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Embryology 1
Bastyr ISF Embryology Terms
55
Medical
Graduate
07/12/2012

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Term
Trophoblast
Definition
The outermost layer of cells of the blastocyst that attaches the fertilized ovum to the uterine wall and serves as a nutritive pathway for the embryo. Also called trophoderm.
Term
Totipotent vs Pluripotent
Definition
Totipotent -- can become anything

Pluripotent -- can become many things
Term
Morphogenesis
Definition
Differentiation of cells and tissues in the early embryo which results in establishing the form and structure of the various organs and parts of the body.
Term
3 types of cell signaling
Definition
Diffusible signal – morphogen
• BMPs
• Wnt

– Cell-­‐matrix
• integrins

– Cell-­‐cell
• induction
• Notch-­‐delta
Term
Induction
Definition
A cell secretes a substance that instructs a neighboring cell to adopt cell fate X.
Term
How different combinations of cell signals can yield different outcomes (4)
Definition
• Pattern formation (organization)
• Migration
• Proliferation (growth)
• Determination (differentiation)
Term
Transcription Factor
Definition
Proteins that are made that bind DNA and regulate gene transcription.
Term
Important Morphagens We Must Know (4)
Definition
•Retinoic acid
– Anterior-­‐posterior axis, limb patterning

• Transforming Growth Factor (TGF)-­‐β/Bone Morphogenic Proteins (BMPs)
– Dorsal-­‐ventral
axis, cell fate, organogenesis

• Hedgehog proteins
– Neural tube
D-­‐V patterning, limb (digit) formation

• Wnt/β-­‐catenin
– Posterior nervous system, planar cell polarity
Term
Fertilization Age vs Gestational Age
Definition
Gestational age is fertilization age + 2 weeks.

Fetilizational age used in embriology; Gestational age used clinically.
Term
Morula
Definition
The spherical embryonic mass of blastomeres formed before the blastula and resulting from cleavage of the zygote/fertilized ovum.
Term
Zona Pellucida
Definition
The strong membrane that forms around an ovum as it develops in the ovary. The membrane remains in place during the egg's travel through the fallopian tube. To fertilize the egg, a sperm must penetrate the thinning zona pellucida. If fertilization takes place, the zona pellucida disappears, to permit implantation in the uterus.
Term
Syncytiotrophoblast (4)
Definition
– Multinucleated, no cell membranes
– Invasive
– produces hCG
– Doubles every 48h for 1st month
Term
Amnion
Definition
The membrane of the amniotic sac specifically.
Term
Epiblast
Definition
The upper layer of the bilaminar embryonic disc present during the second week; it gives rise to ectoderm.
Term
Cytotrophoblast
Definition
“Stem cells” of the trophoblast; The inner layer of cells of the trophoblast of the early mammalian embryo that gives rise to the outer surface and villi of the chorion.
Term
Hypoblast
Definition
The lower layer of the bilaminar embryonic disc in a human embryo, present during the second week, that gives rise to the endoderm.
Term
Exocoelomic Membrane
Definition
A short lived combination of hypoblast cells and extracellular matrix; It surrounds the exocoelomic cavity. I.E. it lines the inner surface of the cytotrophoblast. Becomes the yolk sac.
Term
Cleavage
Definition
Series of mitotic divisions without cell growth; Zygote becomes a morula made up of blastomeres
Term
Compaction
Definition
Blastomeres change shape – more epithelial; Line up tightly together, just before blastocyst formation
Term
Blastocyst
Definition
A cluster of cells representing multiple cell divisions that have occurred in the fallopian tube after successful fertilization of an ovum by a sperm. This is the developmental form which must leave the fallopian tube, enter the uterus, and implant itself in the uterus to achieve actual pregnancy.

