Development of the Heart Flashcards
When does Heart develop?
From mesoderm on day 18 from mesodermal cells placed in cardiogenic area
in response to endoderm cells forms strands called cardiogenic cords cords develop hollow centre endocardial tubues on day 20 lateral folding of heart forms primitive heart tube day 22
5 distinct regions of heart?
Sinus venosus Primitive Atrium Primitive Ventricle Bulbus cordis Truncus arteriosus
What happens on day 23?
Primitive heart tube elongates and bublbus cordis and prim ventricle grow, tube loops and fold from u to s shape
What happens on day 28?
Primitive atria and ventricle of future heart reorientated to final position
remainder of heart remodels chamber and forms septa for 4 chambred heart
What does Sinus venosus forms?
Part of R atrium, coronary sinus and SA node
What does primitive atrium form?
Part of R,L atrium and auricle
What does primitive ventricle form?
Left ventricle
What does bulbus cordis form?
Right ventricle
What did truncus arteriosus form?
Semilunar valves
What happens at week 4?
sinus venosus recieves blood from sinus horns
What happens at week 5?
Left sinus becomes redundant so left sinus horn disappear , right sinus horn enlarges and with sinus venosus forms right atrium
What happens to sinoatrial orifice?
Flanked by septum spurium
What does right sinus horn and RA form?
Left venous valve and septum spurium for atrial septum in superior region of right venous valve inferior into inf.V.cava and coronary sinus
When does septal formation occur?
Between 27th and 37th day involves 2 mechanisms
What 2 mechanisms for septal formation?
Formation of actively growing masses - endocardial cushions to grow across a chamber
A region of wall failing to grow whilst regions either side grow does not allow partition of heart chambers
What is the 4 division process in septal formation?
Division of atria
Formation of AV canal
Septum formation in truncus arteriosus
Formation of ventricular septum
What is septum primum at week 4?
Extends across lumen to endocardial cushion, ostium primium is hole remaining before septum primum is close, as extends superiorly closes ostium primum
What prevents partitioning of atria?
Formation of ostium secundum and which develops septum secundum, extends posteriorly anterior forms interatrial valve - after birth closed and forms fossa ovalis
What forms end of week 4?
Stria connected to LV via Single AV canal
What happens at week 5?
AV canal enlarges to right so blood enters both ventricles directly - superior and inferior AV cushions extend to lumen of AV canal and fuse - seperate AV canal into orificies by end of week - bordered by proliferations of mesenchymal tissue
What does mesenchymal tissue do?
Extend down ventricle as mature, more narrow for mesenchymal extension , extensions form tricuspid and mitral valve
Why is septum of truncus arteriosus important?
divides outflow of heart
Left ventricle to aortic arch
Right ventricle to pulmonary artery
When does truncus swelling s grow?
Week 5, right superior truncus swells and extends to left inferior truncus to right - fuse to form aorticpulmonary septum
What happens when trucus swellings extend?
Additional swellings form r and l conus cordis wall - extend with aorpul septum dividing outflow of heart , partion near primordial of SV form
What does intraventricular septum do?
Seperates 2 chamber RV AND LV - intraventricular forament closed by inferior endocardial cushioon towards septum
When does AV valves form? and SV?
AV - week 5-8
SV - week 5-9
Where does heart pacemakers initially lie?
left cardiac tube in caudal position, later assumed by sinus venosus incorporated to RA - SA node near Sup.Vena.Cav
Where are AV node and bundle of His derived from?
Cells in left wall of sinus venosus
Cells of AV canal
What are most heart defects associated with?
Abnormalities in cardiac looping
atrial septal defects
defects of AV cana;
Ventricular septal defects
How does abnormal cardiac loops arise?
heart tube loops to left not right in dextrocardia - complete reversal asymmetry so called situs inversus or heterataxy - can have additional defects
When do atrial septal defects occur?
2:1 in females
6/10k
Ostium secundum hole shunting blood from left to right atria
Total lack of atrial septa known as cor triloculare biventriculare with oteher serious defects
Premature closure of oval forament in extensive hypertrophy of RA and RV and underdevelop LA LV
What defects with AV canal?
Integrity of AV depends on endocardial cushions
cross like formation distinct
AV septa form AV cushions
if cushion fail to fuse this will be persistent AV canal or ostium primum defect or both
What is VSD?
12/10K
found in isolation
abnormal partion of SLV conotruncal region
Shunt of blood from LV to RV 1.2 x more blood pass
