18. Thorax III - Heart

Question 1

How does the endocardium form?

Answer 1

When the laterla mesoderm fuses in the midline to form the primitive heart tube, which becomes the endocardium of the adult heart.

Question 2

How does the myocardium form?

Answer 2

When the mesoderm surrounding the primitive heart tube secretes cardiac jelly and forms the myocardium of the adult heart.

Question 3

How does the epicardium form?

Answer 3

When the mesoderm from the coelomic wall forms the epicardium of the adult heart.

Question 4

What is dextral looping?

Answer 4

The primitive heart tube undergoes dextral looping (bend to the right).

Question 5

What are the 5 dilations of the primitive heart?

Answer 5

Truncus Arteriosus, Bulbus Cordis, Primitive Ventricle, Primitive Atrium, Sinus Venosus. [TBPPS]

Question 6

What does the Truncus arteriosus evolve to?

Answer 6

Aorta and Pulmonary trunk.

Question 7

What does the Bulbus cordis evolve to?

Answer 7

Smooth part of right ventricle (conus arteriosus) and Smooth part of left ventricle (aortic vestibule).

Question 8

What does the primitive ventricle evolve to?

Answer 8

Trabeculated part of right ventricle and Trabeculated part of left ventricle.

Question 9

What does the primitive atrium evolve to?

Answer 9

Trabeculated part of right atrium and Trabeculated part of right atrium.

Question 10

What does the sinus venosus evolve to?

Answer 10

Smooth part of right atrium (sinus venarum), Coronary sinus, Oblique vein of left atrium.

Question 11

How is the smooth part of the left atrium formed?

Answer 11

It is formbed by incorporation of parts of the pulmonary veins into its wall.

Question 12

What is the name of the junction of the trabeculated and smooth part of the right atrium?

Answer 12

Crista terminalis.

Question 13

What is the foramen ovale (FO)?

Answer 13

The opening pathway between septum primum (SP) and septum secundum (SS).

Question 14

What causes the closure of the foramen ovale (FO)?

Answer 14

Closure usually occurs immediately after birth due to the increase left atrial pressure that results from changes in the pulmonary circulation and decreased right atrial pressure caused by the closure of the umbilical cord.

Question 15

How is the atrial septum formed?

Answer 15

The formen secundum (FS) forms within the Septum Primum (SP). The septum secundum (SS) forms to the right of the SP and fuses (after birth) with the SP to form the atrial septum.

Question 16

Where is the foramen primim (FP) located?

Answer 16

It is located between the edge of the SP and AV spetum; it is obliterated when the SP fuses with the AV septum.

Question 17

What does premature closure of the Foramen Ovale (FO) cause?

Answer 17

Hypertrophy of the right side of the heart and underdevelopment of the left side.

Question 18

How does the membranous IV septum (the one that closes the IV foreman) close?

Answer 18

By the fusion of 3 things: Right bulbar ridge, left bulbar ridge and the AV cushions.

Question 19

What is the aorticopulomary (AP) septum and how does it form?

Answer 19

The AP septum divides the truncus arteriosus into the aorta and pulmonary trunk. It forms when the neural crest cells migrate into the truncal and bulbar ridges, which grow in a spiral fashion and fuse to form it.

Question 20

How does the transposition of the great vessels occur?

Answer 20

When the aorticopulmonary septum fails to develop in a spiral fashion and results in the aorta opening into the right ventricle and the pulmonary trunk opening into the left ventricle. This causes right-to-left shunting of blood with resultant cyanosis.

Question 21

What are the 3 shunts of fetal circulation?

Answer 21

Ductus venous, ductus arteriosus, and foramen ovale.

Question 22

How does tetralogy of Fallot occurs?

Answer 22

When the aorticopulmonary septum fails to align properly and results in pulmonary stenosis, overriding aorta, intraventricular septal defect, and right ventricular hypertrophy. This causes right-to-left shunting of blood with resultant cyanosis.

Question 23

How does persistent truncus arteriosus occur?

Answer 23

When there is only partial development of the AP septum. This results in a condition in which only one large vessel leaves the heart and it receives blood from both the right and left ventricles. This causes right-to-left shunting of blood with resultant cyanosis.

Question 24

What other disease always accompanies persistent truncus arteriosus?

Answer 24

Ventricular septal defect.

Question 25

What happens after the closure of the right and left umbilical arteries?

Answer 25

They turn to medial umbilical ligaments in adult.

Question 26

What happens after the closure of left umbilical vein?

Answer 26

Ligamentum teres.

Question 27

What happens after the closure of ductus venosis?

Answer 27

Ligamentum venosum.

Question 28

What happens after the closure of foramen ovale?

Answer 28

Fossa ovale.

Question 29

What happens after the closure of ductus arteriosus?

Answer 29

Ligamentum arteriosum.

Question 30

From where does vasculogenesis start from?

Answer 30

From the mesoderm surrounding the yolk sac.

Question 31

Where does hematopoyesis first start and change later in the fetal life?

Answer 31

Starts first in the mesoderm surrounding the yolk sac and later in the fetal liver, spleen, thymus, and bone marrow.

Question 32

What is patent ductus arteriosus (PDA) and how does it occur?

Answer 32

PDA occurs when the ductus arteriosus (a connection between the pulmonary trunk and aorta) fails to close after birth. Normally, said structure is supposed to close within a few hours after birth via smooth muscle contraction to form the ligamentum arteriosum. This is commmon in premature babies and mothers with rubella infection. It causes left-to-right shunting of blood (the ductus arteriosus during fetal development is a right-to-left shunt).

Question 33

How do we promote patency of the ductus arteriosus?

Answer 33

Prostaglandin E and intrauterine or neonatal asphyxia.

Question 34

How do we promote closure of the ductus arteriosus?

Answer 34

Prostaglandin E inhibitors (indomethacin), acetylcholine, histamine, and catecholamines.