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55 Cards in this Set

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what stage does the zygote progress to in order to being implantation
During the first weeks following fertilization, the zygote progresses to the blastocysts stage and beings implantation into the endometrium
What is occurring in the Bilaminar germ disc in the 2nd weeks Outer Cell Mass
Outer Cell Mass: Trophoblast
1. During implantation the blastocyst settles on its embryonic pole and the trophoblast over the embryoblast differentiates into two layers:
2. The cytotrophoblast, syncytitrophoblast, and extraembryonic somatopleuric mesoderm form the components of the fetal side of the placenta
what forms the components of the fetal side of the placenta in the 2nd week of development?
Extraembryonic somtopleuric mesoderm
Describe the Inner cell mass during the 2nd week of development
1. Hypoblast (primary endoderm): first recognizable layer to form and gives rise to the extraembryonic endoderm that lines the primary yolk sac
2. Epiblast (primary ectoderm): this layer develops concurrently with the hypoblast and is immediately adjacent to the trophoblast. This layer eventually gives rise to the 3 definitive germ layers of the embryo
what is the first recognizable germ layer to form in the bilaminar germ disc?
Hypoblast (Embryoblast)
where does the amniotic cavity develop?
develops within the epiblast
what gives rise to the 3 definitive germ layers of the embryo?
what are the 3 definitive germ layers of the embryo?
describe the Extraembryonic mesoderm
derived from primary yolk sac cells and cells from the epiblast which ultimately surround the germ disc, amniotic vesicle, and primary yolk sac.
This mesoderm forms a loose meshwork between the embryo and trophoblast. A secondary cavity forms in this mesoderm, the chorionic cavity, which splits the mesoderm except in one area which suspends the embryonic disc into the cavity. This uncleaved mesoderm is the connecting stalk which will become the umbilical cord
what is the most important event during the 3rd week of development?
what is Gastrulation?
occurs during the 3rd week of development
Formation of 3 definitive germ layers, three structures, and a third fetal membrane
what are the 3 definitive germ layers formed during Gastrulation?
What are the three structures formed during Gastrulation?
Primitive Streak
Neural Plate
What is the third fetal membrane formed during Gastrulation?
What indicates the beginning of Gastrulation?
appearance of the primitive streak
Where does the primitive streak appear?
It appears at the caudal end of the disc and is the structure that imparts bilateral symmetry to the embryo as well as a craniocaudal aspect
what structure imparts a bilateral symmetry to the embryo?
Primitive streak
How is the intraembryonic mesoderm formed?
Epiblast cells move toward the primitive streak then invaginate and assume a new position below the epiblast and above the hypoblast.
The cells of this layer spread in all directions and become continuous with the extraembryonic mesoderm at the periphery of the disc
What forms the definitive endoderm
Epiblast cells displace the hypoblast and form the definitive endoderm
what do the remaining cells of the epiblast become?
Definitive Ectoderm
True or False
The epiblast forms all three germ layers of the trilaminar germ disc
Describe the formation of the Notochord
1. Prenotochordal cells move from primitive pit of the primitive node and extend to the prechordal plate.
2. As the hypoblast is replaced with the endoderm the prenotochordal cells lift from the hypoblast and from the definitive notochord
3. Neurenteric canal: is a small canal that brings the amniotic and yolk sacs into continuity for a brief time
4. The notochord plays a major inductive role in the formation of the neural plate and serves as the axis of formation of the axial skeleton and associated musculature.
what does the notochord persist as in the adult?
Nucleus puplosus
How long does the primitive streak persist in the embryo?
The primitive streak will persist until the 4th week and eventually disappear.
What happens if remnants of the primitive streak persist?
Remnants of the primitive streak may persist and may give rise to multiple tissue tumors called teratomas
Intraembryonic mesoderm is derived from what?
Intraembryonic mesoderm is derived from the primitive node and the primitive streak
what is the Notochord derived from?
