Heart Development

Question 1

What are the precursors of the cardiovascular system? When and where do they appear?
What are they derived from?

Answer 1

Angioblasts.
They appear on day 13 in the walls of the yolk sac.
They are derived from the extraembryonic mesoderm.

Question 2

When do blood islands appear? What are they made of?

Answer 2

They are made of angioblasts, which cluster on day 16 to form blood islands.

Question 3

The more _____ located cells form the primitive blood cells, whereas the more _____ located cells will become the _____ ______ lining the blood vessel.

Answer 3

centrally, peripherally, endothelial cells

Question 4

How does a vascular plexus form?

Answer 4

Adjacent blood islands with lumens fuse.

Question 5

When are INTRAEMBRYONIC blood vessels formed?

What type of cells do they come from?

Answer 5

Around day 18-22, from angioblasts.

Question 6

Angioblasts are a type of what?

Answer 6

mesenchyme

Question 7

What is the difference between angiogenesis and vasculogenesis?

Answer 7

Vasculogenesis is the formation of a blood vessel from blood islands, whereas angiogenesis is the formation of a blood vessel from an existing vessel.

Question 8

What hormone promotes vasculogenesis? What secretes it?

Answer 8

VEGF, from the mesenchyme.

Question 9

What hormone promotes angiogenesis?

Answer 9

VEGF and angioprotein

Question 10

What causes the migration of endothelial cells? What secretes it?

Answer 10

PDGF, from endothelium.

Question 11

What hormone causes the differentiation of vascular smooth muscle cells? What secretes it?

Answer 11

TGF- β, from endothelium.

Question 12

What are two endogenous inhibitors of angiogenesis? what might they be useful in?

Answer 12

Endostatin and angiostatin. Might be useful in preventing tumor growth.

Question 13

Heart precursor cells originate from what? It is located between what two things?

Answer 13

The splanchnic mesoderm (cardiogenic plate, cardiogenic mesoderm). Located between the pericardial cavity and endocardial tube.

Question 14

What hormones drive the formation of the cardiogenic plate? What secretes them?
What does this induce? What is special about it?

Answer 14

BMP-2 and BMP-4 from the anterior endoderm.

Induces the Nkx 2.5 gene, which is the master gene for heart development.

Question 15

1. Following its formation, cells from the cardiogenic plate go where? What do they form?
2. Then, what forms the endocardium?
3. What does the cardiogenic plate then do, and what does it form?
4. What unites the two endocardial tubes?

Answer 15

1. They migrate to the space between the foregut and the cardiogenic plate itself, and form an endothelial plexus.
2. An endothelial tube forms the endocardium.
3. The cardiogenic plate then surrounds the endocardium, forming the myocardium.
4. Lateral folding, forming a single heart tube.

Question 16

How does the heart get to where it is in an adult?

Answer 16

Heart precursors are originally dorsally located, but during cranio-caudal folding, they relocate ventrally.

Question 17

Where is cardiac jelly in the tubular heart, and what forms from there?

Answer 17

Located between the endothelium and the myocardium. Transitional zones form from there.

Question 18

1. The epicardium is derived from what? What is that thing’s precursor?
2. The epicardium gives rise to what?
3. The epicardium also contributes to the formation of what?

Answer 18

1. From the proepicardial organ, which is derived from the coelomic EPITHELIUM overlying the LIVER.
2. Gives rise to the epithelium of the visceral pericardium.
3. Also contributes to the formation of coronary vessels.

Question 19

Septum transversum gives rise to part of what?

Answer 19

The diaphragm.

Question 20

1. Initially, the heart tube has how many segments? What are they?
2. What forms after that?
3. Originally, what is connected to the aortic sac? What develops between these two structures? This thing is a type of?

Answer 20

1. Two, which are the primitive ventricle, and bulbus cordis.
2. The primitive atrium forms next.
3. The bulbus cordis. The outflow region develops between the aortic sac and the bulbus cordis. The outflow region is an example of a Transitional Zone (TZ)

Question 21

What develops between the primitive atrium and primitive left ventricle?

Answer 21

The atrioventricular canal.

Question 22

Note: Tubular segments DO NOT equal chambers of adult heart

Answer 22

.

Question 23

1. The tubular heart receives blood via what?
2. What is the venous inflow to this structure? Where do they come from? Are they oxygen rich or oxygen poor?
3. How does blood then flow out of the tubular heart?

