Placenta Flashcards
Function of placenta
Respiration Nutrition Excretion Hormone production Immunological protection of fetus Passage of maternal IgG antibodies
How does the placenta develop?
Placenta develops when the blastocyst implants into the decider and forms from trophoblastic cells
Some of these cells are invasive penerating endometrial blood vessels forming sinuses (lacunae)
Ttophoblastic cells become primitive villi then secondary and tertiary villi with a core of fetal blood vessels
Villi formation starts at 6 weeks
Placenta continues to grow in circumference and thickness until 16 weeks, hence the need to start aspirin in those at risk by 16 weeks to prevent pre-eclampsia.
What are placental villi? How many? How are they grouped?
Functional units of the placenta
Each placenta has 60 villi
these are grouped into cotyledons containing 3-4 villi.
On the maternal surface is the syncytiotrophoblast which is in direct contact with the maternal blood
Then, cytotrophoblast, basement membrane, mesenchymal stroma, basement membrane of fetal blood vessels
Describe the layers of the placenta
On the maternal surface is the syncytiotrophoblast which is in direct contact with the maternal blood
Then, cytotrophoblast, basement membrane, mesenchymal stroma, basement membrane of fetal blood vessels
Describe the fetal surface of the placenta
Smooth and shiny covered by the amnion and the umbilical cord attached at the centre
Look for the branching of the umbilical vessels to and from the placenta
What are the circulations in the placenta
Uteroplacental:
Maternal blood travelling through intervillous spaces
Spiral arteries of uterus become dilated, low-pressure, high flow vessels to maximise blood flow
Fetoplacental circulation:
2 umbilical arteries which carry deoxygenated blood from the fetus to the placenta
These arteries subdivide into many branches entering the stem of the chorionic villus then into arterioles and capillaries
Blood is then oxygenated and picks up nutrients flowing into its relevant venous drainage system, eventually becoming the singular umbilical vein
Maternal and fetal circulations never mix, they form a countercurrent
What are functions of the placenta?
Ogan of gaseous exchange
Endocrine (hCG, growth factors, oestrogen, progesterone)
Barrier to infection and drugs
Transfer of nutrients
What changes occur in the placenta?
Calcium is depostive in the villi and fibrin on them
Excess fibrin may be dpeosited in diabetes and rhesus disease leading to reduced fetal nutrition
What should you do with placenta after delivery?
Examine for abnormalities:
Clots, infarcts, vasa praevia, single umbilical artery
Bloods taken from cord for pH, Hb, Coombs; test, LFTs and blood group or for infection screen
What is the journey of nutrients from mother to fetus
Maternal blood space Syncytiotrophoblast Trophoblast basement membrane Capillary basement membrane Capillary endothelium Fetal blood
What happens in pre-eclampsia?
Trophoblast invasion is too shallow and there is no progress beyond superficial portions of uterine spiral arterioles
Spiralarterioles retain their endothelial linings and remain narrow-bore, high resistance vessels resulting in poor maternal blood flow - mothers may raise her BP to compensate
