Early Development Flashcards
Which system is the first to function in the embryo and why?
The cardiovascular system. The growing embryo needs an efficient method of acquiring oxygen and nutriens and disposing of carbon dioxide and waste products.
When does the blood begin to circulate in the embryo?
By the end of the third week.
When does the heart begin to beat?
On the twenty first or the twenty second day.
What are blood islands?
Aggregations of cells with angiogenic potential (angioblasts).
What are initial stages of angiogenesis?
- Angioblasts aggregate to form blood islands.
- Cavities appear within blood islands by confluence of intercellular clefts.
- Angioblasts flatten and form endothelial-lined cavities which fuse to form network of endothelial channels.
What are the extra-embryonic sites of the haematogenesis?
Yolk sac and allantois.
What is the origin of muscular and connective tissue elements of blood vessels?
Mesenchymal cells surrounding endothelial channels.
Can primitive blood vessels be distinguish structurally as arteries and veins?
No. In the embryo they are name according to their future fates and relationship to the heart.
Where in the embryo is the cariogenic area?
Cranial to the oropharyngeal membrane, on either side of the neural plate.
What is the origin of endothelial heart tubes?
Splanchnopleuric mesenchyme.
How is the primitive heart tube formed?
Bilateral angioblastic cords canalise and fuse into a single tube.
What does separate the primitive heart tube from the primitive myocardium?
Cardiac jelly
How does the craniotomy-caudal folding of the embryo affects the position of the primitive heart and pericardial cavity?
They come to lie ventral to the foregut and caudal to the oropharyngeal membrane.
How does the transverse pericardial sinus form?
Central part of the dorsal mesocardium degenerates.
Why does the hart tube bend during the accelerated grow of the bulbs cords and primitive ventricle?
It is because the arterial and venous ends of the heart are fixed to the pharyngeal arches and septum transversum, respectively.
