The Placenta Flashcards
Where does the placenta come from?
Begins 2nd week
Specialisation of the amniochorionic membrane
2 parts
1) foetal placenta = devel from outer layer of the blastocyst (forms foetus) the syncytiotrophoblast
2) maternal placenta = devel from maternal uterine tissue
When does implantation begin and what occurs?
Day 6
Zona pellucida is lost
Initial contact, blastocyst becomes embedded in endometrium
Conceptus has implanted by end of 2nd week
Briefly outline the cell stages from day 0 to implantation
0 = fertilisation in ampulla, zygote
1 = first cleavage
2 = 2 cell stage
3-4 = 4/8 cell stage
6-7 = zona pellucida lost, allows syncytiotrophoblast to make contact with endometrium
What does implantation achieve?
Establishes structure that allows for exchange
Anchors placenta
Establish maternal blood flow within placenta
How does the placental membrane change with the needs of the foetus?
Becomes progressively thinner as the needs of the foetus increases
Describe the structure of the placenta
2 umbilical arteries = deoxygenated
1 umbilcal vein = oxygenated
Chorionic villi = trophoblast extensions into the uterine wall – contain foetal capillaries
Cotyledons filled with intervillous space = contains maternal blood
Maternal arteries/veins = suppling intervillous spaces
What is a chorionic villus?
Villi that sprout from the chorion (outermost layer of embryo) to provide maximum contact area with maternal blood inside the intervillous space
Contain capillaries
How does the first trimester villus vary from the third trimester villus?
First = thick barrier, continuous cytotrophoblast
Third = optimal thinness, occasional cytotrophoblast cell
What implantation defects can occur?
Wrong place = ectopic preg, placenta praevia
Incomplete = placental insufficiency, pre-eclampsia
What controls invasion in implantation?
Transformation of endometrium in presence of conceptus = decidua
Decidua = control of trophoblast invasion
Ectopic preg = no decidua = no implantation control = adverse preg outcomes
Outline the foetal circulation of the placenta
2 umbilical arteries = deoxygenated blood from foetus to placenta
1 umbilical vein = oxygenated blood from placenta to foetus
What are the endocrine functions of the placenta?
Protein = hCG (human chorionic gonadotrophin)
Steroid = progesterone, oestrogen (takes over the role of corpus luteum = maintain preg state)
What is human chorionic gonadotrophin?
Prod during first 2 months of preg
Prod by syncytiotrophoblast = preg specific
Excreted in maternal urine = basis for preg test
How do the placental hormones influence maternal metabolism?
Progesterone = increased appetite (lay down fat store to support late preg and breast feeding)
hPL (human placental lactogen) = increase glucose availability to foetus
What are the transport functions of the placenta?
1) simple diffusion = water, electrolytes, urea, gas exchange
2) facilitated diffusion = glucose
3) active transport = AA, iron, vits
4) receptor mediated endocytosis = IgG
