Weeks 1-2 Flashcards Preview

CBNS169 Human Embryology > Weeks 1-2 > Flashcards

Flashcards in Weeks 1-2 Deck (27):
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Early embryonic development (just a simple image)

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CLEAVAGE

THESE FIGS SHOWN PREIMPLANTATION EMBRYOS GOING THROUGH CLEAVAGE

OCCURS IN THE OVIDUCT

THE FINAL STAGE IS THE BLASTOCYST - NOTE TROPHOBLAST, INNER CELL MASS AND BLASTOCYST CAVITY

COMPACTION OCCURS DURING CLEAVAGE
FIRST DIFFERENTIATION EVENT DURING DEVELOPMENT

Cleavage and the first 4-5 days of development occur in the isthmus of the ampulla

 

Mitotic division. 2 cell

ZP stays intact until zygote is in the uterus. Cells called blastomeres  (2 cell stage) divide, etc.

 

 

A mature blastocyst has about 250 cells

 

 

Inner cell mass vs. trophoblast

Cavity in middle=blastocyst cavity.

Older stage plastocyst has no zona pellucida

inner cell mass becomes the embryo

Trophoblast has extra embryonic tissue (esp. placenta)

cannot implant without the ZP around the blastocyst. 

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COMPACTION

UNCOMPACTED VS COMPACTED EMBRYO

DIAGRAM SHOWS MECHANISM OF COMPACTION

5 CELLS ORGANIZE ON  PERIPHERY OF EMBYRO

THREE CELLS ARE LOCATED IN THE CENTER OF EMBRYO

IMPORTANT BECAUSE IT IS THE FIRST DIFFERENTIATION EVENT IN HUMAN DEVELOPMENT

 

Boundaries "zip up" harder to tell if cells are separate or together. 

Cut through, 3 cells middle, 5 outside. 3 middle cells-->inncer cell mass------>30 cells

5 outside--> trophoblast-------->200 cells

No cavity at the 8 cell stage.

E-Cadherin is the molecule for cell to cell adhesion. Extracellular domains bind to other calhedrins. homophilic=binding where 2 protiens are the same.

 

There is an antibody treatment that blocks compaction.

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ROLE OF CADHERIN IN COMPACTION

WHAT MOLECULE BRINGS ABOUT COMPACTION?

CELL ADHESION MOLECULES- CAUSE CELL TO STICK TO CELLS OR TO ECM

CADHERIN = CELL ADHESION MOLECULE
DIAGRAM OF DOMAINS OF CADHERIN
EXTRACELLULAR DOMAIN FUNCTIONS IN BINDING

CADHERIN IS CALCIUM DEPENDENT

HOMOPHILIC BINDING – CAUSES ADJACENT PMs TO ZIP UP

 

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EXPERIMENTAL EVIDENCE THAT E-CADHERIN FUNCTIONS IN COMPACTION

antibodies specific to E-Cadherin blocks compaction

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HOW DO YOU KNOW THE FUNCTION OF A PROTEIN??

RNA Gene KO, antibody, knock down mRNA (no translation)

synthesize complementary strands, mRNA destroyed. knock down. 

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BLASTOCYST FORMATION AND HATCHING

Strysin? 

Sense mRNA strypsin increases mRNA---> hatches

no mRNA--->hatches

antisense mRNA to strypsin hybridizes to strypsin mRNA (gets destroyed)--> no hatching

 

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Size of the Blastocyst

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Another Huge Achievement in IVF 2010

Video microscopy and video bioinformatics
Study from Renee Peras lab provided new information that enables prediction of which embryos will develop into normal blastocysts by events occurring during the first two cleavages

 

IVF lab had > 100 zygotes. Let the oocytes divide on plate. Time lapse videos made from that. 

