CVS S2+3 - CVS Embryology (with labelling exercises) Flashcards
What and where is the cardiogenic area?
When is it created?
A region of the mesoderm by the cranial end of the embryo which develops into the heart, blood vessels and blood cells
Created during gastrulation
What structures arise from the cardiogenic area and how are they affected by embryo folding?
A pair of endocardial tubes arise in the 3rd week
Lateral folding creates the heart tube
Cephalocaudal folding brings the tube into the thoracic region
Describe the location of the heart tube post-embryo folding
Suspended in the pericardial cavity by a membrane (which later degenerates leaving the heart tube free In the thoracic region
Describe the way blood flows through the primitive heart tube
Linear:
- Blood inflow through sinus venosus caudally
- Blood outflow from the aortic roots at the cranial pole
Describe the structure of the primitive heart tube
Four segments
- Primitive atrium caudally (Blood inflow through sinus venosus)
- Primitive ventricle
- Bulbous cordis
- Truncus arteriosus (outflow through aortic roots from here)
Describe the looping of the primitive heart tube
Continued elongation of the heart tube results in bending beginning at day 23 and is complete at day 28
Cephalic portion bends ventrally, caudally and to the right
Caudal portion bends dorsally, cranially and to the left
What are the consequences of heart tube looping to blood flow and internal structure?
What feature of the adult heart is formed?
Looping places the inflow and outflow cranially with inflow behind outflow
After looping the atrium communicates with the ventricle via the atrioventricular canal, this a constriction, creating the first division between atrium and ventricle
Looping creates the transverse pericardial sinus (space between the outflow and inflow into which the finger can be inserted)
Describe the early development of the sinus venosus
At first the left and right inflow horns are equal size
But as venous return shifts to the right the left horn recedes
The enlarging right atrium absorbes the right sinus horn
Describe the early development of the atria
What feature of the adult heart is created by atrial development at this stage?
Right:
- RA develops from most of the primitive atrium and absorbs the right horn of the sinus venosus
- Begins to receive venous return from the body directly (venae cava) and the heart (coronary sinus)
Left:
- Develops from a small portion of the primitive atrium
- Absorbs proximal parts of the pulmonary veins (initially one inflow, becomes 4 as the first 4 branches are absorbed) to become smooth walled atrial area
Oblique pericardial sinus formed as left atrium expands (posterior heart surface, ‘cul de sac’)
What are the aortic arches?
A bilaterally symmetrical system of arched vessels 6 arches on each side
They undergo remodelling to create major arteries leaving the heart
Describe the remodelling of the aortic arches
4th arch:
- Right = Proximal subclavian artery
- Left = Arch of the aorta
5th arch:
- Has no derivative in humans
6th arch:
- Right = Right pulmonary artery
- Left = Left pulmonary artery and ductus arteriosus
How does foetal circulation differ from adult?
Lungs non functioning, deoxygenated blood is oxygenated at the placenta via the umbilical artery, returns to the heart via the umbilical vein
Right to left atrium shunt (foramen ovale)
Backup right ventricle to aortic shunt (ductus arteriosus)
Blood bypasses the liver
Describe how the aortic arches relate to nerves
Each arch has a corresponding nerve
Nerve corresponding to 6th is the reccurent larangeal nerve (from the vagus (CN X)
Two factors influence the course of this nerve:
- Caudal shift of heart and expansion of the developing neck region
- Need for a foetal shunt between Pulmonary Trunk and aorta
Describe the process of septation in overview
After looping the atrioventricular canal is set up
First step in septation is development of the endocardial cushions on the dorsal and ventral sides of the AV canal
These grow towards each other and divide heart into the left and right channels
Atrial and ventricular septation then occur and the four chambers of the heart are formed
Describe in detail atrial septation
Involves the formation of two septa with 3 holes
The septum primum grows down towards the endocardial cushions
The ostium primum is the hole present before the septum primum fuses with the endocardial cushions
Before the ostium primum closes the ostium secundum appears in the cephallic septum primum (apoptosis)
Finally a crescent shaped second septum called the septum secundum forms, the hole in this septum is called the foramen ovale, located more caudally than the ostium secundum
The two patent holes form the right to left foetal shunt
Describe in detail ventricular septation
Septum has a muscular and membranous component
Muscular portion forms most of the septum and grows upwards towards the fused endocardial cushions
A hole is left at the top, the primary interventricular foramen
Membranous portion grows down and closes the primary interventricualr foramen It is derived from the spiral septum that grows down to separate the truncus arteriosus into the outflow vessels
Describe the formation of the conotruncal septum
Endocardial cushions also appear in the truncus arteriosus
As they grow towards each other they twist around each other to form a spiral septum separating the aorta and pulmonary trunk
Describe how a foetus’ circulatory system must change to begin gas exchange in the lungs
After birth the baby takes a massive breath, massively decreasing pressure in the lungs
This results in more blood entering the lungs and as a result more blood returns from the left atrium
When pressure in the left atrium > right atrium the foramen ovale is close (one way shunt)
The ductus arteriosus contracts
Placental support has been removed, so no blood enters the umbilical vein or the ductus venosus, so this shunt is also closed
List the fates of the foetal shunts
Foramen ovale becomes:
- Fossa ovalis
Ductus arteriosus becomes:
- Ligamentum arteriosum
Ductus venosus becomes:
- Ligamentum venosum
Umbilical vein becomes:
- Ligamentum teres
What is this picture of?
What is indicated by the arrow?
Name the sections of the heart each depicted by a different colour
The heart tube
Direction of blood flow
White - Aortic roots
Black - Truncus arteriosus
Green - Bulbus cordis
Blue - Primitive ventricle
Red - Primitive atrium with sinus venosus
What is shown here?
What does the blue arrow indicate?
The folded heart tube is shown
Blue arrow indicates the newly formed atrioventricular canal
What is shown here?
The right horn of the sinus vensosus being absorbed by the right atrium and the left horn receding
Label the white boxes from top to bottom, left row first, then right row
What process is shown?
Left 5, top to bottom:
- Pulmonary veins
- Primordial pulmonary vein
- Primordial left atrium
- Right and left pulmonary veins
- Primordial left atrium
Right 5, top to bottom:
- Left atrium tissue formed by absorbed pulmonary vein tissue
- Primordial left atrium
- Entrance of 4 pulmonary veins
- Smooth walled left atrium
- Left auricle
Early development of the left atrium prior to septation
What structure is shown?
Where does the vessel circled by a blue arrow connect to?
The aortic arches
Connects to the aortic sac, in turn connected to primitive heart tube
What process is being shown
Label the two arrows
Development of the endocardial cushions at the beginning of septation
Top to bottom:
- Atrioventricular canal
- Endocardial cushions
Label the white boxes
Left to right, top row first
What is this process?
Boxes:
- Septum primum begins to form, growing downwards, ostium primum left open
- Ostium secundum appears in septum primum
- Ostium primum closes
- Septum secundum begins to form growing downwards
- Foramen ovale
- Right to left feotal shunt
Label the white boxes from top right progressing anticlockwise
Ductus arteriosus
Superior vena cava
Pulmonary vein
Foramen ovale
Inferior vena cava
Ductus venosus
Inferior vena cava
Umbilical vein
Umbilical arteries
Descending aorta
Pulmonary artery
Pulmonary vein
