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Link to the Original UNSW Embryology Glossary L

labyrinth

inner ear system of fluid-filled passages which provides the sense of balance (semicircular canals, vestibule). Named by analogy with the Greek mythology maze that imprisoned the Minotaur.

lactation

(Latin lactans = suckling) production of milk through action of prolactin and other hormones on breast tissue. Therefore associated mainly with mammals.

(More? Normal Development - Milk | Integumentary Development - Mammary Glands)

lacuna

Anatomical and histological description of a small pit or cavity.

lacunae

A blood-filled spaces within endometrium, formed following blastocyst implantation and trophoblast erosion of the maternal sinusoids.

(More? Week 2 Notes | Placenta Notes)

lanugo

A fine coat of body hair found on the fetus.

(More? Integumentary Development | Integumentary Development - Hair)

lamellae

A term describing the concentric layers of bone.

(More? Musculoskeletal Notes)

lamina

A term describing a thin layer or sheet.

lamina propria

The layer of loose connective tissue underneath the epithelium of mucosa.

laparoscopy

A surgical procedure in which a fiber optic instrument (a laparoscope) is inserted through a small incision in the abdomen to view the inside of the pelvis.

large intestine

gastrointestinal tract between the end of the ileum (cecum) and anus. The large intestine can be further subdivided into parts: cecum, colon (ascending, transverse, descending, and sigmoid), and rectum. Functions in the resorption of water, vitamin K metabolism, and the formation of faeces.

(More? Gastrointestinal Tract Notes)

laryngeal webs

(congenital laryngeal webs) Laryngeal abnormality due to embryonic (week 10) incomplete recanalization of the laryngotracheal tube. Rare abnormality occuring mainly at the level of the vocal folds (glottis).

(More? Respiratory Abnormalities)

laryngotracheal groove

Early embryonic foregut developmental feature, forms on the anterior (ventral) wall of pharynx and gives rise to larynx, trachea, respiratory tree.

(More? Respiratory Notes | Head Notes | Stage 13/14 Embryo Section B3 Section B4)

larynx

Site of the the vocal folds in the neck. Embryologically develops from the foregut with the lining derived from endoderm and the cartilage from pharyngeal arch 4 and 6. Beginning as a simple foregut groove, the [L.htm#laryngotracheal_groove laryngotracheal groove] which folds to form the laryngotracheal bud, then the larynx and trachea.

(More? Gastrointestinal Tract NotesRespiratory Notes | Head Notes)

last menstrual period

(LMP) Clinical term used to describe the menstrual period that occurs before a pregnancy and is used as the date to calculate clinical pregnancy development (gestational age). Note that in humans this is approximately two weeks different from embryonic development, which begins at [F.htm#fertilization fertilization] around the mid-point of the menstrual cycle.

late-gestation lung protein 1

(LGL1) a glycoprotein secreted by fetal lung mesenchyme and fetal kidney, involved in retinoic acid stimulated branching morphogenesis. (PMID: 17670908)

(More? Respiratory Notes)

lateral

An anatomical description for away from the midline (paired with medial, towards the midline).

lateral cervical anomaly

(branchial cleft anomaly) Abnormality which can be four different types: first, second, third and fourth.

(More? Head Notes - Abnormalities)

lead

An environmental heavy metal linked to developmental defects.

(More? Defects - Chemical Notes | Defects - Heavy Metals )

lectins

Class of carbohydrate-binding proteins originally found in plants. Can be used to specifically bind/identify glycoproteins.

Lee-Boot Effect

Reproductive change in female mice housed together (in groups) results in a synchronization of their estrus cycles. In addition, the extended absence of male pheromones leads to a state of anestrus (lack of a normal estrus cycle).

