Cardio Embryology

Question 1

What is gastrulation?

Answer 1

Mass movement and invagination of the blastula to form three layers – ectoderm, mesoderm (middle layer) and endoderm

Question 2

What comes from the layers?

Answer 2

Ectoderm – (outside) – skin, nervous system, neural crest (which contributes to cardiac outflow, coronary arteries)
•Mesoderm – middle – all types of muscle, most system, kidneys, blood, bone
•Endoderm – gastrointestinal tract (inc liver, pancreas, but not smooth muscle), endocrine organs

Question 3

Where is most of the cardio system derived from?

Answer 3

Most of the cardiovascular system is derived from cells which were situated in the mesoderm (blood, heart, smooth muscle, endothelium)

•There is some contribution from cardiac neural crest cells from the ectoderm

Question 4

What do the heart fields become?

Answer 4

First heart field – future left ventricle
Second heart field – outflow tract,
future right ventricle,
atria

Question 5

How do the heart fields develop?

Answer 5

The first heart field generates a scaffold which is added to by the second heart field and cardiac neural crest

Question 6

What is a gene?

Answer 6

Gene – DNA which when expressed is transcribed into RNA which is translated into protein with a function

Question 7

What is a transcription factor?

Answer 7

Transcription Factor; type of protein which when expressed “turns on/off” many other gene(s) expression: master regulators of complex processes

Question 8

What are stages of cardiac formation?

Answer 8

Formation of the primitive heart tube
II.Cardiac looping
III.Cardiac septation

Question 9

What increases heart size?

Answer 9

Overexpression of Nkx2.5 by injecting RNA

Question 10

What induces cardia bifida?

Answer 10

Preventing GATA4 transcription - failure of the endocardial tubes to fuse

Question 11

Why is left important?

Answer 11

All vertebrate hearts have a leftward ventricle
•Many mutations are associated with improper left-right positioning (e.g. Kartagener’s syndrome)
•During development, the node secretes nodal, which circulates to the left due to ciliary movement

A cascade of transcription factors (e.g. Lefty, Pitx2, Fog-1) transduce looping

Question 12

What prevents cardiac looping?

Answer 12

Preventing Fog-1 transcription

Question 13

Why do we need a circulation?

Answer 13

Every cell in our body needs to be bathed in fluid and within 2mm of a source of oxygenation
•This reproduces the extracellular environment of primitive uni- and multicellular organisms in the primeval ocean

Question 14

What does the arterial system do?

Answer 14

Conduits of blood; physical properties (elastic arteries) increase efficiency whilst regulatory control (muscular arteries) control distribution

Question 15

What does the arterial system contain?

Answer 15

Elastic arteries – major distribution vessels (aorta, brachiocephalic, carotids, subclavian, pulmonary)
•Muscular arteries – main distributing branches
•Arterioles – terminal branches (<300mm diameter)

Question 16

What are capillaries?

Answer 16

The functional part of the circulation
•Blood flow regulated by precapillary sphincters
•Between 3-40 microns in diameter

•Three types of capillary; continuous (most common), fenestrated (kidney, small intestine, endocrine glands), discontinuous (liver sinusoids)

Question 17

What does the venous system do?

Answer 17

Return blood to the heart
•System of valves allows “muscular pumping”
•Some peristaltic movement

Question 18

What occurs on day 17?

Answer 18

Formation of blood islands

Question 19

What occurs between day 17-21?

Answer 19

Vascularisation of the yolk sac, chorionic villus and stalk

Question 20

What occurs on day 18?

Answer 20

• Vasculogenesis commences

Angioblasts (from splanchnopleuric mesoderm) coalesce to form angioblastic cords throughout embryonic disc

• Added to by angiogenesis

Question 21

What is angiogenesis driven by?

Answer 21

Angiogenesis is driven by angiogenic growth factors and takes place via proliferation and sprouting

Question 22

What drives embryonic vessel development?

Answer 22

Angiogenic growth factors – vascular endothelial growth factor, angiopoietin 1 & 2
•Repulsive signals – Plexin / semaphorin signalling, ephrin / Eph interactions

Question 23

What is the difference between arteries and veins?

Question 24

What do the 1st and 2nd aortic arches become?

Answer 24

Become minor head vessels
•1st – small part of maxillary
•2nd - artery to stapedius

Question 25

What does the 3rd aortic arches become?

Answer 25

Portion between 3rd and 4th arch disappears
•Become common carotid arteries, and proximal internal carotid arteries
•Distal internal carotids come from extension of dorsal aortae

Question 26

What does the right dorsal aorta and the right 4th aortic arch become?

Answer 26

R dorsal aorta looses connections with midline aorta and 6th arch, remaining connected to R 4th arch
•Acquires branch 7th cervical intersegmental artery, which grows into R upper limb
•Right subclavian artery is derived from right 4th arch, right dorsal aorta, and right 7th intersegmental artery

Question 27

What does the left dorsal aorta and left 4th aortic arch form?

Answer 27

Left dorsal aorta continues into trunk
•Left 7th cervical intersegmental artery, which grows into left subclavian artery
•Right subclavian artery is derived from right 4th arch, right dorsal aorta, and right 7th intersegmental artery

Question 28

What do the 6th aortic arches become?

Answer 28

Right arch may form part of pulmonary trunk
•Left arch forms ductus arteriosus – communication between pulmonary artery and aorta