Pregnancy Parturition And Late Fetal Development Flashcards
What nutrition is early embryo dependent on
reliant on uterine gland secretions and breakdown of endometrial tissues
Histiotrophic
What type of support is embryo fetal growth dependent on at the second trimester
Haemotrophic
Achieved in humans through a haemochorial-type placenta where maternal blood directly contacts the fetal membranes.
What is the connecting stalk/what does it do?
connects the embryo unit to the chorion
What are trophoblastic lacunae
Large spaces filled with maternal blood formed by breakdown of maternal capillaries and uterine glands
Become intervillous spaces aka maternal blood spaces
Amnion
The inner fetal membrane
Arises from the epiblast (but does not contribute to the fetal tissues)
Begins to secrete amniotic fluid from 5th week – forms a fluid filled sac
Amniotic sac
Encapsulates and protects fetus
closed, avascular sac, with the developing embryo at one end
Chorion
The outer fetal membrane
Formed from yolk sac derivatives and the trophoblast
Highly vascularized
Gives rise to chorionic villi
outgrowths of cytotrophoblast from the chorion through syncitiotrophoblaststhat form the basis of the fetal side of the placenta
What is the allantois/
Outgrowth of the yolk sac
Grows along the connecting stalk from embryo to chorion
How does allantois form the umbilical cord
Becomes coated in mesoderm and vascularizes to form the umbilical cord.
How does the amniotic sac form?
Expansion of the amnion by fluid accumulation forces the amnion into contact with the chorion, which fuse, forming the amniotic sac
2 layers amnion on inside chorion on outside
- Why are chorionic villi important?
Provide a substantial surface area for exchange of gases & nutrients
primary phase of chorionic fetal development
Cytotrophoblast forms finger-like projections through syncitiotrophoblast layer, Into maternal endometrium, and branching of these extensions
- outgrowth of cytotrophoblast cells from the chorion
secondary phase of chorionic fetal development
growth of the fetal mesoderm into the primary villi
tertiary phase of chorionic fetal development
growth of the umbilical artery and umbilical vein into the villus mesoderm, providing vasculature.
Terminal villus microstructure; what does the convoluted knot of vessels and vessel dilation do?
Slows blood flow enabling exchange between maternal and fetal blood
Maternal blood supply to endometrium
Uterine artery → arcuate arteries → radial arteries → basal arteries → spiral arteries
U AR BS
What do spinal arteries do
provide the maternal blood supply to the endometrium
What do Extra-villus trophoblast (EVT) cells do?
cells coating the villi invade down into the maternal spiral arteries,
Form endovascular EVT when this happens
What is conversion
transition from spinal arteries to non-spinal arteries
turns the spiral artery into a low pressure, high capacity conduit for maternal blood flow.
Endothelium and smooth muscle is broken down – EVT coats inside of vessels
How is calcium exchanged
actively transported against a concentration gradient by magnesium ATPase calcium pump.
How are amino acids exchanged
active transport of amino acids to fetus
reduced maternal urea excretion
Which 4 changes occur in the maternal circulatory system
- Maternal cardiac output increases 30% during first trimester (stroke vol & rate)
- Maternal peripheral resistance decreases up to 30%
- Maternal blood volume increases to 40% (near term (20-30% erythrocytes, 30-60% plasma)
- Pulmonary ventilation increases 40%
Why is the O2 content and saturation of fetal blood similar to maternal blood, even though fetal O2 tension is low? (what major difference does fetal Hb have to maternal Hb)
Embryonic and fetal hemoglobins: greater affinity for O2 than maternal hemoglobin.
Placenta consumes 40-60% glucose and O2 supplied by the mother
How does fetal circulation differ from neonatal circulation
Ventricles act in parallel rather than in series (series in neonatal)
Achieved by vascular shunts which bypass pulmonary & hepatic circulation, these shunts close at birth to give rise to normal pulmonary & hepatic circulation
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What occurs in the lungs around 20 weeks and 28 weeks
primitive air sacs form
surfactant production
Lung vascularises at 28
At which point is the endocrine pancreas functional, and at which point does insulin secretion occur?
start of 2nd trimester
from mid 2nd trimester
Which carbohydrate is progressively deposited towards the time of delivery
Glycogen
The early fetus swallows large amounts of amniotic fluid, debris from this fluid along with bile acids form the first stool of the fetus, delivered just after birth, what is the name of this stool?
