Cardiovascular system: Lecture 3 - Development of the Cardiovascular System 1

Question 1

When does the formation of the heart begin?

Answer 1

week 3

Question 2

What day is the first heart contraction?

Answer 2

Day 22

Question 3

What are the 3 layers that the heart is composed of?

(from inner to outer)

Answer 3

1. Endocardium - derived from the heart tube
2. Myocardium - derived from the viscerla mesoderm overlying the heart tube
3. Epicardium - this is the visceral layer of the pericardium and is also derived from the visceral mesoderm

Question 4

What does the myocardium go onto form?

Answer 4

Muscular cells that allow contraction of the heart

Question 5

What is vasculogenesis?

Answer 5

Making new vessels from scratch

Question 6

Explain how vasculogenesis works?

Answer 6

• the endoderm induces some cells of the overall visceral mesoderm to differentiate into angioblasts
• angioblasts differentiate into endothelial cells and form endocardial tubes

Question 7

When does embryonic folding begin?

Answer 7

Day 17/18

Question 8

What do endocardial tubes form when they fuse during lateral folding?

Answer 8

The primitive heart tube

Question 9

What does the myocardium secrete and why is this important?

Answer 9

The myocardium secretes cardiac jelly which is important in cardiac looping and septation of the heart

Question 10

How is the developing heart tube brought into the thorax?

Answer 10

Craniocaudaul folding

Question 11

What does th endocardium and myocardium go on to form?

Answer 11

The internal endothelial lining of the heart and muscular wall respectively

Question 12

What is the cardiac jelly?

Answer 12

gelatinous connective tissue separating the myocardium and heart tube endocardium

Question 13

What occurs in the caudaul region during week 4 of embryobic development?

Answer 13

3 paired veins drain into the tubular heart via the right and left horn of the sinus venosus: heart is already beating at this point

(blue branches in image)

Question 14

With differential growth of the heart tube, which 5 dilations become apparent?

Answer 14

Truncus arteriosus

Conus arteriosus

Ventricle

Atrium

Sinus venosus

These develop into the adult structures of the heart

Question 15

Which direction does blood flow through the heart tube?

Answer 15

Bottom to top (caudal to cranial) - from sinous venosus to truncus arteriosus

Question 16

What happens during day 23?

Answer 16

The heart tube starts to fold in preparation for dividing into 4 chambers

Question 17

Explain the sequence of events in looping of the heart

Answer 17

1. Straight heart tube
2. C-shaped loop
3. S-shaped loop

Bulbus cordis moves caudally, ventrally and to the right

Primitive ventricle is displaced before moving back to midline

Primitive atrium displaces cranially and dorsally

Question 18

When does the sinus venosus degenerate?

Answer 18

In week 5

Question 19

What happens to the remnants of the sinus venosus?

Answer 19

It remains as part of the wall of the right atrium (right horn) and contributes to the venous drainage (left horn) of the heart

Question 20

What does the left horn of the atrium go on to form?

Answer 20

The left horn forms the oblique vein of the left atrium and coronary sinus

Question 21

What does the right horn form?

Answer 21

the smooth-walled part of the right atrium – sinus venarum

Question 22

How can the part of the right atrial wall formed from the right horn be distinguished from the rest of the right atrial wall (the majority)?

Answer 22

As the rest appears rough - trabeculated and was derived from the primitive atrium

Question 23

What is the crista terminalis?

Answer 23

The clear border between the trabeculated part of the right atrium and the sinus vernarum

Question 24

Annotate this image (Name the rough parts and the smooth parts)

Answer 24

Question 25

How does the ventricular wall form?

Answer 25

Majority by the primitive ventricle, with a small contrbution from the conus arteriosus

Question 26

What does the conus arteriosus form?

Answer 26

the smooth walls of the left and right ventricles that lead into the aorta (aortic vestibule) and pulmonary trunk (conus arteriosus) respectively

Question 27

What is the trabeculae carneae?

Answer 27

muscular ridges - the rest of the ventricular wall that is trabeculated (rough) and formed from the primitive ventricle

Question 28

Annotated image of the right ventricle

Answer 28

Question 29

What does an outgrowth of the left atrial wall form?

Answer 29

Initially, it forms a single pulmonary vein. The pulmonary vein branche into left and right veins which then bifurcate to form 4 pulmonary veins

Question 30

What is intussusception?

Answer 30

In week 5, the 4 pulmonary veins are incorporated into the wall of the left atrium. This makes the left atrial wall smoother than the right

Question 31

Where is the right sinus horn encorporated into?

Answer 31

The right artrium, enlarging it

Question 32

What is the majority of the atrial wall made from?

Answer 32

the primitive atrium

Question 33

At the end of week 4, explain how the primitive atrium divides into right and left atria

Answer 33

-begins with a crescent-shaped outgrowth from the dorsal wall – septum primum

Question 34

Explain how the atria is seperated from the ventricles

Answer 34

- As the septum primum extends into the atrium, the endothelium lining the boundary between the atrium and ventricle expands to form dorsal and ventral endocardial cushions - These cushions fuse in the midline to form the atrioventricular septum with 2 channels communicating between the future left atrium/ventricle and right atrium/ventricle

Question 35

In what week has the septum primum has fused with the atrioventricular septum? What is obliterated?

Answer 35

Week 6 ## Footnote The ostium primum is obliterated

Question 36

How do the foramen secundum and the septum secundum form?

Answer 36

foramen secundum - Apoptosis occurs in the upper part of the septum primum to form the foramen secundum seutum secundum - on the right side of the foramen secundum, a second crescent shaped projection forms from the dorsal wall of the atrium – septum secundum

Question 37

What is the opening left in the septum secundum called? Why is this important?

Answer 37

the foramen ovale- this allows blood to flow from the right atrium to the left atrium, bypassing the lungs and goes straight to the systemic circulatory system Foetuses don't need to send blood to the lungs because the mother provides us with oxygen

Question 38

What is the foramen primum?

Answer 38

The diminishing connection between the left and right sides of the primitive atrium as the septum primum extends

Question 39

How is an interventricular foramen formed?

Answer 39

At the end of week 4, a muscular part that projects from the floor of the primitive ventricle towards the endocardial cushions, leaving an interventricular foramen

Question 40

When is the intraventricular foramen closed?

Answer 40

Week 7 ## Footnote Membranous part that projects inferiorly from the endocardial cushion - seperates ventricles from right and left

Question 41

What does the truncus arteriosus septate into?

Answer 41

The aorta and pulmonary trunk

Question 42

How is the truncus arteriosus divided?

Answer 42

into two channels by endocardial swellings - cronotruncal ridges

Question 43

What do the conotruncal ridges fuse to?

Answer 43

They fuse to form a septum (a conotruncal septum) that separates the outflow of left and right ventricles and fuses with interventricular septum

Question 44

Where are neural crest cells contained?

Answer 44

The conotruncal swellings

Question 45

Explain how foetal circulation works

Answer 45

- oxygenated blood enters through umbilical vein - some blood enters liver and rest enters ductus venosus to bypass liver and enter IVC - blood passes through the foramen ovale to the left atrium, ventricle and aorta - blood also travels through the SVC and passes through the ductus arteriosus

Question 46

What happens to the ductus venosus when umbilical circulation stops?

Answer 46

It closes and degenerates Forms the ligamentum venosum in aduls

Question 47

What other foetal strucuture closes?

Answer 47

the foramen ovale - fossa ovalis in adults