Embryology parts 1-4 Flashcards Preview

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When is conceptus referred to as foetus

8 weeks


For how long does development within fallopian tube usually occur

Preimplantation development normally occurs within the Fallopian tube (oviduct) over a period of ~6 day


What development happens in fallopian tube

Define morula

Series of cleavage divisions, which sequentially double the number of cells in the conceptus (2, 4, 8, 16 cells) to produce a ball of undifferentiated cells (the Morula)


What does the morula differentiate into

First level of differentiation, into



What is blastocyst

From morula.

Still has zona pellucida

Outer layer of cells=trophoblast

Inner cell mass

Fluid-filled cavity


T/f the zona pellucia implants into the lining of the uterus



What happens to blastocyst

The Blastocyst then hatches from the Zona Pellucida (within which it has developed up to this time, about day 6 after fertilisation), and begins to implant in the uterine lining


By what day is the blastocyst implanted

complete about 10 days post-fertilisation


What is the structure of the blastocyst after it has implanted into uterus

he inner cell mass, which was a group of undifferentiated cells has become a bilayer disk, composed of hypoblast and epiblast cells


What is the importance of the bilayer in the blastocyst

his bilayer disk gives rise to all the tissues of the human fetus, through a complex series of changes.


What is the first change that occurs to the blastocyst

Gastrulation. Day 14-18 PA

Converts bilayer--> trilaminar embryo with 3 layers of germ cells:

1. Ectoderm
2. Mesoderm
3. Endoderm


How are each of the 3 layers formed in gastrulation

The ectoderm originates from the epiblast cells.

Epiblasts also differentiate into mesoderm cells.

These mesoderms cells move into the space between epiblast and hypoblasts.

The mesoderm cells form mesoderm layer, but also differentiate into endoderm cells.

Hypoblast layer lost by apoptosis


What does ectoderm give rise to

skin and the central nervous system


What does mesoderm give rise to

muscles, blood, skeleton, heart and kidney


What does the endoderm give rise to

gut, lungs and liver


T/F tissues usually originate from a single germ layer type

F.... Muscular and vascular tissue are generally of mesodermal origin, so tissues are normally a mixture of germ layer types (e.g. muscle in the skin and gut).


What stage is next from gastrulation

Neurulation. Occurs before gastrulation is complete.


What is neurulation. What controls it

ifferentiation of the Ectoderm (Epiblast) to generate the central nervous system (Brain and Spinal cord), under the control of the notocord in the mesoderm of the developing embryo.


Outline the formation of the neural tube

development of the neural plate on the ectoderm; this develops two folds, which increase in size until the meet over the neural groove and fuse to form the neural tube


When does fusion of the neural plate occur

during week 4 of development.
Now the neural tube is formed


What cell groups are outside the embryo proper

primordial germ cells (PGC) --> in yolk sac endoderm at caudal end

cardiac and vascular progenitors--> in primary heart field at cranial end


Where do each of the cell types that were outside the embryo proper move to

PGCs to hindgut

Heart progenitors under head of embryo


Which folding occurs in the third week of development

LATERALLY --> the sides curve round to fuse at the front (ventral midline)

ANTEROPOSTERIOR --> folds the PGCs into the hind gut, and the developing heart progenitors under the head of the embryo


What sacs are there, dorsal and ventral to embryo

Dorsal is the amnionic cavity
Ventral is the yolk sac


What happens in the transverse plane in day 19-28

Fig 5.2.8

You can see the ecto, endo and meso derm

The ectoderm is undergoing formation of neural tube

The amniotic cavity is just an extension of ectoderm

The yolk sac is continuous with the endoderm

There is a visceral part of mesoderm which is in contact with the endoderm/yolk (i,,e the pink layer around the yellow from the first image)

Then there is a somatic or parietal layer of mesoderm which comes to surround the endoderm and the visceral layer

Look back to year 1 abdo anatomy

Note that in the foregut and the hindgut, it will look like E and the gut tube closes

In the midgut, there is still connection to the yolk sac, which can be seen in D


What happens in longitudinal plane

Image 5.2.9

Left is cranial

Right is caudal

The top of the image is dorsal and the bottom is ventral

You can see how the heart progenitors have moved from the angiogenic cell cluster (outside of embryo proper) into the embryo by AP folding

You can also see how there is movement of the PGCs from outside to behind the foregut


When is all the lateral and transverse foling occurring

Week 3-4


By what time have the precursors of all internal tissues have been laid down

End of week 4


Development of what happens in month 2 of development

Urogenital, cardiac, facial and lung and limb


Where do the limbs grow out from

lateral plate mesoderm rapidly under control of special signalling regions