HSF - Development of Heart I (L1,B2)

IGNORE: What happens in an Ostium Secundum Defect?

(ASD) 1. Excessive Resorption of the Septum Primum. 2. Failure of the development of the septum secundum.

How are pulmonary veins incorporated into the heart?

**Smooth part of the ventricle - incorporation of parts of pulmonary veins.

What occurs in Membranous VSD's? Shunt? Cyanotic? Increased blood flow where? Patient Complaints?

1. Blood from the left -to-right ventricle through the interventricular foramen. 2. Non-cyanotic but causes increased blood flow & pressure to the lungs-pulmonary hypertension 3. Patients complain excessive fatigue upon exertion.

Outflow Tract Development

1. Division of the bulbus cordis and truncus arteriosus into the outflow tracts begins with formation of the aorticopulmonary septum. 2. Two parallel outflow tubes result; one the pulmonary trunk (PT) and the other the ascending aorta (AA). 3. These two tracts twist on one another to form the PT and AA. 4. The neural crest plays an important role in the development of these vessels.

What happens if the oval foramen closes prematurely? Hypertrophy of what? Underdevelopment of what?

1. Leads to massive hypertrophy of the right atrium & ventricle & underdevelopment of the left side of the heart. 2. Death usually occurs shortly after birth.

What does the Sinus Venosus of the Heart Tube become?

1. Left Horn of Coronary Sinus 2. Right Horn of Smooth part of atrium (sinus venarum)

What are the Major Outflow Tracks derived from?

1. Paraxial 2. Lateral Plate Mesoderm 3. Neural Crest

What are the Major Outflow Tracks?

1. Pulmonary Trunk 2. Aorta

How do the Aorta and Pulmonary Trunk develop?

1. Septum formation begins in the Bulus. a. the truncus b. the conus c. the smooth walled portion of the right ventricle. 2. A pair of conotruncalswellings / cushions, grow and twist around each other forming: a. spiral aorticopulmonary septum (AP) ;(conotruncal septum) b. pulmonary trunk (PT) c. ascending aorta (AA). **The neural crest plays an important role in the development of these vessels.

What does the Bulbus Cordis of the heart tube become?

1. Smooth Part of Right Ventricle (conus arteriousus) 2. Smooth Part of Left Ventricle (aortic vestibule)

Where is the horseshoe-shaped heart tube located?

1. Splanchnic Layer of the lateral plate mesoderm.

IGNORE What are the types of Truncus Arteriosus Defects?

1. Tetralogy of Fallot 2. Transposition of the Great Vessels 3. Persistent Truncus Arteriosus (no septum formation)

What occurs during the "S" bend of the heart tube?

1. The Bulbus Cordis and Truncus Arteriosus go DOWN and RIGHT 2. The Sinus Venosus swings UP and LEFT.

What does the heart tube sprout/form?

1. aortic arch vessels from the outflow (aortic) region. 2. venous pole remains paired.

When does the Primitive Heart Begin to beat?

19-20th Day of Embyonic Development (4th Week)

When does the looping end?

28th - 29th day. *appearance of chambers.

Where do the Semilunar Valves develop from and where?

3 swellings of the subendocardial cushions at the orifices of the pulmonary trunk and aorta.

IGNORE What is Tetralogy of Fallot?

A Truncus Arterious Defect. *No Septum *Cyanotic *Right to Left Shunt. FallotOccurs in 9.6/10000 births. Most commonly occurs in the conotruncal region, Due to unequal division of the conusresulting from anterior displacement of the aorticopulmonary septum (AP). Related to failure of neural crest cells to migrate into the Truncus arteriosus resulting in 4 cardiovascular alterations: 1. A narrow right ventricular outflow pulmonary stenosis. 2. Ventricular Septal Defect (VSD) 3. Overriding aorta arises directly above the septal defect. 4. Right ventricular hypertrophy -higher pressure on right side Right-to-left shunting of blood Cyanotic sometime after birth Imaging shows boot shaped heart due to the enlarged right ventricle.

A single Truncus arterioles from what?

Forms a midline septum and then the two resulting outflow channels crisscross each other to form the pulmonary trunk and ascending aorta.

How is the septum formed in the AV canals?

From 4 endocardial cushions.

The Septum Primum

Is a one way valve. At birth, it pushes agains the septum secundum and fuses.

What is essential for normal heart development?

Laterality establishment during gastrulation because it specifies cells contributing from right and left sides of the heart.