(More? Mouse Development- Estrous Cycle

leiomyoma

(= uterine fibroids) A benign smooth muscle tumor of the [U.htm#uterus uterus]. These are also one of the most common gynecologic neoplasm in women, often detected on pelvic examination or by a range of diagnostic tools (endovaginal sonography, sonohysterography, hysterosalpingography, magnetic resonance imaging, computerized tomography, radionucleotide scanning, serum markers). The condition is difficult to distinguish from another uterine disease [A.htm#adenomyosis adenomyosis].

(More? Reproductive System - Abnormalities | Medlineplus - uterine fibroids)

leptin

(Greek, leptos = thin) a polypeptide hormone (16 kDa) produced in adipose and many other tissues. Hormone receptor (OB-R, leptin receptors) found in many different tissues. Hormone levels associated with fertility and reproductive maturity in many species. Other hormonal roles include: satiety, adiposity, and metabolism, body mass control, angiogenesis, immunity, wound healing, bone remodelling cardiovascular function, and specific metabolic pathways.

(More? Endocrine Adipose Endocrine Notes | Henson MC, Castracane VD. Leptin in pregnancy: an update. Biol Reprod. 2006 Feb;74(2):218-29.)

lesser omentum

The smaller of two splanchnic mesoderm peritoneal folds (lesser/greater), the lesser extends from lesser curvature of the stomach to liver. The [G.htm#greater_omentum greater omentum] extends from the greater curvature of the stomach and hanging down "like an apron" ventrally over the small intestine.

(More? GIT Notes)

lesser omentum

The stomach has 2 peritoneal folds attached to each of the stomach curvatures. The lesser omentum is the peritoneal fold extending from lesser curvature of the stomach to liver. The greater omentum is the peritoneal fold extending from the greater curvature of the stomach to the colon, and hanging down over the small intestine.

(More? GIT Notes)

levonorgestrel

A synthetic progesterone used in oral contraceptives and as an emergency contraceptive. (Other Progestins: 3-keto-desogestrel, dienogest, drospirenone, Nestorone, nomegestrol acetate and trimegestone) Note that Trimegestone and Nestorone are currently the most potent fourth-generation progestins with no androgenic or estrogenic actions.

(More? Human Menstrual Cycle)

Leydig cells

(interstitial cells) Testis (male gonad) cell which secrete testosterone, beginning in the fetus. These cells are named after Franz von Leydig (1821 - 1908) a German scientist who histologically described these cells.

(More? Genital Notes | Urogenital Notes)

Leydig cell hypoplasia

(LCH) or male pseudohermaphroditism is an autosomal recessive disorder in individuals with a 46,XY karyotype with a predominantly female phenotype

(More? Hermaphroditism | Reproductive System - Abnormalities)

leukocyte

(Greek, l~ukos = clear, white) white blood cell.

LGL1

acronym for Late-Gestation Lung Protein 1, a glycoprotein secreted by fetal lung mesenchyme and fetal kidney, involved in retinoic acid stimulated branching morphogenesis. (PMID: 17670908)

ligamentum arteriosus

The postnatal ligament remnant structure formed from the ductus arteriosus, a prenatal vascular shunt.

(More? Cardiovascular Notes)

ligamentum teres

(ligamentum teres uteri, Hunter's ligament) The round ligament of [U.htm#uterus uterus] which maintains the ventral uterine position.

 

ligamentum venosus

The postnatal ligament remnant of the ductus venosus, a vessel which prenatally connects (shunts) the portal and umbilical veins to the inferior vena cava and also acts to protect the fetus from placental overcirculation.

(More? Cardiovascular Notes)

ligand

(Latin, ligare = to bind) A molecule that binds to a specific binding site in a protein.

Lim

Acronym for LIM domain proteins were named after the worm proteins (===Li===n11 and ===M===ec3) and vertebrate protein which specify cell lineage and organ development (also involved in cytoskeleton organization and oncogenesis). Ldb genes encode LIM domain-binding (Ldb) factors and have been identified as a regulator of neural tube differentiation at the spinal cord level (Lim hox gene expression).

