Session 3 Flashcards
What is the cardiogenic field? * (* = notes)
Tissue in the paraxial mesoderm that differentiates to form blood vessels and blood
What are the blood islands? *
Cells that give rise to vascular endothelia and blood cells.
How does lateral folding affect the development of the heart?
Creates a heart tube
How does cephalocaudal folding affect development of the heart?
Brings the heart tube into the thoracic region
How is the primitive heart tube formed? *
Blood islands move towards each other and fuse together to create the primitive heart tube
What are the features of a primitive heart tube?
- Inflow at bottom
- Outflow at top
- No valves and no chambers
What is the pericardial cavity?*
Where the primitive heart tube is suspended
What are the segments of the primitive heart tube?*
(top to bottom)
- Aortic roots
- Truncus arteriosus (outflow)
- Bulbus cordis
- Primitive ventricle
- Primitive atrium
- Sinus venosus (inflow)
Why does the primitive heart tube loop?
It runs out of room for expansion
What is looping?*
- Tube elongates
- Twists and folds up
- Places inflow and outflow in correct orientation (atrium pushed up posterior)
How does the sinus venosus develop?*
- At start both sides of the body are symmetrical
- REMODELLING OCCURS
- Venous return shifts to right sinus horn so left sinus horn recedes
- Right sinus horn absorbed by enlarging RA
(will form vena cava?)
How does the right atrium develop?*
- From primitive atrium and sinus venosus
- From receiving venous drainage from venae cava and coronary sinus
- Absorbs right sinus horn
How does the left atrium develop?
- Small bit of primitive atrium
- Absorbs proximal parts of pulmonary veins
- Receives oxygenated blood from lungs
What is the process of forming the left atrium?*
- Part of atrium forms from absorbed primordial pulmonary vein tissue
- Expands
What is the oblique pericardial sinus?*
- A structure that forms as left atrium expands and absorbs pulmonary veins
- Separates left atrium from aorta and oesophagus
What is present in the foetal circulation that is NOT in mature circulation?
- Lungs do not function
- Oxygenation of blood and CO2 removal occur at placenta
What is needed to allow foetal circulation to occur?*
Shunts that must close when the baby takes its first breath.
What are features of mature circulation that are absent in foetal circulation?
- Reoxygenation and CO2 removal at the lungs
- Reoxygenated blood returned to heart
- Reoxygenated blood pumped around body.
Where does blood from placental circulation enter the heart in the fetus?
- Right atrium
- Wrong side so must move around (via foramen ovale)
Why is there a shunt to bypass the liver in the foetus?
Liver is highly metabolically active and can use up the oxygen so must be bypassed.
Why is there a shunt to bypass the lungs in the foetus?
The lungs are underdeveloped and would be unable to cope with the volume and pressure of blood.
What is the ductus venosus?
The shunt that exists to bypass the liver and deliver blood from placenta to inferior vena cava
What is the ductus arteriosus?
The shunt that bypasses the lungs and connects the pulmonary trunk to the aorta
What is the foramen ovale?
The shunt that connects right and left atria to allow the movement of blood in the right direction.
What happens to the shunts after birth?
Shut when respiration begins due to increases in pressure. At first must be maintained but over time seal naturally.
How are the major arteries leaving the heart created?*
Bilaterally similar (1, 2, 3, 4, 6, with 5 missing in humans) system of arched vessels - Will undergo rapid, extensive remodelling.
What are the derivatives of the 4th aortic arch?
- Left: arch of aorta
- Right: proximal part of right subclavian artery
What are the derivatives of the 6th aortic arch?
- Left: left pulmonary artery and ductus arteriosus
- Right: right pulmonary artery
Where is the left recurrent laryngeal nerve?*
- Becomes ‘hooked’ around the shunt between the pulmonary trunk and aorta (ductus arteriosus) (6th arch)
- Descends down further than the right recurring laryngeal nerve
What is the function of the ductus arteriosus?
- Allows communication between aorta and pulmonary artery
What happens if the ductus arteriosus fails to close physiologically?
- Blood will shunt from left to right (from aorta to pulmonary trunk)
- Will shunt from high pressure to low pressure
What happens after the looping of the heart tube?
- Atrium and ventricle are linked by ATRIOVENTRICULAR CANAL
- Still remains as a single contractile tube and beats 3 weeks after conception
What are the types of septation and how do they happen?
All types of septation happen SIMULTANEOUSLY.
- Interatrial septum - forms 2 atria
- Interventricular septum - forms 2 ventricles
- Separation of ventricular outflow tract give aorta and pulmonary trunk
What is the function of interatrial septation?
