Development of the heart Flashcards
At what stage of heart development can situs invertus occur?
During the formation of the four chambered heart tube
At what stage of heart development can Dextrocardia occur?
During cardiac looping
At what stage of heart development can Ventricular septal defect occur?
During the division of the atrioventricular canal into the left and right channels
At what stage of heart development can Atrial septal defect (foramen ovalae) occur?
During the formation of the atrial septa
At what stage of heart development can Tetralogy of Fallot occur?
During the formation of conotruncal cushions and division of the outflow tract
What is the first sign of fertilization?
The fertilized egg has 2 propnuclei
What is a Morula?
- Day 4
- Solid ball of cells formed as the zygote undergoes cleavage
What is the early Blastocyst?
- Day 6
- Hollow ball of cells with a fluid-filled cavity
- Comprises an inner cell mass, a blastocyst cavity and trophocytes forming the outer layer
What is the late Blastocyst?
- Day 10
- It is the pre-embryo
- It contains an embryonic disc (which are two layers that will become the proper embryo) between the amniotic cavity and yolk sac
what is a Gastrula?
- DAY 16
- It is the embryo with the three primary germ layers; ectoderm, mesoderm and the endoderm
What is made from the Ectoderm?
- skin (epidermis)
- brain
- spinal cord (CNS)
- sensory organs etc
What is made from the Mesoderm?
- heart
- skeletal muscle
- kidneys
- urogenital organs
- connective tissue etc
What is made from the Endoderm?
lining of the GI tract and lungs, liver etc
Where can all cells in the body be traced back to?
Ectoderm, Mesoderm and Endoderm
Describe the strcuture of the embryo during Gastrulation (day 18)
- At the head end, have a primary heart field with blood islands in it
- At the tail end, we have the primitive node, a group of cells on the anterior portion of the primitive streak
- This node is where gastrulation first begins
What are the structures present in the Trilaminar embryo?
- Amniotic cavity
- Ectoderm
- Mesoderm
- Blood islands
- Notochord
- Endoderm
- Yolk sac
What is the Notochord and what is its function?
The Notochord is a cartilage type cord, giving stability to the embryo before vertebrae formation. Also a source of signalling molecules
What do blood islands go on to form?
The heart
Describe what occurs during formation of the heart tube at 18 days
The heart develops from the primitive streak via the blood islands in the splanchnic mesoderm
Describe what occurs during formation of the heart tube at 20 days
The blood islands slowly form together into 2 tubes called cardiogenic cords
Describe what occurs during formation of the heart tube at 21 days
The tubes fuse down the middle to make one heart tube
Describe what occurs during formation of the heart tube at 22 days
Further development gives rise to a tube with asymmetric openings forming an arterial and venous end. Beginnings of asymmetry due to bulge in the left
What is situs invertus?
Condition in which all the heart and other organs of the body are transported through the sagittal plane to lie on the opposite side from normal (basically the organs are inverted in the body).
- Occurs if anything goes wrong during formation of the heart tube
Describe what occurs during Cardiac looping at 22 days
The cells at each end of the heart proliferate making the tube longer. The entire structure is in a confined space so begins to fold up on itself
Describe what occurs at day 23 & 24 during Cardiac looping
The primitive atrium loops up above and behind the primitive ventricle. The looping process brings teh primitive areas of the heart into the proper spatial relationship for development.
What is Dextrocardia?
Condition where all of the organs are in their normal position, with the exception of the heart, which is on the opposite side.
- Occurs if anything goes wrong at 24 days, during the looping process
Describe what occurs on day 24 during Cardiac looping?
The primitve atrium we see from the front, when viewed from the side is growing out of the back and become two atria.
The future right ventricle grows downwards at the front
Describe what happens on day 35 during Cardiac looping
The heart is beating at this stage and the foetal heart can be seen on the ultrasound. The four interior chambers are not yet divided.
The heart is iesentially a little pulsing tube.
Describe what happens on day 30 during divison of theatrioventricular tract
- The septum primum grows along the midsagittal plane, separating the atria, except for a temporary space called the foramen primum
- The left side of the atrium grows pulmonary veins, sending the growing veins to the lungs
- The posterior and anterior endocardial cushions fuse, dividing the atria from the ventricles
- A ventricular septum will eventually grow upwards to form a division between the two ventricles
- This will attach to the divisions between the atria and the ventricles
Describe one cause of ventricular septal defect
Failure of the endocardial cushions to provide an anchor point for the developing ventricular septum
What are the two main effects of ventricular septal defect?
