Development Of Heart And Pericardium

Question 1

What is the Foramen ovale?

Answer 1

Foramen ovale- opening between right and left atria during fetal life

Question 2

What is septae?

Answer 2

Septae-connective tissue partition separating structures

• Interventricular- found between the ventricles
• Interatrial- found between the ventricles
• Aorticopulmonary-found between the ascending aorta and pulmonary trunk

Question 3

What is partitioning?

Answer 3

Dividing of embryological parts to enhance function

Question 4

What is the ventricular septal defect?

Answer 4

A breach in the interventricular septum, with resultant consequences

Question 5

What is the atrial septal defect?

Answer 5

A breach in the interarterial septum, with resultant consequences

Question 6

What does the heart develop from?

Answer 6

Develops from carcinogenic mesoderm

Embryo folding and flexion causes repositioning of the heart and the establishment of normal anatomical relationships

Question 7

Describe formation of the heart tubes

Answer 7

3rd week

• Angioblastic cords/endothelial strands
• Canalize to form two heart tubes
• Lateral folding of the embryo occurs
• Heart tubes fuse to form the tubular heart (a single tube )
  
  • Fusion occurs from the cranial to the caudal end
    
    • Beginning of development of pericardial cavity

Question 8

How is the epicardium formed?

Answer 8

From mesothelium all cells arising from the external surface of the sinus venosus spreading over the myocardium

Question 9

What is the myocardium formed from?

Answer 9

From myoblasts from the first heart field (cardiac mesoderm)

Question 10

What is the endocardium formed from?

Answer 10

From the primitive heart tube

Question 11

Describe the formation of transverse sinus?

Answer 11

• Communication between both of the pericardial cavity
  
  • formed be degeneration of central part of dorsal mesocardium
  • In adult: pericardial reflection located posterior to aorta and pulmonary trunk, anterior to superior vena cava (SVC), superior to left atrium

Clinical significance: cardiothoracic surgeons can separate arteries from veins allowing for temporary ligation

Question 12

What are the subdivisions of the tubular heart?

Answer 12

• Truncus arteriosus
• Bulbus cordis
• Primitive ventricle
• Primitive atrium
• Sinus Venosus

Cephalic arterial end- continuous with aortic sac

Caudal venous end- opens into the sinus venosus
-from placenta, embryo and yolk sac

Question 13

What does sinus venosus receive paired veins from?

Answer 13

• The vitelline veins (omphalomesenteric vein)- from the umbilical vesicle
• Common cardinal veins- from the embryo
• Umbilical veins- from the chorion

Question 14

Describe cardiac looing

Answer 14

Day 23-28

Bulbous cordis and ventricle grow faster than other regions causing it to bend itself

• Viewed from the front the bulbus cordis and primordial ventricle undergoes a de trail loop forming the U-shaped bulboventricular loop resulting in the apex of the heart to the left
• Primitive atrium and sinus venosus move dorsal (posterior) to truncus arteriosus, bulbus cordis and ventricle

Question 15

What is the fate of the primitive atrium?

Answer 15

Left auricle
-Internal surface has a rough, trabeculated appearance

Right auricle
-Internal surface has a rough, trabeculated appearance

Question 16

What is the fate of the sinus venosus?

Answer 16

Left horn- mostly obliterates
-remnants- the coronary sinus and the oblique vein of left atrium

Right horn- seen as sinus venarum
-smooth- walled part of right atrium

Question 17

What is the fate of primitive ventricle?

Answer 17

Trabeculated part of the wall of the right and left ventricles

Question 18

What is the fate of the bulbus cordis?

Answer 18

Majorly contribute to form outflow tracts of the right and left ventricles

• Right- conus arteriosus (infundibulum)
• Left- Aortic vestibule

Question 19

What is the fate of truncus arteriosus?

Answer 19

Left- ascending aorta

Right- pulmonary trunk

Question 20

Explain the partitioning of the atrioventricular (AV) canal

Answer 20

-Towards the end of the 4th week

• AV Endocardial cushions develop
  
  • from cardiac jelly and neural crest cells
  • forms on dorsal and ventral walls of AV canal
• Endocardial cushions grow towards each other and fuse
  
  • divides canal into right and left AV canals
  • forms AV valves
  • partially separate primitive atrium from primitive ventricle

Question 21

Summarize formation of the right atrium

Answer 21

-right horn of the sinus venosus enlarges

• Simultaneously primitive atrium enlarges
  
  • absorbs right horn forming right atrium
    
    • later becomes the sinus venarum (smooth part of the right atrium)

-Rough walled auricle is formed by primitive atrium

Question 22

Summarize the formation of the left atrium

Answer 22

Primordial pulmonary veins
Forms the left atrium
-primordial pulmonary veins persistently become incorporated into walls of the left atrium
-forms the oblique pericardial sinus
-Most of the wall is smooth
-Rough walled auricle is formed by primitive atrium

Question 23

Where is the oblique sinus?

