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Lumbar vertebrae
Lumbar vertebrae (L1-L5), the five largest vertebrae of the lower back between T12 and the sacrum; large thick bodies for weight bearing, lumbar lordosis, common sites of disc herniation and transitional vertebrae.
Lung
Lung: paired respiratory organ exchanging oxygen and carbon dioxide across ~70 m² of alveolar surface; right lung three lobes, left two; five diseases dominate global lung deaths; 2025 WHO lung health resolution.
Luteal phase
Luteal phase: the post-ovulatory half of the menstrual cycle, when the corpus luteum secretes progesterone; normally 11–17 days. Covers luteal phase deficiency (≤10 days), its contested diagnosis, and IVF luteal support.
Luteinizing hormone
Luteinizing hormone (LH, ICSH, lutropin) is an anterior pituitary gonadotropin with alpha and beta subunits that drives gonadal steroidogenesis, the midcycle ovulation surge, and testosterone production, and is measured in fertility testing.
LX101, RPE65 AAV gene therapy for inherited retinal dystrophy
LX101 (LX-101), Innostellar Biotherapeutics' rAAV2-RPE65 subretinal gene therapy for biallelic RPE65 mutation-associated inherited retinal dystrophy; phase 3 STAR trial in China, commercialization rights held by Golden Age Health.
Lymph
Lymph, or lymphatic fluid, is the clear fluid formed from blood plasma filtrate that drains through lymphatic vessels and nodes, returning 2–3 L of fluid daily and carrying immune cells; discovered as a system by Rudbeck and Bartholin in the 1650s.
Lymph node
A lymph node, also called a lymph gland, is a small bean-shaped organ of the lymphatic system that filters lymph and helps the immune system respond to infection.
Lymph trunks and the right lymphatic duct
The lymph trunks are large collecting vessels formed by converging lymphatic vessels, and the right lymphatic duct returns lymph from the body's right upper quadrant to the veins.
Lymphadenopathy
Lymphadenopathy, also called swollen lymph nodes or adenopathy, is abnormal enlargement of lymph nodes, usually >1 cm. Most causes are infectious, inflammatory, or malignant; evaluation is clinical, with ultrasound first-line imaging in children and core needle biopsy preferred for tissue sampling.
Lymphangiectasia
Lymphangiectasia, pathologic dilation of lymphatic vessels, primary (congenital) or secondary (obstructed). Intestinal form is Waldmann's disease: hypoalbuminemia, lymphopenia, edema; treated with fat-free diet and MCT.
Lymphangiogenesis
Lymphangiogenesis is the formation of new lymphatic vessels from pre-existing ones through lymphatic endothelial cell growth, regulated by VEGF-C/VEGFR-3 signaling, and linked to lymphedema and cancer spread to lymph nodes.
Lymphangioleiomyomatosis
Lymphangioleiomyomatosis (LAM, lymphangiomyomatosis) is a rare cystic lung disease almost exclusively affecting women, caused by TSC1/TSC2 mutations, treated with sirolimus, and sometimes requiring lung transplantation.
Lymphangiomatosis
Lymphangiomatosis, now called generalized lymphatic anomaly (GLA) within complex lymphatic anomalies, is a rare congenital disorder of proliferating lymphatic vessels affecting bones, lungs, spleen, and other organs, treated with sirolimus.
Lymphangion
Lymphangion: the valved, smooth-muscle segment between two intraluminal valves in collecting lymphatic vessels; the functional pumping unit, or "primitive heart", that propels lymph, regulated by preload, afterload, frequency, and contractility.
Lymphangitis
Lymphangitis, also called inflamed lymph vessels or acute lymphangitis, is infection of peripheral lymphatic channels, usually streptococcal or filarial, marked by red tender streaks toward swollen nodes, diagnosed clinically, and treated with antistreptococcal antibiotics.
Lymphangitis carcinomatosa
Lymphangitis carcinomatosa (lymphangitic carcinomatosis, carcinomatous lymphangitis): cancer cells infiltrating and blocking lymphatic vessels, usually pulmonary. Common with breast, lung, gastric cancers; severe dyspnea; poor prognosis.
Lymphatic capillary
Lymphatic capillary, or initial lymphatic: blind-ended ~50 µm microvessel with oak-leaf endothelial cells, button junctions, and anchoring filaments that absorbs interstitial fluid, immune cells, and chylomicrons to form lymph.
Lymphatic disorders
Lymphatic disorders are diseases that alter the structure or function of lymphatic vessels and nodes, causing lymphedema, lymphangitis, and lymphadenopathy; over 200 million people have lymphedema worldwide.
Lymphatic filariasis
Lymphatic filariasis (elephantiasis), a mosquito-borne neglected tropical disease caused by Wuchereria bancrofti, Brugia malayi, and Brugia timori worms; 657 million people in 39 countries need preventive chemotherapy, and 21 countries are validated as eliminating it.
Lymphatic system
The lymphatic system, also called the lymphoid system, is the network of vessels, nodes, and organs that returns lymph to the bloodstream, filtering pathogens and supporting immunity.
Lymphatic transport of nanoparticles
Lymphatic transport of nanoparticles is the movement of engineered particles injected into tissues into lymphatic vessels and draining nodes, governed chiefly by particle size, enabling vaccine and immunotherapy delivery.
Lymphatic vessel
Lymphatic vessel (lymphangion network): thin-walled tubules carrying lymph, returning 8–12 L of interstitial fluid daily without a central pump via initial and collecting lymphatics, valves, and the thoracic duct.
Lymphedema
Lymphedema is a chronic swelling, usually of a limb, caused by fluid buildup when the lymphatic system fails to drain it, affecting up to 250 million people worldwide.
Lymphocele
Lymphocele: a fibrous-walled, non-epithelialized collection of lymph caused by lymphatic injury, usually after pelvic, vascular, or transplant surgery; incidence 8–48%, treated by drainage, sclerotherapy, or marsupialization.
Lymphocutaneous sporotrichosis
Lymphocutaneous sporotrichosis, the most common form of sporotrichosis (rose gardener's disease), is a Sporothrix fungal infection following skin inoculation, producing ascending nodular lymphangitis; treated with itraconazole 200 mg daily for 3–6 months.
Lymphocyte Activation
Lymphocyte activation: B and T cells triggered through antigen-specific receptors (BCR, TCR), requiring signal 1 plus costimulatory signal 2 (two-signal model, Bretscher and Cohn 1970), leading to proliferation, cytokine release, and differentiation into plasma, memory, or cytotoxic effector cells.
Lymphoedema due to lymphatic filariasis
Lymphoedema due to lymphatic filariasis: chronic limb swelling from Wuchereria bancrofti or Brugia worms, a chronic LF manifestation affecting over 15 million people, managed with hygiene-based self-care.
Lymphogranuloma venereum
Lymphogranuloma venereum (LGV, Durand–Nicolas–Favre disease) is a systemic STI caused by invasive Chlamydia trachomatis serovars L1–L3, presenting as proctocolitis in MSM or inguinal buboes, treated with 21 days of doxycycline.
Lysosomal storage disease
Lysosomal storage diseases (LSDs, lysosomal storage disorders): over 70 inherited metabolic disorders caused by defective lysosomal enzymes or transporters; treated mainly by enzyme replacement therapy since 1991 (Gaucher disease).
Lytico-bodig disease
Lytico-bodig disease, also called ALS/PDC or Guam disease, is a neurodegenerative ALS-parkinsonism-dementia syndrome endemic to the Chamorro people of Guam, peaking in the 1950s and linked to the cycad toxin BMAA hypothesis.