Vascular pt 6 (embryology)

Question 1

When and how (general) does the vascular system begin to develop?

Answer 1

During the third week, angiogenic clusters form blood vessels in the yolk sac, cardiogenic area and placenta (mesoderm)

Question 2

What are hemangioblasts and what do they do?

Answer 2

• Developed from mesoderm cells

- differentiate between mesenchyme and yolk sac cells via FGF; the cells cluster into islands

Question 3

What are VEGFs?

What do they do?

Answer 3

• Vascular endothelial growth factors secreted from mesodermal cells
• differentiate hemangioblasts into hematopoietic stem cells *precursor of all blood cells) and endothelial cells (vessel walls)

Question 4

What does VEGF secretion by mesenchymal cells do?

Answer 4

Generates capillaries which consolidate into arteries and veins

Question 5

What does PDGF do?

Answer 5

(platelet derived growth hormone) differentiates mesenchymal cells into SM and pericytes

Question 6

During gestation, where is the site of blood formation? (three stages)

Answer 6

1. yolk sac
2. liver and spleen
3. Bone marrow

Question 7

What is the initial process of cardiogenic area formation?

Answer 7

• Precardiac mesoderm migrates laterally to heart-forming region
• Endoderm replaces hypoblast and secretes signaling factors to regulate endochardial cell and myocyte formation

Question 8

Explain heart tube formation

Answer 8

• Develop from myoblast clusters
• heart tubes fuse to make a ventral heart tube and a dorsal aorta during folding
• pericardium formed from intraembryonic coelom

Question 9

Explain head folding

Answer 9

(bending of endocardial tubes)

• ventral fusion produces heart tube
• dorsal fusion produces aorta

Question 10

Explain bulboventricular loop formation

Answer 10

Heart tube forms: truncus arteriosus, bulbus cordis, ventricle/atrium, sinus venosus
The bulboventricular loop is formed by the twisting of heart tube

Question 11

Explain heart beat formation

Answer 11

• Contractions begin when heart tubes fuse (21-23 days)
• Contractions are peristaltic waves from primitive atria into ventricles (no initial valves)
• Blood flow begins in 4th week
• Heart rate accelerates with chamber formation

Question 12

What is the bulboventricular loop?

Answer 12

Blood flows from sinus venous, thru atria, thru ventricles, thru bulbus cordis and to truncus arteriosus

Question 13

Explain heart chamber partitioning

Answer 13

• endocardial cushions project from anterior and posterior walls and fuse
• this separates atria from ventricles leaving AV canals where tricuspid and mitral valves develop
• cushions form interatrial and interventricular septa

Question 14

What are the primary and secondary septa of atrial partitioning?

Answer 14

primary: separates atria, then forms a secondary foramen
secondary: forms and covers secondary foramen

Question 15

What is the foramen ovale?
What is its purpose prenatally?
What is its purpose postnatally?

Answer 15

• opening in secondary septum
• prenatally directs blood flow from the right to left atria
• postnatally, nothing. L. atrial pulmonary pressure keeps it closed and forms the fossa ovalis

Question 16

What are two types of atrial septal defects?

Answer 16

1. probe patent foramen ovale: primary and secondary septums don’t adhere well; few symptoms
2. secundum type SD: excessive resorption of primary septum or inadequate development of secondary; leads to patent foramen ovale (increases work of heart by permitting blood flow from L to R or R to L [cyanosis])

Question 17

Explain the formation of the aorta and pulmonary trunk

Answer 17

Spiral aortico-pulmonary septum divides bulbis cordis/truncus arteriosus into aorta and pulmonary trunk; semilunar valves form at the TA and BC junctions

Question 18

How is the ventricular septum formed?

Answer 18

Bulbar ridge, endocardial cushions and ventricular wall fuse, closing off interventricular foramen and forming the septum

Question 19

What are the two portions of the ventricular septum?

Answer 19

1. Muscular portion: develops from ventricular wall; separates AV valves
2. Membranous portion: derived from endocardial cushions and bulbar ridge

Question 20

What is VSD?

Answer 20

(Ventricular septal defect)

• most common defect of heart
• 25% of these defects occur in the membranous portion
• allows oxygenated blood to flow from L to R ventricle (can lead to cyanosis)
• small ones close on own, large ones need surgery

Question 21

What are some defects in BC/TA division?

Answer 21

1. persistant truncus arteriosus (no septum)
2. transposition of aorta and pulmonary trunk (no spiral)
3. unequal division of BC/TA (override)
4. pulmonary or aortic stenosis

Question 22

What is the tetralogy of fallot?

Answer 22

• condition due to unequal dividion of BC/TA

- leads to: VSD, pulmonary stenosis, R. ventricular hypertrophy, overriding aorta

Question 23

What is a neural crest malformation?

Answer 23

When neural crest cells migrate from the ectoderm and interact with mesenchyme to form the face and heart

Question 24

What is a heart malformation?

Answer 24

Endocardial cushion is malformed due to abnormal migration, proliferation and differentiation of neural crest cells

Question 25

Where does the sinus venous receive blood from? (3)

Answer 25

1. cardinal veins (drain body) 2. vitelline (drain yolk sac and become portal veins) 3. umbilical (bring blood from placenta)

Question 26

What are aortic arches?

Answer 26

Branches from truncus arterioles that form the major vessels leading to the heart

Question 27

What does the asymmetry of the arches lead to?

Answer 27

- aorta on the left - left recurrent laryngeal nerve under aorta - right recurrent laryngeal nerve under right subclavian artery

Question 28

What is the ductus arterioles?

Answer 28

- Persistant branch of aortic arch - connects pulmonary trunk to aorta - permits blood flow from pulmonary trunk into aorta (bypasses lungs)

Question 29

What does the trophoblast differentiate into?

Answer 29

- syncytiotrophoblast: jelly mass that expands into endometrium - cytotrophoblast: forms chorionic villi containing fetal blood vessels (b/w intervillous spaces)

Question 30

What is the fetal-maternal placental barrier? What normally crosses the barrier? What is potentially harmful if crossed the barrier?

Answer 30

Barrier formed by layers of cytotrophoblasts, syncytiotrophoblasts and mesoderm (around fetal vessels) - normal transfer includes metabolic substances - viruses, alcohol, dilantin, valproic acid, retinoic acid, androgens, antibiotics, etc.

Question 31

What is the fate of vitelline/umbilical veins?

Answer 31

- liver tissue develops around vitelline veins - umbilical and vitelline veins converge to form hepatic sinusoids - ductus venosus forms internal bypass thru liver

Question 32

What are the three shunts of prenatal circulation?

Answer 32

1. Ductus venosus: diverts blood around liver 2. Foramen ovale: shunts blood from R to L atrium 3. Ductus arteriosus: shunts blood from pulmonary trunk to aorta, bypassing lungs

Question 33

What are the three shunts of postnatal circulation?

Answer 33

1. Ligamentum venosum: in liver 2. Fossa ovalis: in atrial septum 3. Ligamentum arteriosum: b/w aorta and pulmonary trunk

Question 34

How is oxygen distributed in prenatal circulation?

Answer 34

1. ductus arteriosus shunts deox. blood into aorta, reducing ox. blood in lower limb 2. blood in umbilical veins and vena cava are separate when entering R. atrium 3. More ox. blood enters L. atrium, more deox. blood enters R. ventricle and pulmonary trunk