CVS S2+3 - CVS Embryology (with labelling exercises) Flashcards Preview

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Flashcards in CVS S2+3 - CVS Embryology (with labelling exercises) Deck (27):

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


- 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?


- 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)



- 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?


- 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