Lecture 14 - Fetal Physiology Flashcards
Where does maternal blood end up at the placenta?
In the intervillous spaces (between the chorionic villi) of the placenta
What blood vessel carries oxygenated blood from placenta to fetus?
What blood vessel carries deoxygenated blood away from fetus to placenta?
Ox = umbilical vein
Deoxygenated = umbilical artery
What are the 3 factors that facilitate the transport of oxygen from maternal blood to fetal blood across the placenta?
High Partial pressure gradient of oxygen between fetal and maternal blood
Fetal Hb has higher affinity for Oxygen than maternal Hb
Double Bohr effect and double haldane effect
How does HbF differ to Adult Hb?
Adult = 2a and 2b subunits
Fetal = 2a and 2gamma subunits
Why does Fetal Hb have a higher affinity for oxygen than adult Hb?
The gamma subunits make it say 2,3-diphosphoglycerate cant bind as easily compared to HbA
What is the double Bohr effect and how does it aid gas exchange?
When the Bohr effect is acting on both the maternal and fetal side of the placenta
Fetus gives up CO2 at placenta making maternal bloo more acidic asking the HbA have a decreased affinity for O2
This makes fetal blood more alkaline so HbF has a higher affinity for O2
How does the Double Haldane effect assist with the gas exchange and fetal uptake of oxygen at the placenta?
As the material HbA gives up O2 it has an increased affinty for CO2 so fetus gives up more CO2 (decreased HbF affinty for CO2) this helps with Bohr effect by making the maternal blood more acidic
What are the 2 main organs that blood is shunted to avoid in the fetus to maintain as high oxygen saturations as possible?
Lungs
Liver
What are the 3 main fetal shunts?
Ductus venosus
Foramen ovale
Ductus Arteriosus
What 2 blood vessels does the Ductus venosus connect?
What organ is shunted?
Umbilical vein and the inferior vena cava so oxygenated blood can be taken to the right atrium
What does the Foramen ovale connect?
What is the purpose of it?
Shuts oxygenated blood from the right atrium to the left atrium so blood can be pumped through aorta to brain
Allows lungs to be bypassed since blood already oxygenated and lungs not functional
What is the function of the ductus arteriosus?
Shunts blood from the pulmonary artery into the aorta to ensure any blood that made it into the pulmonary trunk can be shunted from the lungs
What is the fetal response to hypoxia?
Decreased Heart rate (bradycardia) to decrease O2 demand
Detected by chemoreceptors (low pO2 or high pCO2)
What negative effects occur as a result of chronic Hypoxaemia to the fetus?
Growth restriction
Reduced fetal movement
What are the 2 main functions of amniotic fluid?
Protects fetus
Contributes to lung development
What is the danger with babies being delivered late?
Amniotic fluid depletes so it means the baby has less protection in-utero
When does fetal urine start being produced?
Week 9
What organ produces the most amniotic fluid?
Fetal urinary tract (kidneys)
How is amniotic fluid recycled to prevent polyhydramnios?
Fetal GI tract
Fetus swallows the amniotic fluid and the debris accumulates in its gut
How can preeclampsia lead to Oligohydramnios?
Poor fetal-placental circulation may lead to poor fetal renal perfusion
Reduces kidney function (GFR)
Means reduced urine production so reduced amniotic fluid
How can oesophageal atresia lead to polyhydramnios?
Cant swallow the fluid so it builds up since its not recycled
What is Oligohydramnios?
What is polyhydramnios?
Oligohydramnios = too little amniotic fluid
Polyhydramnios = too much amniotic fluid
What is contained in amniotic fluid?
Essentially fetal urine:
98% water
Fetal cells
Hormones
Electrolytes
Bile
Creatinine
Urea
What is meconium?
The first shit a baby takes after birth which contains all the debris from fetal development
Is passing meconium before birth normall?
No its often a sign of stress
Can tell if they have by the green bile staining seen in amniotic fluid
What is amniocentesis?
When amniotic fluid is sampled
The fetal cells in the amniotic fluid can be used for fetal karyotypinngg/diagnostic testing
What is a risk of amniocentesis?
Risk of miscarriage (1%)
What are some Intra partum monitoring techniques?
Intermittent heart auscultation
Cardiotocograph (CTG) (only really used when theres concern)
What type of ultrasounds are done early in the pregancy?
Transvaginal ultrasound
Before fetal urine starts being produced, how is amniotic fluid produced?
Fetal sweating
Amnion cells
How will a mother smoking affect oxygen flow to fetus?
Decreased
Mother breathing in more CO2 and CO decreasing Hb affinity for O2
What 4 signs can suggest Fetal distress?
Meconium before birth
Bradycardia
No movements
No accelerations (no tachycardia with contractions/Fetal movements)
What are normal accelerations?
When the baby moves it should be accompanied by tachycardia/increased heart rate
