Development of the heart & blood vessels Flashcards
List the stages of heart development
1) Formation of the 4 chambered heart tube
2) Cardiac looping
3) Division of the atrioventricular canal into left and right channels
4) Formation of the atrial septa
5) Formation of the conotruncal cushions and division of the outflow tract
List the potential defects at each stage
1) Situs inversus
2) Dextocardia
3) Ventricular septal defect
4) Atrial septal defect - foramen ovale
5) Tetralogy of fallot
Stages of human embryo development
1) Fertilised egg has 2 pronuclei - 1st sign of fertilisation
2) Developing embryo contains 6-8 cells 3 days after fertilisation
3) 5 days after fertilisation is is called a blastocyst and has approximately 100 cells
Morula
Solid ball of cells formed as the zygote undergoes cleavage
Early blastocyst
Hollow ball of cells with a fluid filled cavity
Late blastocyst
Pre-embryo, with the embryonic disk, 2 layers of cells that become the embryo proper
Gastrula
Embryo with 3 primary germ layers: ECTODERM, MESODERM, and ENDODERM
Ectoderm
Skin (epidermis) brain spinal cord (CNS) sensory organs
Mesoderm
Heart, skeletal muscle, kidneys, urogenital, connective tissue
Endoderm
Lining of gastrointestinal tract and lungs, pancrease, liver
18 days
Gastrulation
Formation of the heart tube
18 days - heart develops from the primitive streak via the blood islands in the splanchinic mesoderm
20 days - the blood islands slowly form together into 2 tubes called CARDIOGENIC CORDS
22 days - further development gives rise to tube with asymmetric openings forming a arterial and venous end. Beginning of asymmetry in bulge to the left
Situs inversus
congenital condition in which the major visceral organs are reversed or mirrored from their normal positions.
Cardiac looping
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
23 days/24 days - the primitive atrium loop up above and behind the primitive ventricle. The looping process brings the primitive areas of the heart into proper spatial relationship for development
35 days - The beating foetal heart can be seen on ultrasound. But the 4 interior chambers are not yet divided
Dextrocardia
Rare heart condition in which your heart points toward the right side of your chest instead of the left side.
Division of the atrioventricular canal
30 days - the left side of the atrium grows pulmonary veins sending growing veins to the developing lungs
SEPTUM PRIMUM - grows along the midsagital plane separating the atria except for a temporary space called the FORAMEN PRIMUM
A ventricular septum will eventually grow upwards to forming a division between the 2 ventricles. It will attach to the division between atria and ventricle
Ventricular septal defect
During ventricular contraction some of the blood from the left ventricle leaks into the right ventricle, passes through the lung re-enters the left ventricle via the pulmonary veins and left atrium
2 main effects of ventricular septal defect
1) Systemic circulation doesn’t receive all the blood being pumped by the left ventricle
2) Leakage of blood into the right ventricle elevates right ventricular pressure and volume, causing pulmonary hypertension
What is a cause of ventricular septal defect
Failure of the endocardial cushions to provide an anchor point for the developing ventricular septum
Formation of the atrial septa
40 days - Initially, the temporary hole in the septum primum called the FORAMEN PRIMUM permits the right to left shunt of foetal blood, because there is no pulmonary circulation
This closes before a 2nd hole called the FORAMEN SECUNDUM opens
Anterior and posterior endocardial cushions have fused leaving left and right atrio-ventricular canals
43 days - septum secundum grows but leaves the FORAMEN OVALE, a space permitting the right to left shunt of blood
Septum primum - foramen secundum is partially obscured by the septum secundum, but foramen ovale remains providing an alternative left to right shunt the foramen primum is closed
ventricular septum grows to fuse with the now fused endocardial cushions
SEPTUM SECONDUM
A 2nd more muscular and robust septum grows down from the roof of the atria just lateral to the septum primum. It obscures the place where the foramen primum was
Separation of the ventricles results from the union of the:
Conotruncal septum
Endocardial cushions
Ventricular septum
CONOTRUNCAL SEPTUM
Grows as a spiral down the CONUS ARTERIOSUS
Meets the endocardial cushions and the ventricular septum
All 3 of them makes the final full separation of the left and right sides
If misaligned - get differently sized aorta and pulmonary artery. Or it won’t meet with the endocardial cushion correctly giving rise to a septal defect - ultimate complication - TETROLOGY OF FALLOT
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 deoxygenated 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 left ventricle
RIGHT VENTRICULAR HYPERTROPHY
Right ventricular wall increases in size to deal with obstruction in pulmonary artery
DUCTUS ARTERIOSUS
Blood vessel connecting the main pulmonary artery to the proximal descending aorta. It allows most of the blood from the right ventricle to bypass the foetal fluid filled non functioning lungs
Upon closure at birth, it becomes ligementum arteriosum
FORAMEN OVALE
Allows blood to enter the left atrium from the right atrium. Along with the ductus arteriosis it allows blood to bypass the pulmonary circulation
In most individuals, the foramen ovale closes at birth. It later forms the FOSSA OVALIS
