Flashcards in CVS - development of the CVS Deck (59):
What is created in the first two weeks of early embryonic development?
The tissues of the future embryo and placenta are created.
What is created in the third week of early embryonic development?
Three germ layers - ectoderm, mesoderm and endoderm (the primordia of all tissues)
What is created in the fourth week of early embryonic development?
A recognisable body form and the beginning of mesoderm organisation.
Where does the cardiogenic area (future heart) originate from?
Rostral to the buccopharyngeal membrane (future mouth).
What does lateral folding of the embryo do to the developing heart?
Creates the primitive heart tube by fusion of the pair of endocardial tubes.
What does cephalocaudal folding of the embryo do to the developing heart?
Brings the tube into the thoracic region.
What happens to the blood islands found in the cardiogenic field?
They coallesce into blood vessels creating a pair of heart tubes (endocardial tubes) - one on either side of the midline.
List the components of the primitive heart tube (caudal to rostral).
In which direction does blood flow through the primitive heart tube?
Caudal to rostral (sinus venosus to aortic roots)
What causes looping of the primitive heart tube?
Continued elongation in the fixed space of the pericardial cavity.
Describe the looping that the primitive heart tube undergoes:
Cephalic portion: ventrally, caudally and to the right
Caudal portion: dorsally, cranially and to the left
What are the consequences of the looping of the primitive heart tube on the inflow and outflow tract of the primitive heart?
It places arteries infront of veins and thus creates the transverse pericardial sinus.
What is the transverse pericardial sinus?
A passage in the pericardial sac between the origins of the great vessels, that is, posterior to the intrapericardial portions of the pulmonary trunk and ascending aorta and anterior to the superior vena cava and superior to the atria; it is formed as a result of the flexure of the heart tube, partially approximating the great venous and arterial vessels.
What does looping acheive?
1. Puts primordium of right ventricle closest to outflow tract
2. Puts primordium of left ventricle closest to inflow tract
3. Puts atrium dorsal to bulbus cordis (inflow dorsal to outflow)
What happens, after looping, to the communication between the atrium and ventricle?
A narrowing occurs which creates the atrioventricular canal. This is very important for cardiac partitioning.
How does the sinus venosus (inflow tract) develop?
It starts off with right and left sinus horns of equal size but as venous return shift to the RHS, the left sinus horn recedes. The right sinus horn is absorbed into the enlarging right atrium.
What does the right atrium develop from?
1. Most of the primitive atrium
2. Right engulfed sinus venosus
What does the left atrium develop from?
1. A small portion of the primitive atrium
2. Large bulk is the absorbed proximal portions of pulmonary veins
What venous drainage does the right atrium receive?
1. From the body - venae cava
2. From the heart - coronary sinus
Why are parts of the walls of the left atrium smooth?
They are parts which are formed from the absorbed primodial pulmonary vein tissue.
How is the oblique pericardial sinus formed?
It is formed as the left atrium expands absorbing the pulmonary veins. This creates a recess in the pericardium cavity caused by a reflection of the serous pericardium onto the pulmonay veins of the heart - on the posterior surface of the heart.
What are the blood vessels in the foetus that transfer oxygenated blood from the placenta and transfers back deoxygenated blood to the placenta?
Oxygenated blood from placenta - umbilical VEINS
Deoxygenated blood to the placenta - umbilical ARTERIES
What do the three fetal circulatory shunts bi-pass?
1. Ductus arteriosus - PT to aorta
2. Foramen ovale - right to left atrium
3. Ductus venosus - umbilical vein to IVC
What is the adult remnant of the ductus arteriosus?
What does the ductus arteriosus do?
It connect the pulmonary trunk to the aorta, thus bi-passing the lugns which are non-functional.
Why are the lungs non-functional in the foetus?
1. They are not developed enough to have blood vessels that can cope (develop later)
2. Blood already oxygenated
What is the primordia of the major arteries of the head, upper limb, pulmonary trunk, ascending, arch and descending thoracic aorta?
