Development of the heart

Answer 1

• In babies, the head is big so 2/3 of the blood is coming into the heart from the superior vena cava and 1/3 is coming from the inferior vena cava.
• In adults, the body is bigger so 2/3 of the blood is coming from the inferior vena cava and 1/3 is coming from the superior vena cava.

Question 2

Echocardiogram (heart scan)

Answer 2

• The red colour denotes the blood that is going to the camera
• the blue us going away from the camera
• In the picture on the top right, you can see that there is a defect between the two atria and this is know as an atria septal defect.

–whenever there is a septal defect, blood flows from the left side of the heart to the right side because the pressure on the left side is higher..

• The picture in the bottom left shows a defect in the ventricular septa. this is called a ventricular septal defect. the defect can happen anywhere along the length of the seopta.
• This sort of heart disease is much more common in children with down’s sydnrome
• The image on the lower right shows a defect of the lower part of the atria septum and ventricular septum. this is known as an atria ventricular speta defect. in this situation, the AV valve is just one valve, you can’t see a mitral and tricuspid valve.

Question 3

Other types of heart diseases

Answer 3

1. Pulmonary stenosis- narrowing of the pulmonary valave. when the right ventricle contracts, the blood has to be squeezed through the small hole. this can cause problems because insufficient blood will be going to the lungs.

2. Aortic Valve stenosis- the left ventricle has to push blood harder and the harder the heart pushes, the more thickened it becomes. you end up with left ventricular hypertrophy. if there is severe obstruction, it can lead to coronary ischemia chest pain and also cause syncope when there is less blood supply going to the brain.in severe cases, it can cause heart failure.

3. Coarctation of the aorta is a birth defect in which a part of the aorta is narrower than usual. If the narrowing is severe enough and if it is not diagnosed, the baby may have serious problems and may need surgery or other procedures soon after birth.

Question 4

More heart defects

Answer 4

1. Transposition of the great vessels; Transposition of the great arteries is a condition where that the two main blood vessels leaving the heart, the pulmonary artery (which takes blood to the lungs to pick up oxygen) and the aorta (which takes blood from the heart to the body) are swapped over (switched).

In the picture, you can see how blood from the pulmonary artery is supplying blood into the aorta instead of the lungs. so blood coming into the body from the vena cava is going back into the body through the sort. likewise, blood coming from the lungs through the left atria is going back into the lungs.

Life is not possible in this situation except there is a shunt in place.

2. Truncus Artreriosus- Truncus arteriosus is a rare type of heart disease in which a single blood vessel (truncus arteriosus) comes out of the right and left ventricles, instead of the normal 2 vessels (pulmonary artery and aorta).

The truncus is a large vessel which comes out of the heart and is a single vessel in primitive fetal life; later on at about 5-6 weeks of gestation, it divides into the pulmonary artery and the aorta. if this division is defective, then it leads to different conditions. this can lead to atresia, tetralogy of fallout and other truncal anomalies.

3. Tetralogy of fallot- here there are 4 abnormalities (tetra). Tetralogy of Fallot consists of the combination of four different heart defects: a ventricular septal defect (VSD); obstructed outflow of blood from the right ventricle to the lungs (pulmonary stenosis); a displaced aorta, which causes blood to flow into the aorta from both the right and left ventricles (dextroposition or overriding aorta); and abnormal enlargement of the right ventricle (right ventricular hypertrophy). This is a defect int he Truncal development.

Question 5

Heart Development

Answer 5

In the development of the heart, we should recognise 4 distinct aspects.

1. Heart Tube fusion- starts with 2 heart tubes which fuse together. This happens between wk 2-3.

2. Heart looping- Happens in the 4th week.

3. Septation- happens in the 5th week.

4. Valve development

Answer 6

• At day 18, the 3rd week of development. you can see the small red dots formed in the splanchnic mesoderm and that region is called the cardiogenic region.
• The heart primordium arises in that splanchnic mesoderm, its cardiogenic region.
• The tubes are formed int he above regional nd then they fuse together.

Question 7

Folding and fusion of the heart

Answer 7

Lateral folding of the embryo brings the heart tubes into the ventral midline, allowing them to fuse to form a single primordial heart tube. Fusion of the heart tubes begins cranially and extends caudally and is facilitated by apoptosis. The animation below shows a cross section of the embryo and the development of the endocardial heart tubes as well as their migration and fusion in the midline.

Question 8

Migration of the heart

Answer 8

Question 9

Embryonic chambers of the heart

Answer 9

Answer 10

Question 11

Heart Looping

Answer 11

Answer 12

Question 13

Heart septation

Answer 13

Question 14

Division of the Atrioventricular (AV) Canal

Answer 14

Two endocardial cushions form on the dorsal and ventral surfaces of the AV canal, referred to as the superior and inferior cushions respectively. The cardiac jelly in this region expands while mesenchymal cells from the endocardium invade the cushions, allowing them to grow and fuse. This fusion divides the common AV canal into the right and left canals, hence partially separating the primitive atrium and ventricle. Two smaller endocardial cushions also form on the lateral walls of the AV canal, which later help to form the mitral and tricuspid heart valves.

Question 15

Septation of the Atria

Answer 15

Membranous tissue forming the septum primum grows from the roof of the atrium, dividing it into left and right halves. The space between the septum primum and the endocardial cushions is referred to as the foramen primum.

Apoptosis-induced perforations appear in the centre of the septum primum to produce the foramen secundum. At this time the strong, muscular septum secundum grows immediately to the right of the septum primum and gradually overlaps the foramen secundum during the fifth and sixth weeks of development. The incomplete partition of the atrium by the septum secundum forms the foramen ovale.

Blood flows from the right atrium through the foramen ovale and foramen secundum to the left atrium, forming a right-to-left shunt. The remaining portion of the septum primum acts as the valve of the foramen ovale. Blood cannot flow in the opposite direction, as the muscular strength of the septum secundum prevents prolapse of the septum primum.

Question 16

Atria septal defects

Answer 16

Question 17

Septation of the Ventricles

Answer 17

Minor trabeculations appear during early development of the primordial ventricle. Following growth of the ventricles further trabeculations appear and grow as larger, muscular structures. The more commonly described theory of septation begins with the appearance of a primordial muscular interventricular (IV) ridge developing in the floor of the ventricle near the apex. As either side of the ventricle grows and dilates, their medial walls fuse forming the prominent IV septum. The foramen located between the cranial portion of the IV septum and the endocardial cushions: the IV foramen, closes by the end of the seventh week as the bulbar ridges (see next section) fuse with the endocardial cushions.

Answer 18

Question 19

Truncus arteriosus

Answer 19

Answer 20

Answer 21

Answer 22

Answer 23