(More? Other Embryo - Worm)

lin-35

(lin-35 Rb) A retinoblastoma tumor suppressor (Rb) related gene in worm C. elegans, identified as a synthetic multivulva (synMuv) class B gene.

(More? Other Embryo - Worm)

Lingo/LERN

(Leucine-Rich Repeat Neuronal Protein, LRRN6A) gene family encoding type 1 transmembrane proteins, with 12 extracellular leucine rich repeats, an immunoglobulin C2 domain and a short intracellular tail. Expressed in neural and nonneronal developing tissues: developing cranial ganglia (trigeminal, facio-acoustic) and dorsal root ganglia, somites (dermomyotome), spinal cord (motor horn), otic vesicle and developing gut epithelium.

(More? Neural Notes | OMIM - Leucine-Rich Repeat Neuronal Protein | Haines BP, Rigby PW. Expression of the Lingo/LERN gene family during mouse embryogenesis. Gene Expr Patterns. 2008 Jan;8(2):79-86.)

lingual

(Latin, lingua = tongue) Term used to describe structures and features related to the tongue: lingual papilla, lingual plate, lingual plexus, lingual thyroid nodule.

(More? Tongue Notes | Head Notes)

lipophorin

(Lp) lipoprotein particle formed in insect cells that has been identified as having a role in Hedgehog (Hh) signaling during development. Lipophorins (Lp) contain two apolipophorins I and II (ApoLI and ApoLII). Similar lipoprotein particles can be found in vertebrates and consist of a phospholipid monolayer surrounding a core of esterified cholesterol and triglycerides which is scaffolded by apolipoproteins. Reference: Callejo A, Culi J, Guerrero I. Patched, the receptor of Hedgehog, is a lipoprotein receptor. Proc Natl Acad Sci U S A. 2008 Jan 15

(More? Molecular Development - Sonic Hedgehog | Molecular Development - Patched Receptor)

lissencephaly

(smooth brain) A developmental brain abnormality resulting from an absence (agyria) or the paucity (pachygyria) of cerebral convolutions.

(More? Neural Notes | Fetal Neural)

listeria

A large family of bacteria found throughout the environment (soil, dust, water, unwashed raw produce, fish, undercooked poultry, prepared meats such as hot dogs and deli meats, and faeces of domestic and wild animals). Listeria monocytogenes is the specific bacteria form that causes the infection "listeriosis". The most common human source of infection is contaminated foods: delicatessan meats, unpasteurized milk or dairy products, soft cheeses, and paté. Once infected, Listeria lives in the gastrointestinal Maternal listeriosis with symptoms has a risk (2-14 days after maternal infection) of for miscarriage, stillbirth, uterine infection, premature labor, and death in the newborn period.

(More? Abnormal Development)

Littre hernia

(hernia of the Meckel diverticulum) The protrusion of a Meckel diverticulum through a potential abdominal opening. The hernia sites are: inguinal (50%), umbilical (20%), and femoral (20%). Named after Alexis de Littre (1700) who initially reported ileal diverticula.

(More? GIT Abnormalities)

live birth

The delivery of one or more babies with any sign of life. World Health Organization (WHO) definition: "Live birth is the complete expulsion or extraction from its mother of a product of conception, irrespective ot the duration of pregancy, which, after separation, breathes or shows evidence of life, such as the beating of the heart, pulsation of the umbilical cord, or definite movement of voluntary muscles, whether or not the umbilical cord has been cut or the placenta is attached; each product of such a birth is considered liveborn."

liveborn

See the term [#live_birth live birth] definition above.

LMP

Acronym for [#last_menstrual_period Last Menstrual Period] that occurs before a pregnancy and is used as the date to calculate clinical pregnancy development (gestational age).

lobule

Term used to describe a small lobe. Can be used to describe part of a gland, ear, organ structure.

lunatic fringe

A gene encodes a secreted signaling protein that signals formation of boundaries between groups of cells during development. One mechanism is by modifying Notch and inhibits signaling through the Notch pathway. In neural tube, regulates early neural crest differentiation. In mesoderm, regulates somite formation (segmentation).