PDA

Left (aorta) to right (Pulmonary Trunk) shunt!

What happens if we have abnormal development of the endocardial cushions?

Membranous VSD's ASD's! Left to right shunt via VSD

Coarctation of the Aorta? Clinical Sign?

Narrowing of the Aorta. Primary Clinical Sign is Diminished femoral Artery Pulse

Where are endocardial cushions derived from?

Neural Crest

What is Valvular Stenosis?

Occurs when the semilunar valves are fused for a variable distance. 1. Pulmonary valvular atresia and a normal aortic root. **The only access route to the lungs is by reverse blood flow through a PDA. 2. Aortic valvular stenosis: **Fusion of thickened valves may be complete except with a Pinhole opening.

What occurs in Gastrulation?

Primitve Streak, New Germ Cells, Endoderm (epithelial lining of GI), Mesoderm (heart), Ectoderm, all from EPIBLAST.

What do the fusions of opposing cushions form?

Right and Left AV Canals.

Explain Septum Primum

Septum Primum is a one way valve. At birth...it pushes against septum secundum and FUSE!

What does the Primitive Atrium of the heart tube become?

Trabeculated portions of the left and right atrium (pectinate muscle)

What does the Primitive Ventricle of the heart tube become?

Trabeculated portions of the right and left ventricle.

What are VSD's? What cells are associated with it? How are VSDs repaired? Shunt?

Ventricular Septal Defects. *Associated with failure of migration of endocardial cushions to meet. *NON-cyanotic Req. open heart surgery. Left to Right Shunt via VSD

What happens when fusing occurs in regards to the primitive heart tube tube?

We get a single tube with aortic and venous poles.

Why do we bypass the lungs?

We want to get the blood in and out of the heart as fast as possible! LISTEN 3:35

What happens at day 30th?

1) *The atrium and ventricle become partitioned with the appearance of endocardial cushions (neural crest derivative) in atrioventricular (AV) canal. 2) *The interatrial septum develops from a septum premium and septum secundum. *A septal opening, called the foramen ovale remains until birth, shunting blood from the right to left atrium. *When pressure in the left atrium increases, two septa press each other and close the foramen oval. 3) The intraventricular septum grows up front the base of the common ventricle and fuses with the midline endocardial cushion.

What does the Truncus Arteriousus of the heart tube become?

1. Ascending Aorta 2. Pulmonary Trunk **Smooth part of the ventricle - incorporation of parts of pulmonary veins.

What are the Congenital Heart Defects

1. Atrial septal defect (ASD) 2. Ventricular septal defect (VSD) (30% of all CHD) 3. Patent ductus arteriosus (PDA) 4. Tetralogy of Fallot (VSD, pulmonary stenosis, overriding aorta, right ventricular hypertrophy) 5. Valvular stenosis or atresia 6. Coarctation of the aorta

What are Atrial Septal Defects? What type of shunt? How can it be repaired?

ASD's - Left to Right Shunt, NON- cyanotic. FAILURE OF PRIMUM AND SECUNDUM TO FUSE. Shunts via Foramen Ovale This can be repaired via vein.

What do the fusion of the Right and Left conotruncal ridges form?

Aortic Pulmonary Septum

Where do the Tricuspid and Mitral Valves develop from?

Atrioventricular endocardial cushion tissue (fibrous part).

How does the primitive heart tube begin?

Begins as a single tubular structure. It comes from Splanchnic mesoderm.

How is the primitive heart tube formed?

By the fusion of two endocardial tubes.

What kind of cell condense to form pairs of primordial heart tubes that later fuse to a single horse-shoe shaped tube?

Cardiogenic Cells

How does the blood flow from the developing placenta into the heart tube go?

Cranially through the primitive atrium, ventricle, bulbus cordis and then out the trunucs arteriosus into the aortic arch.

Where is the primitive heart derived from?

Splanchnic Mesoderm

When is the primitive heart derived? Where?

The 3rd week (day 16 of development) at the cardiogenic area of the cranial end of embryo.

Where does the primitive heart tube receive blood from the developing placenta?

The sinus venosus.

Explain Valve Formation:

The tricuspid and mitral valves develop from swellings that surround the atrioventricular canals. The semilunar valves (pulmonic and aortic) develop from three swellings of the subendocardial cushion at the orifices of the pulmonary trunk and aorta. The neural crest contributes to the formation of the semilunar valves.