Cardio Development

Question 1

When do embryonic blood vessels and heart start to develop? Where do they form?

Answer 1

• 18 days of development

- form in splanchnic layer of the extaembryonic mesoderm (angioblasts)

Question 2

Vasculogenesis in yolk sac?

Answer 2

1. mesenchymal cells differentiate into endothelial precursor cells, angioblasts, which aggregate to form blood islands
   - contain pluripotent hematopoietic stem cells
2. small cavities begin to appear and angioblasts form endothelial cell lining
3. cavities fuse to form channels

Question 3

Angiogenesis in yolk sac?

Answer 3

• branching or sprouting of new blood vessels from pre-existing ones
• they connect to the primitive heart tube that is forming simultaneously

Question 4

Why does vasculogenesis and angiogenesis occur at this stage in the embryo?

Answer 4

-simple diffusion of nutrients across the placenta is no longer sufficient to support the growing embryo

Question 5

What is the first sign of gastrulation?

Answer 5

primitive streak in epiblast

Question 6

Where does the pericardiac mesoderm derive from?

Answer 6

epiblast

Question 7

Outflow tract in relation to inflow tract in the primitive streak?

Answer 7

-outflow pass through primitive streak more cranially

Question 8

Where do cells giving rise to the ventricles pass through the streak?

Answer 8

mid region

Question 9

Precardiac mesoderm derived from?

Answer 9

-once pericardiac cells go through the streak they migrate as part of the splanchnic mesoderm to form a region in the anterior half of the embryo

Question 10

What does the precardiac mesoderm become?

Answer 10

tubular heart during embryonic folding

Question 11

What is the first step in the formation of the heart?

Answer 11

appearance of bilateral, parallel endocardial tubes that form by vasculogenesis in rostral splanchnic mesoderm

Question 12

When and where does the bilateral cardiac tubes fuse (embryonic folding)?

Answer 12

along the midline of the embryos when the embryo folds in the cranial to caudal and lateral directions

Question 13

How do bilateral endocardial tubes fuse?

Answer 13

-by ventral flexure of the head fold and ventral convergence of the lateral body folds

Question 14

What do the bilateral endocardial tubes become?

Answer 14

-they fuse at the midline to form a single endocardial tube that is surround by myocardium

Question 15

What separates the endocardium and myocardium?

Answer 15

cardiac jelly

Question 16

What forms next after fusion of the endocardial tubes?

Answer 16

formation of 3 layers:

1. endocardium
2. myocardium
3. epicardium

Question 17

Where does the epicardium come from?

Answer 17

migration of epithelial and mesenchymal cells on surface of myocardium

Question 18

When does the primitive heart tube loop form?

Answer 18

• between 21-28 days

- after fusion of bilateral endocardial tubes

Question 19

What shape does the primitive heart tube loop form? why?

Answer 19

S

-to allow segmentation into different chambers

Question 20

Outflow vs inflow tract direction after heart tube loops?

Answer 20

OFT: dextrocaudally
-ventricular segment

IFT: dorsocranially
-great veins to enter heart

Question 21

Primary heart field?

Answer 21

• inflow segment
• left ventricle
• half of right ventricle

Question 22

Secondary heart field?

Answer 22

• outflow

- half of right ventricle

Question 23

Third heart field?

Answer 23

Proepicardium

-progenitor to epicardium, coronary vessels, and cardiac fibroblasts

Question 24

Fourth heart field?

Answer 24

Cardiac neural crest

Question 25

What are the 5 core transcription factors that commit to cardiac lineage?

Answer 25

- NKX-2 - MEF-2 - GATA - Hand - Tbx

Question 26

How do Cushions form?

Answer 26

convergence of endocardial prominences at AV border and Contruncus through endocardial mesenchymal transition (EndMT)

Question 27

What do Cushions separate?

Answer 27

1. atria and ventricles (dorsal and ventral) | 2. aortic and pulmonary trunks of outflow tract Conotruncus

Question 28

What will be the future AV valves?

Answer 28

-when dorsal and ventral cushions bulge into lumen but retain openings on both sides

Question 29

When do partitioning of the atria and ventricles take place?

Answer 29

-occur simulaneously during 4th-8th weeks of gestation

Question 30

Septum primum?

Answer 30

-divides right and left atria

Question 31

Foramen primum?

Answer 31

- opening in membrane of septum primum | - shunts oxygenated blood from right to left atria

Question 32

Cardiac septation steps at 28 days?

Answer 32

1. Septum primum grows from dorsal wall toward AV cushions 2. Foramen primum shunts oxygenated blood from right to left atria 3. Muscular inter ventricular septum grows toward AV cushions and bulbar ridge 4. Dorsal cushion forming

Question 33

Cardiac separation steps 32-35 days?

Answer 33

1. septum primum fuses with AV cushions to obliterate the foramen primum 2. perforations in septum primum coalesce to form the foramen secundum 3. foramen secundum grows 4. Muscular IV septum grows 5. Membranous IV septum begins to form

Question 34

Cardiac septation 5-8 weeks?

Answer 34

1. septum secundum grows and overlaps foramen secundum in septum primum leaving foramen ovale 2. inferior remnant of septum primum forms valve of foramen ovale 3. foramen ovale permits shunting of oxygenated blood from right to left atria

Question 35

What forms the bulbar and truncal ridges?

Answer 35

-active proliferation of mesenchymal cells in the walls of the bulbus cordis and truncus arteriosus

Question 36

Where is ridge mesenchyme derived from?

Answer 36

-endocardium via epithelial mesenchymal transition and neural crest cells

Question 37

Where do cardiac neural crest cells migrate to to from the ridges?

Answer 37

through PA 3, 4, 6 to form bulbar and truncal ridges

Question 38

What do the ridges create when they fuse together?

Answer 38

undergo 180 degree spiral to form aorticopulmonary septum

Question 39

what does the aorticopulmonary septum divide?

Answer 39

divides the Bulbis cordis and truncus into two arterial channels, Aorta and Pulmonary trunk

Question 40

What does the bulbus cordis become?

Answer 40

- becomes incorporated into walls of ventricles - right: becomes conus arteriosus (infundibulum) to form pulmonary trunk - left: forms walls of aortic vestibule inferior to aortic valve

Question 41

When do semilunar valves form?

Answer 41

when partitioning of truncus is complete