Made up of embryoblast, blastocoel (blastocyct cavity), trophoblast, and zona pellucida.
Term
Implantation (6)
Definition
Usually Around day 6

Blastocyst invades endometrium

• Trophoblast proliferates and differentiates into
– Cytotrophoblast
– Syncytiotrophoblast

• Embryoblast differentiates into
– Epiblast
– hypoblast
Embryonic cells flatten forming a bilaminar disk (Hypoblast, Epiblast)

• Begins week of 2s

Also forms two cavities
– Amniotic cavity
– Umbilical vesicle (yolk sac)
Term
Endometrial Decidual Cells (2)
Definition
– Engulfed by syncytiotrophoblast
– Early source of nutrients
Term
[DIAGNOSTICS] Signs of Ectopic Pregnancy (4)
Definition
1. hCG not doubling every 48 hours

2. Spotting around time of period* or abnormal period, but not always recognized

3. Abdominal pain

4. Referred shoulder pain

* Especially in tubal pregnancies

* NOTE: spotting in placenta previa is more~~~
Term
hCG (stands for)
Definition
Human Chorionic Gonadotropin
Term
Human Chorionic Gonadotropin (hCG)
Definition
Maintains the development of spiral arteries in the myometrium and formation of the synctiotrophoblast.
Term
Extraembryonic Mesoderm
Definition
Any mesoderm in the uterus that is not involved with the embryo itself. Included are mesoderms in the amnion, chorion, yolk sac, and connecting stalk; Develops as bilaminar embryo pulls away from cytotrophoblast.
Term
Extraembryonic Coelom
Definition
A cavity external to the developing embryo that forms between the mesoderm of the chorion and that covers the amniotic cavity and yolk sac; Becomes chorionic cavity/sac; Also called exocoelom.
Term
Gestational trophoblastic neoplasia (GTD)
Definition
A group of neoplastic disorders that originate in the placenta, including hydatidiform mole, chorioadenoma destruens, and choriocarcinoma.
Term
Chorioadenoma
Definition
A hydatidiform mole in which molar chorionic villi enter the myometrium or parametrium or, rarely, are transported to distant sites, most often the lungs; an epithelial cell tumor of the outermost fetal membrane that is the intermediate in the malignant development of a hydatid mole to invasive choriocarcinoma.
Term
[DIAGNOSTICS] Hyatidiform Mole (3)
Definition
• Marked proliferation of trophoblast
–usually blastocyst isn’t formed (or dies)

• hCG levels continue to rise (excessively)
–may be mistaken as pregnancy

• Preeclampsia in 1st trimester
–proteinuria and hypertension
Term
Choriocarcinoma (4)
Definition
A type of cancer germ cell containing trophoblast cells; usually of the placenta. May also arise in a testicle or ovary.

• Uncommon, often curable if detected early
• 50% of time follows a hydatidiform mole
Term
Chorionic Villi
Definition
Finger-like projections that emerge from the outer sac of an embryo; they will eventually form the placenta.
Term
Umbilical Vesicle (2)
Definition
As the embryo grows and folds, the umbilical vesicle gets pinched and incorporated into the embryo as gut tube and the walls contribute to the umbilical cord

• Germ cells also originate in umbilical vesicle and migrate into the embryo just before the formation of the gonads.
Term
What 7 things happen during Gastrulation?
Definition
Beginning of morphogenesis

Cell shape changes and rearrangement

Cell movement

Changes in cell contact properties

Development of three germ layers

A bit of overlap with neurulation

As gastrulation finishes, neurulation begins
Term
Trilaminar Embryo (3 germ layers)
Definition
Ectoderm

Mesoderm

Endoderm
Term
What 5 things does the ectoderm become?
Definition
Skin, nervous system, eye, inner ear, cerebral connective tissue
Term
What 3 things does the endoderm become?
Definition
Endoderm
Respiratory and GI epithelium, some glands
Term
What 5 things does the mesoderm become?
Definition
Skeletal muscle, blood, cardiovascular endothelium and muscle, connective tissue
Term
3 Cavities (what really happens at the end of week 2)
Definition
Umbilical vesicle

Amniotic sac

Chorionic sac (was extraembryonic coelom)
Term
Primitive Streak
Definition
An ectodermal ridge in the midline at the caudal end of the embryonic disk from which the intraembryonic mesoderm arises.

Note: the primitive streak is just a sign of gastrulation; it does not become anything and in fact disappears after gastrulation is complete
Term
Notochord Formation (4)
Definition
Some cells that move through the primitive streak migrate cranially through the mesoderm along the midline

Begins centrally and proceeds cranially as gastrulation is completing

Extends caudally once gastrulation is complete and primitive streak recedes

Important signaling structure subsequently signals neural tube and somite formation
Term
Somites
Definition
A segmental mass of mesoderm in the vertebrate embryo, occurring in pairs along the notochord.

