Pregnancy and delivery Flashcards
what happens with oocyte once released from ovary for fertilisation
= ovulation
fimbriae guide to fallopian tubes where meets sperm
sperm able to get to fallopian tubes because oestradiol has thinned cervical mucus
describe days 1 to 4 post fertilisation (include fertilisation)
oocyte fertilised by sperm into zygote
first divisions= cleavage divisions, embryo increases in cell number but not in size
cleavage divisions are asynchronous
cleavage divisions= 2 to 8 cells
describe the blastocyst stage post-fertilisation
blastocyst forms days 4-5 blastocyst when 32-64 cells first stage cell differentiation has 2 regions blastocyst hatches day 6-7 to allow implantation
the 2 regions of the blastocyst
inner cell mass: these cells become the embryo. pluripotent stem cells.
trophoblast: ring of cells around inner cell mass
form extraembryonic component of placenta
forms extraembryonic tissues
describe implantation of embryo
-embryo secretes proteases for deep invasion of uterine stroma
-embryo implants interstitially in endometrium
on anterior or posterior wall of uterus body
- synciotrophoblast sends out projections which erode maternal tissues
- blastocyst binds with endometrium then buries itself under
-overgrowth of endometrial surface over embryo so securely held
outline 1st trimester of pregnancy
1st trimester= 0-13 weeks,
rapid growth of placenta,
organogenesis week 3-10
riskiest period
outline 2nd trimester pregnancy
14-26 week
overall growth
outline 3rd trimester pregnancy
27-40 week
rapid fetal growth of 250 grams/week
placental growth slows but efficiency increased
what are: yolk sac amnion chorion allantois
yolk sac: 1st site blood cell formation
amnion: surrounds embryo, makes amniotic fluid cavity
chorion: becomes principle part of placenta
allantois: bacomes vascular connection between embryo and placenta
label the embryo, yolk sac, amnion, chorion, allantois
b
what happens next with the inner cell mass
bilaminar embryonic disc, whereby the inner cell mass forms two layers, the epiblast and hypoblast
epiblast
lies above the hypoblast and gives rise to the 3 germ layers, amnion, allantois, part of the yolk sac
appears day 8
what does the ectoderm go on to form
skin, CNS, PNS, brain
what does the mesoderm go on to form
kidneys, repro organs, bones, muscles, vascular system
what does the endoderm go on to form
intestines, liver, lungs
what are the cephalic and caudal ends of the embryo
cephalic= head caudal= tail
when does gastrulation happen and why is it so important
day 14-16 post fertilisation
organs must be correct size and orientation w correct differentiated cell types
gastrulatioon allows cell movement to orientate and locate organs correctly
what is gastrulation
establishment of the 3 germ layers
induces shape changes in embryo
what is the 1st visible sign of gastrulation
an invagination occurs in caudal half of epiblast, formin primitive streak
cells migrate through primitive streak
this forms the mesoderm and changes embryo shape
first system to start developing after gastrulation?
nervous system, at 3 weeks post fertilisation
neural plate in cephalic region will be brain
neural tube along dorsal region will be spine
outline neural tube closure
neural tube starts as neural plate folds to form neural groove folds further to form nerual fold rolls into neural tube spinal region closes first, cephalic and caudal neuropores still open, then they close
why is it so important neural tube closes
if cephalic neuropore left open= exencephaly
if spine of tube left open= spina bifida
neural crest formation
once spinal tube closes
neural crest cells form at boundary with ectoderm in dorsal region
neural crest cells migrate out of dorsal neural tube
become incorporated in a vairety of tissues
somite development
blocks of mesoderm tissue in pairs along neural tube
develop in succession, anterior to posterior
44 pairs total
produce muscle and ribs
sensory organ development
sensory organs develop from placodes- visible ectodermal thickening on surface
otic placodes visible from week 4, disappear week 5 forming inner ear
optic placodes also visible week 4, form the lenses
limb development
limbs develop from limb buds, external structures visible from week 4
forelimb develops first (for both arms)
then hindlimb develops (for both legs)
patterning is important to specify
hands, feet, finger development
limb buds undergrow outgrowth,
hands and feet vivible week 7
condensation of cartilage show precursors of digits, then apoptosis between digits seperates
