Vascular Development

Question 1

What are the two things hemangioblasts differentiate into?

Answer 1

-hematopoietic lineage
+influenced by Runx-1
+pluripotent
+give rise to large nucleated RBCs for the first 6 weeks

-endothelial lineage
+influenced by Hoxa3

Question 2

What is the primary pathway of intra embryonic hematopoiesis?

Answer 2

Primitive streak -> yolk sac -> liver (spleen and thymus at 5-6weeks of gestation) -> bone marrow

Question 3

Yolk sac RBCs

Answer 3

Large nucleated

Question 4

Liver RBCs

Answer 4

-larger than normal, non-nucleated

Question 5

Liver is major producer of blood cells from week 6 through month 6. Then what happens?

Answer 5

• during month 6, blood cell formation switches over the bone marrow
• switch is controlled by fetal adrenal gland cortisol

Question 6

What composes early embryonic hemoglobin (Gower 1)? What chromosomes are associated with this?

Answer 6

• 2 zeta chains(chromosome 16)

- 2 epsilon chains (chromosome 11)

Question 7

What composes early embryonic hemoglobin (Gower 2)?

Answer 7

• 2 alpha chains (chromosome 16)

- 2 epsilon chains (chromosome 11)

Question 8

What composes fetal hemoglobin?

Answer 8

• 2 alpha chains (chromosome 16)

- 2 gamma chains (chromosome 11)

Question 9

What composes adult hemoglobin?

Answer 9

• 2 alpha chains (16)

- 2 beta chains (11)

Question 10

What are the three mechanisms for blood vessel formation?

Answer 10

-coalescence in situ (vasculogenesis)
+population of angioblasts become organized into a primary capillary plexus -> dorsal aortae

-migration of angioblasts into organs
+endocardium

-sprouting from existing vessels (angiogenesis)
+intersegmental vessels

Question 11

How does vasculogenesis work?

Answer 11

-recruitment of angioblasts
+appearance of VEGFR-2 on membrane surfaces
+production of VEGF-A by surrounding mesenchyme

Question 12

What is sprouting?

Answer 12

-angiopoietin-1 + Tie-2 (receptor)

-Notch signaling pathway
+appearance of VEGFR-2 on membrane surfaces
+production of VEGF-A by surrounding mesenchyme

Question 13

How is the vascular wall built?

Answer 13

-endothelial cells release platelet-derived growth factor
+stimulates immigration of mesenchymal cells
+release of TGF and myocardium stimulates differentiation of mesenchymal cells into smooth muscle cells

Question 14

How are blood vessels differentiated?

Answer 14

-arterial pathway
+arteries are the first to differentiate
>initial signal pathway via Shh
>Notch leads to expression of Ephrins-B2 and inhibits Eph-B4
+signaling pathway involves Shh and Notch

Question 15

What ligands are expressed in developing arteries and veins?

Answer 15

Arteries -> Ephrins-B2

Veins -> Eph-B4

Question 16

How are veins differentiated?

Answer 16

-initiated via transcription factor COUP-TFII

+inhibits arterial pathway by inhibiting Notch

Question 17

Differentiation of lymphatics

Answer 17

-branch off veins

+require Sox-18 followed by Prox-1

Question 18

Dorsal aorta

Answer 18

-paired cranially due to lack of expression of noggin and chordin by notochord

Question 19

What is. The basic vertebral aortic arch pattern?

Answer 19

• six pairs of aortic arches, one pair per bronchial arch

- aortic arches connect ventral aorta to paired dorsal aorta

Question 20

What is the aortic arch pattern in mammalian embryos?

Answer 20

• 1st and 2nd pairs of aortic arches form but later degenerate
• 3rd pair form internal carotids
• common carotids are derived from the ventral aortae between the 3rd and 4th aortic arches
• right 4th aortic arch forms the right subclavian artery
• left 4th arch form the aortic arch
• 5th pair of arches degenerate
• 6th pair of arches become associated with the pulmonary system

Question 21

What is included in the dorsal intersegmentals?

Answer 21

• cervical, thoracic (intercostals), lumbar intersegmentals
• subclavians
• iliac arteries

Question 22

What is included in the lateral intersegmentals?

Answer 22

• mesonephric arteries
• adrenal arteries
• renal arteries
• gonadal arteries

Question 23

What is included in ventral intersegmentals?

Answer 23

-vitelline vessels
+celiac artery
+superior/inferior mesenterics

-allantoic vessels
+umbilical arteries

Question 24

What are the pairs of cardinal veins?

Answer 24

• anterior, posterior, common
• anterior and posterior pairs of Cardinal veins empty into the paired common cardinals, which empty into the sinus venosus

Question 25

What is the fate of the anterior Cardinal veins?

Answer 25

• anterior cardinals form the internal jugulars
• connection between the two is the left brachiocephalic vein
• all blood from the head is shunted to the right and drained into the right Cardinal vein -> superior vena cava

Question 26

What are the additional Cardinal veins?

Answer 26

• subcardinals

- supracardinals

Question 27

How is the inferior vena cava formed?

Answer 27

-the inferior vena cava is built as a patchwork quilt asymmetrically from remnants of the following
    \+vitelline vein
    \+subcardinals
    \+supracardinals
    \+iliacus

Question 28

What are hemangioblasts?

Answer 28

• originate from posterolateral mesoderm during gastrulation
• organize into blood islands in yolk sac around day 18
• bipotential
• seed sites of intra embryonic hematopoiesis