pregnancy Flashcards
what are the weeks for the trimesters of pregnancy and what are the changes through these *
term 1 - 0-13wks
13-26wks
26-39wks
maternal changes occur throughout
baby is embryo at start, by end of 1st trimester is fetus and viable by 26wks w/o intensive care unit, at term at 39wks
placenta changes are complex and mainly occur in 1st half
the trimesters are made by experience not science - if get past 1st trimester it is likely that the pregnancy will continue
what are the maternal physical and anatomical changes in pregnancy *
at end of trimester 1 - cant necessarily tell from appearance that pregnant
in 2nd and 3rd trimester the baby grows fast
angle of back changes = ache and pain
Increased weight [3rd]
Increased blood volume [2nd & later] - more material is needing to be fed from maternal blood
Increased blood clotting tendency [2nd & later]
Decreased blood pressure [2nd]
Altered brain function [1st & later] - because exposed to high levels of steroids, varies between people
Altered hormones [1st & later]
Altered appetite (quantity and quality) [1st & later] – GI imbalance - bump so less space for stomach so smaller meals and eat more often
Altered fluid balance [2nd & later] - kidney goes into overdrive, drink more - linked to the increased blood vol
Altered emotional state [1st & later] - can be elated or depressed
Altered joints [3rd] - more flexible (eg pelvis has to chamnge shape to let the fetus out)
Altered immune system [1st & later] - change to allow pregnancy to continue and remain resistant to disease
morning sickness - doesnt just occur in the morning
the extent of the changes occur at differnt times in the 9months - so need to knwo the way that timings in pregnancy are organised
describe the maternal hormonal changes in pregnancy *
much higher hormone levels than experienced in menstruation
HCG is released from placenta - peak in trimester 1 (starts to rise before the end of the menstrual cycle, a week after implantation) stops bleeding and acts on the corpus luteum to keep progesterone and oestrogen production
HCG falls after first trimester but is still present
maybe HCG is related to morning sickness because that is also mainly in 1st trimester - maybe wome affected have a higher sensitivity to HCG
oestrogen, progesterone and placental lactogen increase towards the end of pregnancy - they mirror the increased size of the placenta
low progesterone levels = loss of fetus at any stage in pregnancy
the high levels of steroids suppress the HPG = low LH and FSH = no cyclic uterine/ovarian functions
when is the main risk to the mother’s health *
delivery - remodelling of teh spiral arteries mean the vessels can lose large volumes of blood in birth - limited by contraction of the uterus after placenta has been delivered
must check no placenta missing - inflexible so any left in uterus will prevent contraction = blood flow into uterine lumen
define conceptus *
everything resulting from the fertilised egg - baby, placenta, fetal membranes, umbilical cord, amniotic fluid and chorion
define embryo *
the baby before it is clearly human
define fetus *
the baby for the rest of pregnancy - when it is clearly human and still in uterus
define infant *
less precise - normally applied after delivery
describe a blastocyst *
at 9days
contains a disk in the middle
developed from the egg
has 2 layers of cells in it
where does embryo and fetus make RBC
liver - no limbs with bones
(fetus will have limbs and embryo might have buds but cant make RBC)
what is the difference in time frame of pregnancy and embryology *
pregnancy is the 1st day of last period - done because the mother can identify this easily
embryology times are from time of fertilisation
implication is that when premature babies are delivered 2wks makes a difference to their chance of survival - if very young resus is not done because it would give them a severe handicap/they wouldnt live
at term the 2 weeks doest make much difference because term is 37-41 wks
how can we look at pregnancy *
observe it with MRI or US
measurements can be made of circulating factors in the mother’s blood, or dimensions
ethics of research into this makes it difficult to know how the measurements fit into development of the baby
what is the benefit of embryos from different species looking similar
can look at what is likely to be happening in humans
eg eye development in fish - expect genes of same family to be present in humans
therefore some careful conclusions can be drawn - cant overestimate
how does gestation time vary between species
usually smaller animals = smaller gestation time
not always the case
describe how teratogens interfere with development *
the more rapidly developing tissue is more suseptible to damage
teratogen = any factor that damages development
CNS is vulnerable throughout pregnancy
heart, limbs, palate and ear are more suseptible in trimester 1
