kallmann syndrome and congenital hypogonadotropic hypogonadism.
Hypothalamic–pituitary–adrenal axis
Hypothalamic–pituitary–adrenal (HPA) axis: neuroendocrine system linking hypothalamus, anterior pituitary, and adrenal cortex. CRH/AVP drive ACTH and cortisol; glucocorticoid negative feedback, circadian and hourly ultradian rhythms, stress response, and suppression by chronic glucocorticoids.
Hypothalamic–pituitary–gonadal axis
Hypothalamic–pituitary–gonadal (HPG) axis, also called the reproductive endocrine axis: GnRH pulses drive LH/FSH, which drive gonadal steroids with feedback; active in fetal life and mini-puberty, quiescent in childhood, reactivated at puberty.
Hypothalamus
Hypothalamus: small ventral brain region below the thalamus, about 2% of brain volume, controlling the pituitary via releasing hormones (TRH, GnRH, CRH, dopamine) and homeostasis, appetite, temperature, and circadian rhythm; mapped in 2025 as HYPOMAP with 452 cell types.
Hypothenar hammer syndrome
Hypothenar hammer syndrome (HHS, ulnar hammer syndrome): a vascular overuse injury where repeated palm trauma compresses the ulnar artery against the hook of the hamate at Guyon's canal, causing thrombosis, aneurysm, corkscrew angiographic appearance, and digital ischemia in dominant hands of male manual workers.