Cardiovascular Embryology

Question 1

prior to birth, fetal circulation is designed for what type of environment?

what oxygenates the blood?

Answer 1

in utero aqueous environment

placenta

Question 2

1) at birth, what does shifting and constriction of umbilical arteries cause?
2) reduced venous return throught ___________ allows latter to gradually close
3) what is increased in secretion and by what? what else is increased?
4) what is lost by the placenta?
5) All of these things happening result in what?
6) What is it converted to?
7) Increased blood flow to __________ and ___________ causes what?
8) What does this result in?

Answer 2

1) shifts fetal blood flow from placenta to fetus
2) left umbilical vein and ductus venosus
3) bradykinin by expanding lungs; increased oxygen concentration in blood
4) prostaglandins generated by placenta
5) trigger rapid constriction of ductus arteriosus
6) a fibrous structure, the ligamentum arteriosum
7) lungs and to the left atrium causes an equalization in pressure in the two atria
8) closure of foramen ovale that eventually grows permanent

Question 3

1) When does the CV system develop?
2) What does this allow the embryo to do?

Answer 3

1) week 3
2) allows embryo to grow beyond the short distances which were efficient for diffusion of O2, CO2, nutrients and wastes

Question 4

1) The heart begins as _________ and develops from what specific type of germ layer?
2) While the heart grows into a 4-chambered structure, it pumps blood where?

Answer 4

1) a single tube and develops from splanchnic mesoderm
2) throughout embryo and into extra-embryonic membranes

Question 5

1) What are the steps of Angiogenesis?
4) What does the transition from fetal to adult circulation involve?

Answer 5

1) blood islands form in splanchnic mesoderm of yok sac and allantois
2) blood islands coalesce, sprout buds and fuse to form vascular channels
3) Blood cells form (hematopoiesis) occurs in liver and spleen and eventually in bone marrow
4) new vessel formation, vessel merger and degeneration of early vessels

Question 6

1) What is the first evidence of heart development?
2) What is the cardiogenic plate?
3) Where does it move?
4) How does a single endocardial tube form and what does it eventually become?
5) Where do cardiac muscle cells form from?

Answer 6

1) bilateral vessel formation within the cardiogenic plate
2) splanchnic mesoderm situated anterior to the embryo
3) moves ventral to pharynx as head process grows upward and outward
4) Bilateral endocardial tube meet at midline and fuse; single eendocardial tube becomes future heart
5) splanchnic mesoderm surrounding the tube –> capable of pumping blood

Question 7

1) Name and describe the primitive heart regions (what they become)

Answer 7

1) Truncus arteriosus - output region –> ascending aorta and pulmonary trunk
2) Bulbus cordis - bulb-shaped region –> R ventricle
3) Ventricle - enlargement –> L ventricle
4) Atrium - will expand to become R and L auricles
5) Sinus venosus - paired region into which veins drain

L sinus venosus –> coronary sinus

R sinus venosus –> incorporated into wall of R atrium

Question 8

1) What is the first step in forming a 4-chambered heart?
2) How does this change orientation of regions?
3) What is the 2nd step?
4) What happens to the R and L sinus venosus

Answer 8

1) Endocardial tube lengthens and loops on itself
2) puts bulbus cordis (RV) beside the Ventricle (LV) and atrium dorsal to ventricle
3) Venous return is shifted to R side
4) larger R sinus venosus (R auricle) –> incorporated into future RA

smaller L sinus venosus joins future RA as the coronary sinus

***embryonic atrium expands and overlies ventricle chamber –> common AV opening connects two chambers –> contstriction (future coronary groove) separates atrium and ventricle

Question 9

1) What is the third step in forming a 4-chambered heart?
2) Growth of _________partitions the common A-V opening into R and L?
3) What causes the interventricular foramen to close?
4) Where was the original opening?
5) Incomplete closure of interventricular septum (also known as what?) results in what?

Answer 9

1) Atrio-ventricular opening is partitioned
2) endocardial “cushions” partitions common AV opening
3) ventral growth of cushions contributes to a septum that closes the foramen
4) between bulbus cordis and ventricle
5) ventricular septal defect results in blood flow from L to R ventricle and an associated murmur; large defects –> cardiac insufficiency

Question 10

1) What is the 4th step in heart formation?
2) How do the R and L ventricles form?
3) the interventricular septum, AV valves, chordae tendineae, papillary muscles and irregularities of wall are sculptured by what process?
4) What is the 5th step?
5) Describe set up of septum formation?
6) What is the septal opening?

