3. Embryology Of The Heart Flashcards
Inner cell mass differentiates – into 2 discs
- Epiblast
* Hypoblast
Prechordal plate
where epiblast and hypoblast fuse together
• Cranial and caudal part
Gastrulation steps - 4 steps
Inner cell mass differentiates
Prechordial plate formation
Form primitive groove
Form germ layers
Formation of primitive groove
Some cells in epiblast – differentiate, proliferate, disintergrate to form the primitive groove
Formation of germ layers
- Cells near primitive groove start to migrate into the groove down into the hypoblast layers
- Migrating cells replace the hypoblast anf form the the first gem layer – endoderm
- More migrating cells from mesoderm
- More migrating cells form ectoderm
Formation of notochord
—> near primitaive groove more cells migrate down and form the tube = notochord
• Notochord is pushed into mesoderm layer
Formation of neural groove
—> near primitaive groove more cells migrate down and form the tube = notochord
• Notochord is pushed into mesoderm layer
What does the heart develop from
Mesoderm
Heart develops from
Splanchnic mesoderm
VEGF– vascular endothelial growth factor
- Released by endodermal cells
* Differentiates mesodermal cells, specifically in lateral splanchnic part of mesoderm
Splanchnic mesoderm
- structure
= 2 pericardial cavities
= 2 heart tubes
• One of each on each side
• 2 heart tubes fuse together
• 2 pericardial cavities fuse together
○ Heart tube (fused) is pushed inside pericardial cavity, endoderm lines the organs
○ Dorsal mesocardium = structure that anchors heart tube to pericardial cavity
Dorsal mesocardium
structure that anchors heart tube to pericardial cavity
Layers of heart week 3
Medial → lateral
Endocardium
Cardiac jelly
Myocardium
Dorsal mesocardium
How does heart develop - location
• Heart develops on the top of your head, then it moves down into chest cavity (when cranial caudal folding of embryo occurs)
Cranial → caudal
6 parts of heart tube
AS: Aortic Sac TA: Truncus Arteriosus BC: Bulbus Cordis PV: Primitive Ventricle PA: Primitive Atria SV: Sinus Venosus
3 structures of sinus venomous
- CCV: Common Cardinal Vein
- UV: Umbilical Vein
- VV: Vitelline Vein
How does blood pass through heart tube
Blood comes from bottom and out from top
Looping of the heart
- what happens
• Form s shaped loop
PA and SV = pushed to back
* PA at back (top) * TA, BC,PV - middle triangle (Ta middle) * SV hanging from PA (back bottom)
Looping of the heart - when it happens and duration
Looping takes 45 days
22nd - 23rd day
Formation of visceral pericardium around the recent
Special cells migrate from sinous venossus – and produces visceral pericardium around the heart
Cells that form pacemaker
- Spinous venossus cells from the spinous venossus also acts as the pacemaker
- Heart starts to beat at day 22
Location of primitive heart tube pacemaker
• The pacemaker of the primitive heart tube is located in the caudal portion
AS: Aortic Sac -forms
Ascending aorta+ (aortic arch specifically) right brachiocephalic trunk
TA: Truncus Arteriosus - forms
Pulmonary trunk+ Ascending aorta
BC: Bulbus Cordis - forms
Right ventricle + outflow tracts
PV: Primitive Ventricle - forms
Left ventricle
PA: Primitive Atria→ forms
Left atrium (have cells coming from outside the heart from lung bud) + Right atrium
Sepation of the heart
• Endocardial cushions start to form = from neural crest cells
Endocardial cushions fuse to form septum intermedium seperating heart tube into 2 corrals
2 canals formed during Sepation of the heart
○ Right atrioventricular canal
○ Left atrioventricular canal
Formation of av values - week 4
- Septum intermedium starts to produce valves that are conencted in little rings = valvular annulus
- Chordae tendinae also formed and they attach to papilalry muscles
Formation of Interatrial septum
Ridge appears between 2 primitve atria PA = ridge is called septum primum
• Osteum primum is the space/ cavity between septium primum and septum intermedium
• Septum primum moves down to attach to septum intermdium
• Second space forms = ostium secundum (channel foramen ovale)
• Septum secundum forms
Septum primum
Ridge between 2 primitive atria
Osteum primum
is the space/ cavity between septium primum and septum intermedium
