Fetal Circulation Flashcards
Placenta features:
- discoid in shape
- approximately 20cm diameter
- has a maternal and fetal surface
Features of maternal surface of placenta:
- dark red
- made up of 40 cotyledons
- cotyledons made up of lobules, each containing a single villus
-cotyledons separated by sulci
Features of fetal surface:
- shiny due to amnion covering it
- umbilical veins and arteries are visible, branching from the centre where umbilical cord is
Purpose of placenta:
-exchange of substance between maternal and fetal circulatory system without mixing
-establishes a diffusion gradient
- placenta releases hormones
Features of umbilical cord:
-about 50cm long
- has 2 arteries and 1 vein
-wrapped in soft connective tissue and surrounded by whartons jelly
How does o2 diffuse to the fetus?
- o2 diffuses through the wall of the villi and binds to fetal haemoglobin
- fetal haemoglobin has a higher o2 affinity
Metabolism and the placenta:
- placenta can metabolise proteins, fats and carbs into simple molecules
- fats can cross the placenta easily
- placenta stores glycogen
Excretion of waste and the placenta:
- waste products of metabolism (co2) diffuse from fetus to mother
Placenta and protection:
- protection against most bacteria
- smaller microorganisms can pass (HIV, syphilis)
- placenta transfers igG antibodies and rhesus antibodies to fetus
What produces hCG and what is its function:
- trophoblast produces hCG
- maintains corpus luteum
What produces progesterone?
-corpus luteum
- provides a nourishing environment
What is the purpose of there being high concentrations of oestrogen and progesterone?
To maintain the pregnancy
How does the pregnant body become insulin resistant?
-human placental lactogen hormone produced
- regulates metabolism and frees up glucose
How is the fetus protected from immune rejection?
The trophoblast has unique immunological properties
Placenta and stem cells:
- placenta tissue and whartons jelly and cord blood has potential stem cells
Features of fetal circulation:
- fetal lungs are filled with fluid and play no role in gaseous exchange as this happens at the placenta
- fetal blood is circulated around organs that require it as gastrointestinal and kidneys do not function until after birth
Three shunts and their function:
- directs o2 blood to essential areas
- ductus venousus
- foramen ovals
- ductus arteriosus
What is the ductus venosus and what is its function?
- continuation of umbilical vein
- shunts portion of umbilical vein blood flow to the inferior vena cava
- allows o2 blood from placenta to bypass liver
What is foramen ovale?
-opening in the septum that separates two atria
-covered by tissue acting as a valve
-blood flows from right to left atria
-bypasses lungs
What is the ductus arteriosus and what does it do?
-connects pulmonary artery to descending thoracic arch
- diverts blood so very little passes through the lungs
Path of fetal blood:
- umbilical vein has o2 blood
-vein carries o2 blood through D.V and joins the I.V.C
-to the R.A and through the F.O to the L.A
-to the L.V and then the aorta to the brain and body - umbilical artery brings blood back to the placenta for oxygen
Why is it important that fetus’ chest is squeezed on descent though the vagina?
Fluid is squeezed out of the lungs so breathing can begin with inflation
Stimuli that initiate breathing:
1) thermal- being cold
2) tactile- physical stimulation
3) chemical- cortisol and ADH increase
What happens when the lungs inflate for the first time?
- increase in thoracic pressure
- remaining fluid in lungs is absorbed into bloodstream
What happens to the cord after birth?
Whartons jelly constricts as temperature falls
How does the foreman ovale close?
Pressure in left atria becomes higher than the right
