5&6 Embryology Flashcards
By what week is the cardiovascular system active in the embryo?
- Beginning of 4th week
- (Placenta unable to meet demands of of growing embryo)
What does the development of the heart begin with the formation of?
Primitive heart tube
Lateral folding is the first type of folding to occur.
What does it achieve?
- Creates heart tube
- Brings two precursor regions together
The second type of folding to occur is cephalocaudal folding.
What does this achieve?
- Positions heart tube in future thorax
- Initially suspended in pericardial cavity by membrane
- Membrane subsequently degenerates
Name the 6 regions of the primitive heart tube?
After lateral and cephalocaudal folding, what are the next two steps in the development of the heart?
- Heart tube elongates
- Looping begins
On roughly what day of development does looping of the primitive heart tube begin?
23 days
In 2 steps, with reference to the bulbis cordis and the caudal portion (primitive ventricle), how does looping occur?
-
Bulbus cordis:
- Moves ventrally, caudally, right (forward, down and right)
-
Caudal portion:
- Moves dorsally, cranially, left (backwards, up and left)
At the fourth week where does the primitive atrium receive venous blood from?
- Right and left sinous horns
- Sinus venosus
What eventually happens to the right and left sinus horns?
(Formation of venous return to the right atrium)
Left: recedes as venous return shifts to right side of heart- forms coronary sinus
(responsible for drainage of venous blood from heart itself)
Right: Absorbed by growing right atrium- eventually forms part of inferior vena cava
How is venous return to the left atrium formed?
4 pulmonary veins incorporated into left atrium
Describe the early arterial system.
- Bilaterally symmetrical system
- Arched vessels
(Undergo extensive remodelling)
Each of the aortic arches has a corresponding nerve during development.
Which nerve is the 6th aortic arch associated with?
Recurrent laryngeal nerve
What happens to the right and left laryngeal nerves?
-
Right:
- Hooks around right 6th aortic arch
- Distal part of right 6th arch eventually disappears
- Nerve moves up
- Hooks around right subclavian artery (4th arch)
-
Left:
-
- Hooks around left 6th aortic arch
- Distal part of left 6th aortic arch persists as ductus arteriosus
- Nerve remains in position
The left recurrent larygeal nerve has a long course, why might this be relevant clinically?
Susceptible to pathology in chest
eg. compression by aortic aneurysm
Fill in the missing labels:
What is Patent Ductus Arteriosus (PDA)
Persistent communication between:
descending aorta and pulmonary artery
In which direction does blood shunt in Patent ductus arteriosus?
Left to Right
The septation of the primitive atrium requires the formation of how many septa and how many holes?
(Formation of left and right atria)
- Two septa
- Three ‘holes’
Outline how the first septum of the primitive artrium forms.
-
Septum primum forms
- Extends towards endocardial cushions
Outline how the ostium primum is formed.
- Ostium primum = hole (before septum primum completes fusion with endocardial cushions)
Outline how the ostium secundum is formed.
- Before ostium primum closes
- Ostium secundum appears in septum primum
What happens after the ostium secundum has closed?
Second septum begins to grow
What is the hole that is present in the second septum called?
Foramen ovale