external genitalia are vulnerable from late 1st throughout
most of the major congenital abnormalities happen in 1st trimester, with functional abnormalities and minor congenital anomolies happening later
how does maldevelopment help our understanding
helps us identify when things are most vulnerable and which bits are
describe the placenta *
it is a disk 20cm across
the foetal membrane is the thin tissue around the outside, it encloses the amniotic fluid which surrounds the baby and keeps the baby safe
umbilical cord carries waste from the baby to the mother’s circulation and nutrients to the baby
describe the maternal side of the placenta *
contact point between fetus and mother - in direct contact with the maternal blood
subdivided into 30-60 cotyledons - they vary in size and are a subdivision of the placenta - the gaps between them are made by the maternal tissue behind the uterus
each cotyledon contains at least 1 villus
the cotyledons are bigger in the middle and smaller at the edge
the size and number doesnt affect how well the placenta does
describe the basic placental structure *
maternal arterioles contain oxygenated blood - supply blood to the foetus
maternal blood leaves through the venule
the maternal and fetal blood dont come in contact
the deoxygenated fetal blood comes from the umbilical artery (comes from heart) and enters a villus - a highly branched structure to increase the SA (11m sq)
arterial and venous vessels are connected to smaller capillaries ion the terminal parts of the villus
nutrients and oxygen are exchanged with the mother’s blood and the oxygenated fetal blood leaves through the umbilical vein
the highly branched villus tree also anchors the placenta securely for the pregnancy
there is intimate contact between fetal and maternal tissues - making interesting immunology
what are the functions of the villus/placenta *
separation of maternal and fetal blood
exchange between the vascula systems
biosynthesis - makes HCG, oestrogen, progesterone and placental lactogen
immunoregulation - contain Ag on surface that indicate that the tissue is human but not which human - hardlyany HLA variation on the placenta. Know that placenta is important for immune reg because in ectopic pregnancy with placenta, baby is still protected from mother’s immune system
connection - placenta connected to maternal decidua otherwise fetus is lost
describe placental development *
at day 9 PF teh coinceptus is implanted into the maternal decidualising endometrium
the outer layer of conceptus are multinucleated syncytiotrophoblast whcih contains fluid called lacunae
the underlying layer of cytotrophoblast is proliferating next to embryo - this is where the placenta develops
following implantation the cytotrophoblast proliferates into the syncytium - 1st a columnar structure is formed (cytotrophoblast column) whihc then undergoes branching (villus sprouts)
at centre of each villus are mesenchymal (extra-embryonic mesoderm) cells from which the villus vascular system develops
inbetween the villus stems are the intervillus spaces that develop from the syncytial lacuna
branching continues
at term there are fewer cytotrophoblast so there can be closser connection between the syncitium and capillaries - maximise nutrient transfer and enhance fetal growth in later pregnancy
placenta is 5cm across at this stage - in 2nd and 3rd trimester grows to 20cm - because of increased branching
describe how the contact of the placenta changes during pregnancy *
at earliest stages of pregnancy conceptus is in contact with endometrium
in early embryo development, the cytotrophoblast shell limits the blood and oxygen going to the embryo by 4wks - so that there isnt a high level of flow - this is because the rapidly dividing cells in trimester 1 are especially suseptible to oxygen free radicals - so less oxygen at this stage is safer
teh decidual glands hypertrophy during 1st trimester - provide nutrients for the placenta and devloping baby - placenta is the soutrce of the nutrients (histotrophic nutrition) rather than maternal blood
the cytotrhopblast shell remains in place until about 8weeks post fertilisation - spiral arteries are blocked
the maternal blood is supplied to the placenta through the spiral arteries - at 8wks they are remodelled by cytotrophoblasts that infiltrate them and remove their sm and underlying epithelium from periphery 1st then centre (cyrotrophblasts replace the epi and sm) - begins during 1st trimester and continues to 16-18wk
now maternal blood supplies nutrients (haemotrophic nutrition)
baby grows dramatically in the second and third trimester - a lot of blood is needed from the mother
the remodelling of the spiral arteries widens the blood vessels (because they cant contract becausse the sm has gone) so large volumes of blood and nutrients can go to the fetus = increase in rate of growth
