Embryology - Formation of cardiac septa

Question 1

describe the formation of atrial septum and the mode of septation

Answer 1

• passive expansion of atria and endocardial cushion fusion
  DAY 30
  1. Septum primum and endocardial cushion gap: ostium primum
  2. upper portion of septum primum: cavities: coalesce: ostium secundum
  3. closure of ostium primum by anterior growth of endocardial cushion

DAY 35
1. atrial expansion = invagination of muscular atrial roof = septum secundum
2. septum secundum free end: covers ostium secundum
= only opening: foramen ovale
3. regression of the upper septum primum, remaining = valve of oval foramen
birth, LA pressure greater, valve closes agains the septum secundum, foramen ovale shut

Question 2

what is the role of foramen ovale in utero

Answer 2

allow passage of blood from RA to LA (placental blood into RA via superior and inferior VC)

Question 3

what is the cause and outcome of atrial septal defect

Answer 3

1. excessive resorption of septum prima
2. insufficient development of septum secundum
3. absence of both septum primum and secundum

outcome: right to left shunt
female more than male

Question 4

what is the AV canal and the endocardial cushion

Answer 4

• AV canal is the internal connection between atrial and ventricle space
• endocardial cushion: found in AV canal, anterior, posterior left and right

Question 5

describe the blood flow route at this stage of development

- explain why no outflow, why RV no blood

Answer 5

placenta - superior inferior VC - RA - LA - LV - no outflow yet

1. AV canal not on the right side, so RV no blood received from RA
2. no outflow as the truncus arteriosus is blocked by the bulboventricular flange

Question 6

describe the process of AV canal septation, completes by 5th week

Answer 6

1. endocardial cushion fusion: posterior and anterior cushion fuse. L R AV canal formed. Also reposition so each is aligned to the L R atria and ventricle
2. regression of the bulboventricuar flange to allow out flow

Question 7

describe the formation of AV valve

Answer 7

AV canal surronded by local proliferation of mesenchymal cells

• blood hollows and thins the mesenchymal cells, valve formed.
• attached to muscular cords on ventricles initially, those generate and replaced by cordae

Question 8

what is tricuspid atresia

Answer 8

obliteration of AV canal: so no/ fusion of tricuspid valve

Question 9

describe process of aortico-pumonary septation

Answer 9

1. both the truncus arteriosus and conus cordis seperated by CONOTRUNCAL SEPTUM
2. swellings arise in the truncus arteriosus: grow towardss each other and towards atria. Fuse and twist in right handed manner
3. inferior to truncus swellings: conus swellings, aslo fuse
4. fusion of conus septum and aorticopulmonary septum = conotruncal septum

Question 10

name the 3 sections on the bulbus cordis

Answer 10

1. truncus arteriosus (actual tube tract)
2. conus cordis
3. tuberculated part of RV

Question 11

describe the formation of membranous inter-ventricular septum

Answer 11

fusion of posterior AV cusion and conotruncal sepum = membranous part of interventricular septum

Question 12

describe the formation of semilunar valve

Answer 12

before the truncal swellings fuse:

• small tubercles arise, 3 in each pulmonic and aortic channels
• blood hollows out these tubercle (top of it) = valve formed