Answer 23

1. The Sinus Venosus.
2. a. Two umbilical veins from the placenta: oxygen rich
   b. Two vitelline veins from the gut: oxygen poor
   c. Two common cardinal veins from the head and trunk: oxygen poor
3. Blood then flows out of the tubular heart via the bulbus cordis to the aortic sac, and aortic arches.

Question 24

What are the only veins running to the sinus plexus that stay, and what do the others become?

Answer 24

The vitelline veins remain, and the others remodel to form the IVC

Question 25

1. Heart tube looping almost always happens in what direction?
2. What first forms a loop? This defines the?
3. What forms the cranial leg and the caudal leg?
4. The “inner curvature” serves as what?

Answer 25

1. To the right.
2. The bulbus cordis and ventricle. (so the left and right ventricle). Defines the inner curvature.
3. Bulbus cordis forms the cranial leg, and the ventricle, AV canal, atrium, and sinus venosus form the caudal leg
4. The inner curvature serves as the hinge point for bending.

Question 26

1. Bulbus cordis is also known as the?
2. During early looping, what is the outflow and what is the inflow?
3. At this time the outflow segment divides into?

Answer 26

1. Right ventricle.
2. Bulbus cordis is the outflow, and the sinus venosus is the inflow
3. The conus cordis, and the truncus arteriosus (connects to the aortic sac)

Question 27

Explain the movements of the bulbus cordis, primitive ventricle, primitive atrium, and sinus venosus during looping.

Answer 27

1. Bulbus cordis moves inferiorly, anteriorly, and to the right.
2. Primitive ventricle moves to the left.
3. Primitive atrium and sinus venosus move superiorly and posteriorly; sinus venosus is then posterior to primitive atrium.

Question 28

Proper looping is critical for the alignment of? Issues with this will lead to?

Answer 28

Segments and septa. Issues will lead to permanent embryonic blood flow pattern.

Question 29

1. The heart begins to beat when? What does this coincide with?
2. When does blood flow become unidirectional?
3. By day 28 what happens to flow?

Answer 29

1. Around day 21-22. Coincides with the start of looping.
2. Day 26
3. Two separate streams spiral around one another, and leave heart. This happens without physical separation.

Question 30

1. Blood stream from primitive left ventricle goes through?

2. Blood stream from primitive right ventricle goes through?

Answer 30

1. The left 4th aortic arch (eventually the aortic arch)

2. The left 6th aortic arch (eventually the pulmonary arteries and ductus arteriosus).

Question 31

What happens to all the aortic arches?

Answer 31

1st arch: Maxillary artery
2nd arch: Disappears
3rd arch: ventral part- common carotid artery
dorsal part- internal carotid artery
4th arch: right- proximal part of right subclavian artery
left- part of aortic arch
5th arch: disappears
6th arch: right (ventral)- right pulmonary artery (right dorsal is useless)
left ventral- left pulmonary artery
left dorsal- ductus arteriosus

Question 32

1. The right recurrent laryngeal nerve wraps around what? what arch was this?
2. Why does it wrap around this?
3. What does the left recurrent laryngeal nerve wrap around?

Answer 32

1. The right subclavian artery, which was the right 4th aortic arch.
2. It does this because the dorsal part of the right 6th aortic arch was obliterated.
3. Wraps around the ductus arteriosus, Because the left dorsal part of the 6th aortic arch became this.

Question 33

What does the ductus arteriosus become after birth?

Answer 33

The ligamentum arteriosus.

Question 34

What can an aortic aneurysm present as? Why?

Answer 34

A persistent cough, due to pressure applied on the left recurrent laryngeal nerve.

Question 35

How/why does a double aortic arch form?

What does it do?

Answer 35

When the DISTAL part of the right dorsal aorta persists.

Constricts trachea and esophagus, causing wheezing, crying, flexion of neck.

Question 36

When does a right arch of the aorta happen?

Answer 36

When the ENTIRE right dorsal aorta persists, and the distal part of the left dorsal aorta disappears.
CAN form ring around trachea and esophagus.

Question 37

How does a retroesophageal right subclavian artery form? What can it cause?
In both cases, what can happen?

Answer 37

Arises from distal arch of aorta, and passes behind the esophagus. Can form ring around esophagus and trachea.
In both cases, it can apply pressure on trachea during exercise, interfering with breathing.