embryology of the CVS

Question 1

what are the 4 major stages in heart development

Answer 1

primitive heart tube

heart looping

atrial and ventricular septation

outflow tract septation

Question 2

stage 1 - what happens in the 3rd week of development

Answer 2

lateral plate splanchnic mesoderm forms the circulatory system and other viscera

angiogenic cell islands collect in the lateral plate splanchnic mesoderm, move towards midline and coalesce to form the 2 primitive heart tubes

Question 3

stage 1 - what is the first major system to function in the embryo and why

Answer 3

cardiovascular system

primordial heart starts to funciton at the beginning of week 4

rapidly growing embryo - nutrition by diffusion isnt enough to satisfy it

Question 4

stage 1 - creation of cardiogenic field (primitive heart and blood vessels)

Answer 4

blood vessels first appear in the wall of the yolk sac, allantois, connecting stalk and chorion

week 3 - appearance of paired endothelial strands (angioblastic cords) appear in the cardiogenic mesoderm

angioblastic cords canalise to form heart tubes

tubular heart joins blood vessels in other areas to form the primordial CVS

Question 5

stage 1 - formation of pericardium

Answer 5

cranial folding of embryo - reorientation of heart tube dorsal to pericardial cavity

pericardium derived from intra-embryonic coelom

pariteal layer of serous pericardium and fibrous pericardium are formed from somatic mesoderm

visceral layer of serous pericardium is derived from splanchnic mesoderm

Question 6

stage 1 - development of the heart tube, which end is which?

Answer 6

cranial end - arterial

caudal end - venous

Question 7

stage 1 - order of sections in the fused primitive heart tube (top to bottom)

Answer 7

1. truncus arteriosus
2. bulbus cordis
3. ventricle
4. atrium
5. sinus venosus (right and left horns)

Question 8

which direction does the fused primitive heart tube fold

Answer 8

up towards the right hand side

if it folds towards the left you get dextrocardia

Question 9

stage1 - venous and arterial end of the heart tube

Answer 9

sinus venosus - venous end, two hornds, each horn gets venous blood from yolk sac (vitelline vein), placenta (umbilical vein) and body of the embyro (common cardinal vein)

truncus arteriosus - arterial end, continuous cranially with the aortic sac, aortic arches arise from the aortic sac and terminate in the dorsal aorta

Question 10

stage 2 - formation of cardiac (bulboventricular loop)

Answer 10

bulbus cordis and ventricle grow faster than other regions forming a U shaped bulboventricular loop

Question 11

abnormal cardiac looping

Answer 11

leads to dextrocardia

heart tube loops to the left side instead of the right, ends up lieing facting the right

most frequnt positional abnormality of the heart

dextrocardia can be associated with situs inversus - transposition of viscera

Question 12

stage 3 - partitioning of primordial heart

Answer 12

seen around 27th and 37th days of embryonic development

involves 1 or 2 actively growing masses of tissues

1. endocardial cushion formaiton - separates RA and RV from LA and LV to form L and R AV canals
2. septum formation - separates RA from LA and RV from LV

Question 13

stage 3 - partitioning of primordial heart, clinical issues

Answer 13

many cardiac malformations are associated with defective formation of endocardial cushion and septum formation e.g. ASD and VSD

Question 14

stage 3 - partitioning of primitive atrium into LA and RA

Answer 14

1. formation of the septum primum, formation of the ostium primum
2. the ostium secundum begins to form by apoptosis of the septum primum (breaks down towards the top as it grows down and forms a foramen)
3. formation of the septum secundum, formation of the ostium secundum is complete, closure of the ostium primum as the septum primum meets the endocardial cushions (the septum secundum perforates in an oval shape to form the foramen ovale)
4. formation of the foramen ovale is complete, one way shunt allowing blood to move from the RA to LA

