Developmental anatomy Wk 5

What is vasculogenesis?

the formation of new blood vessels from undifferentiated tissue which first commences in the yolk sac

What is angiogenesis?

the budding off and branching of new blood vessels from an existing vessel

What is the yolk sac a first supplier of?

blood cells to the embryonic circulation

What happens by day 60 with the yolk sac and haematopoiesis?

haematopoiesis (production of red and white blood cells) occurs in the liver, spleen and thymus, with the majority of blood cells being formed in the liver during the foetal period. after birth the process of haematopoiesis occurs solely in the bone marrow of the skeleton

What are the 3 stages of vasculogenesis?

1. mesoderm cells differentiate into angioblasts and cluster to form blood islands

2. a lumen forms in each blood island to initiate formation of blood vessel. cells forming lining of this cavity differentiate to become endothelial cells

3. angioblasts differentiate into blood cells including erythrocytes

4. adjacent blood islands fuse together to form long blood vessels

Where does the major veins of the trunk begins from?

paired cardinal and subcardinal veins, which reorganise themselves through a series of fusion and regression steps to result in the formation of a number of asymmetrical structures including the superior/inferior vena cava

What do primordial veins consist of?

paired anterior (cranial end) and posterior (caudal end) cardinal veins which connect with the common cardinal veins that terminate in the primordial heart tube

What happens to the posterior cardinal veins?

largely degenerate and are replaced with the subcardinal veins

Why does the anastomosis form?

to join the left and right anterior cardinal veins and shunt blood from left to right anterior cardinal vein

How does the anastomosis become the left brachiocephalic vein?

when the caudal end of the left anterior cardinal vein degenerates

How does the super vena cava and right brachiocephalic vein form?

from the persisting right anterior cardinal vein and right common cardinal vein

How is the inferior vena cava formed?

from portions of the subcardinal and supracardinal veins

How is the aorta formed?

begins as paired vessels, the dorsal aortae that run through the entire length of the embryo. the caudal portions of the aortae fuse to form a single inferior thoracic/abdominal aorta

How is the aortic arch formed?

begins as a bilateral structure until the right side regresses to form a left sided aortic arch

How is the cardiovascular system formed?

• paired, longitudinal endothelial-lined channels (endocardinal heart tubes) develop during the third week and fuse to form a primordial heart tube during lateral folding of the embryo

  • the tubular heart joins with the newly developed blood vessels which connects with the maternal vascular system via the placenta

How is the heart formed?

• the embryo starts to undergo ventral folding, the heart tube elongates and develops alternate dilution and constrictions to form the chambers and great vessels of the heart

• the heart tube undergoes a right-handed looping at approximately 23-28 days, forming a U-shaped loop that results in a heart with the apex pointing to the left of the body

How is dextrocardia situs inversus a result of?

the heart tube undergoing a reversal of the normal looping pattern, producing a heart that is a mirror image of the normal heart

What is the foramen ovale?

• the septum secundum forms an incomplete partition between the atria

• the cranial part of the septum primum regresses and the remaining caudal part forms the flap-like valve

How do the foetal shunts close after birth?

a decrease in the right atrial pressure from occlusion of placental circulation and an increase in the left atrial pressure due to the increased venous return from the lungs upon baby taking first breath

What does the right and left umbilical arteries turn to in adults?

medial umbilical ligaments

What does the left umbilical vein turn to in adults?

ligamentum teres

What does the ductus venosus turn to in adults?

ligamentum venosum

What does the Formen ovale turn to in adults?

fossa ovalis

What does the ductus arteriosus turn to in adults?

ligamentum arteriosum

What happens if the ductus arteriosus fails to regress at birth?

a patent ductus arteriosus may present allowing blood to continue to be shunted into the aortic arch, reducing blood supply to lungs for gas exchange in the breathing baby