Embryology Flashcards
Where does the heart originate?
It is a mesodermal structure that comes from the visceral mesoderm
What makes a midline tube structure in the development of the heart?
As the embryo folds the 2 sides of the horseshoe shape come together
What type of folding moves the heart down to the thoracic cavity?
Cranial caudal folding
How many dilatations does the heart tube develop?
5
Where does blood flow from and to in the embryological heart?
From the sinus venous at the caudal end to the truncus arteriosus at the cranial end
What does the truncus arteriosus form in the adult heart?
Aorta and pulmonary trunk
What does the bulbus cordus form in the adult heart?
Trabeculated (muscular ridges) part of the right ventricle and the outflow part of both ventricles
What does the embryological ventricle form in the adult heart?
Trabeculated part of the left ventricle
What does the embryological atrium form in the adult heart?
Trabeculated part of both atria
What do the sinus venosus form in the adult heart?
Smooth part of the right atrium and the coronary sinus
5 dilatations that the heart tube develops
Truncus arteriosus, bulbus cordus, ventricle, atrium, sinus venosus
On which day does the heart begin to loop and fold?
Day 23
As the heart loops and folds, what happens to the:
- Atrium
- Ventricle
- Bulbus cordis
- Atrium moves dorsally and cranially, which impacts the ventricle
- Ventricle is displaced left, which impacts the bulbus cordis
- Bulbus cordis is moved inferiorly and ventrally to the right
How many pairs of vessels are there in the development of the vasculature?
6
Development of the vessels:
- What do vessels 1 and 2 contribute to?
The neck
Development of the vessels:
- What do vessels 3 give rise to?
The common carotid arteries, first part of internal carotid artery
Development of the vessels:
- What does the right and left part of vessel 4 give rise to?
Right gives rise to subclavian artery, left contributes to part of the aortic arch
Development of the vessels:
- Vessel 5
Rudimental or absent
Development of the vessels:
- What does the right and left vessels from pair 6 give rise to?
Right = sprout branches that form pulmonary arteries Left = forms the ductus arteriosus
3 things each horn of the sinus venosus receives
Common cardinal vein (anterior and posterior), vitelline vein, oxygenated blood comes from the placenta via umbilical vein
What does most of the venous drainage in the unformed embryological heart
Common cardinal veins
What happens to the following as development of the heart progresses:
- Umbilical veins
- Vitelline veins
- Communication between left and right umbilical veins is lost
- The right vitelline vein gets a lot larger than the left
What do vitelline veins do?
Drain the yolk sac
What do cardinal veins do?
Give systemic venous system - drain blood
What do the umbilical veins do?
Brings oxygenated blood from the placenta
What do the vitelline veins develop into in the adult heart?
Portal venous system draining gut, hepatic sinusoids and veins, hepatic portions of IVC
What do the anterior cardinal veins drain?
Head and neck
What do the anterior cardinal veins develop into in the adult heart?
Jugular system, left brachiocephalic vein, SVC
What do the posterior cardinal veins drain?
Trunk
What do posterior cardinal veins develop into in the adult heart?
Azygous and hemiazygous systems (body wall), gonadal and renal veins, iliac veins, IVC
Placental functions
- Foetal homeostasis
- Gas exchange
- Acid base balance
- Nutrient transport to the foetus
- Waste product transport from the foetus
- Hormone production
- Transport of IgG – provide immunity to infectious disease after birth
- PGE2 (prostaglandin E2) – important in maintaining foetal circulation
Where does the placenta sit?
End of the umbilical cord. Cross section of the umbilical cord with 2 arteries and 1 vein
What does the foetal heart pump blood to the placenta via?
Umbilical arteries
What does the blood from the placenta return to the foetus via?
Umbilical veins
3 “shunts” specific to foetal life
Ductus venosus, foramen ovale, ductus arteriosus
What does the ductus venosus connect?
Connects the umbilical vein to the IVC
What is the foramen ovale?
An opening in the atrial septum connecting the right atrium to the left atrium
Function of the foramen ovale
Allows oxygenated blood to go into the left atrium, then left ventricle then out the aorta
What does the ductus arteriosus connect?
Connects pulmonary bifurcation to the descending aorta
Function of the ductus venosus
Carries the majority of the placental blood straight to the IVC bypassing portal circulation
What maintains patency of the ductus arteriosus?
Circulating prostaglandin E2 produced by the placenta
Adaption of the pulmonary system just after birth
Baby inflates lungs and cries and goes from blue to pink, the cord stops pulsating and is clamped shut, the fluid within the lungs gets pushed out of the alveoli when the baby cries and it is reabsorbed by the lymphatic system and the alveoli are able to be filled with air
Circulatory changes after birth
Decreased pulmonary vascular resistance, increased systemic vascular resistance, more cardiac output to lungs
What causes decreased pulmonary resistance after birth
The breath in causes the lungs to physically expand, and there is increased circulating oxygen. In lung circulation the oxygen is a vasodilator and this causes decrease in pulmonary resistance
How does the foramen ovale close after birth?
Pulmonary vascular resistance falls, systemic vascular resistance rises and this causes the left atrial pressure to exceed the right atrial pressure and the flap is pushed closed
What causes ductus arteriosus constriction after birth?
Increased pO2, decreased flow and decreased prostaglandin
What does the ductus arteriosus end up as?
Fibrous ligament - ligamentum arteriosum
Treatment options for failure of ductus arteriosus closure
Wait and see (often close by themselves), NSAIDs, surgery
What can be used to keep the ductus arteriosus open when there is ‘duct dependent circulation’
IV prostaglandin E2 until an alternative shunt is established or definitive surgery is carried out
When does pulmonary resistance reach ‘normal’ adult-type levels?
By 2-3 months
What causes persistent pulmonary hypertension of the newborn
Lung vascular resistance fails to fall as shunts remain (foramen ovale and ductus arteriosus)
Risk factors for persistent pulmonary hypertension of the newborn
Sepsis, hypoxic ischaemic insult, meconium aspiration syndrome, cold stress
Oxygen saturation in baby’s hand vs baby’s foot in persistent pulmonary hypertension of the newborn
Both low:
- Baby’s hand = 80%
- Baby’s foot = 60%
Signs and symptoms of persistent pulmonary hypertension of the new born
Blue baby with low oxygen saturations
Management of persistent pulmonary hypertension of the newborn:
- Reduce pulmonary vascular resistance
- Increase systemic vascular resistance
- Reduce PVR = oxygen, ventilation, sedation, thermoregulation, correction of acidosis, treatment of sepsis, inhaled NO
- Increase SVR = maintain blood pressure, inotropes, support of other organ function, extra corporeal life support in severe cases
