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What is created in the first two weeks of early embryonic development?

The tissues of the future embryo and placenta are created.


What is created in the third week of early embryonic development?

Three germ layers - ectoderm, mesoderm and endoderm (the primordia of all tissues)


What is created in the fourth week of early embryonic development?

A recognisable body form and the beginning of mesoderm organisation.


Where does the cardiogenic area (future heart) originate from?

Rostral to the buccopharyngeal membrane (future mouth).


What does lateral folding of the embryo do to the developing heart?

Creates the primitive heart tube by fusion of the pair of endocardial tubes.


What does cephalocaudal folding of the embryo do to the developing heart?

Brings the tube into the thoracic region.


What happens to the blood islands found in the cardiogenic field?

They coallesce into blood vessels creating a pair of heart tubes (endocardial tubes) - one on either side of the midline.


List the components of the primitive heart tube (caudal to rostral).

Sinus venosus
Bulbus cordis
Truncus arteriosus
Aortic roots


In which direction does blood flow through the primitive heart tube?

Caudal to rostral (sinus venosus to aortic roots)


What causes looping of the primitive heart tube?

Continued elongation in the fixed space of the pericardial cavity.


Describe the looping that the primitive heart tube undergoes:

Cephalic portion: ventrally, caudally and to the right
Caudal portion: dorsally, cranially and to the left


What are the consequences of the looping of the primitive heart tube on the inflow and outflow tract of the primitive heart?

It places arteries infront of veins and thus creates the transverse pericardial sinus.


What is the transverse pericardial sinus?

A passage in the pericardial sac between the origins of the great vessels, that is, posterior to the intrapericardial portions of the pulmonary trunk and ascending aorta and anterior to the superior vena cava and superior to the atria; it is formed as a result of the flexure of the heart tube, partially approximating the great venous and arterial vessels.


What does looping acheive?

1. Puts primordium of right ventricle closest to outflow tract
2. Puts primordium of left ventricle closest to inflow tract
3. Puts atrium dorsal to bulbus cordis (inflow dorsal to outflow)


What happens, after looping, to the communication between the atrium and ventricle?

A narrowing occurs which creates the atrioventricular canal. This is very important for cardiac partitioning.


How does the sinus venosus (inflow tract) develop?

It starts off with right and left sinus horns of equal size but as venous return shift to the RHS, the left sinus horn recedes. The right sinus horn is absorbed into the enlarging right atrium.


What does the right atrium develop from?

1. Most of the primitive atrium
2. Right engulfed sinus venosus


What does the left atrium develop from?

1. A small portion of the primitive atrium
2. Large bulk is the absorbed proximal portions of pulmonary veins


What venous drainage does the right atrium receive?

1. From the body - venae cava
2. From the heart - coronary sinus


Why are parts of the walls of the left atrium smooth?

They are parts which are formed from the absorbed primodial pulmonary vein tissue.


How is the oblique pericardial sinus formed?

It is formed as the left atrium expands absorbing the pulmonary veins. This creates a recess in the pericardium cavity caused by a reflection of the serous pericardium onto the pulmonay veins of the heart - on the posterior surface of the heart.


What are the blood vessels in the foetus that transfer oxygenated blood from the placenta and transfers back deoxygenated blood to the placenta?

Oxygenated blood from placenta - umbilical VEINS
Deoxygenated blood to the placenta - umbilical ARTERIES


What do the three fetal circulatory shunts bi-pass?

1. Ductus arteriosus - PT to aorta
2. Foramen ovale - right to left atrium
3. Ductus venosus - umbilical vein to IVC


What is the adult remnant of the ductus arteriosus?

ligamentum arteriosus


What does the ductus arteriosus do?

It connect the pulmonary trunk to the aorta, thus bi-passing the lugns which are non-functional.


Why are the lungs non-functional in the foetus?

1. They are not developed enough to have blood vessels that can cope (develop later)
2. Blood already oxygenated


What is the primordia of the major arteries of the head, upper limb, pulmonary trunk, ascending, arch and descending thoracic aorta?

They all come from an early arterial system that begins as a bilateral symmetrical system of arched vessels, but which undergoes extensive remodelling to create the major vessels leaving the heart.


What is the derivative of the fourth aortic arch?

Right arch -> proximal part of right subclavian artery
Left arch -> arch of aorta


What is the derivative of the sixth aortic arch?

Right arch -> right pulmonary artery
Left arch -> left pulmonary artery and ductus arteriosus


What is of note about the nerves that supply these aortic arches?

Each aortic arch has a corresponding nerve.