Development of Heart

Question 1

Define what gastrulation is

Answer 1

Process by which single layered blastocyst turns into multi-layered structure

Question 2

Describe the first part of the formation of the endocardial tube

Answer 2

Day 17 - lateral plate mesoderm divides into visceral and somatic layers. IN visceral layer, angiogenic cell clusters named blood islands appear.

Question 3

What is the function of blood islands?

Answer 3

They will differentiate into primordial vascular system, heart tube, vessels and primordial erythrocytes.

Question 4

What occurs after the formation of blood islands?

Answer 4

The blood islands coalesce to give right and left endocardial tubes and dorsal aortae. Part of mesoderm differentiates into cardiomyocytes and visceral lateral plate mesoderm approach eachother (day 20)

Question 5

Describe the events that occur after formation of endocardial tubes and dorsal aortae?

Answer 5

The folds of embryo fuse along ventral midline and the space between the visceral and somatic mesoderm becomes the intraembryonic coelom. Myocardium forms deep to visceral lateral plate mesoderm

Question 6

What is the function of the intraembryonic coelom?

Answer 6

It will become the paricardial cavity in the thoracic cavity.

Question 7

Describe the events that occurs after the formation of the intraembryonic coelom

Answer 7

Cephalo-caudal and lateral folding (meet at the umbilicus). Lateral folding allows Right and Left endocardial tubes fuse to form the primary heart tube, anterior to gut tube. The myocardium invests into the cardiac jelly and endocardial heart tube.

Question 8

On what day does the heart start to beat?

Answer 8

Day 22

Question 9

What does cephalo-caudal folding cause?

Answer 9

The heart tube to effectively migrate from head end, through the neck to the thorax

Question 10

Name the parts of the endocardial tube

Answer 10

Aortic arch, aortic sac, bulbus cordis, primordial ventricle, primordial atrium, sinus venosus.

Question 11

What is the function of the sinus venosus?

Answer 11

At the caudal end and it receives the blood from the umbilical, vitelline and cardinal veins

Question 12

What is the function of the vitelline vein?

Answer 12

Drain the yolk sac

Question 13

What is the function of the cardinal vein?

Answer 13

Drain the trunk and head region

Question 14

Describe features of the bulbus cordis

Answer 14

It is the outflow tract and has two parts; Conus cordis - aorta and the truncus arteriosus - pulmonary trunk

Question 15

Describe the looping and folding of the heart tube

Answer 15

Starts at about 22 days. The two ends fold towards each other and to the right which pushes the apex to the left. It rotates slightly so right side is more anterior. Atrium bulges out on each side of bulbis cordis

Question 16

Describe how dextrocardia develops?

Answer 16

It the ends of the heart tube fold to the left then the heart is pushed to the right

Question 17

Describe what parts of the bulbis cordis will form?

Answer 17

Proximal part - Right ventricle, Middle part - Outflow of venticles. Distal part - Pulmonary trunk and aorta

Question 18

What is the narrowing between the atrium and ventricles called? What is it surrounded by?

Answer 18

The avioventricular canal. This is the lumen of the heart tube. It is surrounded by dense mesenchymal tissue called cardiac jelly which is produced by and replaced by myocardium.

Question 19

What is the myocardium derived from?

Answer 19

Splanchnic mesoderm

Question 20

What are endocardial cushions derived from and what do they form?

Answer 20

Derived from neural crest cells, they form the interatrial septum, the membranous part of IV septum, the AV valves and form the PT and aorta from the truncus arteriosus.

Question 21

Describe the formation of the tricuspid and mitral valves, the papillary muscles and chordae tendineae

Answer 21

The tissue in the narrowing between the atrium and ventricle swells to form endocardial cushion that grow and meet in the middle and divide the AV canal into right and left channels. Endocardial cushion growth and cavitation form papillary muscles and chordae tendineae.

Question 22

Describe the formation of the interatrial septum

Answer 22

Septum primum grows towards AV cushions, but blood can still flow from the right atrium to left atrium via the foramen primum

Question 23

Describe the formation of the foramen secundum

Answer 23

Before the septum primum completely builds up the IA septum and the foramen primum closes, a second hole appears high up on the septum primum, called the foramen secundum

Question 24

Describe the formation of the foramen ovale

Answer 24

A second septum begins to grow from the sinus venosus but does not fuse with the endocardial cushion and so it forms the foramen ovale

Question 25

What are the conus cordis and truncus arteriosus? What are their functions?

Answer 25

Neighbouring sections of a single tube. The conus cordis becomes the aortic vestibule on the left side and the infundibulum on the right side. The Truncus arteriosus forms the aortic arch and pulmonary trunk.

Question 26

Describe the formation of the aortico-pulmonary septum

Answer 26

Within the conus cordis and truncus arteriosus, two selling appear and grown from the sides of the bulbis cordis. They meet and spiral together forming the septum.

Question 27

What would occur if there was no spiral to the aortico-pulmonary septum

Answer 27

The left ventricle would pump blood to the pulmonary artery and the right ventricle would pump blood to the aorta

Question 28

Name the three structures must fuse to separate the ventricles

Answer 28

Endocardial cushions, IV septum and spiral septum.

Question 29

What causes a patent foramen ovale?

Answer 29

Failure of fusion of the foramen ovale or the foramen secundum

Question 30

What completes the formation of the IV septum?

Answer 30

Endocardial cushions sending an extension towards the muscular part of the IV septum