Cardiac looping

Question 1

Very 1st heart structure

Answer 1

Paired endocardial heart tubes

Question 2

Paired endocardial heart tubes

Answer 2

Splanchnic mesoderm (cardiogenic chords) of lateral plate mesoderm

Question 3

Folding embryo

Answer 3

lateral folds and fusion cranial to caudal => forms 1 heart tube
Cephalocaudal folding → brings heart into pericardial cavity

Question 4

3 structural layers of heart tube

Answer 4

 Inner endocardial tube = endocardium
 Myoepicardial mantle = myocardium + epicardium
 Cardiac jelly = myocardium + endocardial cushion tissue

Question 5

Heart tube chambers

Answer 5

o Truncus arteriosus: bulge cranially to form aortic sac
o Bulbus cordis => will develop as trabeculated RV
o Primitive ventricle
o Sinus venosus: caudal, receive blood from entire embryo
 Separated from atrium by sinoatrial sulcus (site of future SA node)
 Outside pericardial cavity, fixed by septum transversum

Question 6

Truncus arteriosus

Answer 6

Ascending Ao + PA

Question 7

Conus cordis

Answer 7

Smooth OT

Question 8

Proximal 1/3 of bulbus cordis

Answer 8

RV, trabeculated

Question 9

Bulboventrocular sulcus

Answer 9

IV foramen => IVS

Question 10

Primitive ventricle

Answer 10

LV trabeculated

Question 11

Primitive atrium

Answer 11

rough part of atria

Question 12

What is looping

Answer 12

bending of heart tube before septation => C shape => S shape

Question 13

Normal looping

Answer 13

o Asymmetric activity of lateral  (↑ active) → rapid growth of bulboventricular portion → saccular shape → greater curvature along R border
 Normal looping towards the R
o Cranial aspect of the heart tube bends ventrocaudally and to the R = truncus + bulbus cordis
 Heart tube shifts to the L du to cr (Ao roots) and caudal (sinus venosus) attachment
o Caudal aspect of the heart tube bends toward the dorsocranial aspect and towards the left = primitive atria and sinus venosus
 Result: Placement of the atrium and sinus venosus above and behind the truncus arteriosus/bulbus cordis/ ventricle

Question 14

Convergence

Answer 14

Alignement of developing IVS w/ OT portion and AV canal

connection btwn RA and RV + LV to Ao portion of LVOT
AV canal separate primitive atria and ventricles

Question 15

Wedging

Answer 15

counterclockwise rotation of OT → align LV and AoV
o Wedges between developing MV and TV

Question 16

Sinus venosus

Answer 16

eventually incorporated in RA => coronary sinus + portion of RA wall

Question 17

Faulty development of sinus venosus

Answer 17

Sinus venosus defect: dorsocranial to the fossa ovale
* Incomplete embryologic resorption of sinus venosus
* Type of ASD: dorsocranial to the fossa ovale
o Involve portion of atrial wall derived from sinus venosus
 Interatrial communication = orifice of the unroofed right pulmonary veins as they pass posterior to the RA
 Not true ASD, but hemodynamically similar  L to R shunting
o Abnormal attachment of the R PVs to Cr or CaVC
 Defect just below the orifice in RA
* CrVC type: more common in Hu
* CaVC type: below foramen ovale
 Partial anomalous PV drainage from R lung

Question 18

Faulty development of common PV

Answer 18

if fails to develop => total/partial anomalous pulmonary venous return
* All 4 PVs connect to the RA as collateral channels