structure and embryology of the circulation

Question 1

why do we need circulation

Answer 1

• Every cell in 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 2

Arterial system

Answer 2

• Conduits of blood; physical properties (elastic arteries) increase efficiency whilst regulatory control (muscular arteries) control distribution
• Elastic arteries – major distribution vessels (aorta, brachiocephalic, carotids, subclavian, pulmonary)
• Muscular artery – main distributing branches
• Arterioles – terminal branches (<300 um diameter)
• Capillaries – functional part of the circulation, blood flow regulated by precapillary sphincters, between 3-40 microns in diameter, 3 types: continuous (most common), fenestrated (kidney, small intestine, endocrine glands), discontinuous (liver sinusoids)

Question 3

What drives embryonic vessel development?

Answer 3

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

Question 4

1st and 2nd aortic arches

Answer 4

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

Question 5

3rd aortic arches

Answer 5

• 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 6

Right dorsal aorta and right 4th aortic arch

Answer 6

• R dorsal 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 7

Left dorsal aorta and left 4th aortic arch

Answer 7

• 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 8

6th aortic arches

Answer 8

• Right arch may form part of pulmonary trunk

* Left arch forms ductus arteriosus – communication between pulmonary artery and aorta