Notochord is derived from cranial portion of primitive node
what is the paraxial mesoderm derived from?
from node and cranial portion of primitive streak
what is the intermediate mesoderm derived from?
mid primitive streak
what is the lateral plate mesoderm derived from?
from caudal primitive streak
what is the extraembryonic mesoderm derived from ?
most caudal primitive streak
What expresses genes essential for head formation?
Anterior Visceral Endoderm (AVE)
What initiates and maintains the primitive streak?
What works in concert to ventralize the mesoderm that contributes to kidneys, blood, and body wall mesoderm?
Bone Morphogenetic Protein-4 (BMP-4)
Fibroblastic Growth Factor (FGF)
What does the expression of Noggin, Chordin, and Follistatin cause?
Noggin, Chordin, and Follistatin are expressed in the primitive node and antagonize the action of BMP-4 that results in dorsalization of notochord and paraxial mesoderm (head regions of germ disc)
What does Brachyury (T) genes expression do?
Brachyrury (T) genes regulates mesoderm formation in the middle and caudal regions of the germ disc.
What does Absence of Brachyury (T) gene cause?
Sirenomelia (caudal dysgenesis)
-mermaid syndrome: legs are fused together
what molecule maintains primitive node and is necessary for forebrain and midbrain differentiation?
Hepatic Nuclear Factor 3-beta
how is the left and right side of the body differentiated?
FGF-8: induces expression of nodal and lefty-2 genes on left side of germ disc. This results in upregulation of PITX2 which establishes left side of the embryo.
Lefty-1: is expressed from left side of floor plate of neural tube and acts as a barrier preventing left-sided factors going to right side.
what is Sonic Hedgehog function in left and right side development?
Shh has similar function to lefty-1 and suppresses left-side genes on the right. Shh is expressed by the notochord
what is the function of the amniotic fluid?
symmetrical growth of embryo
prevents adherence of amnion
maintains temperature
prevents mechanical trauma
allows for movement
fluid wedge at partuition
allows for estimation of fetal maturity
describe the growth of the amniotic sac.
Growth of the amniotic sac eventually expands and obliterates the chorionic cavity and completely surrounds the developing embryo and umbilical cord
how is amniotic fluid acquired during early pregnancy?
amniotic fluid is acquired by simple diffusion from the endometrium
how is amniotic fluid maintained during late pregnancy?
the fetal kidney produces urine to increase volume
(normal amount 800-1000 cc)
excess of amniotic fluid in the amniotic sac
-anencephalia, gastrointestinal atresia, diabetes
deficiency of amniotic fluid
-urinary system malformation, renal atresia, hypoplasia, or polycystic kidneys
what is the function of the yolk sac?
1. Never contains yolk in the human but may play a limited role in metabolism of embryonic nutrients
2. Is the first site of hematopoiesis and may produce serum proteins
3. Gives rise to the germ cells that later populate the gonads
4. Normally disappears before birth but its connection to the developing gut may persists as Meckel's diverticulum
what is Merckel's diverticulum?
malformation of the gastrointestinal tract
What does Allantois develop from?
develops from the caudal wall of the yolk sac around the 16th day
what may induce the formation of vitelline and umbilical vessels?
what persists in adults as the median umbilical ligament?
What are derivative of the Ectoderm?
1. Central Nervous System
2. Peripheral Nervous System
3. Sensory epithelium (ear, eye, nose)
4. Epidermis of skin (hair, nails, sweat glands, mammary glands)
5. Pituitary gland
6. Enamel of teeth
What germ layer are:
supporting tissues such as CT, Cartilage, Bone, Muscle (striated & smooth), blood & lymph, heart, blood, and lymph vessel walls, the kidneys, gonads, suprarenal gland cortex, and the spleen derived from?
what are some organs derived from the mesoderm?
Adrenal cortex
what are derivatives of the Endoderm?
1. lining of the gut and parenchyma of associated organs
(Liver, Gall Bladder, Pancreas)
2. Lining of respiratory system
3. Lining of urinary bladder
4. Parenchyma of thyroid and parathyroid
5. Lining of tympanic cavity and auditory tube