Structure and embryology of the circulation

Question 1

Which arteries are elastic?

Answer 1

Aorta, brachiocephalic, carotids, pulmonary (major distribution vessels)
- Can be too elastic (forming an aneurysm)

Question 2

which arteries are muscular?

Answer 2

Main distributing branches

Question 3

What are the three types of capillaries?

Answer 3

1. Continuous (most common)
2. Fenestrated (kidney, small intestine, endocrine glands),
3. Discontinuous (liver sinusoids)

Question 4

Which parts of the artery comes from the embryonic layers?

Answer 4

• (Tunica Intima) Endothelium Basement membrane = Inner (Ectoderm)
• (Tunica Media) Vascular Smooth Muscle Cells = Mesoderm

Question 5

How do blood vessels begin to form on Day 17

Answer 5

• Blood islands begin to form in the mesoderm and within them are the progenitors that will become blood and outside are the progenitors that will become blood vessels

Question 6

What is Vasculogenesis?

Answer 6

• Blood islands move into embryonic cavity and then form an axial vessel in the middle
• Occurs on Day 18

Question 7

What is angiogenesis?

Answer 7

• Also on Day 18
• It is driven by angiogenic growth factors and takes place via proliferation and sprouting
• then other mesodermal cells are recruited (e.g. smooth muscle)
• There is the scaffold from Vasculogenesis and then the endothelial cells grow away from the axial scaffold forming the vessels = this is angiogenesis

Question 8

What are some examples of angiogenic growth factors?

Answer 8

• Vascular endothelial growth factor, angiopoietin 1 and 2
• This makes them grow and divide and move
• Also repulsive signals that push the vessels away (Plexin)
• And attractive signals (e.g. VEGF)

Question 9

What are some heart shunts in embryonic development?

Answer 9

Foramen Ovale (between atria)
Ductus Arteriosus (pulmonary artery to aorta)
SHUNT: Bypassing pulmonary circulation – not required in utero

Question 10

What did the umbilical vein and artery carry?

Answer 10

Umbilical vein carries oxygenated blood
Umbilical artery carries deoxygenated blood

Question 11

How does the first breath lead to newborn circulation?

Answer 11

• First breaths of life -> lungs expand → the alveoli in the lungs are cleared of fluid.
• An increase in the baby’s BP and a significant reduction in the pulmonary pressures reduces the need for the ductus arteriosus to shunt blood → closure of the shunt.
• These changes increase the pressure in the left atrium of the heart → decrease the pressure in the right atrium -> foramen ovale closes → newborn circulation.

Question 12

What does the 1st and 2nd aortic arch become?

Answer 12

• Minor head vessels
• 1st: small part of maxillary
• 2nd: artery to stapedius (small bones in ear)

Question 13

What does the 3rd aortic arch become?

Answer 13

common carotid arteries

Question 14

What does the right 4th aortic arch become?

Answer 14

• Right dorsal aorta

Question 15

What does the left 4th aortic arch become?

Answer 15

Left dorsal aorta

Question 16

What does the 5th aortic arch become?

Answer 16

NO 5th arches

Question 17

What does the 6th aortic arch become?

Answer 17

• Right arch: part of pulmonary trunk
• Left arch: ductus arteriosus (communication between pulmonary artery and aorta)