Fetal Circulation Flashcards
High blood flow to lung is NOT required during gestation
True or false?
True
Blood is diverted from the fetal lung by the
Ductus arteriosus
Dilation of the lung blood vessels is inhibited by
suppressing Nitric Oxide (NO) production in the vessels.
Characteristics of fetal lung
- Increase resistance from low oxygen tension
- Low pulmonary blood flow
- Contracted blood vessels
How much oxygen is in the placental blood?
80%
Blood doesn’t go in the fetal lung cause?
Lungs are not working and are just growing and developing
How does oxygen enter the fetus?
- Enters through the umbilical vein, travels through the liver via Ductus venosus
- Moves into right atria from the inferior vena cava and moves into the left atria through the Foramen Ovale (FO)
- High pressure to low pressure
How does deoxygenated blood exit the fetus?
- Deoxygenated blood comes in to the right atria via the superior vena cava.
- Blood diverted from the lungs into the descending aorta by the Ductus Arteriosus
- Blood returns to the placenta via the Umbilical Arteries
Blood returning to the placenta via the Umbilical Arteries is ?
58% oxygenated
Fetal system has points where blood is mixed or diverted:
Liver
Inferior vena cava (IVC)
Right atrium (RA)
Left Atrium (LA)
Ductus arteriosus
What happens at the Liver in the fetal system?
blood from the portal system mixes with umbilical blood
What happens in the IVC in the fetal system?
Returning blood from the legs, pelvis and kidneys
What happens in the RA in the fetal system?
deoxygenated blood from head and upper limb, mixes with oxygenated blood from placenta
What happens in the LA in the fetal system ?
deoxygenated blood enters from the lungs
What happens at the Ductus arteriosus in the fetal system?
diverts blood away from lungs to the descending aorta
What happens during labours at the Ductus venosus?
Contractions close off the ductus venosus via a sphincter.
Why is the Ductus venosus closed during labour?
Protection of fetus
What happens during the first breath?
- Increase of surface area for gas exchange as lungs inflate
- Decrease of Pulmonary vascular resistance as bradykinin dilates blood vessels
- Increase lung blood flow.
What stimulates the contraction of umbilical arteries?
Oxygenated blood and temperature change
Placental blood flow stops at?
3-5 minutes
Maintaining placental blood flow does what?
Maintaining blood flow for this period ( 3-5 minutes) increases juvenile jaundice but increases iron levels and prevents iron level drop at 4-6 months.
Posta al changes
- Umbilical vein closes and becomes Ligamentum Teres
- Foramen Ovale closes and fuses
- Ductus Arteriosus closes becomes smaller
- Umbilical arteries close and become Medial Umbilical Ligaments
What is the purpose of postnatal changes ?
This stops mixing of blood and separates the pulmonary and systemic circuits
Function of Foramen ovale before birth
LA BP is lower so blood travels from R To L
Effects of Ductus arteriosus closure in Foramen ovalis
- Increases lung circulation and increases the pressure in the LA
- Increased pressure pushes the septum primum against the secundum, closing the Foramen ovalis
- Septum primum and secundum (from opposing ends of the atria) close and fuse over a period of a few days.
Steps of Ductus arteriosus closure
- Breath
- Lung expansion
- Pulmonary vessel expansion
- Decreased P in pulmonary vessel
- Blood flow to lung
- Bradykinin release
- Muscular contraction
- DA closure
Bradykinin release causes?
Muscular contraction which closes DA
Foramen Ovale- closure is reversible for first few days, until the tissue fuses
True or false
True
Closure of Foramen Ovale is reversible for first few days,
Why?
Crying and dehydration- cyanotic (blue tinge to skin) periods
Crying INCREASES pulmonary vascular resistance, decreases blood supply to the lungs
Symptoms of Persistent cyanosis
fingers, lips, general pallor
Symptoms of Patent DA
minimal symptoms at birth.
•Distinctive heart murmur may be detected.
•Low weight gain and breathing difficulties (apnoea)
Patent DA may actually help in some cases ie transposition of great vessels
