What is the purpose of the first two weeks of embryonic development?
To create the tissues of the future embryo and future placenta, achieving the right cells of the right type in the right place
What does the third week of embryonic development achieve?
Creates the three germ layers, the ectoderm, mesoderm and endoderm
Where does the cardiovascular system develop from?
The mesoderm
What happens in the fourth week of embryological development?
It creates a recognisable body form Mesoderm begins to organise
Where does the cardiogenic area initially lie on the embryonic disc?
In the wrong place- anterior to the buccopharyngeal membrane
What is the cardiogenic field of the embryonic disc?
A collection of specialised mesodermal cells that’s creating vascular like tissue and all its constituents
What forms about the cardiogenic field?
The pericardial cavity
What happens within the pericardial cavity?
Specialisation of the mesoderm, and differentiation of blood cells, tiny vessels and ultimately, the primitive heart
What is found within the jelly of the pericardial sac?
Blood islands
What happens as blood islands continue to develop?
You get tiny blood vessels beginning to appear
What creates a heart tube?
Lateral folding
What brings the heart into the thoracic region?
Cephalocaudal folding
Where is the heart after cephalocaudal folding?
Still more cranial than is ultimately the case
What is the overall result of folding?
It puts the tube into the first big shared cavity, the intraembryonic coelom
What ultimately happens to the intraembryonic coelom?
This cavity ultimately becomes divided by the diaphragm, into the thorax and the abdominal cavity
How many heart tubes develop?
Two, one on either side of the midline
What happens when lateral folding pushes the two tubes together?
They fuse together to give the primitive heart tube
What has happened once cephalocaudal folding has put the heart tubes in the right place?
The primitive tube is sitting within a space that has opened up to accommodate it, the pericardial cavity
How is the heart tube suspended in the pericardial cavity?
A very thin membrane
What happens to the thin membrane suspending the heart tube?
It degenerates, leaving the heart tube tethered cranially and caudally, but free to move around
What does the primitive heart tube consist of?
Aortic roots Truncus arteriosus Bulbus cordis Ventricle Atrium Sinus venosus
What happens as the heart tube moves up from the atrium to the ventricle to bulbus cordis?
It becomes tapered, becoming narrower as we proceed out of the heart tube and into outflow
What is looping fundamental for?
The normal proceeding of cardiac development
What does continued elongation of the heart tube result in?
Bending
Why does the heart tube continue to elongate?
To meet the advancing needs of the foetus as it grows
Why does the heart tube bend as it elongates?
Because it is growing into a space that is fixed by the pericardial sac, and so as the tube gets longer, it needs to fold up
When does the elongation of the heart tube process begin?
Day 23
When is the elongation of the heart tube process complete?
Day 28
What does the early occurrence of the heart tube elongation illustrate?
That the embryo needs a cardiovascular system to support itself, as it’s outgrown the capacity to support its need via simple diffusion alone
In what direction does the cephalic portion of the heart tube grow?
Ventrally, caudally, and to the right
