W9.0 - fetal physiology Flashcards
Which fetal vessel carries oxygenated blood from the mother?
-Umbilical vein
Which fetal vessel(s) carries deoxygenated blood from the mother?
-Umbilical arteries
Regarding the placenta, where are the fetal capillaries?
-Within the chorionic villi
What happens to the placental barrier as pregnancy progresses?
-Gets thinner until it comprises only fetal capillary endothelium and syncytiotrophoblast
Why is a gradient of partial pressure required at the placental barrier?
-Allow O2 to pass into fetal blood and CO2 to pass into maternal blood
What 3 factors establish the pO2 gradient between mother and fetus?
- Increased production of 2,3-BPG in the mother
- Fetal haemoglobin variant
- Double bohr effect?
How does an increase in 2,3-bpg in the mother help create the pO2 gradient?
-Promotes the T state and thus more O2 is given up into the blood, thus more is available to cross the diffusion barrier
How does fetal Hb help create the pO2 gradient?
-Fetal Hb has 2 a and 2 g chains. g chains have a lower affnity for 2,3-bpg and this promotes the R state of Hb, thus there is a higher affinity of fetal Hb for O2
What is the double bohr effect and how does it help create the pO2 gradient?
- A process which helps to speed up O2 transfer
- As CO2 passes into intervillous blood, there is a decrease in pH causing promotion of the T state and thus more O2 is given up
- As CO2 leaves fetal blood, there is an increase in pH causing promotion of the R state which has a higher affinity for oxygen
What 2 factors promote CO2 transfer between fetus and mother?
- Progeterone-driven hyperventilation causing more acid to be blown off producing a physiological respiratory alkalosis -> This generate a concentration gradient between mother and fetus
- Double haldane effect -> As maternal Hb gives up O2 it can accept more CO2 and as fetal hb accepts more O2 it gives up more CO2
How does oxygenated blood from the umbilical vein bypass the lungs?
- Enters right atrium and streams across into left atrium through foramen ovale
- If pumped into right vetricle-> leave pulmonary trunk through ductus arteriosus into aorta
What is ductus venosus? Why is it important?
- Bypass of liver between umbilical vein to IVC
- Allows oxygenated blood to enter the right atrium and go to the brain without being desaturated by the liver
Why is it significant that ductus arteriosus joins after the supply to the head and the heart?
-Blood from DA is highly deoxygenated as it mixed into the RV with the blood returning via the SVC -> therefore by joining after supply to the head/heart it makes sure that they recieve oxygenated blood.
Describe the fetal response to hypoxia
- HbF and Hb conc increases
- Redistribution of flow to protect vital organs cuah as head and heart (GIT, renal and limbs reduced)
- Slowing of fetal HR due to vagal stimulation via chemoreceptors detecting drop in O2 or rise in CO2
What is the result of chronic hypoxaemia on the fetus?
- Growth restriction
- Behavioural changes
Name the hormones important for fetal growth and state when they are most dominant
-Insulin
-IGFI -> dominant in T2 and T3
-IGFII -> dominant in T1
-Leptin
(EGF and TGF-a)
Which hormone required for fetal growth is nutrient dependent? What does this mean?
- IGF 1
- The ability for growth is dependent upon the utrient status of the mother
When does symmetrical growth restriction occur and why?
- Malnutrition upto 28 weeks
- Growth is affected in a symmerrical way as hyperplasia is the most significant growth mechanism
When does asymmetrical growth restriction occur and why?
-28+ weeks as the dominant growth mechanism is hypertrophy
What are the 2 main functions of amniotic fluid?
- Protection
- Development of lungs
State the approximate volumes of amniotic fluid at 8 weeks and 38 weeks?
- 10 ml at 8 weeks
- 1L at 38 weeks
What happens to the amniotic fluid post EDD?
-Falls away due to placental senescence
What is the main system in the production of amniotic fluid? Why?
- Urinary system
- Urine makes up the majority of amniotic fluid
What systems/tissues are involved in the recycling of the amniotic fluid and how?
- Recycled by the baby through breathing into the lungs and swallowing into the GI tract -> returned to the amniotic sac by the urinary system
- Placental and fetal membranes also recycle the amniotic fluid by the intramembranous pathway
Describe the composition of amniotic fluid
- 98% water
- Urea, electrolytes, creatinine, bile pigments, renin, glucose
What is lanugo?
-Fine hair which covers the fetus duing development
what is vernix caseosa?
-White liquid which covers the baby to prevent the skin drying out on contact with air
What is meconium?
- Debris from amniotic fluid and intestinal secretions which accumulates in the gut -> first baby faeces
- Can pass on delivery id baby is under stress eg hypoxia
What is amniocentesis?
- Sampling of amniotic fluid allowing collection of fetal cells
- Used for diagnostic testing eg fetal karyotyping
What happens to the bilirubin metabolism in utero?
-Bilirubin is handled suffieicntly by the placenta as the liver is immature and lacks enzymes for conjugation and excretion
Why is physiological jaundice common in pre-term baby?
-Physiological processes to deal with bilirubin occur late in development and thus the liver is too imature to handle bilirubin