heart development
visible on ventral surface heartbeat begins day 22 circulation begins 28 days first organ to function required for embryonic and foetal growth
lung development
through branching morphogenesis
endoderm and mesoderm alveoli
mesoderm for musculoskeletal, ectoderm for neural
kidney development
kidneys develop in close association with genitals in the urogenital ridge
develop through branching morphogenesis
in stages:
pronephros, mesonephros, metanephros
what is branching morphogenesis
generates epithelial trees
large subvessels become divided into smaller vessels
GI system development
GI system develops in different cavities
foregut: oral cavity, oesophagus, trachea, stomach
midgut: small intestine, pancreas
hindgut: colon
what is special about midgut development
intestines develop through herniation
undergoes series of rotations to package smaller into adult morphology
ventral abdominal wall will close around the midgut
what are the 3 types of causes of birth defects
genetic- inherited or de novo mutations
environmental- exposure to teratogens
infectious- maternal disease
how common are birth defects in england
1 in 47 live and still births
how does timing to exposure of teratogen in embryo/foetus influence outcome
organs developing in window of time exposure occurs will be most affected
so depends on when as to which organ system and how early on
the later it occurs, the better the outcome
what do the trophoblast cells produce
trophoblast cells produce hCG (human chorionic gonadotrophin hormone) around day 8
hCG ensures corpus luteum continues to make oestrogen and progesterone to maintain pregnancy and prevents other follicles developing
what would hapen in hCG didn’t rise
corpus luteum would shrivel day 10 and oestrogen and progesterone would fall, endometrium would slough off as period taking embryo with
why is the corpus luteum so important in first trimester
corpus luteum produces oestrogen and progesterone
progesterone maintains pregnancy, if don’t have triggers labour/miscarriage
what happens with hCG and corpus luteum week 9
at 9 weeks hCG levels peak then drop off, corpus luteum shrivels
placenta takes over hormone production, done by syncytiotrophoblasts
mother and fetal circulation are?
completely seperate. placenta is the barrier.
what is the placenta formed of
chorionic villi, which are projections from fetal tissue, consist of 2 layers-
syncytiotrophoblast- the outer layer
cytotrophoblast- the inner layer
uterine capillaries break down so chorionic villi are bathing in mothers blood
what happens as the chorionic villi mature
cytotrohoblasts reduces to produce single layer of syncytiotrophoblast so there is closer contact of maternal and fetal blood and v high SA
what do the syncytiotrophoblasts do
in direct contact with maternal blood in intervillous space
hormone production of oestrogen/progesterone/hPL
how do O2/CO2/nutrients get from placenta to foetus
umbilical veins bring O2 and nutrients to foetus
umbilical arteries carry deoxygenated blood/CO2 away from foetus to placenta
CO2/O2 diffuse in/out of veins/arteries through the bathing of chorionic villi in intervillous space
what are the functions of the placenta
exchange of gases
metabolic transfer
endocrine function
immunological transfer
exchange of gases in placenta
occurs via passive diffusion in chorionic villi
Bohr and Haldene effects faciliate O2 release and CO2 removal
foetal haemoglobin has greater affinity for O2 than adult so further enhanced
metabolic transfer in placenta
glucose transferred from maternal blood via facilitated diffusion
fatty acids, amino acids, water, Na, K, Ca, Fe vitamins
metabolic transfer in placenta
glucose transferred from maternal blood via facilitated diffusion
fatty acids, amino acids, water, Na, K, Ca, Fe vitamins
endocrine function of placenta
produces hCG to maintain corpus luteum in 1st trimester so that it will make oestrogen and progesterone
produces oestrogen and progesterone and hPL from week 9
produces human growth hormone
hPL
human placental lactogen-
encourages insulin resistance in mother, thereby increases her blood glucose levels and accumulation of fat, ensures glucose availability for foetus
human growth hormone in pregnancy
stimulates gluconeogenesis so energy for foetus
immunological transfer in placenta
IgG antibodies transfer and give passive immunity
rest of immunoglobulins too large
placental transfer most be considered when prescribing
discuss changes in fundal height of uterus in pregnancy
uterus grows into abdomen.
20 weeks at umbilicus
36 weeks at xiphoid process
fundal height is distance from syphysis pubis to fundus of uterus
how can fundal height be used to estimate gestational age
plus/minus a couple cm, fundal height in cm= week
ie 36cm= 36 week
what does the mothers cardiovascular system do in pregnancy
must expand to accommodate growing foetus and prepare for loss of blood at delivery
high volume state
physiological anaemia of pregnancy
heart rate rises by 20bpm
bp falls
explain why pregnancy is a high volume state
circulating blood volume increases by 30-50%, ie 5L to 7.5L in 3rd trimester
what is physiological anaemia of pregnancy
RBC increases a bit but plasma volume increases a lot, so haemocrit (% of RBCs) goes down
why does bp fall in pregnancy
progesterone causes vessels to dilate
why may we see varicose veins in pregnancy
uterus presses against pelvic veins, leads to varicose veins and swelling in lower legs/ankles
what does increased cardiac output mean for the kidneys in pregnant mother
more fluid passing through kidneys=
increased glomerular filtration rate and urinary output, uterus also puts pressure on bladder=
greater urinary frequency
how do kidneys compensate for additional workload in pregnancy
increase size, calcyes and renal pelvis dilate, leads to physiological hydronephrosis
increased size ureters leads to physiological hydroureter, progesterone causes hypomobility of ureters
- leads to incr capacity store urine and hypomobility of ureters leads to urinary stasis= increased risk upper UTI
why and how do the lungs compensate for growing uterus
uterus pushes up on diaghragm so harder to breathe comfy
so progesterone relaxes ligaments in thorax= increases transvaers diameter of rib cage= increases tidal volume
what effect does oestrogen have on respiratory system
causes increased vascularisation and capillary engorgement in upper respiratory tract
may cause stuffy nose, congestion, nosebleeds
how does pregnancy affect gait of woman
progesterone and relaxin loosen ligaments around sacroiliac joints and symphysis pubis to prep for fetal passage
causes waddling gat, maybe pain in other joints
changes to breats in pregnancy
oestrogen and progesterone promote breast development and milk producing machinery
incr blood flow to breasts and budding of breast tissue
oestrogen stimulates production of prolactin, but high progesterone inhibits until after birth
how do pregnancy tests work
hCG is secreted from day 8 post fertilisation so should only be present in pregnant urine
- urine sample deposited on reaction zone
- if hCG present it binds to complementary antibodes that are associated with an enzyme that activates dye molecules in reaction zone
- moves up through capillary action to test zone, hCG- antibody complex will bind with immobilised antibodies associated with dye molecule
- dye-activating antibody enzyme will bind with them to release colour, indicating pregnancy
- at control zone are other antibodies that will bind with first antibodies regardless of hCG presence
clinical dating in pregnancy
pregnancy dated from first day of last menstrual period (LMP)
expected date of delivery (EDD) is 40 weeks from LMP
when should labour start and what is labour
starts spontaneously between 37 and 42 weeks gestation, 40 weeks avg
labour= regular uerine contractions causing cervical dilation
what are the 3 stages of labour
stage 1: cervical dilation from 0-10cm
stage 2: descent and delivery of baby
stage 3: delivery of placenta and membranes
what type of contractions are required for delivery of placenta and why
sustained contraction rather than intermittent to prevent haemorrage
role of oxytocin in labour/delivery
how produced
stimulates contractions
oxytocin is a peptide hormone secreted in pulses by pituitary, under hypothalmic ocntrol
pulsatility increases in labour and is also prodced by uterus
acts via myometrial receptors
role of prostaglandin in labour/delivery
how produced
prostaglandin- PGF2alpha
stimulates action potentials and calcium channels of smooth muscle, stimulating contractions
synthesised by COX enzymes
produce by decidua and fetal membranes
role of oestrogen in labour/delivery
involved in activation of myometrium by:
increasing oxytocin receptor expression
increasing prostaglanding and oxytocin levels
there is an increase in oestrogen production and increased oestrogen receptor expression in myometrium prior to birth
at end of pregnancy, oestrogen becomes dominant over porgesterone
role of progesterone in labour/delivery
progesterone has a suppressive effect on myometrium throughout pregnancy
it is thought there is a functional progesterone withdrawal before birth- ie progesterone levels remain high but unable to act as usual
evidence:
blocking progesterone induces delviery- mifeprestone drug used to terminate pregnancy
before birth myometrium less responsive to progesterone
role of placenta in labour/delivery
placental clock, dictates timing of delivery
placenta triggers fetal HPA axis by synthesising cortisol releasing hormone
placenta converts DHEA from fetal HPA axis to oestrogen
role of foetus in labour/ delivery
foetal HPA axis matures before birth, triggered by placenta,
produces cortisol and DHEA
foetal cortisol upregulates COX enzymes, causing increased prostaglandin synthesis= contractions
DHEA converted to oestrogen by placenta, causes oestrogen surge
summarise how the hormones work together in labour and delivery
placenta triggers foetal HPA axis by making cortisol releasing hormone
foetal HPA axis then makes cortisol and DHEA
cortisol upregulates COX enzymes so increased prostaglandin= contractions
DHEA from foetal HPA axis converted by placenta to oestrogen
oestrogen becomes dominant to progesterone, progesterone sensitivity reduced, myometrial contractions no longer suppressed
oestrogen increased oxytocin levels and receptors, oxytocin pulsatility increaes= contractions
oestroged increases prostaglanding levles, stimulate action potentials and calcium channels of smooth muscle of myometirum= contractions
cervical changes in labour and delivery
cervix is 85% connective tissue remains closed until onset of labour undergoes: - ripening - softening - effacing (shortening) - dilation
occurs due to mechanical stmulation and pressure of baby’s head, stimulated by inflamm mediators
how is the myometrium controlled in pregnancy and what is it
myometrium is the middle muscular layer of uterine wall
under influence oestrogen, myometrium grows and expands for foetal growth in pregnancy
myometrial contraction suppressed by progesterone in rpegnancy
before birth, sensitised to effects of oxytocin and prostaglandins, less sensitive to progesterone
outline fetal adaptations at birth
lungs inflate + surfactant
foramen ovale closes
ductus arteriosus closes
adaptations in lungs at birth
in womb gas exchange occurs across the placenta, at birth lungs filled with fluid and not inflated
at birth, aspirate mucus, first breath within 10 secs
baby often blue at birth
baby first cry inflates lungs and forces absorption of remaining fluid
role of surfactant at birth
surge of production at 34 weeks
role: reduce surface tension of alveoli in lungs so they can expand and prevents them collapsing at exhale
after first breath, surfactant thins alveolar membrane and increases alveolar SA
where does oxygenated blood flow in fetus in womb
oxygenated blood goes from, to: placenta umbilical vein fetus shunted to ductus venosus inferior vena cava right atrium shunted via foramen ovale left atrium ascending aorta body
where does deoxygenated blood flow in fetus in womb
doxygenated blood flows from, to: body right atrium right ventricle pulmonary artery shunted to ductus arteriosus descending aorta umbilical artery placenta
umbilical vein and artery carry de/oxy blood in which direction
umbilical vein carries oxygenated blood placenta to fetus
umbilical artery carries deoxygenated blood away from fetus to placenta
how does the blood travel from placenta to body of foetus t
oxygenated blood via umbilical vein to fetus, shunted into ductus venosus which shortcuts to the heart. enters right heart via inferior vena cava into right atrium
blood flows from right atrium to left atrium via foramen ovale
pumped into ascending aorta to body
how does blood travel from body of foetus to placenta
deoxygaenated blood returns to right atrium into right ventricle
pumped into pulmonary artery but shunted into descending aorta via ductus arteriosus
descending aorta joins umbilical artery to placenta
thereby bypasses the lungs
where is there high pressure in the heart in the womb
right side (right atrium)
what 2 things change in fetal circulation at birth
foramen ovale closes
ductus arteriosus closes
why does the foramen ovale close
umbilical cord is occluded so blood flow through ductus venosus stops
baby also takes first breath, aerating lungs
both combined cause pressure in right atrium to fall so foramen ovale closes
why/when does ductus arteriosus close
rising O2 levels over next few days cause ductus arteriosus to close
why do babies look blue at birth
in womb have lower O2 level than adults so look blue until circulation closes
sats go 65 to 95 %
importance of skin to skin
important to leave on mothers bare chest for an hour/ up to after first feed
clams/relaxes both
regulates baby hr and breathing
stimulates digestion and interest in feeding
enables colonisation with mums friendly bacteria
stimulates release of hormones in mum for breastfeeding
how are contraceptive methods classified
tier 1: most effective, <1 preg/100 women/year, long active reversible contraception (Larc) (IUDs, implants) and vasectomies and bilateral tube ligation
tier 2: 4-7/100/year contraceptive pills, patches, injections
tier 3: least effective, >13/100/year, condoms, diaphagms, cervical cups
how do oral contraceptives work
combined oral contraceptives have both oestrogen and progestin
inhibit secretion of GnRH and so fsh and lh
FSH inhibition= follicles don’t develop
LH inhibition= ovulation doesn’t happen
progestin thins endometrial lining so implantation can’t occur
thickens cervical mucus so harder for sperm
issues with oral contraceptives
contraindications: risk of DVT and cardiovascular events, highest in smokers and those over 35
hormonal contraceptives interact with other meds and may decrease contraceptive efficiency- antibiotics, anti seixure, HIV protease inhibitors
