CVS development Flashcards
When does the formation and looping of the primitive heart tube take place?
Week 4 after fertilisation
What event forms the primitive heart tube?
Lateral folding of the embryo
What event moves the primitive heart tube and diaphragm into the thoracic region?
Cephalo-caudal folding of the embryo
Name the 5 regions of the primitive heart tube:
1) Aortic roots
2) Truncus arteriosus
3) Bulbus cordis
4) Ventricle
5) Atrium + Sinus venosus
What causes the primitive heart tube to loop?
- Continued elongation of the tube, but within constricting pericardial sac
Where is the primitive heart tube tethered?
At cranial and caudal ends
What happens to the cephalic portion of the primitive heart tube during looping?
Moves ventrally, caudally, and to the right
What happens to the caudal portion of the primitive heart tube during looping?
Moves dorsally, cranially and to the left
Name the parts of the primitive heart tube which gives rise to the right atrium:
- Most of the primitive atrium
- Sinus venosus
What structures form the left atrium?
- Small portion of primitive atrium (forms left auricle)
- Proximal parts of pulmonary veins
The recurrent laryngeal nerves are branches of which cranial nerve?
Cranial nerve X (Vagus nerve)
Which recurrent laryngeal nerve becomes looped around the ductus arteriosus?
Left recurrent laryngeal nerve
What is the first process in septation of the heart?
The junction between the atrium and ventricle becomes constricted, creating a narrow atrioventricular canal
Name the cushions which form in the atrioventricular canal, and divide the heart into left and right canals:
Endocardial cushions
Describe inter-atrial septation:
- Septum primum grows down towards endocardial cushions
- Ostium secondum forms in the septum primum
- Septum secondum grows down in a crescent shape (hole = foramen ovale)
Is the foramen ovale in the septum primum or secundum?
Septum secundum
Why is the foramen ovale shunt so important to foetal life?
- Allows blood to flow from right atrium to left atrium
- Allows blood to bypass the lungs
- Protects underdeveloped lungs
Describe inter-ventricular septation:
- Muscular portion grows upwards towards endocardial cushions, leaving a small primary interventricular foramen
- Membranous portion derived from the endocardial cushions fill the gap
What is the most common defect of inter-ventricular septation?
Undeveloped/faulty membranous portion
What are the 2 different parts to the inter-ventricular septum?
1) Superior membraneous portion
2) Inferior muscular portion
Describe outflow-tract septation:
- Endocardial cushions appear in the truncus arteriosus
- Grow towards each other in staggered growth, forming a spiral aortico-pulmonary septum
- Divides truncus arteriosus into the aorta and pulmonary trunk
Name the vessel supplying the foetus with oxygenated blood from the placenta:
Umbilical vein
What 2 structures form the shunt allowing blood to bypass the lungs in foetal circulation?
1) Foramen ovale
2) Ductus arteriosus
What structure allows blood to bypass the liver in foetal circulation?
Ductus venosus
Why is it important for the foetal circulation to bypass the liver?
To allow enough oxygenated blood to the developing brain, as the liver is a highly vascular organ.
What causes the foramen ovale to close after birth?
Respiration begins, so left atrial pressure rises above that in the right atria, pushing the septum primum and secondum together.
Foramen’s are not aligned, so are blocked when septa pushed together.
What causes the ductus arteriosus to close after birth?
Placenta synthesises prostaglandins, which keep it open. Once placenta removed, levels of circulating PGs drops, causing it to close.
(Also lungs are activated after birth, which metabolise PGs.)
Name the 4 foetal shunts:
1) Foramen ovale
2) Ductus arteriosus
3) Ductus venosus
4) Umbilical vein
What are the names of the foetal shunts after birth?
- Foramen ovale
- Ductus arteriosus
- Ductus venosus
- Umbilical vein
- Fossa ovalis
- Ligamentum arteriosum
- Ligamentum venosum
- Ligamentum tere hepatis
What is the most common congenital heart disease?
Patent foramen ovale
In a patient with a ventricular septal defect, which direction will blood flow in between the ventricles? Why?
From left ventricle to right ventricle, due to pressure gradient
Name the 4 types of ventricular septal defects:
1) Membraneous VSD
2) Muscular VSD
3) Inlet VSD
4) Outlet VSD
What is the most common type of Ventricular Septal Defect?
Membraneous VSD
When do ventricular septal defects usually present?
Infancy
unless very small
Name the 3 types of atrial septal defects:
1) Ostium primum ASD
2) Ostium secundum ASD
3) Sinus venosus ASD
What is the most common type of atrial septal defects?
Ostium secundum ASD
What are the possible complications of an untreated ventricular septal defect?
- Heart failure
- Growth failure
- Arrhythmias
- Pulmonary hypertension
What are the possible complications of an untreated atrial septal defect?
- Arrhythmias
- Stroke (via embolism)
- Pulmonary hypertension
- Eventual RH failure
When do atrial septal defects usually present?
Late adulthood
Why does an ASD or VSD lead to pulmonary hypertension and right heart failure?
- Blood flows from left heart to right heart
- Increased blood flow to lungs
- Damages blood vessels, they become fibrotic
- Right heart must work harder to pump blood around pulmonary system
How can an ASD or VSD cause arrhythmia’s?
- Blood flows from left heart to right heart
- Increased pressure stretches right heart, disrupting electrical activity
How can a VSD cause growth failure?
- Blood flows from left heart to right heart
- Less blood in systemic circulation
- Less nutrients to tissues for growth/repair
Describe Eisenmenger syndrome:
L->R shunt (ASD/VSD) results in pressure in pulmonary system exceeding that of the systemic circulation
= reverses, becoming R->L cyanotic shunt
List some known causes of congenital heart defects:
- Alcohol
- Medication (Lithium, Thalidomide, Valproate)
- Rubella
- Diabetes
- Smoking
- Down’s syndrome
What type of congenital heart defect is common in people with Down’s syndrome?
Atrial Septal Defect
List the 5 cyanotic congential heart defects:
1) Tetralogy of Fallot
2) Transposition of great vessels
3) Hypoplastic left heart
4) Pulmonary atresia
5) Tricuspid atresia
What is the usual presentation of someone with a Tetralogy of Fallot?
Usually infancy or early childhood
Cyanotic spells
What is a Tetralogy of Fallot?
- Pulmonary stenosis
- Right ventricular hypertrophy
- Ventricular septal defect
- Over-riding aorta
Is a patent ductus arteriosus a cyanotic or acyanotic shunt? Why?
Acyanotic
Blood flows from Aorta to Pulmonary artery ue to pressure gradient
What is ‘coarctation’ of the aorta? What are the 3 types?
Narrowing of the aorta
1) Pre-ductal
2) Ductal
3) Post-ductal
