Embryology of circulatory system Flashcards
What are the functions of the placenta?
- fetal homeostasis
- gas exchange
- acid base balance
- nutrient transport to foetus
- waste product transport from foetus
- hormone production
- transport of IgG
- PGE2 (maintain ductus patency)
How does life in foetus differ from adults?
- placenta is included in circulation
- lungs are filled with fluid and are unexpanded
- liver has little role in nutrition and waste management
- the gut is not in use
How dies foetal circulation work?
blood comes from placenta to the heart. A little bit goes to the lung but most of it supplies the body and brain then goes back to placenta
What is contained within the umbilical cord?
-2 arteries and 1 vein
What differs about the blood in foetuses?
In foetal circulation veins have oxygenated blood and arteries have deoxygenated blood
What are the three shunts specific to foetal life?
- ductus venosus
- formamen ovale
- ductus arteriosus
What is the anatomy of the ductus venosus?
It connects the umbilical vein to the inferior vena cava
What is the anatomy of the foramen ovale?
Opening in atrial septum connecting RA to LA. Allows blood to flow from right side of circulation to the left
What is the anatomy of the ductus arteriosus?
Connects pulmonary bifurcation to the descending aorta. Specific to foetal development
What is th role of the ductus venosus?
-carries most o the placental blood straight to the IVC bypassing th portal circulation
What is the role of the formamen ovale?
- allows blood to pass from RA to LA through the pass of least resistance.
- Allows the best oxygenated blood to enter left atrium and then on to LV, ascending aorta and carotids
What is the pressure gradient in foetal circulation?
- pressure in right side is greater than on left side
- It is the opposite in adults where the increased pressure causes the flap to close
What is the function of the ductus arteriosus?
-A duct through which most of the RV output joins into the descending aorta
How is patency of ductus arteriosus maintained?
Circulating prostaglandin E2 produced by the placenta
What happens to the O2 stats from birth until a few hours later?
- low O2 at birth (~65%)
- increases rapidly in first couple minutes (transition from blue to pink)
- increases gradually then after until reaches normal sats values
What are the circulatory changes that occur?
- pulmonary vascular resistance drops as soon as the baby starts to breath
- systemic vascular resistance increases once cord is clamped and cut as the low resistance flow is cut off
Describe the mechanism of duct constriction
- duct will start to constrict
- unlike lung circulation where oxygen is a vasodilator, in duct the rising oxygen concentration is a vasoconstrictor causing it to shut
- the source of prostaglandin gets removed
- few days after birth the duct is still a vessel that can be reopened if needed
What occurs when the duct fails to close?
You get excessive blood circulating to lungs which can cause a few different things including the restriction of blood to other areas of the body
What can be used to close the duct?
- wait and see
- surgery (high risk)
- ibuprofen or other non steroidal anti inflammatory.
Why do non steroidal anti inflammatory drugs work to close the duct?
They inhibit prostaglandin production
What is a duct dependent circulation?
A circulatory defect that depends on the duct being open to keep the baby alive
What is an example of a duct dependant circulation?
Interruption of aortic arch
- The aortic arch terminates prematurely therefore cannot supply the body with blood. Therefore the body is supplied by the ductus.
- need to maintain duct patency until definitive surgery can be carried out
When is persistant pulmonary hypertension most common?
In sick babies ie those with sepsis, cold stress etc
What occurs in persistant pulmonary hypertension of the newborn?
- resistance to flow in lung circulation doesn’t drop
- therefore pressure in the right side is still higher than the left
- therefore blood flows across the atrium via duct
- this causes mixing of blood
What are the signs of PPHN?
- blue baby
- large difference between pre and post ductal O2 sats
How can you treat PPHN?
- ventilation
- oxygenation
- high systemic blood pressure
- inhaled nitric oxide
- ECLS (life support)
