L6: Development of the CVS

Question 1

At the end of the first two weeks of development what has been formed?

Answer 1

Tissue of embryo and placenta

Question 2

What are the main stages in week 3?

Answer 2

Gastrulation–> formation of germ layers
Ectoderm–> Dermis and CNS
Mesoderm–> Bone, muscles, cartilage etc…
Endoderm–> lining of the GI tract and mucosal membranes

Question 3

What has happened by the end of the 4th week?

Answer 3

Cephalocaudal folding
Lateral folding
Cardiogenic region in midline of body
Mesoderm–> organised

Question 4

How does the primordial heart tube develop?

Answer 4

Blood island –> lateral folding –> primordial heart tube

Cephalocaudal folding–> midline of body

Question 5

Label the different areas of the primitive heart tube?

Answer 5

(bottom) 
Sinus Venosus
Primordial atria
Primordial ventricles 
Bulbus cordis
Truncus Arteriosus
Aortic roots
(top)

Question 6

What needs to happen to the primitive heart tube to from the heart?

Answer 6

Dividing–> 4 chambers

Inflow and outflow vessels–> remodelled

Question 7

Where is the heart tube suspended? What consequence does this have?

Answer 7

Suspended in pericardial cavity
Fixed superiorly and inferiorly
Cardiac looping–> rapidly elongates –> runs out of room–> uses lateral space–> twists and folds up –> atria posterior to ventricles –> inflow and outflow tracts in correct position

Question 8

What sinus is created by the folding of the primitive heart? How?

Answer 8

Transverse pericardial sinus
Looping of heart
Arteries are in front of veins
Atria posterior

Question 9

How is the sinus venosus created?

Answer 9

Right and Left sinus horns of equal size
Venous return shifts–> right hand side, L horn recedes
Right sinus horn absorbed by enlarging RA

Question 10

How do the atria develop?

Answer 10

RA --> majority primitive atrium 
--> sinus venosus
--> Mature--> deO2 from vena cava (body) and heart (coronary sinus)
LA --> small primitive atrium 
--> Proximal pulmonary veins 
--> Mature --> O2 blood --> lungs

Question 11

Explain why the left atrium is smooth inside?

Answer 11

Smooth wall–> absorbed primordial pulmonary veins
4 veins enter
Auricle –> remnant of primordial atria

Question 12

What is the other sinus in the heart? How is it formed?

Answer 12

Oblique sinus

Formed –> left atrium absorb veins

Question 13

Why does the heart require shunts?

Answer 13

Lungs don’t work

O2 and CO2 exchanged in placenta

Question 14

What are the names of the shunts? Where are they located?

Answer 14

Ductus venosus–> bypass liver –> placenta to IVC
Foramen Ovalae–> bypass RV–> RA-LA
Ductus arteriosus–> bypass lungs–> pulmonary artery to aorta

Question 15

What is unusual about fetal circulation?

Answer 15

IVC and RA contain oxygenated blood

Question 16

What happens at birth?

Answer 16

Placenta no longer required–> Lungs work –> DV closes
Pressure in LA> RA foramen ovalae closed
DA contracts

Question 17

What are the aortic arches?

Answer 17

Arterial system begins as bilateral aortic arches
5 in humans –> numbered 1,2,3,4,6
Remodelling–> major arteries formed

Question 18

What are the main derivatives of the aortic arches?

Answer 18

4th arch --> R --> proximal part of R subclavian artery 
               --> L --> arch of aorta
6th --> pulmonary arch
--> R --> R pulmonary artery
--> L --> L pulmonary artery and DA

Question 19

What is a consequence of remodelling of the aortic arches?

Answer 19

Left recurrent Laryngeal nerve–> hooks around 6th aortic arch–> around shunt between PT and aorta

Question 20

What is a (potential) consequence of the ductus arteriosus?

Answer 20

Patent Ductus Arteriosus–> communication between PT and Aorta maintained
Blood shunt from L–> R (high to low pressure)