Question 15

stage 3 - what happens to the septum primum and secundum when the child is born

Answer 15

they snap together and the fossa ovalis is formed

Question 16

where does the septum secundum grow in relation to the septum primum

Answer 16

to the right of it

Question 17

in which septums are the foramens the opening in

Answer 17

foramen secundum is opening in septum primum

foramen ovale is opening in septum secundum

Question 18

role of foramen ovale before birth

Answer 18

allows most of the blood to pass from RA to LA

prevents the passage of blood in the opposite direction

Question 19

role of the foramen ovale aften birth

Answer 19

normally closes (increased pressure in LA due to increased pulmonary circulation)

septum primum fuses with septum secundum

fossa ovalis of the adult heart is a remnant of foetal oval foramen

non closure resuluts in PFO (patent foramen ovale) = atrial septal defect (ASD)

baby can be cyanotic at birth

Question 20

atrial septal defect

Answer 20

common congenital heart anomaly

f>m

common form is PFO

Question 21

what are the 4 clinically significant types of ASD

Answer 21

foramen secundum defect

endocardial cushion defect wih foramen primum defect

sinus venosus defect

common atrium

first 2 types are more common

Question 22

stage 3 - partitioning of primitive ventricle

Answer 22

muscular ventricular septum forms, opening is called interventricular foramen

bottom of spiral aorticopulmonary septum fuses with muscular ventricular septum to form membranous interventricular septum, closing interventricular foramen

(aorticopulmonary septum divides bulbis cordis and truncus arteriosus into aorta and pulmonary trunk)

growth of endocardial cushions also contributes to membranous portion of interventricular septum

Question 23

stage 4 - partitioning of bulbus cordis and truncus arteriosus

Answer 23

week 5 of development

aorticopulmonary septum divides BC and TA into aorta and pulmonary trunk

Question 24

ventricular septal defect

Answer 24

most common type of congenital heart disease - 25% of defects

common in males

can appear in any part of septum

small VSDs close spontaneously (30-50%)

membranous type of VSD is most common

Question 25

development of the conducting system of the heart

Answer 25

early pacemakers - primitive atrium then sinus venosus SAN develops during week 5 SAN is located in the RA near the entrance of the SVC in adults AVN and bundle of his develops from cells of AV canal and sinus venosus

Question 26

sudden infant death syndrome

Answer 26

cot death caused by abnormalities of conducting tissue

Question 27

what does the truncus arteriosus become in adults

Answer 27

aorta pulmonary trunk

Question 28

what does the bulbus cordis become in adults

Answer 28

smooth part of RV and LV

Question 29

what does the primitive ventricle become in adults

Answer 29

trabeculated part of RV and LV

Question 30

what does the primitive atrium become in adults

Answer 30

trabeculated part of RA and LA

Question 31

what does the sinus venosus become in adults

Answer 31

smooth part of RA coronary sinus oblique vein of LA

Question 32

aetiology of congenital heart disease

Answer 32

multifactorial rubella infection in pregnancy (PDA) maternal alcohol abuse (septal defects) maternal drug treatment and radiation gentic - 8% chromosomal - 2% (Down's and Turner's syndrome)

Question 33

congenital heart disease - VSD and ASD

Answer 33

VSD and ASD account for ~30% of congenital heart disease (VSD 20%, ASD 10%) girls have ASDs twice as often as boys VSDs are also slightly more common in females than males

Question 34

transposition of the great vessels

Answer 34

common cause of cyanotic disease in newborns associated with ASD and VSD permit exchange of systemic and pulmonary circulation causes: 1. failure of aorticopulmonary septum to take a spiral course 2. defective migration of neural crest cells e. g. tetralogy of Fallot

Question 35

Tetralogy of Fallot

Answer 35

made up of 4 cardiac defects: 1. pulonary stenosis (obstruction of RV outflow) 2. VSD 3. dextroposition of aorta (overriding aorta) 4. RV hypertrophy cause: unequal division of the conus due to anterior displacement of aorticopulmonary septum

Question 36

what are the 2 methods by which blood vessels develop

Answer 36

vasculogenesis - the _new_ formation of a primitive vascular network angiogenesis - the growth of new vessels from _pre-existing_ blood vessels

Question 37

formation of aortic sac

Answer 37

extension of TA of primitive heart tube first arteries to appear in the embryo are R and L primitive aortae each primitive aorta has a ventral and dorsal part after the fusion of the 2 endothelial tubes the 2 ventral aortae partially fuse to form aortic sac aortic branches arise from the aortic sac

Question 38

development of pharyngeal arch arteries and aortic branches

Answer 38

pharyngeal arches (future neck) develop during week 4-5 each arch recieves its own nerve and artery pharyngeal arteries communicate with aortic branches (now called aortic arches) 6 aortic arches are formed on each side, all are in communication with the dorsal aortae

