Development of the Heart and Blood Vessels Flashcards
Heart development stages and defects
- Formation of the four-chambered heart tube
- Situs inversus
- Cardiac looping
- Dextrocardia
- Division of the atrioventricular canal into left and right channels
- Vetricular septal defect
- Formation of the atrial septa
- Atrial septal defect – foramen ovale
- Formation of the conotruncal cushions and division of the outflow tract
- Tetralogy of Fallot
Describe the stages of the human embryo development the first 5 days.
• The fertilised egg has 2 pronuclei.
• The developing embryo contains 6-8 cells 3 days after fertilisation
• Five days after fertilisation, it is called a blastocyst and has approximately 100 cells.
- It has a fluid filled cavity, the inner cell mass and trophoblast. The cell mass then divides into 2 cell types: epiblast and hypoblast
- The trophoblast becomes the placenta – They are responsible in implanting into the endometrium (the wall of the uterus), and become the placenta.
- These are the embryonic stem cells obtained.
What happens at day 10 of development?
• You have another fluid filled cavity called the ‘Amniotic cavity’.
What takes place at day 18?
Gastrulation - an early phase of embryonical development in which the implanted blastula develops the 3 distinct germ layers
• Ectoderm forms skin and the brain – surface ectoderm and neural ectoderm
- Becomes the amniotic fluid that surrounds the embryo.
• Endoderm forms the GI and respiratory tract
- Becomes yolk sac
• Mesoderm forms all the blood vessels, muscles, ligaments, tendons
• Ring of blood islands towards the head – The blood islands are the little gaps between the mesoderm and the endoderm.
• Primitive streak is formed.
• In the middle of the three layers, there is the notochord – which is a cartilaginous skeletal rod supporting the body in the embryo – not entirely the backbone, but part of it.
Outline the formation of the heart tube
- 18 days – Heart develops from the primitive streak via the blood islands in the splanchnic mesoderm. -
- 20 days – The blood islands slowly form together into 2 tubes called cardiogenic chords
- 21 days – The tubes fuse down the middle to make one heart tube.
- 22 days – Further development gives rise to a tube with asymmetric openings forming an arterial and venous end. Beginning of asymmetry in bulge to the left. – the ends of the tubes attach to the rudimentary blood supply that is starting to circulate around the embryo.
What does the primitive streak do?
- The presence of the primitive streak (crease in the little embryo) will establish bilateral symmetry, determine the site of gastrulation and initiate germ layer formation.
- Left and right is determined by transcription factor lefty.
- All our organs are asymmetrically distributed, e.g. pancreas is on one side, and no two lungs are the same. – determined by the asymmetry along the primitive streak.
What is situs inversus?
When the organ location is a mirror image - they still are perfectly healthy.
Caused by the cardiac loop being pushed the other way.
Outline 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 and bulges.
- 23-24 days – The primitive atrium loop up and behind the primitive ventricle. The looping process brings the primitive areas of the heart into the proper spatial relationship for development.
- 24 days – The primitive atrium we see from the front, when viewed from the side is growing out of the back and become two atria. And the future right ventricle grows downwards at the front.
What is dextrocardia?
When all the organs in the body are in the right location, except the heart.
What happens inside the heart at the same time as cardiac looping?
- The heart is beating by this stage and foetal heart can be seen on ultrasound. But the 4 interior chambers are not yet divided.
- The one tube leaving the heart and oxygenated blood comes from the placenta. – Rudimentary heart is sufficient enough for the foetus.
Outline the formation of the atrial septa, at day 30
- Septum primum - Grows along the midsagittal plane separating the atria except for a temporary space called the Foramen primum.
- Pulmonary veins - The left side of the atrium grows pulmonary veins sending growing veins to the developing lungs.
- Endocardial cushions - The posterior and anterior endocardial cushions fuse dividing the atria from ventricles.
- Ventricle - A ventricular septum will eventually grow upwards to forming a division between the two ventricles. It will attach to the division between atria and ventricle.
What is ventricular septal defect? effects? and cause?
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.
2 main effects…
1. Systemic circulation doesn’t receive all the blood being pumped by the left ventricle.
- Leakage of blood into the right ventricle elevates right ventricular pressure and volume, causing pulmonary hypertension.
One cause of ventricular septal defect is the failure of the endocardial cushions to provide an anchor point for the developing ventricular septum.
Outline the formation of atrial septa at day 40.
• 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 second hole called the Foramen secundum opens
• A second 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.
• Anterior and posterior endocardial cushions have fused leaving left and right atrio-ventricular canals
Outline the formation of atrial septa at day 43.
- Septum secundum - The septum secundum grows but leaves the Foramen ovale, 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 shuntthe foramen primum is closed.
- Ventricular septum - The ventricular septum grows up to fuse with the now fused endocardial cushions.
What happens to the lungs at birth?
At birth the lungs become functional, pulmonary vascular pressure decreases and the left atrial pressure exceeds that of the right forcing the septum primum against the septum secundum, functionally closing the foramen ovale. In time the septa eventually fuse.
