Those Followed by F Indicate Figures
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G-1 Page numbers followed by b indicate boxes; f, figures; t, tables. GLOSSARY B C D E F G H I J K L M N O P Q R S T U V W X Y Z A Abducens nerve. Cranial nerve VI, the nerve, that innervates the lateral rectus, the extraocular eye muscle that moves the globe laterally. 260f, 559, 614b Abductor. That which draws a body part away from the median line; typically associated with a muscle.* 241–242, 242t Abembryonic pole. The side of a blastocyst opposite the embryonic pole, that is, the side opposite the inner cell mass. 43 Abnormal spindle-like microcephaly associated microcephaly (ASPM). A gene that plays an essential role in embryonic neuroblasts in normal mitotic spindle function, and is expressed in proliferating regions of the cerebral cortex during neurogenesis. 290b–291b Abortifacient. That which causes an embryo or fetus to abort. 45b Accutane. A drug taken orally for the treatment of acne. 161–162 Acetazolamide. A carbonic anhydrase inhibitor with a wide variety of uses, including the treatment of glaucoma. 638b Acheiropodia. A disorder resulting in the absence of hands and feet. 634t, 636t Achondroplasia. The most common and most recognizable form of dwarfism. It is caused by mutations in Fibroblast growth factor receptor 3 (Fgfr3). 219b, 220f, 239b, 602b Achondroplasia/hypochondroplasia syndrome. Skeletal dysplasia caused by the Fgfr3 mutation, which results in brachydactyly (abnormal shortness of the fingers) and rhizomelia (shortening of the proximal limbs). 635t Acoustic meatus, external. The ear canal. 572 Acro-dermato-ungual-lacrimal-tooth (ADULT) syndrome. A syndrome that affects ectodermally derived structures, caused by mutations in the transcription factor Tumor protein P73-like (Tp73l; also known as P63). 203b Acromegaly. A condition in which growth hormone production is increased. 241b * Selected definitions adapted from Dorland's Illustrated Medical Dictionary, 31st ed, 2007. Philadelphia: Elsevier. Schoenwolf - Glossary G-2 Acrosome. The apical vesicle, filled with hydrolytic enzymes (e.g., acrosin, hyaluronidase, and neuraminidase), that caps the head of the spermatozoon. It plays an essential role in fertilization. 25 Actin-binding protein. Any of a number of proteins that binds to actin, which is a protein of the cytoskeleton. Acting along with myosin, it is responsible for changing and maintaining cell shape.* 111b Activin. A member of the Tgf-β family. 157 Acvr2b. An activin receptor. 383b Adactyly. A disorder resulting in the absence of all the digits on the hand or foot. 634t ADAM. A superfamily of proteins in which all 30 or so family members contain a disintegrin and a metalloprotease domain. 39 ADAM2. Also known as Fertilinβ. A protein present on male germ cells and/or mature sperm, it is a member of the ADAM superfamily. 39 Adductor. That which draws a body part toward the median line; typically associated with a muscle.* 242, 242t Adenohypophysis. The anterior lobe of the hypophysis (pituitary gland).* 282 Adenoids. The tonsils. 576 Adherens junction. An intercellular junction associated with the deposition of E-Caderin, a calcium-dependent cell adhesion molecule, on lateral cell surfaces. 43 Adrenal cortex. The outer, firm, yellowish layer that comprises the larger part of the adrenal gland, consisting of the zona glomerulosa, the zona fasciculata, and the zona reticularis. It secretes, in response to release of corticotropin by the pituitary gland, many steroid hormones.* 499–500 Adrenal gland. A flattened organ found in the retroperitoneal tissues at the cranial pole of the kidney.* 499f, 499–500 Adrenocorticotropic hormone (ACTH). A polypeptide hormone that stimulates the adrenal cortex.* 500b Afadin. An actin filament-binding protein. 81b Agyria. Lack of gyri, a malformation in which the convolutions of the cerebral cortex are not fully formed, so that the brain surface is smooth (lissencephaly).* 287b Schoenwolf - Glossary G-3 Ala orbitalis. Also called orbitosphenoid. Cartilage that, along with the ala temporalis, or alisphenoid, develops around the eye. They will ultimately contribute to the greater and lesser wings of the sphenoid. 547 Alagille syndrome. Also called arteriohepatic dysplasia. A disorder, caused by mutation of the Jagged1 or Notch2 genes, that affects the skeletal, cardiovascular, and gastrointestinal systems. 92b, 159, 230b, 231b, 233b, 383b, 416b, 449b Alar (dorsal) plates. Combined with the pair of ventral (basal) plates, these structures make up the mantle zone of the spinal cord and brain stem. 247b, 257, 257f Albinism. A general term for pigmentation defects. 128b Albumin. A hepatic marker within the endoderm. 449b Alpha-Fetoprotein (AFP). A protein produced by the fetal liver, whose level steadily increases during pregnancy. 114b, 180, 182, 184 Alisphenoid. A cartilage of the fetal chondrocranium on either side of the basisphenoid bone. Later in development it forms most of the greater wing of the sphenoid bone.* 547, 553, 554f Allantois. One of four extraembryonic membranes. The umbilical arteries and veins form in the mesoderm of the allantois. 