They all come from an early arterial system that begins as a bilateral symmetrical system of arched vessels, but which undergoes extensive remodelling to create the major vessels leaving the heart.
What is the derivative of the fourth aortic arch?
Right arch -> proximal part of right subclavian artery
Left arch -> arch of aorta
What is the derivative of the sixth aortic arch?
Right arch -> right pulmonary artery
Left arch -> left pulmonary artery and ductus arteriosus
What is of note about the nerves that supply these aortic arches?
Each aortic arch has a corresponding nerve.
What is the nerve that corresponds to the 6th aortic arch?
Recurrent laryngeal nerve (branch of vagus)
Why does the right recurrent laryngeal nerve descend to T1-T2 level whereas the left recurrent laryngeal nerve descends to T4-T5?
They are affected by:
1. The caudal shift of the developing heart and expansion of the developing neck region
2. The need for a fetal shunt between PT and aorta
As the heart "descends" the nerve hooks around the 6th aortic arch and "turns back on itself". The left recurrent laryngeal nerve becomes hooked around the shunt between the pulmonary trunk and aorta.
Which germ layer gives rise to the cardiovascular system?
What week does the embryo fold in?
Describe cephalocaudal folding.
Folding where the head and tail fold under.
Describe lateral folding
Folding where the edges fold under and meet each other
What septation must occur to the heart in development?
Ventricular outflow tract septation (pulmonary and systemic outflow tract)
In the process of septation what is the first structure to develop?
The endocardial cushions. These develop in the atrioventricular canal from the outside and fuse together in the middle,forming a right and left atriventricular canals.
In atrial septation two septa develop and three "holes". Name the septa and holes in order of development (first to last).
Septa: septum primum, septum secundum
"Holes": ostium primum, ostium secundum, foramen ovale
Describe the process of atrial septation.
1. Septum primum grows down towards the fused endocardial cushions
2. The ostium primum is the hole present before the septum primum fuses with the endocardial cushions
3. Before the ostium primum closes, a second hole, the ostium secundum appears in the septum primum
4. Finally a second crescent shaped septum, the septum secundum grows. The hole in the septum secundum is the foramen ovale.
What is the adult remenant of the foramen ovale?
What are the two components of the ventricular septum?
Muscular and membranous components
How does the muscular component of the ventricular septum form?
It grows upwards towards the fused endocardial cushions (in the atrioventricular canal), but stops just short leaving a gap called the primary interventricular foramen.
How does the membranous component of the ventricular septum form?
It is formed from connective tissue derived from the endocardial cushions which grows downwards to fill the gap.
Which is the most common area for a congential cardiac defect?
Membranous portion of the interventricular septum.
How does the conotruncal septum (septation of the outflow tract) occur?
Endocardial cushions appear in the truncus arteriosus. As they grow together they twist around each other and form a spiral septum.
What is the names of the adult remnants of the three fetal shunts?
1. Ligamentum arteriosus
2. Fossa ovalis
3. Ligamentum venosum
What becomes of the umbilical vein in the adult?
It's remnant is the ligamentum teres.
How does the foramen ovale close after birth?
First breath, respiration begins -> increase in intrathoracic pressure increases LA pressure increases relative to RA pressure and the septum primum is pushed against the septum secundum and the foramen ovale closes.
How does the ductus arteriosus close after birth?
It contracts due to a physiological muscular contraction caused by the higher oxygen content of the fetal blood (higher oxygen saturation).
How does the ductus venosus close after birth?
When placental support is removed it closes.
What becomes of the primitive atrium?
It becomes the auricles of the definitive atria.
What becomes of the primitive ventricle?
It becomes the left ventricle.
What becomes of the bulboventricular sulcus (narrowing between ventricle and bulbus cordis)?
It becomes the primary ventricular forament
What happens to the proximal 1/3 of the bulbus cordis?
It becomes the right ventricle (trabeculated)
What happens to the conus cordis of the bulbus cordis?
Outflow tracts of left and right ventricles
What happens to the truncus arteriosus?
It becomes the roots and proximal aorta and pulmonary trunk.
What are the most common heart defects?
The congenital defects: