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CBNS169 Human Embryology > Week 3 > Flashcards

Flashcards in Week 3 Deck (24):
1

Lewis Wolpert Quote

It is not birth, marriage or death, but gastrulation, which is truly the mostimportant time in your life. Lewis Wolpert (1986) ...

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WEEK 3 OF DEVELOPMENT

RAPID DEVELOPMENT OF CONCEPTUS (embryo+placenta)

TRILAMINAR EMBRYONIC DISC FORMS (week 2=bilaminar, week three-->trilaminar)

FORMATION OF:
PRIMITIVE STREAK, EMBRYONIC MESODERM, NOTOCHORD
NEURAL TUBE
SOMITES
INTRAEMBRYONIC COELOM
BLOOD VESSELS AND CELLS
CHORIONIC VILLI

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PRIMITIVE STREAK AND FORMATION OF THE TRILAMINAR EMBRYO

ORIENTATION

BILAMINAR EMBRYONIC DISK SITS ON TOP OF YOLK SAC

BIRD’S EYE VIEW OF EMBRYO SHOWING POSITION OF PS

 

migration of epiblast cells move towards line, pinch off groove, move away. 

Oropharyngeal membrane-remains bilaminar

Cardiogenic area-heart formation

most of hypoblast replaced by migrating cells from epiderm-->endoderm

Rest of epiderm=mesoderm

Gastrulation continues through week 4

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GASTRULATION

Formation of the three germ layers

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GASTRULATION- an epithelial to mesenchymal transition

mesoderm goes everywhere except oropharangeal membrane and cloacal membrane.

the three layers formed in gastrulation become everything. 

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MIGRATION OF EPIBLAST CELLS

OROPHARYNGEAL MEMBRANE AND CLOACAL MEMBRANE – DISC REMAINS BILAMINAR

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IF DEVELOPMENT PROCEEDS NORMALLY THE 3 GERM LAYERS GIVE RISE TO THE TISSUES/PORGANS INDICATED IN THIS SLIDE

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 CONGENITAL DEFECTS OF PRIMITIVE STREAK

Teratoma in female

TERATOMA = TUMOR OF PRIMITIVE STREAK ORIGIN
EXPLAIN SITES AND CONTENTS
MORE COMMON IN FEMALES THAN MALES

MAY CONTAIN TISSUES FROM ALL THREE GERM LAYERS

CAN BECOME MALIGNANT - REMOVED SURGICALLY

Sacrococygeal teratoma=tumor. Forms when primitive streak fails to recede. Pluripotent cells, so inside tumor there are all tissue types. Surgically removed after birth. Typically benign, but can develop to become malignant. happens in 1/35,000 births. Most common form of cancer in newborns. 

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Other Examples of Teratomas

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CONGENITAL DEFECTS OF PRIMITIVE STREAK-CAUDAL DYSGENESIS

CAUDAL DYSGENESIS OR DISPLASIA
Sirenomelia

CAUDAL DYSGENESIS
NOT ENOUGH MESODERM IN CAUDAL REGION
EFFECTS DEVELOPMENT OF LIMBS (SHORT AND FUSED)
VERTEBRA, KIDNEYS AND GENITAL ORGANS ALSO AFFECTED - SMALL OR AGENESIS
 

Not enough mesoderm. Caudal area most affected. under-developed lower half of body. Might be affected by the gene Brachyury, which encodes a transcription factor that causes teh formation of mesoderm. Graded affects

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NEURULATION - WEEK 3

NEURULATION = DIFFERENTIATION OF NEURAL ECTODERM - IMPT

ECTODERM OVER NOTOCHORD THICKENS = NEURAL PLATE
NOTOCHORD INDUCES FORMATION OF PLATE

NEURAL PLATE INVAGINATED AND SOME CELLS CAUGHT AT CREST OF INVAGINATION DIFFERENTIATE

NEURAL FOLDS MEET AND FUSE DORSALLY
CLOSURE BEGINS IN MIDDLE OF EMBRYO AND PROCEEDS ANT  AND POSTERIORLY

CLOSURE FORMS:
NEURAL TUBE
NEURAL CREST CELLS
SURFACE ECTODERM  RESEALS
NCC LATER MIGRATE TO MANY PLACES - HAVE MANY DERIVATIVES
 

 

Neural tube: plate of thick cell layers

cells on edge of fold pinch together. the neural tube becomes teh spinal cord and brain

 

Neural crest cells have many derivatives. It begins formation in the middle of the embryo and works its way out. 

