Fetal circulation and neonatal cardio-respiratory adaptation Flashcards
The structure of the fetal circulation
The structures:
Ductus Venosus: oxygenated blood is directed from the umbilical vein directly to the inferior vena cava
Foramen Ovale: situated between the atria through which the blood flows to bypass the pulmonary circulation
Ductus Arteriosus: between the pulmonary arteries and the aorta which prevents blood flow into the pulmonary circulation
Two hypogastric arteries: direct deoxygenated blood from the lower back through the umbilical arteries to the placenta.
Fetal circulation before birth
Oxygen diffuses from maternal blood through four layers of cells in the chorionic villi into the branches of the umbilical vein towards the inferior vena cava and into the fetal abdomen.
Ductus venosus directs most of the blood into the inferior vena cava.
Remaining blood travels along the portal vein in the liver where oxygen and nutrients are provided.
Oxygenated blood from the ductus venosus mixes with the deoxygenated blood from the hepatic artery and therefore there is a mixture of blood.
From the venae cavae the blood enters the heart through the right atrium where majority of the blood is directed into the foramen ovale (opening in the septum).
Blood then travels from the left atria into the left ventricle into the aorta- by passing pulmonary circulation and non functioning lungs and brain receives oxygen.
Some blood does go through the right ventricle into the pulmonary arteries- to prevent majority of the blood entering the lungs, the ductus arteriosus directs the blood into the aorta
Branching from each iliac artery are two hypogastric arteries that return blood to the placenta and some blood flows to the lower limbs.
Fetal blood
A few adaptations allow adequate oxygenation since the lungs are non functioning:
Red blood cells are more plentiful and larger
HBf enables oxygen to be carried at lower pressures.
HBf survives for 90 days whereas HBa survives for 120 days
Fetal circulation after birth
After birth, the newborn infant takes its first breath and the lungs expand and respiration commences due to lungs in the fluid, surfactant, inflation and ventilation breaths
This is bought by several stimuli:
Slight hypoxia due to the compression of the placental circulation during uterine contractions
Compression and decompression of the chest wall and fetal skull
Changes to the sensory input- different environment.
Alteration of the fetal circulation to that required to in extrauterine life.
Inflations of lungs → blood is pulled into the network of capillaries which surround the alveoli in the lungs → pressure is lowered in the right atrium → pulmonary blood is returned to the left atrium and pressure is raised → difference in pressure closes the foramen ovale taking 72 hours to do so.
Ductus arteriosus is bypassed and takes 72 hours to close up
Blood clots forms once placenta is removed
1:100 neonates are born with cardiac conditions
What does the Apgar score consist of
Apgar Score Heart rate Respiratory effort Muscle tone Response to stimuli Colour
Deduced at one minute after birth, then 5 minute then 10 minute.
The score given is 1,2,0 for each of the signs when added up 10 is the ideal score
A score of 8 shows the neonate is in good condition
4-7 indicates that the neonate may need some resuscitative measures
1-3 urgent resuscitation