Formation of Interventricular septum
Ridge forms = muscular portion of interventricular septum (not attached to septum intemedium yet)
• Membraneous portion of intraventricular septum is formed that attaches to septum intermedium
Venticular septum defecst
○ Venticular septum defecst = the memrnaeous portion of intraventricular septum is not formed
2 parts of Interventricular septum
muscular portion of interventricular septum ‘ (not attached to septum intemedium yet)
Membraneous portion of intraventricular septum is formed that attaches to septum intermedium
3 inflow tracts to right citrus
- Inferior vena cava
- Superior vena cava
- Coronary sinus
3 veins in left horn of sinus venosous
- All veins in left horn degenerate
- Sinus venosus gets absorbed into right atrium
- Remaining left horn gets absorbed into right atrium becomes coronary sinus
3 veins in right horn of sinus venomous
- Umbilical vein degernates
- Only CCV and VV remain
- CCV forms superior vena cava
- VV forms inferior vena cava
What forms coronary sinus
• Remaining left horn of sinus venous gets absorbed into right atrium becomes coronary sinus
What forms superior vena cava
CCV - common cardinal vein from right horn of sinus venous
What forms inferior vena cava
V V - vitelline vein from right horn of sinus venous
Formation of outflow tracts
TA trunkus airteriosis and BC bulbus cordis form outflow tracts
* Neural crest cells migrate and form ridges on truncal and bulbar part (top and bottom) form truncal ridges and bulbar ridges * Bulbar ridges and truncal ridges fuse, create 2 tracts that twist and rotate * Aortic pulmonary septum rotates and differentiates into pulmonary trunk and aorta
Central part of BC forms ridges that fuse to form semi lunar valves
2 outflow tracts
• Pulmonary artery
Aorta
What happens to dorsal mesocardium when outflow tracts are formed
• Dorsal mesocardium disintegrates/ degenerates
Pressure in utero
• In foetus pressure is higher in left side rather than right side
-– Lung is not functional – very constricted in foetus
– Hypoxic vasoconstriction of pulmonary arteries
Hypoxic vasoconstriction
- Partial pressure of oxygen is very very low in foetus , so pulmonary arteries and veins constrict
- Increase in pressure as the vessels constrict
Foetal circulation - where does oxygenated blood come from
Placenta = oxygenated blood from mum
Foetal circulation - flow of oxygenated blood
• Oxygenated blood from placenta carried by umbilical vein into the liver
• In liver – the ductus venosus – shunts blood from umbilical vein into inferior vena cava
• Blood passes from IVC to right atrium→ Foramen Ovale→ Left atrium
○ Due to pressure gradient as pressure in right side > left side pressure
• Blood passes from left atrium→ Left ventricle→ Aorta→ Body
ductus venosus
shunts blood from umbilical vein into inferior vena cava
Foremen ovale
Gap between right atrium, and left atrium
- ra pressure > La pressure
Effect of gravity on oxygenated blood in foetal circulation
• Some blood (10-20%) from right atria passes into right ventricle-> pulmonary trunk→ Ductus arteriosus (shant between pulmonary artery and arch of aorta)→ Aorta
Ductus arteriosus
shant between pulmonary artery and arch of aorta)
Foetal circulation: deoxygenated blood
• Deoxygenated blood carried by superior vena cava (SVC)→ Right atrium
• Blood passes from right atrium→ Right ventricle→ Pulmonary arteries→ Ductus arteriosus→ Aorta
○ Deoxygenated blood flows into right atrium and down into right ventricle as it flows down to enter to the heart
• Descending aorta→ Internal iliac artery (2 umbilical veins carrying deoxygenated blood back into placenta)→ Umbilical arteries→ Placenta
Pressure after birth
– Pressure lower in the right side of the heart compared to the left side
Fetal circulation: after birt
– Lung is functional
– No hypoxic vasoconstriction of pulmonary arteries
– Pressure lower in the right side of the heart compared to the left side
– Blood level in pulmonary arteries increase
– Pulmonary veins empty blood into left atrium
Partial pressure of oxygen in alveoli is high = no hypoxic vasoconstriction, pulmonary arteries and veins filled with blood
6 foetal shunt s.