Answer 10

1) R and L ventricles formed
2) by ventral growth and interior excavation of bulbus cordis and ventricle
3) selective excavation of ventricular wall tissue
4) R and L atria divided by a septum
5) need for an open spetum that allows blood to flow from R to L atrium (until birth)
6) foramen ovale

Question 11

Describe steps of interatrial septum and foramen ovale

Answer 11

1) interatrial septum 1 grows from dorsal atrial wall toward endocardial cushions
2) pre-existing foramen is obliterated with septum 1 meets cushions
3) foramen 2 develops by fenestration of dorsocranial region of septum 1 (before step 2)
4) interatrial septum 2 grows from cranial wall of R atrium toward caudal wall
5) spetum remains incomplete and free edge forms boundary of an opening - foramen ovale

Question 12

1) What is the 6th step of heart formation?
2) What happens to the truncus arteriosus?
3) How is the spiral septum formed?
4) Failure of this step results in what?
5) what two things contribute to proper closure of interventricular septum?*
6) selective erosion of cardiac/vessel wall form what?
7) what directs partitioning of truncus arteriosis

Answer 12

1) Aorta and pulmonary trunk formed
2) partitioned in a spiral pattern to form aorta and pulmonary trunk
3) ridges appear along lumen wall, grow inward and merge to create spiral septum
4) leaves aorta connected to R ventricle and pulmonary turnk to L ventricle –> fatal
5) endocardial cushions and spiral septum
6) aortic and pulmonary semilunar valves (like AV valves)

excessive erosion –> valvular insuffieciency

vessel stenosis –> narrow lumen, not enough erosion

7) migration of neural crest cells

Question 13

1) What is tetralogy of fallot

Answer 13

1) cardiac anomaly –> combo of four defects –> defective spiral septum formation in truncus arteriosus and bulbus cordis
- ventricular spetal defect
- stenosis of pulmonary trunk
- enlarged aorta (overrides R ventricle)
- hypertrophy of R ventricle

Question 14

1) What pairs develop as arteries in embryo?
2) What do the aortic arches connect?
3) What is each situated within?
4) What happens to the dorsal aortae?
5) What happens to the ventral aortae?

Answer 14

1) paired ventral and dorsal aortae
2) ventral and dorsal aortae
3) pharyngeal arch
4) merge to form a single descending aorta
5) receive blood from truncus arteriosus and fuse to form the brachiocephalic trunk

Question 15

1) Describe what happens to each aortic arch

Answer 15

1) first two arches degenerate
2) 5th is rudimentary or absent
3) 3rd aortic arch –> internal carotid artery and proximally the common carotid artery; external carotid artery buds off from third arch
4) dorsal aorta degenerates btw 3rd (head) and 4th (caudal region) arches
5) L 4th arch –> adult arch of aorta

R 4th arch –> R subclavian artery (distal connection btw arch and aorta degenerates)

6) 6th arch (proximal part) –> pulmonary artery

distal part on R degenerates but persists on L side as ductus arteriosus

Question 16

1) What happens if connection between 4th arch and aorta persists?
2) What does ductus arteriosus do?
3) What happens at birth?
4) What does it become?
5) What happens if it persists?

Answer 16

1) compression of esophagus –> difficult swallowing and enlarge esophagus cranial to compression
2) shunts blood from pulmonary trunk to aorta –> exercises R ventricle in case limited blood return from lungs
3) abrupt constriction of it shiffts pulmonary trunk output to lungs
4) ligamentum arteriosum
5) continuous murmur (systole and diastole)

Question 17

1) What does each dorsal artery give off?
2) What does the 7th cervical one become?
3) What do the cranial to the 7th become?
4) What do the caudal to the 7th become?
5) When heart shifts into thoracic cavity, what happens?

