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Anatomy Exam 1 > Embryology > Flashcards

Flashcards in Embryology Deck (49):
1

Zygote

Union of egg + Sperm

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Cleavage

Process by which zygote divides via mitotic division. Rapid cell cycles w/ no significant growth. Product of cleavage is called Blastomeres

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Blastomeres

Cells produced by cleavage

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Morula

At 16 blastomeres (approx 4 days) zygote becomes morula. Named after mulberries. Continues to move toward uterus.

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Blastocystic Cavity

Uterine fluid invades the morula, forming a cavity

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Blastocyst

Morula transitions to blastocyst when blastomeres begin to arrange into masses/structure. Hollow structure. Two components: Embryoblast and Trophoblast

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Embryoblast

Inner cell mass. Future embryo

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Trophoblast

Outer cell mass. Future embryonic placenta

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Hypoblast

Layer of embryoblast becomes the hypoblast (primitive endoderm)

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Events of implantation

By end of week one (day 6). Blastocyst attaches to endometrium (lining of uterine wall). Trophoblast contacts endometrium and begins differentiation into cytotrophoblast and syncytiotrophoblast.

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Cytotrophoblast

Inner layer of trophoblast. Contributes to burgeoning trophoblast

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Syncytiotrophoblast

Outer layer of trophoblast. Means "without cells". Undifferentiated, invades into uterine wall. Releases many enzymes that allows it to penetrated aggressively further/deeper into endometrium. Produces HCG: Human coreanic gonadotropin, + on pregnancy tests, important for maintain endometrium of uterus so not expelled

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Ectopic Pregnancy

Implantation usually occurs in posterior uterine wall, but ectopic pregnancies can occur (usually in uterine tube [tubal], rare cases in abdominal cavity [intraabdominal])

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Bilaminar Disc

Occurs at week 2. 2 layers form: Epiblast and Hypoblast in addition to several cavities.

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Epiblast

Floor of the amnitotic cavity, continuous with the amnion. Upper level of bilaminar disc

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Amnion

Thin membrane that closely covers the embryo, surrounds and forms the amniotic cavity

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Amniotic Cavity

fluid-filled cavity that surrounds the developing embryo.

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Hypoblast during Implantation

roof of the exocoelomic cavity (was the blastocyst cavity), and is continuous with the exocoelomic membrane. Lower level of bilaminar disc

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Exocoelomic Cavity

Artist formerly known as blastocystic cavity. lined by hypoblasts and the exocoelomic membrane. It will become the primary umbilical vesicle (aka the “yolk sac” in older texts).

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Exocoelomic Membrane

Lines exocoelomic cavity along with hypoblast.

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Primary Umbilical Vesicle

Primary Yolk Sac. Develops from exocoelomic cavity around day 12. Fully implanted by this point

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Extraembryonic Mesoderm

Mesoderm not part of the embryo. Mesoderms of the amnion, chorion, umbilical vesicle

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Extraembryonic Coelem

arises within the extraembryonic mesoderm. It will become the chorionic cavity.

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Chorionic Cavity

Formed by extraembryonic coelom. part of the chorionic sac, whose walls are formed by the chorion (extraembryonic mesoderm + trophoblasts). The embryo, amniotic sac, and secondary umbilical vesicle hang within the chorionic sac via the connecting stalk (future umbilical cord).

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Secondary Umbilical Vesicle

Largery than Primary umbilical vesicle. Forms around end of 2 weeks and the primary umbilical vesicle pinches off and disappears. Surrounded by splanchnic mesoderm

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Splanchnic mesoderm

surrounds umbilical vesicle. Will form gut wall.

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Connecting Stalk

Will become umbilical cord. Attaches

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Uteroplacental Circulation

As the syncytiotrophoblast burrows into uterine wall, lacunae appear and fill with maternal blood. Syncitiotrophoblast produce HCG hormone. iii. Decidual reaction (cells) in the endometrial connective tissue will respond to the invading syncytiotrophoblast, providing an immunological privileged site. These cells will become the maternal contribution to the placenta. Primary chorionic villa appear from the cytotrophoblast, and will be the embryonic contribution to the placenta

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Decidual Cells

swell with glycogen and lipid to form a boundary in order to protect embryo from immune response. This becomes the mother’s contribution to placenta

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Primary Chorionic Villi

Appear from the cytotrophoblast, become the embryonic contribution to placenta.

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Gastrulation

Conversion of bilaminar disc into trilaminar disc. Begins with formation of primitive streak, formed from migrating epiblasts. Epiblasts migrate medially and “dive into” primitive pit, migrating to different layers. Near the cranial end, the primitive node and primitive pit form, with the primitive groove extending caudally

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Trilaminar Disc

Ectoderm, Mesoderm, and Endoderm

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Ectoderm

outer layer, stay where they are after migration (previously the epiblast) will become the epidermis & nervous system

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Mesoderm

middle layer, will become various muscle & connective tissues (mesenchyme

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Endoderm

Inner layer, replacing the hypoblastwill become the lining of the gut tube

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Notochord

mesenchymal cells thicken into the notochordal plate within the mesoderm, and will fold into a rod known as the notochord. Defines embryo's axis, forms basis for axial skeleton, induces ectoderm to form the nervous system. Remains part of intervertebral discs in adults

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Formation of Neural Tube (Neuralation)

After induction of the ectoderm by the notochord, the neural tube will start forming via the process neurulation. Neural tube will become the CNS. Neural crest will become the PNS and other structures (melanocytes).

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Spina bifida

Improper fusion of the neural tube caudally results in spina bifida, a disease of varying degrees and symptoms.

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Spina Bifida Oculta

Mildest and frequently asymptomatic. Neural tube does not fuse completely, but spinal cord does not poke through

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Spina bifida meningocele

Least common. Vertebrae/spinal cord develop normally, but meninges poke through gap in spinal cord.

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Spina Bifida Myelomeningocele

More severe. Unfused portion of spinal cord allows spinal cord AND meninges to protrude through

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Spina bifide myeloschesis

Most severe. Spinal cord passes through unfused portion with no meningeal protection leaving it exposed

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Paraxial Mesoderm

Most medial to notochord. will form most of the axial skeleton, muscles, & dermis. Gives rise to somites.

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Somites

Differentiate into myotomes, dermatomes, sclerotomes

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Intermediate Mesoderm

Between paraxial and lateral mesoderms. will form the urogenital system

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Lateral Mesoderm

continuous with the extraembryonic mesoderm. will form the body walls. It divides into two layers: the somatic (parietal) and the splanchnic (visceral) layer.

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Somatic (Parietal) Layer

somatopleure (somatic mesoderm + embryonic ectoderm) will form the outer body wall

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Sphlanchnic Mesoderm

Splanchopleure (splanchnic mesoderm + embryonic endoderm) will form the gut wall.

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Intraembryonic Coelem (Body Cavity)

begins as small spaces within the lateral mesoderm that coalesce. (It is these spaces that cause the lateral mesoderm to divide into the 2 layers.) Eventually divides into pleural, pericardial, and peritoneal cavities.