Early Human Development

Front 1

ovulation

Back 1

process by which the ovum is released from a mature oviarian follicle; ovum is swept through the peritoneal cavity into the uterine tube

Front 2

zona pellucida

Back 2

mucopolysaccharide shell of mature ovum

Front 3

corona radiata

Back 3

outer layer of ovum, follicular cells of cumulus oophorus

Front 4

fertilization

Back 4

joining of sperm and egg; sperm must penetrate both external barriers before union of pronuclei

Front 5

site of fertilization

Back 5

ampulla of the uterine tube

Front 6

embryo transport

Back 6

first 10-12 days of pre-embryo; cleavage occurs while it is moved out of the unterine horn into the uterus by sweeping cilia action

Front 7

cleavage

Back 7

division of the single zygote cell over 4 days into a 12-16 cell morula, stays roughly the same size

Front 8

morula

Back 8

12-16 cell stage of embryo; size resembles a mulberry; still surrounded by the zona pellucida

Front 9

blastocyte

Back 9

"hatching" from zona pellucida; central cavity forms surrounded by blastomeres; two cell types: trophoblast and embryoblast

Front 10

trophoblast

Back 10

outer cell layer of blastocyte; forms wall of blastocytic cavityl will form fetal component of placenta

Front 11

embryoblast

Back 11

inner cell mass of blastocyte; located at one pole of the cell mass (embryonic pole); will form the body of the embryo

Front 12

implantation

Back 12

process by which the free-floating blastocyte adheres to and penetrates the endometrial lining of the uterus; occurs during day 6-12

Front 13

process of implantation

Back 13

trophoblastic blastomeres are sticky and attach to endometrium; they destroy the endometrial cells; they proliferate and invade the tissue

Front 14

cytotrophoblast

Back 14

mononucleated epithelial cells; distinct cell boundaries; surrounds blastocyst cavity

Front 15

syncytiotrophoblast

Back 15

multinucleated protoplasmic mass; no complete cell boundaries; extends out from cytotrophoblast

Front 16

bilaminar disk

Back 16

pre-embryo with two layers of cells, epiblast and hypoblast

Front 17

epiblast

Back 17

pluripotent columnar cells that give rise to the body of the embryo and to amnion

Front 18

hypoblast

Back 18

cuboidal cells that give rise to endoderm of umbilical vesicle

Front 19

trilaminar disk

Back 19

3 cell layers formed from primitive streak: endoderm, mesoderm, ectoderm

Front 20

primitive streak

Back 20

appears at day 15 as a median groove at caudal end of epiblast; extends cranially

Front 21

gastrulation

Back 21

epiblasts in groove of the primitive streak migrate and invaginate in between epiblasts and hypoblasts to form endoderm and mesoderm; cells that do not migrate become ectoderm

Front 22

endoderm

Back 22

laterially displace hypoblast, will form epithelium of primitive gut

Front 23

mesoderm

Back 23

occupies space between epiblasts and endoderm; migrate laterally and cranially from primitve streak

Front 24

ectoderm

Back 24

develops into nervous system and epidermis; surrounds mesoderm and endoderm

Front 25

prechordal plate

Back 25

day 14; circular area of firm attachment of ectoderm and endoderm; identifies cranial end; precursor of buccopharyngeal membrane and primitive mouth; secretes molecular signals that pattern the head

Front 26

notochord development

Back 26

mesomedian dermal rod, forms from cells invaginating through primitive pit; identifies cranial-cuadal axis; breaks into segments to form core of intervertebral disks; secretes molecular signals to intitate development of nervous system

Front 27

neuralation

Back 27

morphogenesis of the neural tube; order: neural plate, neural groove, neural tube, neural crest

Front 28

neural plate formation

Back 28

from ectoderm cells that proliferate and change shape; elevated ridges form neural folds; induced by underlying notochord

Front 29

neural groove formation

Back 29

folding of the neural plate: median V-shaped, axial depression in neural plate

Front 30

neural tube formation

Back 30

midline fusion of the neural folds; spearates from adjacent surface ectoderm, "sinks;" CNS precursor

Front 31

neural crest formation

Back 31

derived form neural folds as the neural tube closes; precursor to neurons of DRG and cranial sensory ganglia, Schwann and satellite cells of peripheral nerves and ganglia, neurons of sympathetic and parasympathetic ganglia, bone and cartilage derivatives of pharyngeal arches(facial skeleton)

Front 32

neuroepithelium

Back 32

precursor to ependyma

Front 33

mantle layer

Back 33

precursor to gray matter

Front 34

marginal layer

Back 34

precursor to white matter

Front 35

alar plate

Back 35

precursor to sensory/afferent dorsal horn

Front 36

basal plate

Back 36

precursor to motor/efferent ventral horn

Front 37

subdivision of the mesoderm

Back 37

paraxial, intermediate, lateral plate

Front 38

paraxial mesoderm

Back 38

breaks into paired segmental blocks called somiates; forms adjacent to notochord

Front 39

somites

Back 39

form vertebrae, dermis of skin of the back, and most skeletal muscles of the body; approx 40 in total

Front 40

intermediate mesoderm

Back 40

cells immediate lateral to somites; forms nephrogenic cord (kidneys) and genital ridge

Front 41

lateral plate mesoderm

Back 41

two layers: somatic and splanchnic

Front 42

somatic lateral plate mesoderm

Back 42

associated with ectoderm; forms outer lining of body cavity

Front 43

splanchnic lateral plate mesoderm

Back 43

associated with endoderm; inner lining of body cavity

Front 44

intraembryonic coelom

Back 44

U-shaped cavity between somatic and splanchnic mesoderm; will be subdivided into pleural, pericardial, and peritoneal cavities

Front 45

body folding

Back 45

late 3rd week; cranial-caudal and lateral; results in tubular embryo (alimentary tract, body cavities, body wall); yolk stalk is reduced in size; essentially complete by 6th week

Front 46

ectoderm derivatives

Back 46

forms CNS; PNS and adrenal medulla (neural crest); Sensory epithelia of ear, nose, and eye; epidermis; mammary gland, pituitary gland, and subcutaneous glands; enamel of teeth; dentin and pulp of teeth, PDL (neural crest)

SKIN, NERVES, AND TEETH

Front 47

mesoderm derivatives

Back 47

forms CT; all muscle; heart, blood and lymph vessels, and blood and lymph cells; kidneys, gonads, and their ducts; serous membranes lining the pericardial, pleural, and peritoneal cavities; spleen, tonsils, lymph nodes, and cortex of the adrenal gland

CONNECTIVE TISSUE, MUSCLE, AND GUTS

Front 48

endoderm derivatives

Back 48

forms epithelial lining of gastrointenstinal and respiratory tracts; parenchyma of thyroid, parathyroids, thymus, liver, and pancreas; epithelial lining of tympanic cavity and auditory tube; epithelial lining of urninary bladder and urethra

INNER LININGS, GLAND ORGANS