Answer 17

1) intersegmental arteries
2) distal portion of subclavian artery
3) vertebral artery (coming together and lose connection to aorta- degenerate)
4) intercostal and lumbar arteries
5) positions of arches change –> subclavian arteries go from caudal to cranial position

Question 18

1) What also arise from R and L dorsal aortae?
2) What do they supply?
3) What does the R one become?
4) What happens to the L?
5) What results from failure of #4?
6) What do dorsal aorta terminate as?
7) What do they supply?
8) True or False: umbilical arteries persist to urinary bladder in adult
9) How are external and internal iliac arteries developed?

Answer 18

1) vitelline arteries
2) yolk sac
3) cranial mesenteric artery
4) degenerates
5) result in a fibrous band that may cause colic –> entrapping segment of intestine
6) umbilical arteries
7) allantois
8) True –> distal part degenerates
9) outgrowths of umbilical arteries

Question 19

1) What does the embryonic sinus venosus receive?
2) what does transition from embryonic to adult venous patterns involve?
3) What does venous return shift to and what happens to sinus venosus?

Answer 19

1) vitelline veins –> drain yoik sac

umbilical veins –> drain allantois

cardinal veins –> drain embryo

2) formation of new veins, anastomoses btw veins and selective degeneration of embryonic segments
3) shifts to R side adn R sinus venosus incorporated into wall of R atrium (R auricle) and L sinus venosus is reduced and become coronary sinus

Question 20

1) What do cranial cardinal veins become?
2) What buds off cranial cardinal veins?
3) What is the anastomotic vein?
4) What does it become?
5) What happens if this fails?

Answer 20

1) internal jugular veins
2) larger external jugular and subclavian veins
3) develops and runs from L to R cranial cardinal veins shifting venous return to R side
4) L brachiocephalic vein
5) double cranial vena cava

Question 21

1) What do the caudal cardinal veins give rise to?
2) Where are these venous networks located?
3) What do they supply?
4) What forms the caudal vena cava?
5) What develops the azygos vein?
6) What does it drain into on R and L side?

Answer 21

1) supracardinal and subcardinal veins with extensive anastomoses among all veins
2) intermediate mesoderm
3) embryonic kidneys and gonads
4) selective segments of R subcardinal venous network, including anastomosis with proximal end of R vitelline vein
5) supracardinal vein as well as caudal and common cardinal veins of R side (dog cat horse) or L side (pig) or both sides (ruminants)
6) into cranial vena cava on R side or coronary sinus on L side

Question 22

1) What contribute to formation of liver sinusoids?
2) What do the vitelline veins give rise to?
3) What happens to the umbilical veins?
4) Where does the ductus venosus develop?
5) After birth, what does the L umbilical vein become?

Answer 22

1) vitelline veins and umbilical veins
2) portal vein, formed by anastomoses that develop btw R and L vitelline veins and enlargement/atrophy of selective anastomoes
3) R umbilical vein atrophies and L conveys placental blood to liver
4) within liver, a shunt develops btw L umbilical vein and R hepatic vein which drains into caudal vena cava
5) becomes round ligament of liver

Question 23

1) What is the ductus venosus
2) Why can this ductus venosus develop?
3) What’s a portosystemic shunt?
4) What does it cause?
5) What is another cause of the portosystemic shunt?

Answer 23

1) a shunt that diverts blood away from sinusoid and toward system veins
2) fetus isn’t eating, placenta is able to detoxify blood (maternal liver) and its desirable for venous return to bypass fetal liver sinusoids
3) a persistent ductus venosus
4) allows toxic digestive products to bypass liver –> toxic agents affect brain resulting in neuro disorders at some point
5) development error resulting in anastomosis btw portal vein and caudal vena cava or azygos vein

Question 24

1) How are pulmonary veins formed?
2) Describe the process
3) What is lymph vessel formation similar to?
4) What do lymphatics start to develop as?
5) What are the regions they start developing in?
6) How are lymph nodes produced?

Answer 24

1) as outgrowths of L atrium
2) initial growth divides into L and R branches –> subdivide into branches that drains lobes of lung
3) blood angiogenesis
4) lymph sacs
5) jugular (neck - near brachiocephalic veins), cranial abdominal (future cysterna chyla) and iliac region (pelvic)
6) by localized mesodermal invaginations that partition the vessel lumen into sinusoids
- mesoderm develops a reticular fameworks within which lymphocytes accumulate