Answer 23

Area of pericardium between the pulmonary veins

Limited by the reflection of the serous pericardium ion to the back of the heart

Question 24

Describe atrial partitioning

Answer 24

End of 4th week

Septum primum gross from the roof of atrium towards Endocardial cushions

• Foramen primum- space between inferior edge of septum primum & the Endocardial cushions
• Growth of septum primum closes Foramen primum
• Foramen secundum- simultaneously perforations appear in septum primum
• Septum secundum grows downward, eventually overlapping Foramen secundum
• The opening between the free edges septum secundum and septum primum is called Foramen ovale or oval Foramen

Question 25

What is the function of the septum primum in atrial partitioning?

Answer 25

Septum primum (thin and flexible ) acts like a flap valve for Foramen ovale- the flap is open when right atrial pressure exceeds left atrial pressure - allowing shunting of blood from the right atrium to the left atrium This allows the blood to bypass the lungs, which is not yet functional

Question 26

What is the cause of ostium secundum defect?

Answer 26

In the area of the fossa ovale - leads to patent/open Foramen ovale defect - disrupted or absent septa - Intracardiac shunting of blood (left to right) - most common in but least severe in ASD

Question 27

What is the sex ratio of ostium secundum defect?

Answer 27

Female to male ratio: 2:1

Question 28

What are the symptoms of ostium secundum defects?

Answer 28

Defects of both septa primum and secundum: -excess resorption of septum primum- too short to close Foramen - abnormal resorption of septum primum - extra febestrations -defective development of septum secundum with large fossa ovale

Question 29

Describe Endochondrial cushion defect with a Foramen primum defect

Answer 29

- less common atrial septal defect - septum primum-not fused with Endocardial cushions- patent Foramen primum defect - Often associated with a cleft in the anterior cusp of the mitral valve - Fusion of Endocardial cushions forms AV valve - Failed fushion leads to an AV valve defect -intracardiac shunting of blood (left to right)

Question 30

Describe sinus venous defect

Answer 30

Located in the sinus venarum Defect: -incomplete resorption of the right horn of sinus venosus into the right atrium -abnormal development of the septum secundum, or a combination of these factors Intracardiac shunting of blood (left to right)

Question 31

Describe common atrium

Answer 31

- prevelant in patients with ostium primum, ostium secundum and sinus venosus defects - complete absence of interarterial septum

Question 32

What are the atrial septum defects?

Answer 32

- common atrium - sinus venosus defects - Endocardial cushions defect with a Foramen primum defect Ostium secundum defect

Question 33

Explain the partitioning of the common ventricle

Answer 33

Muscular interventricular (IV) septum-develops first - formed from myocytes from the primitive ventricle - has a concave superior free edge (forms the IV Foramen) - ventricular dilation leads to an increase in size of septum IV foramen -allows for communication between the right and left ventricles - bulbar ridges and muscular IV septum fuses with the Endocardial cushion forming membranous IV septum - later fuses with the articopulmonary septum - once membranous IV septum formed, leads to closure of the IV foramen - pulmonary trunk now forced to communicate with right ventricle - ascending aorta now forced to communicate with left ventricle

Question 34

Discuss the partitioning of Bulbus Cordis and Truncus Arteriosus by aorticopulmonary (spiral) septum

Answer 34

5th week -Bulbar ridges from within the bulbus cordis (middle 1/3) - Truncal ridges develop within the truncus arteriosus - ridges grow towards each other, spiraling around each other (180 degrees) - fuses forming the aorticopulmonary septum - septum divides the truncus arteriosus and bulbus cordis into the pulmonary trunk and aorta

Question 35

What are the types of ventricular septal defect?

Answer 35

Muscular Membranous

Question 36

What is common in both types of ventricular septal defect?

Answer 36

Both types of VSDs: -more common in males than females - accounts for about 25% of congenital heart defects - intracardiac shunting of blood (left to right)

Question 37

Describe muscular ventricular septal defect

Answer 37

No muscular septum results in a common ventricle Occurs anywhere throughout the septum -in isolation or simultaneously (“Swiss cheese” VSD)

Question 38

Describe membranous ventricular septal disease

Answer 38

Most common type No membranous septum- incomplete closure of the IV foramen

Question 39

How are the semilunar valves developed?

Answer 39

3 swellings of subendicardial cushion tissue around the orifices of aorta (aortic vestibule) and pulmonary trunk (infundibulum) Hollowed out and reshaped forming three thin-walled cusps

Question 40

How are the atrioventricular valves?

Answer 40

-localized proliferations of endocardial cushion tissue around AV canals

Question 41

What are the cardiac structures derived from neural crest cells?

Answer 41

- endocardial cushions (in the outflow tract) - bulbar ridges - truncal ridges - spiral septum - membranous interventricular septum - semilunar valves - atrioventricular valves - pharyngeal arches