Embryology Flashcards
How does the heart form?
1) The heart begins life as a tube
2) It is attached at both ends and is free to fold and grow
3)The caudal situated Y junction develops two swellings (these later form R and L atria)
4) The future atria move to the cranial end of the embryo dorsal to the ventricle (moves behind the ventricle)
5) The truncus whish splits longitudinally to form the aorta and pulmonary trunk
6) Each tube develops one way valves (aortic and pulmonary - 3 flaps)
7) The ventricle walls grow thicker, become contractile and communication between the two ventricles becomes smaller as an interventricular septum develops
8) The R and L atria are separated by a thin sheet of tissue called the SEPTUM PRIMUM.
prior to birth blood has to pass from RA to LA through an opening called the OSTIUM PRIMUM in order to bypass the ‘useless’ lungs.
9) The OSTIUM PRIMUM soon closes so the OSTIUM SECONDUM forms, this is oval in shape (AKA foramen ovale.) The ostium secondum is surrounded by tissue that prodives a flap-like valve, this only remains open if the blood in the RA is at a higher pressure than the blood in the LA
10) At birth the pressure in the LA increases due to blood return from the lungs and the hole closes leaving the fossa ovalus
11) Initially the outer muscle wall surrounding the primitive heart tube is contracted as a tube however as the heart develops faster conducting fibres are needed
12) SAN node devleops in RA
13) AVN node develops and transmits signal
12) Bundle of His forms
What three layers are formed in gastrulation?
Ectoderm, mesoderm, endoderm
What does the ectoderm form?
Ectoderm – (outside) – skin, nervous system, neural crest (which contributes to cardiac outflow, coronary arteries)
What does the mesoderm form?
Mesoderm – middle – all types of muscle, most system, kidneys, blood
What does the endoderm form?
Endoderm – gastrointestinal tract (inc liver, pancreas, but not smooth muscle), endocrine organs
What layer is the cardiovascular system derived from?
Most of the cardiovascular system is derived from cells which were situated in the mesoderm (blood, heart, smooth muscle, endothelium)
There is some contribution from cardiac neural crest cells from the ectoderm
What day does the heart start to beat?
Day 22
What are endocardial tubes, why are there two of them?
2 endocardial tubes form by day 19, they fuse to form a single primitive tube