11. Early Embryonic Development - Gastrulation Flashcards Preview

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Why is week 3 of embryonic development know as the week of threes?

Three cavities are formed: amniotic sac, yolk sac and chorionic sac. Also three 'germ' layers are formed: ectoderm, mesoderm and endoderm.


What is gastrulation?

The process that establishes the three germ layers, the trilaminar disc and sets the axes observed in the adult.


What axes form during gastrulation?

Anterior/posterior, dorsal/ventral and right/left.


What marks the onset of gastrulation?

The primitive stream appearing.


What are the primitive streak, pit and node in gastrulation?

The streak is a narrow groove with bulging edges. The node is at the cranial end of the streak and the pit is in the centre of the node.


In what direction does development proceed in embryology?

Cranial to caudal, hence why, until fully developed, the head is always more complete than the limbs.


How is the third layer created in gastrulation?

By displacement of the hypoblast. Cells migrate towards the edges of the primitive streak then displaced, the cells divide and differentiate as they move.


What are the layers in the bilaminar and trilaminar disks?

Epiblast and hypoblast. Ectoderm, mesoderm and endoderm.


What are the two points that mesoderm is not between ectoderm and endoderm?

The future mouth and future anus.


What is the notochord the basis for?

Axial skeleton.


What does the notochord drive the formation of?

The nervous system.


Define totipotent.

The capacity to become any cell type.


Define pluripotent.

The capacity to become one of many cell type.


Define differentiated,

Committed to one fate and one function.


Which germ layer leads to cells that will:
a. Make contact with the outside?
b. Stay as internal structures?
c. Become supporting tissues?

a. Ectoderm
b. Endoderm
c. Mesoderm


What is situs inversus?

When everything is on the wrong side during development, it's a mirror image of what it should be.


What causes twinning?

The embryo splits after the first cleavage and creates two embryos, each with its own placenta.
Or the inner cell mass is duplicated and forms two embryos that share one placenta.


What happens if separation in twinning is not complete?

Conjoined twins.


What is teratogenesis?

The process when normal embyronic development is disrupted.


When is the embryonic period?

Weeks 3 to 8.