104f, 105, 472, 474f Alpha cells. One of the cell types in the periphery of the pancreatic islets that secrete somatostatin (α1 cells) and glucagon (α2 cells).* 453b Alpha-actinin. A cytoskeletal linker protein. 160 Alveolus(i). The bony socket that holds a tooth. 214, 319b, 323, 327b–328b, Amacrine cells. One of five types of retinal neurons that lack large axons, having only processes that resemble dendrites.* 607 Ambisexual phase. Also called the “biopotential phase of genital development.” The period near the end of the 6th week of gestation when the male and female genital systems appear indistinguishable, although subtle cellular differences may already be present. In both sexes, germ cells and somatic support cells are present in the presumptive gonads, and complete mesonephric and Müllerian ducts lie side by side. From the 7th week on, the male and female systems pursue diverging pathways. 502 Amegakaryocytic thrombocytopenia syndrome. A disorder resulting from HoxA11 mutation. 637b Amelia. A disorder resulting in the absence of one or more limb. 632b, 633f, 634t Schoenwolf - Glossary G-4 Ameloblasts. Cylindrical epithelial cells in the innermost layer of the enamel organ that take part in the elaboration of the enamel prism. The ameloblasts cover the dental papilla.* 195b, 210, 212f Amelogenesis imperfecta. The defective development of enamel or dentin resulting from a mutation in Dlx3. 214b Amhr-I receptors. A type of anti-Müllerian hormone receptor, with Amh being a Tgfβ/Bmp family member. Studies have found Alk2, Alk3 (or Bmpr1α), and Alk6 also serve as Amhr-I receptors. When these receptors are knocked out in mice or if their signaling is blocked within the Müllerian duct mesenchyme, Amh-induced Müllerian duct regression is lost. 509, 510 Aminoglycoside antibiotics. Any of a group of antibiotics (e.g., amikacin, gentamicin, streptomycin) derived from various species of Streptomyces or produced synthetically. Aminoglycosides inhibit bacterial protein synthesis by binding with the 30S ribosomal subunit and are bactericidal. Irreversible hearing loss is possible if too high a dose is administered.* 596b, 597b Amniocentesis. The process by which embryonic cells obtained from the amniotic fluid are analyzed to detect many genetic disorders early in pregnancy. 35b, 114b, 169b, 184–185, 185f Amnion. One of four extraembryonic membranes. It completely encloses the fetus and surrounds it with amniotic fluid. 51b, 55f, 57 Amniotic band syndrome. A disorder that involves a complex etiology that in some cases may result from rupture of the amnion and constriction of limbs by fibrous amniotic bands. It is related to limb-body wall complex (LBWC). 107b Amniotic cavity. The first cavity to appear, typically on day 8 of embryonic development. It forms within the amnion at the embryonic pole of the blastocyst between the epiblast and overlying trophoblast. 51b, 57 Amniotic fluid. The fluid that surrounds and cushions the fetus, very similar to blood plasma in composition. It is initially produced by transport of fluid across the amniotic membrane. 179 Ampulla. The second portion of the oviduct (fallopian tube) where a sperm cell undergoes a process of functional maturation that prepares it to fertilize an oocyte. 28, 486 Ampulla of Vater. Also called hepatopancreatica ampulla. A structure created by the junction of the pancreatic and common bile ducts.* 451 Anagen. One of four phases (growth phase) of embryonic hair growth. 204 Schoenwolf - Glossary G-5 Anal agenesis. Failure of the anal orifice to form properly. 538b, 540f Anal atresia. Congenital absence or pathologic closure of the anal orifice. 538b Anal pit. The distal one-third of the anorectal canal formed from an ectodermal invagination. 474, 474f Anal stenosis. Abnormal narrowing or constriction of the anal passage. 538b Anaphase. That stage in meiosis and mitosis, following metaphase, in which the centromeres divide and the chromatids lined up on the spindle begin to move apart toward the poles of the spindle to form the daughter chromosomes.* 22f, 23t, 24 Androgen insensitivity syndrome (AIS). Also called testicular feminization syndrome. A disorder in which, if androgen receptors are disabled or absent, the male fetus may have normal or high levels of male steroid hormones, but the target tissues do not respond and development proceeds as though androgens are absent. 482b, 518, 535b, 535f Anencephaly. Total dysraphism of the brain, with normal formation of the spinal cord. 113b Angelman syndrome. A disorder involving deletions in a region of human chromosome 15 (15q11.2–q13) inherited from the mother. It is called Prader-Willi syndrome when the same defect is inherited from the father. Symptoms include developmental delay, speech and balance disorders, and a unique happy demeanor. 53b, 67b–68b Angioblasts. The mesenchymal tissues of the embryo from which the blood cells and vessels differentiate.* 392 Angiogenesis. The development of embryonic blood vessels that “sprout” from preexisting blood vessels. 377, 385b, 392, 395b–399f Angiogenic factors. Stimulation of blood and lymph vessels to grow into developing organs.