Fetal Circulation Flashcards
Describe postnatal circulation
- separate pulmonary and systemic circulations
- no mixing of oxygenated and deoxygenated blood
- oxygenation of blood occurs in the lungs
- extensive hepatic blood supply
What limitations and special needs does a developing foetus have?
- Lungs are not functioning as in adults
- digestive system is not functioning as in adults
- Foetus has restricted hepatic circulation
What are the 3 shunts/by-passes in foetal circulation to avoid the lungs and liver
- By-pass of hepatic cirulation
- By pass of the pulmonary circulation vua the foramen ovale
- By-pass of the pulmonary circulation by ductus arteriosus
What travels across the placenta?
O2 and nutrients diffuse across the placental barrier from mother to foetus while CO2 and metabolic waste are removed via the placenta
What is the placenta?
Interface between the foetus and mother
Do maternal and foetal blood ever mix?
NO
Where is the placenta located?
at the fundus of the uterus
What surrounds the umbilical cord?
- Fetal membrane
- amnion
- contains Wharton’s Jelly
What is embedded in Wharton’s jelly?
two umbilical arteries and a single umbilica vein
What is another name given to the umbilical vein?
Ductus Venous
What travels in the umblicial vein?
Oxygen- and nutrient-rich blood from the placenta
What 2 branches does the umbilical vein divide into? And where do the branches go?
- Smaller branch, which goes to the liver
- Larger branch, ductus venosus by-passes the liver and drains into the inferior vena cava
What occurs when the umbilical vein/ductus venosus merges with the IVC
arterial blood mixes with venous blood from the lower limbs
The amount of venous blood = insignficant
Where does most of the blood coming through the IVC passes through
Passes from the RA into the LA through foramen ovale then onto the LV and aorta
What is foramen ovale?
The shunt that connects the right atrium to the left atrium.
It means some oxygenated blood travels into the RA
How does the valve of the IVC influence blood flow?
Causes blood to travel through FO with the correct trajectory
Where does blood carried by the superior vena cava (de-oxygenated) travel to?
- RA
- RV
- Pulmonary Trunk
- Ductus Arteriosus (90%)
- Aorta
What is the ductus arteriosus?
connection between the pulmonary trunk and aorta; 90% of the blood = shunted
Where is one thrid of the blood carried in the descending aorta distributed to?
abdomen, pelvis and lower limbs
Where does two thirds of the blood in the descending aorta travel to?
go to the placenta
Iliac artery ⇒ umbilical artery ⇒ placenta
Draw a diagram of fetal circulation
What occurs at birth that is vital to post natal circulation?
Shunts must be obliterated at birth when the pulmonary circulation comes on stream
What occurs when the umbilical cord is tied and cut?
- Loss of blood flow through the placenta
- Increased systemic vascular resistance
- Increased aorta, LV and LA pressures
What occurs when a child takes their first breath?
- Expansion of the lungs (alveoli)
- Decreased pulmonary vascular resistance
- Reduced pulmonary arterial, RV and RA pressures
What occurs when pulmonary circulation is established?
- blood from the lungs is returned to the LA
- Pressure rises in the LA
- Valve of the foramen ovale is pushed rightward and closes the foramen
- This is the functional closure
When does structural closure of the FO occur? And what does this form
4 months
Forms fossa ovalis and falx septi
What is patent foramen ovale (PFO) and what can it cause?
- Consequence of non-closure
- usually asymptomatic
- May cause paradoxical emboli
When does the functional closure of ductus arteriosus occur? And how does it occur?
first hour
constriction of smooth mucle on all of ductus arteriosus. O2 stimulates the bradykinin which causes vessels to constrict. There is also a fall in prostaglandins which are usually repsonsible for vasodilation
When does the structural obliteration of ductus arteriosus occur? And how?
Within 1 and 4 months
Anatomical closure by thickening of the tunica intima
What does the obliterated ductus arteriosus become?
Ligamentus arterosium
Patent Ductus Arteriosus
- Postnatally the aortic pressure i greater than in the pulmonary trunk
- Blood will flow back into the pulmonary circulation
- left to right shunt
- Increased pulmonary blood flow ⇒ pulmonary hypertension
- Congetsive heart failure
What occurs in the obliteration of the umbical vein?
forms the round ligament of the liver (ligament teres hepatis)
What do the distal parts of the umblical arteries become?
Medical umbilical ligaments
What occurs in obliteration of ductus venosus when blood flow through the umbilical vein ceases?
- Muscle wall of ductus venosus contracts
- Portal venous blood flows through hepatic sinuses
- Closes within 1 to 3 hours of birth
- becomes ligamentum venosum
