Development of the Cardiovascular System 2

Question 1

How is the heart developed?

Answer 1

• Begins towards the end of week 3 when the cardiogenic field condenses
• 2 angioblastic cords form the heart tubes
• The heart tubes fuse to one when lateral body folding occurs
• the dilations appear and the tube bends forms a bulboventricular loop when the bulbus cordis and ventricle grow
• The first contraction of the heart = day 22
• blood circulates in the 4th week

Question 2

Explain the genetic Induction of cardiogenic field with the three germ layers

Answer 2

• Endoderm: (perimeters of embryo) This releases BMP2 and 4 which both express NKX2.5 (the master regulator of all cardiac genes)
• Mesoderm: (cranial margin of embryo) This releases NKX2.5
• Ectoderm: (cranial half or embryo) The neural tube releases Wnt3a and 8 which inhibits the development of the heart. To counteract this, the ectoderm ALSO releases crescent and cerberus to inhibit Wnt3a and 8 which activates heart development

Question 3

Explain the graded expression of RA in the dilations of the heart tube

Answer 3

• happens in the mesoderm
• In the sinus venosus, retinal dehydrogenase expression is increased by its self-made retinoic acid making it specified
• The most caudal part of the heart tube (sinus venosus) is with the highest expression of RA, decreasing towards the cranial end (TA)

Question 4

List the dilations of the heart tube and its pathway

Answer 4

• Sinus venosus (SV), Truncus arteriosus (TA), Bulbus cordis (BC), Ventricle (V), Atrium (A)
• PATHWAY SV → A → V → BC → TA

Question 5

What is in the wall of the heart tube and what do they become

Answer 5

• Endothelium: becomes the endocardium
• Cardiac jelly: becomes the subendocardial CT
• Myocardium
• Epicardium: visceral layer of pericardium. forms from mesothelial cells

Question 6

The heart is suspended from the dorsal wall by the _____ ___________ which its central part later degenerates to form the _________ ___________ _____ which communicated between the left and right sides of the pericardium

Answer 6

• Dorsal mesocardium
• Transverse pericardial sinus

Question 7

Explain the pathway of primitive circulation

Answer 7

• SV → A → V → BC → TA → Aortic Sac → Aortic Arches → Dorsal Aorta
  The dorsal aorta flow to:
• The embryo by the intersegmental arteries
• The placenta by the umbilical arteries
• The yolk sac by the vitelline arteries

Question 8

Where do the veins come from to the sinus venosus

Answer 8

• The cardinal veins go from the embryo
• The umbilical vein grows from the placenta
• The vitelline veins go from the yolk sac
  ALL to the sinus venosus

Question 9

When does the partitioning of the heart occur?

Answer 9

• In the 4th week and is complete at the end of the 8th week

Question 10

Explain the division of the atrioventricular canal

Answer 10

• This canal separates the atria from the ventricles and the left from the right side of the heart by the endocardial cushions that form on the ventral and dorsal walls
• The AV canal sends inductive signals which makes the endocardial cells go through Epithelial Mesenchymal Transformation (EMT) and invade the ECM

Question 11

What are the factors for EMT

Answer 11

• TGF-ß1 and TGF-ß2
• BMP-2A and BMP-4
• Slug (zing finger protein)
• ChALK2 (activin-receptor-like kinase)
  They also participate in the formation of the endothelial cushions