- Build new tissue
- Build the ability to allow right and left shunt that can resolve immediately after birth
What does interatrial septation consist of?*
- Septum primum grows towards fused endocardial cushions
- Ostium primum is a hole that is present before septum primum fuses with the endocardial cushions
- Ostium secundum appears before ostium primum disappears
- Septum secundum grows (crescent-shaped septum) an
- Hole = foramen ovale
What do the endocardial cushions do?
- Grow towards each other to develop the heart into the left and right chambers
- Are dependent on getting to the right place at the right time
Describe interatrial septation again. *
- Septum primum grows towards the endocardial cushions
- Ostium primum is a hole in the septum that allows flow of blood from right to left.
- Ostium primum grows over and ostium secundum is formed in the septum primium
- Septum secundum forms, and a hole lower down in the septum secundum forms that is called the foramen ovale
How is the foramen ovale created?
A higher pressure in the right side of the heart pushes the two septa apart and allows shunting of blood.
What are the atrial components derived from primitive atrium?
- Auricles
Increase atrial capacity and the volume of blood that they are able to contain
What does the right atrium absorb?
Sinus venosus
What does the left atrium sprout and what happens to the pulmonary veins?
- Sprouts pulmonary vein
- Absorbs it and the 4 branches
Why is the left atrium smooth?
Developed from the primitive vein.
What is the remnant of the foramen ovale in adults, and what does it look like?
Fossa ovalis.
- Small, thin barrier between two atria formed from
Why is the right atrium not smooth?
Developed from the primitive artery and atrium (pectinate muscles)
What does the ductus arteriosus become after closing in adults?
Ligamentum arteriosum.
Why does the foramen ovale close after birth?*
- Pressure in the left atrium rises above pressure in right atrium
- Septum primum pushes against septum secundum
- Interatrial septum leaves pushed together and fuse over time
What types of atrial septal defects can occur?*
- Septum primum resorbed and too short
- Absence of septum secundum
- Septum secundum too small
- Absence of both septa primum and secundum
What is hypoplastic left heart syndrome?*
The left side of the heart is not fully developed, leading to a very small atrium and ventricle
What are the suspected causes of hypoplastic left heart syndrome?
- Defect in mitral/aortic valve development
- Artresia (prevented flow), limited flow - Ostium secundum is too small
- Inadequate right to left flow in utero
USE IT OR LOSE IT
What is ventricular septation?
Development of the right and left ventricles.
What are the 2 components of the ventricular septum?
- Muscular (main)
- Membranous (secondary)
What is the function of the muscular portion of the septum?
- Grows upwards towards the fused endocardial cushions
- Forms most of septum
- Leaves a gap to be filled by the membranous septum
What is the small gap left by the muscular portion called?*
Primary interventricular foramen.
How does the primary interventricular foramen close?*
- Membranous portion derived from endocardial cushions, so grows downwards towards muscular
- Prevents communication between right and left ventricles
What is the most common cause of ventricular-septal defects?
Membranous part does not develop properly
How is the outflow tract (pulmonary trunk/aorta) septated?*
- Endocardial cushions in truncus arteriousus
- Grow towards each other in a staggered, twisted arrangement
- Form a spiral septum that allows LV to connect to aorta and RV to connect to pulmonary trunk by essentially ‘twisting’ them
What are types of congenital birth defects?
- Structural abnormalities
- Complete absence of a structure
What can be the causes of congenital birth defects?
- Genetic
- Exposure to teratogenic agents (eg. warfarin), drugs, chemicals
- Unexplained causes
When do congenital heart defects occur?
- When there are structural defects of either the chambers or the vasculature
- When there is an obstruction
- When the shunts do not close and communication between pulmonary and systemic circulations remains intact after birth
Why do the heart defects occur in newborns but are okay in the foetus?
The foetus has different circulatory needs (all from placental circulation and no functioning lungs as they do not need to breathe in utero) - less complex than mature
How common are congenital heart defects?
1% of world population
What are the implications of 135,000 people in the UK living with congenital heart defects?
Implications when women with congenital heart defects.
- Highest cause of maternal death
- Drugs are highly teratogenic
What is transposition of the great arteries?*
- No spiral septum
- RV connects to the aorta
- LV connects to the pulmonary trunk
- Relates to the development of pulmonary and aortic valves
What happens when transposition of the great arteries occur?
Cyanosis (not enough oxygen)
What is the tetralogy of Fallot?*
A composition of 4 defects.
- Overriding aorta across both ventricles
- Large ventricular septal defect
- Right ventricular outflow tract obstruction (trunk stenosis)
- Right venticular hypertrophy (due to higher resistance)
- Conotruncal septum (that divides outflow tract) formed defectively