- Umbilical vein
- Umbilical arteries
- Ductus venosus
- Ductus venosus
- Ductus arteriosus
Fate of • Umbilical vein after birth
only one vein → becomes Ligamentum Teres
○ Ligamentum teres is in the liver
Fate of • Umbilical arteries after birth
becomes medial umbilical ligament
Fate of • ductous venous after birth
(in the liver) closes→ becomes Ligamentum Venosum
Fate of • foreman vale after birth
closes→ becomes Fossa Ovalis
Fate of • ductus arteriosus after birth
closes→ becomes Ligamentum Arteriosum
Congenital heart defects - causes
• Significant majority of congenital heart defects occur due to genetic mutations that interfere with cardiac development
Trisomy 21
• Common genetic cause of congenital heart disease is trisomy 21, (down syndrome) which often manifests itself as endocardial cushion defects
Shunts
- Malformations causing shunting – diverting the blood flow (right-to-left or left-to-right) or malformations causing an obstruction
- Shunts are abnormal communications between systemic circulation (the left heart) and the pulmonary circulation (the right side)
- These shunts permit non-physiologic blood flow along pressure gradients
Right to left shunt - what is it
—-> Blood flowing abnormally from the right side of the heart to the left side
Right to left shunt - effect
- Circulation of deoxygenated blood (i.e., blood that has yet to reach the pulmonary system) to the systemic circulation – deoxygenated blood is pumped around the body
- Patients with a right to left shunts present with cyanosis
Left to right shunt - what is it
—> Blood flowing abnormally from the left side of the heart to the right side
Left to right shunt - effect
- The systemic circulation still receives oxygenated blood – oxygenated blood still leaves through aorta to go to the body
- Patients with a left to right shunts do NOT present with cyanosis
Reversal of left to right shunt
- Pulmonary system is a “low-pressure” system incapable of withstanding the increased pressure
- Pulmonary arteries typically respond to the increased blood flow and pressure via hypertrophy and vasoconstriction
- Eventually, pulmonary vascular resistance approaches systemic levels, creating a shunt reversal (now right-to-left) to distribute deoxygenated blood into the systemic system
• Atrial septal defects (ASD)
occur when there is a failure to close the communication between left and right atria = hole in atria blood passes from left to right
• Failure to close will cause mixing of blood in right and left atria
• Defect in formation of interventricular septum
• Membranous portion of interventricular septum is most commonly involved
2 examples of left to right shunt
- Atrial septal defects (ASD)
* Defect in formation of interventricular septum
• Transposition of the great arteries
○ Switching of the arteries as looping of the great vessels doesn’t occur properly they loop the wrong way round
• Aorta arises from right ventricle
• Pulmonary artery arises from left ventricle – Rotational failure
Tetralogy of Fallot = 4 problems
• Characterised by FOUR structural defects of the heart
– Ventricular septal defect
– Pulmonary valve stenosis = blood cannot pass into pulmonary arteries so blood pushed back into left side
– Right ventricular hypertrophy = thickening of right ventricle
– Aorta displacement = aorta sit on the septum defect
2 Right to left shunt – examples
• Transposition of the great arteries
Tetralogy of Fallot = 4 problems
