Histemb Definitions 1

Front 1

zygote

Back 1

the cell formed by the union of pronuclei of the male and female gametes

Front 2

cleavage

Back 2

series of mitotic divisions of zygote

Front 3

blastomeres

Back 3

cells resulting from cleavage divisions

Front 4

morula

Back 4

stage of development characterized by a solid ball of about 12 or more blastomeres

Front 5

blastocyst

Back 5

stage of development characterized by a sphere of cells with a fluid filled central cavity

Front 6

inner cell mass/embryoblast

Back 6

inner group of blastocyst cells located to one side of the central cavity; these cells will give rise to the embryo

Front 7

trophoblast

Back 7

outer layer of cells of the blastocyst which will contribute to the formation of extra embryonic structures

Front 8

conceptus

Back 8

all of the products of conception; i.e. both embryonic and extra embryonic structures

Front 9

zona pellucida

Back 9

acellular membrane surrounding all developmental stages of the conceptus prior to implantation

Front 10

implantation

Back 10

process of attachment of the conceptus in the uterine wall

Front 11

cytotrophoblast

Back 11

inner cellular layer of the trophoblast formed during implantation

Front 12

syncytiotrophoblast

Back 12

outer multinucleate mass of the trophoblast formed during implantation

Front 13

bilaminar embryonic disc

Back 13

arrangement of the inner cell mass into epiblast (future embryonic ectoderm, mesoderm, and endoderm) and hypoblast

Front 14

primary germ layer

Back 14

embryonic ectoderm, mesoderm, and endoderm; these layers will give rise to all tissues and organs of the embryo

Front 15

primitive (primary) yolk sac cavity

Back 15

exocoelomic cavity - cavity lined by hypoblast plus exocoelomic membrane

Front 16

exocoelomic membrane

Back 16

thin membrane of cells probably derived from the hypoblast

Front 17

extraembryonic mesoderm

Back 17

loosely arranged tissue probably formed from the hypoblast; this tissue fills the space between the cytotrophoblast peripherally and the amnioblast layer and the exocoelomic membrane internally

Front 18

extraembryonic coelom

Back 18

large cavity which develops within the extra embryonic mesoderm

Front 19

extraembryonic somatic mesoderm

Back 19

extraembryonic mesoderm which lines the cytotrophoblast and covers the amnion

Front 20

extraembryonic splanchic mesoderm

Back 20

extraembryonic mesoderm which covers the definitive yolk sac

Front 21

amniotic cavity

Back 21

space which appears in the inner cell mass

Front 22

amnion

Back 22

extraembryonic (fetal) membrane consisting of an inner layer of amnioblasts and an outer layer of extra embryonic somatic mesoderm

Front 23

amnioblasts

Back 23

layers of flattened cells derived from the inner cell mass; these cells form a thin membrane over the amniotic cavity.

Front 24

definitive (secondary) yolk sac

Back 24

(third week) extraembryonic (fetal) membrane consisting of an inner layer of endoderm and hypoblast and an outer layer of extra embryonic splanic mesoderm; in the second week, the yolk sac consists only of hypoblast and extra embryonic splanchinic mesoderm

Front 25

allantois

Back 25

extraembryonic (fetal) membrane which forms as a finger-like diverticulum from the definitive yolk sac

Front 26

chorion

Back 26

extraembryonic (fetal) membrane consisting of extraembryonic somatic mesoderm, cytotrophoblast and cyncytiotrophoblast

Front 27

connecting (body) stalk

Back 27

column of extra embryonic mesoderm which attaches the embryo and its amnion and yolk sac to the chorion

Front 28

lacunae

Back 28

isolated spaces which appear in the syncytiotrophoblast

Front 29

lacunar network

Back 29

the fusion of the syncytiotrophoblast lacunae to form an intercommunicating network of spaces

Front 30

uteroplacental circulation

Back 30

the flow of maternal blood through the lacunar network of the syncytiotrophoblast

Front 31

primary villi

Back 31

finger-like outpocketings from the chorion which consist of cytotrophoblast and syncytiotrophoblast

Front 32

secondary villi

Back 32

chorionic outpocketings which consist of cytotrophoblast, cyncytiotrophoblast and a central core of extra embryonic somatic mesoderm

Front 33

tertiary villi

Back 33

chorionic outpocketings which consist of cytoprophoblast, synctiotrophoblast, a central core of extra embryonic somatic mesoderm and a capillary system within the mesoderm

Front 34

outer cytotrophoblast shell

Back 34

peripheral layer of cytotrophoblast which firmly attaches the chorion to the uterine endometrium

Front 35

endometrium

Back 35

the inner lining layer of the uterine wall

Front 36

decidua basalis

Back 36

the uterine endometrium underlying the conceptus

Front 37

decidua capsularis

Back 37

the uterine endometrium overlying the conceptus

Front 38

decidua parietalis

Back 38

all of the uterine endometrium beyond the decidua basal is and capsularis

Front 39

smooth chorion (chorion laeve)

Back 39

portion of the chorion lacking villi

Front 40

villous chorion (chorion frondosum)

Back 40

portion of the chorion with villi

Front 41

placenta

Back 41

organ formed by the villous chorion and the decidua basalis

Front 42

intervillous spaces

Back 42

large blood sinuses bounded by the chorion and the decidua basal is; these sinuses are derived from the the syncytiotrophoblas lacunae

Front 43

primitive streak

Back 43

narrow groove on the surface of the epiblast

Front 44

primitive knot (node)

Back 44

slightly elevated area of epiblast cells surrounding a small pit (primitive pit) at the central end of the primitive streak

Front 45

trilaminar embryonic disc

Back 45

embryo consisting of embryonic ectoderm, mesoderm, and endoderm

Front 46

prochordal (prechordal) plate

Back 46

small circular area of thickened hypoblast cells in the midline near the cranial end of the embryonic disc; hypoblast cells of the prochordal plate are eventually replaced with endodermal cells

Front 47

oropharyngeal (buccopharyngeal) membrane

Back 47

membrane resulting from the fusion of the prochordal plate with overlying epiblast cells

Front 48

cloacal membrane

Back 48

small circular patch of tightly adhering epiblast (future ectodermal) cells and the hypoblast (future endodermal) cells in the midline near the caudal end of the embryonic disc

Front 49

notochordal process

Back 49

a tube-like cellular process between ectodermal and endodermal layers extending from the primitive pit to the oropharyngeal membrane

Front 50

notochordal canal

Back 50

tubular space within the notochordal process

Front 51

notochordal plate

Back 51

roof of the notochordal process remaining after the floor degenerates

Front 52

neurenteric canal

Back 52

temporary connection between the amnion and yolk sac cavities through the primitive pit

Front 53

notochord

Back 53

a cellular rod which forms the primitive midline axis of the embryo