Development of the Heart

Question 1

When does Heart develop?

Answer 1

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

Question 2

5 distinct regions of heart?

Answer 2

Sinus venosus
Primitive Atrium
Primitive Ventricle
Bulbus cordis
Truncus arteriosus

Question 3

What happens on day 23?

Answer 3

Primitive heart tube elongates and bublbus cordis and prim ventricle grow, tube loops and fold from u to s shape

Question 4

What happens on day 28?

Answer 4

Primitive atria and ventricle of future heart reorientated to final position
remainder of heart remodels chamber and forms septa for 4 chambred heart

Question 5

What does Sinus venosus forms?

Answer 5

Part of R atrium, coronary sinus and SA node

Question 6

What does primitive atrium form?

Answer 6

Part of R,L atrium and auricle

Question 7

What does primitive ventricle form?

Answer 7

Left ventricle

Question 8

What does bulbus cordis form?

Answer 8

Right ventricle

Question 9

What did truncus arteriosus form?

Answer 9

Semilunar valves

Question 10

What happens at week 4?

Answer 10

sinus venosus recieves blood from sinus horns

Question 11

What happens at week 5?

Answer 11

Left sinus becomes redundant so left sinus horn disappear , right sinus horn enlarges and with sinus venosus forms right atrium

Question 12

What happens to sinoatrial orifice?

Answer 12

Flanked by septum spurium

Question 13

What does right sinus horn and RA form?

Answer 13

Left venous valve and septum spurium for atrial septum in superior region of right venous valve inferior into inf.V.cava and coronary sinus

Question 14

When does septal formation occur?

Answer 14

Between 27th and 37th day involves 2 mechanisms

Question 15

What 2 mechanisms for septal formation?

Answer 15

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

Question 16

What is the 4 division process in septal formation?

Answer 16

Division of atria
Formation of AV canal
Septum formation in truncus arteriosus
Formation of ventricular septum

Question 17

What is septum primum at week 4?

Answer 17

Extends across lumen to endocardial cushion, ostium primium is hole remaining before septum primum is close, as extends superiorly closes ostium primum

Question 18

What prevents partitioning of atria?

Answer 18

Formation of ostium secundum and which develops septum secundum, extends posteriorly anterior forms interatrial valve - after birth closed and forms fossa ovalis

Question 19

What forms end of week 4?

Answer 19

Stria connected to LV via Single AV canal

Question 20

What happens at week 5?

Answer 20

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

Question 21

What does mesenchymal tissue do?

Answer 21

Extend down ventricle as mature, more narrow for mesenchymal extension , extensions form tricuspid and mitral valve

Question 22

Why is septum of truncus arteriosus important?

Answer 22

divides outflow of heart
Left ventricle to aortic arch
Right ventricle to pulmonary artery

Question 23

When does truncus swelling s grow?

Answer 23

Week 5, right superior truncus swells and extends to left inferior truncus to right - fuse to form aorticpulmonary septum

Question 24

What happens when trucus swellings extend?

Answer 24

Additional swellings form r and l conus cordis wall - extend with aorpul septum dividing outflow of heart , partion near primordial of SV form

Question 25

What does intraventricular septum do?

Answer 25

Seperates 2 chamber RV AND LV - intraventricular forament closed by inferior endocardial cushioon towards septum

Question 26

When does AV valves form? and SV?

Answer 26

AV - week 5-8

SV - week 5-9

Question 27

Where does heart pacemakers initially lie?

Answer 27

left cardiac tube in caudal position, later assumed by sinus venosus incorporated to RA - SA node near Sup.Vena.Cav

Question 28

Where are AV node and bundle of His derived from?

Answer 28

Cells in left wall of sinus venosus

Cells of AV canal

Question 29

What are most heart defects associated with?

Answer 29

Abnormalities in cardiac looping
atrial septal defects
defects of AV cana;
Ventricular septal defects

Question 30

How does abnormal cardiac loops arise?

Answer 30

heart tube loops to left not right in dextrocardia - complete reversal asymmetry so called situs inversus or heterataxy - can have additional defects

Question 31

When do atrial septal defects occur?

Answer 31

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

Question 32

What defects with AV canal?

Answer 32

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

Question 33

What is VSD?

Answer 33

12/10K
found in isolation
abnormal partion of SLV conotruncal region
Shunt of blood from LV to RV 1.2 x more blood pass