Embryology 2 - CVS/ Circulation/ GI/ Respiratory Flashcards
1- Define congenital heart disease.
2- When do they typically arise?
3- How can CHD be broadly classified according to the presence or absence of what?
1- Abnormalitiesofcardiac structure that are present from birth
2- Third to eighth weekof gestation
3- Cyanosis: blueness of the trunk and mucous membranes
> results from levels of deoxygenated haemoglobin of >3–5 g/dL in the arterial circulation.
Why are cardiovascular congenital anomalies frequently seen with abnormal facial development?
- Neral crest cells contribute to the development of facial bones as well as endocardial cells that line the outflow tracts of heart.
> Neural crest cells are very sensitive to toxic insults and can be damaged by retinoids, alcohol, and many other substances.
One reason for this sensitivity may be that they may lack some of the enzymes that help to scavenge and protect cells from cell-killing free radicals.
How is the heart tube formed?
1- 3 germ layers, mesoderm cells collect at the cranial end of embryo in front of pro-chordal plate. (Heart development starts in head)
2- Heart tube develops from splanchnic layer of lateral plate mesoderm.
3- Endoderm starts secreting growth factors (VEGF) causing the splanchnic layer of lateral plate mesoderm to start differentiating
4- Mesoderm starts specialising creating 2x heart tubes and 2x pericardial cavity
5- Lateral body folding causes heart tubes to fuse and pericardial cavities to fuse. Edges come together.
6- Resulting in 1 heart tube and 1 pericardial cavity.
-Whilst lateral folding occurs heart tube is pulled into pericardial cavity.
- Endoderm folding also makes epithelial lining of GI tract
7- Heart tube is held in place to posterior pericardial cavity wall via Dorsal mesocardium.
Label the images showing Lateral body folding to bring the 2 sides of the cardiac regions to the midline to fuse.
Label the heart tube. At what day is this seen?
What is the caudal/cranial part of heart tube?
What are the 3 divisions of Bulbus cords?
- Day 22
-Caudal pole forms the venous end
-Cranial end is the arterial portion, must sprout vessels to create an open path for blood flow
3 divisions:
1- Truncus arteriosus
2- Conus cordis
3- Trabeculated RV
Describe what happens during cardiac looping.
What day is it complete?
What pathology is it when cardiac looping is reflected?
- Day 28
1- T.A/B.C move to the right and anteriorly
2- P.V moves to the left and downwards posteriorly
3- P.A/S.V move to the left upwards posteriorly.
> Dextrocardia
What are the fates of the different sections of the heart tube?
- Aortic sac
- Truncus arteriosus
- Conus cordis
- Trabeculated portion of RV
- Primitive ventricle
- Primitive atria
- Sinus venosus
- Aortic sac: Aorta
- Truncus arteriosus : Aorta + Pulmonary trunk
- Conus cordis : Ventricular outflow tracts
- Trabeculated portion of RV: Muscular wall of RV
- Primitive ventricle: Left ventricle
- Primitive atria: Right and left atria
- Sinus venosus: Smooth part of right atria, coronary sinus, SA node , AV node, Bundle of his
Label the sinus venosus
At the fourth week, the sinus venosus is responsible for….
- The inflow of blood to the primitive heart, and empties into the primitive atrium.
- It receives venous blood from the right and left sinus horns
What are the Embryonic Veins and where do they receive blood from?
What do they form after birth?
3 major pairs of veins – vitelline, umbilical & cardinal
- Right vitelline vein ( from yolk sac) = SMV, proximal HPV, part of IVC
- Left umbilical vein ( from placenta) = ligamentum teres
- Right cardinal vein (from body) = azygos vein
What is the link between the right atrium and the sinus venosus?
1- Most of the right atrium (the smooth-walled part) is derived by incorporation of the sinus venosus and right sinus horn into the primitive right atrium.
2- Venous flow shifts to the right and the vena cava are formed
3- Right sinus horn expands to accommodate the increased blood flow - opening into the right atrium expands.
4- As R. sinus horn expands, it is incorporated into the right atrium
5- As a result, the opening from the left sinus horn diminishes in size.
6- All that remains of the left sinus horn is the coronary sinus and oblique vein of the left atrium
What happens to the left atrium?
- Four pulmonary veins are incorporated into the primitive left atrium, forming the smooth inflow portion of the left atrium and the oblique pericardial sinus.
How is Visceral pericardium formed?
- Sinus venosus allows cells to move into the pericardial cavity forming a layer around the heart.
1- What stage does a heartbeat begin? How?
2- What is key about vessels at this stage ?
3- Where do the 1st blood cells arise from?
1- WEEK 4
> Some cells of sinus venosus infiltrate into heart and form primitive conduction system to allow for the heart to start beating.
2- They are paired
3- Yolk sac
How does Atrioventricular valve formation occur?
> Level of PV/PA cross section
1- Neural crest cells migrate and form anterior and posterior endocardial cushions
2- As they grow towards each other they fuse together and we develop 2 canals forming septum intermedium.
3- Endocardial cells start forming valve falls off septum intermedium.
- Annulus rings connect the valves together
4- Off the valves come chord tendinae
Giving us Bicuspid and Tricuspid valves
What day does atrial septa form?
Describe the process.
- Day 30-33
1- Septum primum grows down the middle of both primitive atria towards septum intermedium, leaving a gap as it does not actually reach it. = osteum primum
2- Septum primum continues to grow and reaches septum intermedium closing of osteum primum
3- Another hole develops due to apoptosis of cells towards the top of septum primum = osteum secundum
4- To the right, septum secundum grows down from endocardial cushions to block osteum secundum
5- Still space below septum secundum and osteum secundum which gives foramen ovale (By week 7, the foramen ovale is functional)
*Fossa ovals after birth
When does inter ventricular septation happen?
How does inter ventricular septation occur?
- What part develops from endocardial cushions, what part develops from myocardial cells?
- Week 7 Day 49
1- At apex of heart we develop tissue that moves upwards creating a septum = muscular portion of inter ventricular septum
2- Space remains between B.C/PV so tissue from the septum intermedium grows downwards and fuses with muscular position of inter ventricular septum. This is known as membranous portion of I.V.S
- Membranous made from endocardial cushions
- Muscular made from myocardial cells