Session 3.1

Question 1

What are the three layers of the embryonic disk?

Answer 1

• ectoderm
• mesoderm
• endoderm

Question 2

What does the cardiogenic field look like in an embryonic disk?

Answer 2

An arch that forms the cardiac system

Question 3

How does the primitive heart tube form?

Answer 3

Two endocardial tubes fuse to form a single heart tube

Question 4

Why must the primitive heart tube be divided?

Answer 4

To create 4 distinct chambers??

Question 5

Where is the primitive heart tube suspended?

Answer 5

In the pericardial cavity

Question 6

How does looping of the primitive heart tube occur?

Answer 6

• tube elongates
• runs out f room
• twists and folds up
• places the inflow and outflow in correct orientation with respect to each other, helping form the transverse pericardial sinus

Question 7

How does the RA develop from the primitive heart tube?

Answer 7

• right and left sinus horns equal in size and symmetrical
• venous return shifts to RHS, left sinus horn recedes
• right sinus horn is absorbed by enlarging RA

Question 8

What does the LA develop from?

Answer 8

• a small portion of the primitive atrium
• absorbs proximal parts of pulmonary veins
• receives oxygenated blood from the lungs

Question 9

How does the oblique pericardial sinus form?

Answer 9

As left atrium expands, stretching out the lining of the pericardial sac and absorbing the pulmonary veins, forms a cul de sac posterior to the heart

Question 10

What’s the circulatory system in the foetus?

Answer 10

• lungs don’t work = no point in pulmonary circulation
• oxygenation and removal of co2 occur at the placenta
• so shunts are required to maintain feral life
• these shunts must be reversible at birth

Question 11

Why does blood mainly avoid the right atrium and why does some enter?

Answer 11

Avoids as lungs don’t work = no point in pulmonary circulation

Some goes in as needs a small amount of blood to pump against to develope normally

Question 12

How do the foremen ovals and ductus arteriosus close?

Answer 12

Birth

• respiration begins
• LA pressure increases, foramen ovale closes
• ductus arteriosus contacts due to a rise in pO2 from start of respiration

Question 13

How does the ductus venosus close?

Answer 13

Birth

• placental support removed
• DV closes

Question 14

What are aortic arches?

Answer 14

Early arterial system begins as a bilaterally symmetrical system of arched vessels

Question 15

Give the two main aortic arch derivatives.

Answer 15

4th arch

• R = proximal part of right subclavian artery
• L = arch of aorta

6th

• R = right pulmonary artery
• L = left pulmonary artery and ductus arteriosis

Question 16

What is patent ductus arteriosis?

Answer 16

• ductus arteriosis doesn’t contract with first breath
• persistent route of communication exists with pulmonary artery and ascending aorta
• appears as a fibrous chord
• blood will shunt from aorta into pulmonary artery