The openings left in the tail and head are neuropores. they eventually close

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NEURULATION (images)

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Mesoderm Development

During week three mesoderm differentiates into distinct regions

Paraxial mesoderm
Intermediate mesoderm
Lateral mesoderm  - somatic and splanchnic
 

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DEVELOPMENT OF NOTOCHORDAL MESODERM

MESODERM DIFFERENTIATE AS SHOWN ABOVE

MENTION DERIVATIVES OF EACH TYPE OF MESODERM
 

Notochord-->below neural tube. Notochord eventually becomes part of spinal cord

Paraxial mesoderm makes blocks of tissue (somites) form caudally ~44 pairs of somites after somatogenesis

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DEVELOPMENT OF PARAXIAL MESODERM

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DEVELOPMENT OF THE SOMITES

SOMITE FORMATION

SOMITES FORM IN PAIRS ON EITHER SIDE OF NOTOCHORD

APPEAR AS BUMPS EXTERNALLY

BEGINS ON DAY 20 AND EXTENDS INTO WEEK 4

42-44 PAIRS OF SOMITES FORM

EACH  SOMITE DIFFERENTIATES AS ABOVE
 

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DEVELOPMENT OF  INTERMEDIATE MESODERM

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DEVELOPMENT OF LATERAL PLATE MESODERM

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Summary of Mesoderms and Their Fates

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BLOOD VESSEL FORMATION

BLOOD VESSELS BEGIN FORMING DURING WEEK THREE

FIRST FORM IN THE WALL OF THE YOLK SAC

LATER FORM IN THE LATERAL PLATE MESODERM

FORM FIRST BY VASCULOGENESIS

FIRST VASCULATURE GROWS AND IS REMODELLED BY ANGIOGENESIS

 

BLOOD VESSELS BEGIN FORMING ON DAYS 13-15 IN WALL OF YOLK SAC - FORM SL LATER IN EMBRYO

 

Angiogenesis-the formation of blood vessels from pre-existing blood vessels

Blast means it will become something else. 

Endothelial cells line blood vessels

 

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VASCULOGENESIS

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VASCULOGENESIS:
MESODERM RESPONDS TO FGF2 – DIFFERENTIATES INTO                  HEMANGIOBLASTS – A PRECURSOR CELL THAT GIVES RISE TO BLOOD VESSELS AND BLOOD CELLS

SOME HEMANGIOBLASTS BECOME PLURIPOTENT STEM CELLS THAT EVENTAULLY GIVE RISE TO ALL THE TYPES OF BLOOD CELLS

SOME HEMAGIOBLASTS RESPOND TO VEGF AND DIFFERENTIATE INTO ANGIOBLASTS. VEGF IS SECRETED BY SURROUNDING MESENCHYME

ANGIOBLASTS THEN RESPOND TO VEGF BY DIFFERENTIATING INTO ENDOTHLIAL CELLS – CELLS THAT LINE OUR BLOOD VESSELS

 

HEMANGIOBLASTS -DEVELOP FROM MESODERM - AGGREGATE TO FORM  BLOOD ISLANDS – EXPLAIN  ISLAND

AS HEMANGHIOBLASTS DIFFERENTIATE, ENDOTHELIUM BECOMES LOCATED ON THE OUTSIDE AND CELLS CAUGHT IN CENTER DIFFERENTIATE INTO BLOOD CELLS.

ADJACENT BLOOD ISLANDS FUSE FORMING PRIMITIVE BLOOD VESSELS

EVENTUALLY BLOOD ISLANDS HOOK UP TO FORM CIRCULATORY SYSTEM

HEART BEGINS FORMING VIA THIS PROCESS IN CARDIOGENIC AREA-  BECOMES FUNCTION BY END OF THIRD WEEK
    FIRST ORGAN SYSTEM TO FUNCTION IN HUMAN

HISTOSECTION SHOWING A BLOOD ISALND

MOUSE HETEROZYGOUS FOR VEGF – ONE MUTATED ALLELE – BLOOD VESSELS DO NOT FORM IN YOLK SAC – IT DIES

 

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ANGIOGENESIS

ONCE PRIMITIVE VASCULATURE HAS FORMED, VESSELS CAN SPROUT AND GROWTH OFF THE FIRST VESSELS

MANY FACTORS CAN REGULATE THE COMPLEX PROECESS OF ANGIOGENESIS

VEGF IS ONE FACTOR IMPORTANT IN THIS PORCESS

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Primitive Circulation as It Appears in A Human Embryo on Day 21

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Teratogenesis and Week 3

Embryo is very sensitive to teratogens during week 3

E.g., alcohol kills cells in anterior midline of embryonic disc during week3

Results in craniofacial deficiencies in midline= holoprosencephaly - craniofacial deficiencies in midline

Woman may not know she is pregnant at this time
 

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