Embryology - Cardiac and Venous Development Flashcards
How are primitive blood vessels laid down?
By angioplasty on the wall of the yolk sac.
How is a single heart tube made?
By the fusion of two primitive blood vessels.
What makes the single heart tube pulsatile?
Muscle fibres are developed in the wall.
What does the single heart tube develop into?
Four parts or cavities.
What are the four parts of the heart tube?
- Bulb.
- Ventricle.
- Atrium.
- Sinus venosus.
Describe the rate of growth of the tube and the cavities in the heart?
The tube will grow at a greater rate than the cavity (primitive pericardium) in which it is suspended.
How does the tube lie/work?
It bends because it’s growing at a faster rate, and it bends in a way that the bulb and ventricle come to lie in front of the atrium and sinus venosus.
How else does the bulb move?
It twists to the right.
How does the ventricle move?
It goes to the left.
What is the upper part of the bulb?
Turn us arteriosus.
What does turn us arteriosus divide into?
Aorta and pulmonary trunk.
What is the lower part of the bulb?
Majority of the right ventricle.
What does the original ventricle form?
The left ventricle.
What does the atrium form?
Two atria.
What happens to the sinus venosus?
It becomes mainly absorbed into the right atrium.
How is blood returned back to the sinus venosus?
From a network of primitive veins, certain longitudinal channels develop to return blood to the sinus venosus.
What are the sources of blood that the sinus venosus receives?
- Placenta - by umbilical veins.
- Yolk sac (becomes alimentary canal) - by vitelline veins.
- General tissue of the embryo - cardinal veins.
What are in each group of the three sources?
- Right vein.
- Left vein.
- Anastomosing cross-channels between each pair.
What happens to each vein?
The whole or part of one longitudinal vein of each pair disappears:
1. Right umbilical.
2. Left vitelline.
3. Left cardinal.
What happens to the umbilical vein pair?
The right umbilical vein disappears. The left umbilical vein joins the left branch of the portal vein.
What happens to the blood once the umbilical vein joins the portal vein?
The blood short-circuits the liver by passing along a venous shunt - ductus venosus.
Where does the ductus venosus join?
The end of the right vitelline vein on the cranial side of the liver.
What happens to the left umbilical vein and ductus venosus after birth?
They become reduced to fibrous cords:
- Ligamentum there’s.
- Ligamenetum venosum.
What happens to the vitelline veins?
These contribute to the portal vein and upper end of IVC.
What veins form the anterior cardinal vein?
Internal jugular and subclavian vein unite.
What veins form the posterior cardinal vein?
External and internal iliac veins unite.
What drains into the posterior cardinal vein?
Segmental veins:
1. Intercostal.
2. Lumbar.
What forms the common cardinal vein (the duct of Cuvier)?
Anterior and posterior cardinal veins.
What does the right anterior cardinal vein in the thorax form?
- Right braciocephalic.
- SVC - as far as entry of azygos vein.
What forms the azygos vein?
Right Posterior cardinal vein.
What develops on the left side in the thorax?
Left hemiazygos system - this is to replace the vanished left posterior cardinal vein.
What happens in the abdomen to the posterior cardinal veins?
Longitudinal channels appear both medically (subcardinal) and dorsally (supracardinally) to the original posterior cardinal.
What is formed from the posterior cardinal veins?
Inferior vena cava.
What structures are anterior to the common iliac veins?
Arteries.
What structures are posterior to the renal veins?
Renal arteries.
Why are the renal arteries posterior to renal veins?
Due to venous development from dorsal or ventral channels. The iliacs are from dorsal, rentals are from ventral.
What are the positions of the IVC?
Lower part - left sided.
Upper part - right of the aorta.
What does the lower part of the IVC join?
Left renal vein.