(More? Neural Crest - Molecular | Molecular Development - Notch | OMIM - lunatic fringe)

lung bud

The term describing the primordia of lung development. Foregut endoderm branches into the surrounding visceral mesoderm, forming the trachea, which brances again into the bronchi and thsi process is repeated over and over again through development. Establishing the major respiratory branches first, followed by minor branches, then terminal branches, then immature alveoli which later mature to form teh functional end structures of the lung.

(More? Respiratory Notes)

luteinizing hormone

(LH, gonadotropin, lutropin, Interstitial Cell Stimulating Hormone, ICSH) Glycoprotein hormone releasd from anterior pituitary hormone that acts on the gonad and has a role in male and female reproduction. In female, increase in concentration during the menstrual cycle triggers ovulation (release of the oocyte). In male, stimulates testis interstital cell (Leydig cell) production of testosterone. Gonadotrophins have been used clinically in humans for the treatment of female infertility.

(More? Human Menstrual Cycle | Genital Notes)

lutenizing hormone

alternative spelling, (LH, gonadotropin) (LH, gonadotropin, lutropin, Interstitial Cell Stimulating Hormone, ICSH) Glycoprotein hormone releasd from anterior pituitary hormone that acts on the gonad and has a role in male and female reproduction. In female, increase in concentration during the menstrual cycle triggers ovulation (release of the oocyte). In male, stimulates testis interstital cell (Leydig cell) production of testosterone.

(More? Human Menstrual Cycle | Genital Notes)

luteinizing hormone/chorionic gonadotropin receptor

(LHCGR) a G protein-coupled receptor expressed in male testis (Leydig cells) and female ovary (granulosa-lutein and theca cells)

(More? Genital Notes)

Lyme disease

Caused by a bacterium, Borrelia burgdorferi, which was cultured from the midgut of Ixodes ticks in the mid-1980s. Named after a small town of Lyme in Connecticut where in the mid-1970s this diesease was initially identified.

(More? NCBI Coffee Break Lyme Disease)

lymphangiogenesis

development or growth of lymphatic vessels.

(More? Lymphatic Notes)

lymphangioma

a disfiguring vascular malformation of early childhood (mostly before 2 years of age) occuring in soft tissues of the head and neck or axilla, may also occur in the limbs, trunk, viscera and serous cavities.

(More? Lymphatic Notes)

lymphedema

abnormal accumulation of interstitial fluid in tissues due to a lack of lymphatic drainage, which in turn leads to localized swelling.

(More? Lymphatic Notes)

lymphopoiesis

(lymphoid hematopoiesis, lymphocytopoiesis) the process of generating lymphocytes (the immune cells) in various tissues (bone marrow, lymph nodes, thymus and spleen).

(More? Blood Notes | Lymphatic Notes)

lyssavirus

A form of virus closely related to classical rabies (though genetically and serologically distinct). A form of this virus carried in bats (Australian bat lyssavirus) has been associated with two human fatalities. Effects on embryonic development are unknown.

(More? Abnormal Development - Virus)

Comments

Use this page to access brief definitions of specific embryology terms. Additional information can be accessed from links listed at the end of each definition. Glossary from the UNSW Embryology program compiled and written by Dr Mark Hill. Reference Material used in preparing this glossary list includes: texts listed on page 1 Reading of each notes section, Department of Anatomy Publications, WWW resources from NCBI, NIH, OMIM, NHMRC (Australia), AMA (USA), Office of Rare Diseases (USA), PubMed Medline Dictionaries, MSDS, Merck Manual home edn.

These notes are for Educational Purposes Only Please email Dr Mark Hill if you wish to make a comment about this current project.

Copyright: Dr Mark Hill Created: 01.06.1997 Updated: 11.05.2009

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