Larsens, Ch 3 - 3rd Week Flashcards
Ectoderm
Will form the nervous system (from the neural tube and neural crest ), sensory placodes and also generates the entire epithelial layer of the skin covering the embryo, formed from the epiblast following gastrulation, with a central columnar epithelium (neural plate) and lateral cuboidal epithelium and is continuous with and forms the epithelium that lines the amniotic cavity, in humans, the ectoderm forms during week 3 and 4 of development
Endoderm
One of the initial 3 germ cell layers (ectoderm, mesoderm, endoderm) formed by the process of gastrulation, forms as a cuboidal epithelium and contributes not only to the trilaminar embryo, but also lines the yolk sac, it will form the entire epithelial lining of the gastrointestinal tract (GIT), contribute to the accessory organs of GIT and also forms the epithelial lining of the respiratory tract, in the GIT it contributes both epithelium and the associated epithelial glands, in humans, endoderm forms during week 3 of development
Epithelium
Cells tightly linked together to form a sheet with little extracellular matrix, most epithelia in the body are embryonically derived from either ectoderm or endoderm germ layers with some also differentiating from mesoderm
Forebrain
The common term used to describe the most anterior neural tube primary brain vesicle that will form the two secondary brain vesicles, in the adult brain form the cerebral hemispheres (neocortex, basal nuclei, palaeocortex, archicortex) and thalmus, hypothalmus and other nuclei respectively, the prosencephalon lumen (cavity of the neural tube) will form the lateral ventricle and third ventricle.
Foregut
The first of the three part/division of the early forming gastrointestinal tract, runs from the buccopharyngeal membrane to the midgut and forms all the tract (esophagus and stomach) from the oral cavity to beneath the stomach, in addition, a ventral bifurcation of the foregut will also form the respiratory tract epithelium
Germ layer
The first three cellular layers (ectoderm, mesoderm, and endoderm) that will form all tissues of the embryo, in humans, these layers begin to form during week 3 of development
Hindbrain
The common term used to describe the early primary brain vesicle lower subdivision of brain development at the stage when there are three primary vesicles or expansions of the early neural tube (forebrain, midbrain, hindbrain), these will in turn generate in the adult brain the cerebellum, pons and medulla, the hindbrain lumen (the cavity of the neural tube) will form the fourth ventricle
Hindgut
The last of the three part/division (foregut - midgut - hindgut) of the early forming gastrointestinal tract, the hindgut forms all the tract from the distral transverse colon to the cloacal membrane and extends into the connecting stalk (placental cord) as the allantois, in addition, a ventral of the hindgut will also form the urinary tract (bladder, urethra) epithelium
Midbrain
The common term used to describe the early primary brain vesicle middle subdivision of brain development at the stage when there are three primary vesicles or expansions of the early neural tube (forebrain, midbrain, hindbrain, this subdivision is the only one present at the later five secondary brain vesicle stage, term is also used in the adult brain to describe brainstem components formed including: tectum, tegmentum, the ventricular mesocoelia, cerebral peduncles, and additional nuclei and fasciculi
Midgut
The middle of the three part/division (foregut - midgut - hindgut) of the early forming gastrointestinal tract, is initially connected on the ventral embryo surface to the external yolk sac by a yolk stalk, a narrow tubular connection, forms all the tract from beneath the stomach (duodenum, small intestine and large intestine) to the distral transverse colon, develops as an external loop “herniated” ventrally, until early fetal growth of the body wall recaptures this external loop, which also undergoes a rotation about the superior mesenteric artery to establish the adult anatomical position
Mesenchyme
Term used to describe the cellular organisation of undifferentiated embryonic connective tissue, mesenchymal tissue is mainly derived from mesoderm and neural crest, which will form most of the adult connective tissues, this connective tissue organization contrasts with the other main form of cellular organization, epithelial tissue
Mesoderm
The middle layer of the 3 germ cell layers of the trilaminar embryo (ectoderm, mesoderm, endoderm), contributes all connective tissues of the body, except in the head region where neural crest also will contribute, mesoderm outside the embryo and covering the amnion, yolk and chorion sacs is extraembryonic mesoderm
Notochord
The rod of cells lying in the midline of the trilaminar embryo mesoderm layer ventral to the neural tube, thought to have at least 2 early roles in development and later roles in patterning surrounding tissues. 1. Mechanical, influencing the folding of the early embryo; 2. Morphogenic, secreting sonic hedgehog a protein which regulates the development of surrounding tissues (neural plate, somites, endoderm and other organs), in humans, the notochord forms in week 3 and is eventually lost during the formation of the vertebral column
Neural crest
A cell region at edge of neural plate, then atop the neural folds, that remains outside and initially dorsal to the neural tube when it forms. These paired dorsal lateral streaks of cells migrate throughout the embryo and can differentiate into many different cell types, Those that remain on the dorsal neural tube form the sensory spinal ganglia (DRG), those that migrate ventrally form the sympatheitic ganglia. Neural crest cells also migrate into the somites and regions throught the entire embryo.
Neural plate
The first stage in early development of the central nervous system. In the trilaminar embryo the central region of the ectoderm (in the midline above the mesodermal notochord) initially forms a columnar epithelium described as the neural plate. This epithelium will fold dorsally to form the neural groove, which then fuses to form an initially open at either end hollow neural tube. The neural tube forms the central nervous system (brain and spinal cord).