These structures give rise to the vertebrae and differentiate into various tissues of the body, including the voluntary muscle, bones, connective tissue, and dermal layers of the skin.
Term
Neurulation (3)
Definition
Formation of the neural tube

-Notochord induces ectoderm to form neural plate
-Epithelial cells thicken and fold
-Neural crest cells form

Also developing at this time:
-Primitive heart tubes, blood vessels
-Somites (lateral signaling from notochord)
-Embryonic folding (dorsoventral and craniocaudal) also occuring
Term
Neural Crest
Definition
A cellular band dorsolateral to the embryonic neural tube that gives origin to the spinal ganglia and other structures.

As neural tube folds, dorsal cells pinch off and become sensory ganglia; Also contribute to pigment cells, adrenal gland, heart and connective tissue of the head
Term
Neurulation Defects (3 types)
Definition
Neural tube defects, vary in severity and location
-Spina bifida (variations)
-Anencephaly or meroencephaly – absence of most of the brain

Chordoma - a rare tumor that develops from the fetal notochord. It is usually located in the midline, behind the sella; it is slow growing but highly invasive.
Remnants of the notochord
Cranial or sacral
Late development in men (>50)

Neural crest defects
many organ systems, especially heart
Term
Malformations of Gastrulation (2)
Definition
Caudal dysplasia
-Varies greatly in severity – fused vertebrae or legs
-Abnormal mesoderm migration
-May be associated with cranial, renal, cardiovascular and anal defects

Sacrococcygeal teratoma
-Remnants of the primitive streak
-More common in females, cranial
-Usually very malignant – must be removed
Term
Blood Island
Definition
A primitive mesenchymal tissue that develops into bone marrow and blood vessels.
Term
Vasculogenesis (5)
Definition
Mesenchymal cells form angioblast blood islands in umbilical vesicle and other extraembryonic mesoderm – week 3

Also happens slightly later in embryo in lateral mesoderm

Angioblasts flatten and form endothelial lining

Budding and fusing arranges blood vessels

Endothelial cells become blood cells in vessels along umbilical vessel
Term
Heart Development (3)
Definition
Paired endocardial tubes develop from mesenchymal cells in cardiogenic region

During folding tubes fuse and form primitive heart tube and join with other vessels

Heart begins to beat and blood is pumping at the end of the 3rd week or very beginning of the 4th week
Term
Integrin
Definition
One of a large and very important family of adhesion molecules that promote stable interactions between cells and their environment. The integrins also act as cellular sensor and signaling molecules.
Term
Chorion
Definition
The cellular, outermost extraembryonic membrane, composed of trophoblast lined with mesoderm; it develops villi, becomes vascularized by allantoic vessels, and forms the fetal part of the placenta.
Term
Progression of embryo from week 0 to beginning of week 2
Definition
Begins as oocte

Becomes fertilized zygote

Cleaves to become a morula made of blastomeres

Compacts to becom blastocyst made of embryoblast (becomes stem cells), trophoblast (beomces placenta), zona pellucida, and blastocoel (blastocyct cavity)

Begin week 2
Implants and forms synctiotrophoblast (from trophoblast), bilaminar embryonic disc (from embryoblast) made of epiblast and hypoblast, amnion and amniotic cavity form, and blastocoel (blastocyct cavity) becomes exocoelomic cavity & membrane briefly before becoming the primary umbilical vesicle, closing plug forms, cytotrophoblast forms from trophoblast, and between disc amnion and cytotrophoblast is the extraembryonic mesoderm
Term
Closing Plug
Definition
A fibrinous coagulum of blood that fills the defect in the endometrial epithelium created by implantation of the blastocyst.
Term
Yolk Sac
Definition
a membranous sac attached to an embryo, providing early nourishment.

Also known as the exocoelomic cavity.
Term
Embryoblast
Definition
Any of the germinal disk cells of the inner cell mass in the blastocyst.

Differentiates into
– Epiblast
– hypoblast
Embryonic cells flatten forming a bilaminar disk (Hypoblast, Epiblast)
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