Question 39

where do the aortic arches form from and how many are there

Answer 39

pharyngeal arch arteries join aortic branches to form aortic arches 6 pairs of aortic arches develop from aortic branches and pharyngeal arch arteries all are not present at the same time they all terminate in the dorsal aorta

Question 40

fate of the aortic arches

Answer 40

1 and 2: both disappear early, remnant of arch 1 forms part of the _maxillary artery_ (branch of external carotid) 3: constitues the commencement of the _internal carotid artery_ (is named the carotid arch), same on R and L **4: R - _R subclavian_, L - _distal part of aortic arch_** 5: either never forms or forms incompletely and then regresses **6: R - proximal part persists as the proximal part of the _R pulmonary artery_** **, L - _L pulmonary artery_ and forms the _ductus arteriosus_,** (within 1-3mths the ductus is obliterated and becomes the ligamentum arteriou**sum**)

Question 41

cause of great arteries anomalies

Answer 41

most defects arise as a result of persistence of aortic arches that normally should regress or regression of arches that normally shouldnt

Question 42

aberrant R subclavian artery

Answer 42

with regression of the R 4th aortic arch and the R dorsal aorta, the R subclavian a sometimes has an abnormal position on the L side. To supply blood to the R arm this forces the R subclavian a to cross the midline behind the trachea and oesophagus, which may constrict these organs usually has no clinical symptoms

Question 43

double aortic arch

Answer 43

occurs with the non-regression of the R aortic arch i.e. abnormal R aortic arch in addition to the normal L aortic arch forms a vascular ring around the trachea and oesophagus usually causes difficulty breathing and swallowing

Question 44

patent ductus arteriosus (PDA)

Answer 44

more frequent in females common anomaly associated with maternal rubella infection - early pregnancy cause - failure of muscular wall to contract, respiratory distress syndrome (low o2), lack of surfactant in the lungs early symptoms are uncommon but in the 1st year of life include increased work of breathing and poor weight gain uncorrected PDA may lead to congestive heart failure with increasing age

Question 45

coarctation of the aorta

Answer 45

aorta is narrowed, normally in the area where the ductus arteriosus inserts coarctations are most common in the aortic arch can proximal to ductus arteriosus (preductal) or distal to it (postductal) 90% of cases coarctation occurs opposite the ductus arteriosus theories of cause: 1. incorporation of muscle tissue of DA into arch of aorta, when DA contracts after birth, part of the arch also constricts 2. genetic/environmental

Question 46

embryonic circulation

Answer 46

vitelline = yolk sac umbilical = placental cardinal = rest of the body

Question 47

fate of vitelline arteries

Answer 47

embryo - supply the yolk sac adult - represented by arteries to the foregut, midgut and hindgut

Question 48

fate of umbilical arteries

Answer 48

before birth - paired branches of the dorsal aorta to placenta after birth - proximal portion persists as internal iliac and superior vesical branches to urinary bladder

Question 49

embryonic venous system

Answer 49

vitelline veins - blood from yolk sac to sinus venosus umbilical veins - originate from placenta, oxygenated blood to the embryo cardinal veins - draining the body of embryo

Question 50

fate of cardinal veins

Answer 50

main venous drainage system of the embryo form vena caval system by anastamosis among the veins carry the blood from the head and lower body into the heart

Question 51

venous system abnormalities

Answer 51

- result of not regressing as they should double IVC at the lumbar level arising from persistence of the L sacrocardinal vein absent IVC - lower half of the body is drained by the azygos vein which enters the SVC. The hepatic veins enters the heart the the site of the IVC Left SVC - normally only have R one double SVC

Question 52

development of the lymphatic system

Answer 52

develops at end of week 6 around main veins 6 1y lymph sacs develop at the end of embryonic period lymphatic vessels will join the lymph sacs later

Question 53

foetal circulation shunts

Answer 53

1. ductus venosus - shunts L umbilical vein blood flow directly to IVC, allows oxy blood from placenta to bypass the liver 2. oval foramen - allows blood to enter LA from RA, bypasses lungs 3. ductus arteriosus - allows blood that still escapes to RV to bypass the lungs

Question 54

neonatal circulation changes after birth - closure of shunts and umbilical arteries

Answer 54

ductus venosus becomes ligamentum venosum of the liver oval foramen closes after birth by tissue proliferation and adhesion of septal structures - fossa ovalis ductus arteriosus obliterates to form ligamentum arteriosum umbilical ateries ligamentous - medial umbilical ligament s