8.1 Reproductive system (embryology) 2 Flashcards
where are the villi found in early embryonic development?
ALL along chorion (chorionic membrane)
where are villi found in week 12?
final disc shape achieved
chorion looses villi on one side (opposite decidua basalis side) - smooth chorion (chorion laeve)
what happens to the chorion and amnion at week 22?
amnion and chorion become a composite membrane
(fuse to form decidua parietalis, decidua basalis still present)
forms: amniochorionic membrane = decidua parietalis
what is the desidual basalis?
The area of ENDOMETRIUM between the implanted chorionic vesicle (amniochorionic membrane) and the myometrium, which becomes the MATERNAL part of the placenta
what is the degree to which membranes are shared in monozygotic twins?
varies:
- 2 amnions and 2 chorions (one of each)
- 2 amnions (inner), but 1 chorion (outer)
- 1 amnion and chorion (both shared)
what is the amnion continuous with?
umbilical cord
how do monozygotic twins with 2 amnions and 2 chorions come about?
originally 1 zygote, but during travel along fallopian tube to implantation, the zygote divided into 2 and 2 implantations result
how do monozygotic twins with 2 amnions but chorion come about?
1 morula, but the embryoblast (inner cell mass) forms 2 separate bilaminar disks
how do monozygotic twins with 1 amnion and chorion come about? (both shared)
1 blastocyst cavity and 1 bilaminar disk
BUT 2 primitive streaks (therefore 2 grooves, 2 notochords etc.)
what is the gross morphology of the placenta? (foetal aspect)
shiny outer - covered by amniotic membrane (enclosing foetus and amniotic fluid)
AM over umbilical cord as well
(extremely vascular organ)
what is the gross morphology of the placenta? (maternal aspect)
amniochorion membrane surrounding outer
within are cotyledons
what are cotyledons?
separations of the decidua basalis of the placenta (implantation side, maternal endometrium), separated by placental septa
(a unit on maternal side separated villus projections from foetal side, villus separated by placental septa on maternal side, which marks the beginning and end of each cotyledon)
what does each cotyledon consist of?
a main stem of a chorionic villus as well as its branches and subbranches etc.
describe a 1st trimester placenta
placenta established in first trimester
placental ‘barrier’ still relatively thick
cytotrophoblast layer under syncytiotrophoblast
what is term placenta?
SA of placenta for exchange INCREASES dramatically
placental ‘barrier’ now THIN
ONLY syncytiotrophoblast layer, cytotrophoblast lost
what happens as the placental ‘barrier’ becomes thinner throughout pregnancy?
the diffusion distnce from maternal blood to foetal blood via foetal endothelium and syncytiotrophoblast decreases
(with lost of cytotrophoblast)
what do umbilical vein and artery carry?
umbilical vein: oxygenated blood to foetus from placenta
umbilical artery: deoxygenated blood form foetus to placenta
where is the maternal blood delivered from?
endometrial spiral arteries and veins
branch to form spiral arteries
what does the cytotrophoblast shell contain?
the maternal blood bathing the foetal chorionic villus from spiral arteries, but the maternal blood doesn’t flow freely past the cytotrophoblastic shell
what happens to the main stem villus form foetus?
it branches continuous towards maternal direction
the end point (tip) is the anchoring villus, attached to the cytotrophoblastic shell on maternal side
how many umbilical arteries and veins do foetus’ have?
2 umbilical arteries: deoxy blood (foetus –> placenta)
1 umbilical vein: oxy blood (placenta –> foetus)
what does the placenta synthesise? (metab)
glycogen
cholesterol
fatty acid
why is cholesterol synthesised by the placenta?
cholesterol is a pre-cursor for oestrogen and progesterone
both are hormones for supporting pregnancy
what are the 2 classes of hormones produced by the placenta? (endocrine)
protein
steroid
what are the steroid hormones produced by the placenta?
progesterone
oestrogen
what are the protein hormones produced by the placenta?
human chorionic gonadotrophin (hCG)
human chorionic somatomammotrophin (hCS)
human chorionic thyrotrophin (hCT)
human chorionic corticotrophin (hCC)
when is hCG produced?
during first 2 months of pregnancy
what is the function of hCG?
supports the secretory function of corpus luteum
acts like LH, so CL produce oestrogen and progesterone to support pregnancy - until placenta take over
what is hCG produced by specifically?
syncytiotrophoblast layer
therefore is pregnancy SPECIFIC
(aside from pathological e.g. testicular tumour)
where is hCG excreted?
in urine
used as basis for pregnancy testing
what are trophoblast diseases?
molar pregnancy
choriocarcinoma - malignant cancer of uterus (womb)
what do trophoblast diseases lead to?
massive overgrowth of placenta tissue, there mass over production of hCG (indication of abnormal pregnancy)
what is molar pregnancy?
non-viable fertilised egg implants in the uterus and will fail to come to term
what are placental steroid hormones responsible for?
(progesterone + oestrogen)
responsible: maintaining pregnant state
when does placenta production of steroid hormones take over form CL?
by the 11th week
which placental hormones influence maternal metabolism?
progesterone
hCS / hPL
how does progesterone influence maternal metabolism?
increases appetite - increase fat store for 2nd half of pregnancy, as baby can only use glucose (BBB), so fat store used by mum to reserve glucose for foetus
how does hCS / hPL influence maternal metabolism?
increases glucose availability to foetus
what are the different types of transports used in pregnancy?
simple diffusion (gas exchange)
facilitated diffusion
active transport
pino-endocytosis
how does simple diffusion work and which molecules utilise this mode of transport?
molecules moving down a concentration gradient - water - electrolytes - urea + uric acid - gases (molecules small enough with no charge)
which molecule uses facilitated diffusion?
glucose
(GI: GLUT 1 from intestine, GLUT 2 into blood,
GLUT 5 then GLUT 2 for fructose)
what limits gas exchange in uteroplacental circulation?
simple diffusion, so FLOW limited, NOT diffusion limited
high flow, low resistance
why is it necessary to maintain an adequate uteroplacental circulation flow?
foetal O2 stores are small
rely heavily on HIGH flow gas exchange (via simple diffusion)
which molecules undergo active transport?
amino acids
iron
vitamins
how does active transport occur across maternal to foetus?
specific ‘transporters’ expressed by the SYNcytiotrophoblast
describe the foetal immune system
immature
how does the foetus gets its immunity?
passive immunity
receptor-mediated process, maturing as pregnancy progresses
which immunoglobulins crosses the placenta ‘barrier’ to be received by the foetus?
IgG only
what type of process is passive immunity in foetus? why?
ACTIVE process
as the IgG concentrations in foetal plasma EXCEEDS those in maternal circulation