- Systemic circulation dosent receive all the blood being pumped by the ventricle
- Leakage of blood into the right ventricle elevates right ventricular pressure and volume, causing pulmonary hypertension
Describe a ventricular septal defect
During ventricular contraction, some of the blood from the left ventricle leaks into the right ventricle, passes through the lungs and re-enters the left ventricle via the pulmonary veins and left atrium.
The extent of the opening may vary from pin size to complete absence of the ventricular septum
How can the ventricular septal defect abnormality be viewed
Using an echocardiogram: the mid-oesophageal four-chamber view demonstrates an atrial septal defect (arrow), right atrium, right ventricle, left atrium, left ventricle
Describe the formation of the atrial septa at 40 days
- Initially the temporary hole in the eptum pimum called the Foramen primum permits the right to left shunt of foetal blood, because there is no pulmonary circulation. This closes before a second hole called the Foramen secundum opens.
- A second more muscular and robust septum called the septum secundum grows down from the roof of the atria just lateral to the septum primum. It obscures the place where the foramen primum was.
- The anterior and posterior endocardial cushions have fused leaving left and right atrio-ventricular canals
Describe the formation of the atrial septa at 43 days
SEPTUM SECUNDUM:
- This grows but leaves the foramen ovalae, a space permitting the right to left shunt of blood
SEPTUM PRIMUM:
- The foramen secundum is partially obscured by the septum secundum, but the foramen ovale remains providing an alternative left to right shunt the formen primum is closed.
VENTRICULAR SEPTUM:
- The ventricular septum grows up to fuse with the now fused endocardial cushions
What happens to the foramen ovalae when we are born?
- At birth, the lungs become functional
- This means that the pulmonary vascular pressure decreases, and the left atrial pressure exceeds that of the right
- This forces the septum primum against the septum secondum, functionally closing the foramen ovale
- In time, the septa eventually fuse, leaving behind the fossa ovalis
What does the separation of ventricles result from?
Union of the:
- Conotruncal septum
- Endocardial cushions
- Ventricular septum
What occurs during division of the outflow tract?
There is no separation between the ventricles: all the blood from the heart is leaving through one vesssel. Eventually they are separated into the left and right sides (pulmonary artery and aorta).
The conotruncal septum grows as a spiral down teh conus arteriosus. It meets with the endocardial cushions and the ventricular septum. The three of them then make the final full separatipn from the left and right sides.
How can Tetrology of Fallot arise?
If the conotruncal septum is misaligned, a different sized aorta and pulmonary artery is formed, or it wont meet with the endocardial cushion correctly, giving rise to a septal defect.
Where is Tetrology of Fallot common?
- Ventricular and atrial septal defects
- Down’s syndrome
Pulmonary stenosis
Spiral valve grown off centre so large aorta and small pulmonary artery, restricts blood to lungs
Overriding aorta
Aortic opening is positioned over a ventricular septal defect allowing blood from both sides of the heart to enter the aorta, some deoxgnated blood pumped around the body
Ventricular septal defect
During systole, blood from the left ventricle leaks into the right ventricle, passes through the lungs and re-enters the left ventricle via the pulmonary veins and left atrium.
Increases pressure in pulmonary circulation and also causes volume overload in the left ventricle
Right ventricular hypertrophy
Right ventricular wall increases in size to deal with obstruction in the pulmonary artery
What is the ductus arteriosus? How does it play a part in foetal circulation and birth?
Ductus arteriosus is a blood vessel connecting the main pulmonary artery to the proximal descending aorta. It alows most of the blood from the right ventricle to bypass the foetal fluid-filled non-functioning lungs. Upon closer at birth, it becomes ligamentum arteriosum.
How does the foramen ovalae play a part in foetal circulation and birth?
The foramen ovalae allows blood to enter the left atrium from the right atrium and allows blood to bypass the pulmonary circulation. In most individuals it closes at birth and later forms the fossa ovalis.