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Embryonic Stem Cells

Human embryonic stem cells come from the inner cell mass. We can use antibodies for the trophoblast or mictodissection to obtain them. Can be plated and passaged indefinitely.---Regenerative medicine/Clinical trials

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IMPLANTATION DAY 6

BLASTOCYST ATTACHES TO ENDOMETRIUM - SOON AFTER HATCHING

ATTACHES TO INNER CELL MASS IS CLOSE TO ENDOMETRIUM

ENDOMETRIUM IS IN SECRETORY PHASE
HAS RICH SUPPLY OF BLOOD VESSELS

IMPLANTS IN POSTERIOR WALL 2/3 TIME
IMPLANTS IN ANTERIOR WALL 1/3 TIME
 

Implantation-best =posterior dorsal wall

inner cell mass needs to be adjacent to endometrium

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IMPLANTATION DAY 7

INNER CELL MASS DIFFERENTIATES

FORMS HYPOBLAST

TROPHOBLAST INVADES ENDOMETRIUM

DIFFERENTIATES INTO:
SYNCYTIOTROPHOBLAST
CYTOTROPHOBLAST

BY END OF  FIRST WEEK BLASTOCYST IS SUPERFICIALLY IMPLANTED IN ENDOMETRIUM

 

Two types of trophoblast: cytotrophoblast and syncytiotrophoblast (no plasma membranes. huge cell with many nuclei. Very invasive, fast, anchors blastocyst)

Inner cell mass becomes the bilaminar embryonic disc (epiblast+hypoblast)

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WEEK 2 OF DEVELOPMENT (brief)

BILAMINAR EMBRYONIC DISC FORMS
EPIBLAST
HYPOBLAST

AMNION, CHORION, YOLK SAC,
  CONNECTING STALK FORM

TROPHOBLAST DIFFERENTIATES

 

Inner cell mass becomes the bilaminar embryonic disc. (see above)

 

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IMPLANTATION

EPIBLAST/HYPOBLAST

AMNION/AMNIOTIC CAVITY

HEUSER’SMEMBRANE/
PRIMARY YOLK SAC

SYNCYTIOTROPHOBLAST
LACUNAE

INTERSTITAL IMPLANTATION

 

Interstitial implantion: the blastocyst implants superficially, then burrows into the endometrium, becomes embedded in the uterine wall (endometrium)

Cavities form in the syncytiotrophoblast (lacunae) etc. 

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FORMATION OF THE CHORION
AND EXTRAEMBRYONIC MESODERM

EE RETICULUM

EE SPLANCHNIC MESODERM

EE SOMATIC MESODERM

CHORIONIC CAVITY

CHORION

UTEROPLACENTAL
CIRCULATION
(EE=ExtraEmbryonic)

Heuser's membrane goes around the cytotrophoblast--->blastocyst cavity--->Primary holk sac

Syncytiotrophoblast grows-blood goes into some lacunae. This eventually becomes the placenta. 

Pink between Heuser's membrane and the cytotrophoblast is the extracellular matrix. Blue is the epiblast

yellowish color is the hypoblast

extraembryonic mesoderm-->Splachnic (gut...rises from Heuser's membrane) and somatic (from the cytotrophoblast)

Cavities in the matrix will fuse to become one cavity--the Chorionic cavity. Chorion-wall distal to cavity

Placental tissues > embryo

cytotrophoblast-primary villi form into syncytoblast at the end of week two.

The primary yolk sac--->secondary holk sac

~50% of fertilized eggs last to the end of week 3. 

 

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FORMATION OF THE SECONDARY YOLK SAC

SECONDARY YOLK SAC

CONNECTING STALK

PRIMARY VILLI

 

 

SPACES FORM IN EE-MESODERM FORMING CHORIONIC CAVITY

EE MESODERM IS SLIT INTO 2 LAYERS SOMATIC AND SPLANCHNIC

CONNECTING STALK - NOT SPLIT

CHORION FORMED = EE SOMATIC MESODERM + TROPHOBLAST - THIS BECOMES FETAL PART OF PLACENTA

YOLK SAC GETS SMALLER

EMBRYO HAS NOT CHANGED MUCH - EXCEPT PROCHORDAL PLATE HAS FORMED

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ABNORMAL DEVELOPMENT OF FIRST AND SECOND WEEK

ABNORMAL ZYGOTES/PEs

NON-SURVIVAL OF FERTILIZED OVA

ECTOPIC IMPLANTATION
TUBAL PREGNANCY

PLACENTA PRAEVIA
 

PE EMBRYOS MAY HAVE DEGENERATE CELLS ETC; MAY NOT IMPLANT; HAPPENS OFTEN

ABOUT 50% OF FERTILIZED OVA ARE LOST DURING FIRST 3 WEEKS
GENETIC PROBLEMS
CL MAY NOT FUNCTION PROPERLY
TUMORS OR LESIONS IN UTERUS
BLOCKED TUBES

ECTOPIC IMPLANTATION
MOST COMMON SITE =OVIDUCT
ABDOMINAL IMPLANTATION
DANGEROUS AND LIFE THREATENING TO MOTHER
ABDOMINAL PAIN, BLEEDING
MUST BE TREATED OR MOTHER CAN HEMORRHAGE
LEADING Cause OF MATERNAL DEATH DURING FIRST TRIMESTER

PLACENTA PREVIA - IMPLANTATION NEAR CERVIX
PLACENTA MAY BE SMALL
MAY RUPTURE PREMATURELY
NEEDS WATCHING

 

Placenta Previa: placenta blocks the cervix. could disengage prematurally.

Most ectopic pregnancies are in the oviduct, but sometimes in the abdominal cavity. It's rare, but they can be carried to term. 

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 Places where ectopic pregnancies can occur (image only)

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TUBAL PREGNANCY images

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HYDATIDIFORM MOLE

lots of vesicles (look like grapes)

2 variations:

1. partial-2 sperm fertilize an oocyte (dispermy)-->3 pronuclei-->extra chromosomes. High levels of hCG. months 4-7. results in fetal death

2. Complete-oocyte kicks out nucleus, ends up having only male genes. Dispermy or one sperm divides to give 2 nuclei. If placental tissue is not removed, it leads to the formation of choriocarcinoma (type of cancer), which metastasizes very easily and quickly. Leads to maternal death. 

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PARTIAL HYDATIDIFORM MOLE

PARTIAL HYDATIDIFORM MOLES HAVE FEMALE AND MALE DNA

NOTE THE PARTIAL MOLE IS TRIPLOID
 

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COMPLETE HYDATIDIFORM MOLE

TWO WAYS COMPLETE HYDATIDIFORM MOLE MAY OCCUR

FERTILIZATION BY 2 SPERM WITH LOSS OF FEMALE PRONUCLEUS

FERTILIZATION BY ONE SPERM. FEMLAE PRONUCLEUS IS LOST AND SPERM DUPLICATES ITS DNA TO PRODUCE DIPLOID CELL

NOTE: IN BOTH CASES THE ZYGOTE CONTAINS DNA ONLY FROM MALE
 

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CHORIOCARCINOMA image only

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GENOMIC IMPRINTING

EXPERIMENTS ON LEFT SHOW WHAT DEVELOPS IF GENOME IS DERIVED ALL FROM MALE OR ALL FROM FEMALE

WHAT DO THESE RESULTS SUGGEST?

SOME GENES IN HUMANS ARE IMPRINTED - THINK OF IMPRINTING AS SILENCING

DURING MEIOSIS SOME GENES IN MALES GET TURNED OFF - SAME GENE STAYS ON IN FEMALES

VICE VERSA ALSO OCCURS

IF ZYGOTE INHERITS BOTH MATERNAL AND PATERNAL DNA IT IS OK

IF IT GETS ALL DNA FROM ONE GENDER, SOME GENES WILL NOT WORK AND DEVELOPMENT DOES NOT GO VERY FAR

 

 

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Genomic Imprinting – When Does It Happen?

Genomic imprinting occurs during gametogenesis. Imprints are erased and then later re-established. 

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Gene Inactivation

Genomic Imprinting – regulated in a parent of origin manner-as we just saw  (e.g. IGF2 paternal on; H19 maternal on)

X inactivation- random process- half cells inactivate maternal X chromosome and half inactivate paternal X chromosome

Monoallelic expression of autosomal genes
November 2007 Gimelbrant et al (Science 318:1136) showed that about 1000 genes exhibit monoallelic expression-
Cells may have maternal gene on, paternal gene on or both maternal and paternal gene on
Many are cell surface receptors
Could generate diversity in individual cells and their clonal descendants

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