Meconium
At which point/week does the fetus start to determine movement, and at which point/week is movement detectable by the mother?
late 1st trimester
14 weeks
At which point does the fetus start to respond to stress, and at which point do thalamus-cortex connections form?
18 weeks and 24 weeks
Does fetus show conscious wakefulness
No
In slow wave or REM sleep
- Which hormone sub-class is organ maturation coordinate
Fetal corticosteroids
Main aims of labor
T - safe expulsion of fetus at the correct time
- Expulsion of placenta and fetal membranes
- Resolution/healing to permit future reproductive events
-
What reaction type does labour have the characteristics of?
Pro inflammatory
For Immune cell infiltration
Inflammatory cytokine secretion
Prostaglandin secretion
First stage of labor
Contraction start and cervix dilated
Latent phase-slow dilation of cervix 2-3cm
Active phase-rapid dilation of cervix 10cm
Role of cervix in pregnancy
Retains fetus in uterus
High connective tissue content, (Bundles of collagen fibres embedded in a proteoglycan matrix) provides rigidity and stretch resistance
Softening caused by changes to collagen bundle structure
4 stages if cervical remodeling
Softening-measurable changes in compliance but retains cervicak competence in first trimester
Ripening is where monocytes infiltration IL6 and IL8 secretion and hylarunonan deposition occurs weeks and days before birth
Dilation is where increased hyaluronidase expression occurs and matrix metalloproteinases decrease collagen content
Post party repair recovers tissue integrity
Second stage
Myometrial contractions and fetal expulsion
What do myometrial muscle cells connect to form?
a syncytium (extensive gap junctions, allowing muscle contraction to be coordinated)
When do contractions start from and where do they spread
start from the fundus, spread down upper segment
-
What can myometrial muscle contractions be described as
Brachystatic
Fibres don’t return to fully relaxed state
Causes lower segment and cervix to be pulled up
Third stage
Delivery of placenta
Rapid shrinkage of uterus after delivery
Clamping stops fetal, blood flow so chorionic villi collapse ongoing contraction is expel placenta
Why does uterus remain in contracted state
to facilitate uterine vessel thrombosis
The uterus undergoes uterine involution and the cervix undergoes repair to restore a non-pregnant state, why is this important
- Shielding uterus from commensal bacteria
- Restore endometrial cyclicity in response to hormones
Corticotrophin-releasing hormone (CRH) and the initiation of labor, describe this theory
- The fetus determines timing of parturition through changes in fetal HPA axis
Corticotrophin Releasing Hormone (CRH) levels rise exponentially towards the end of pregnancy
What does an increase in fetal CRH release cause
Promotes fetal ACTH and cortisol release
increased fetal CRH production → increased fetal adrenal cortisol (this travels to the placenta)→ increases placental CRH production → Placental CRH stimulates more fetal CRH release
stimulates DHEAS production by the fetal adrenal cortex, DHEAS is a substrate for oestrogen production
Why are high progesterone levels important to have throughout pregnancy?
Maintains uterine relaxation
How might the oestrogen : progesterone ratio shift during labour?
Increases
The uterus becomes ‘blinded’ (non-responsive) to progesterone action and sensitized to estrogen action, describe two ways this occurs?
- Functional progesterone withdrawal, explain it:switch from PR-A isoforms (activating) to PR-B and PR-C (repressive) isoforms expressed in uterusPR=progesterone receptor
- Increased oestrogen receptor alpha expression
Explain the Ferguson reflex
Stretch receptors in vagina and cervix trigger oxytocin release from the posterior pituitary
- Oxytocin, how does oxytocin production change at the onset of labour?
Uterine oxytocin production increases sharpl
What is oxytocin secreted by
utero-placental tissues
maternal pituitary
What is increased oxytocin production driven by?
Increased placental oestrogen levels
- What receptor does oxytocin signal through?
G coupled oxytocin receptors
- During pre-labour, what effect does progesterone have on the OXTR expression?Inhibits OXTR expression, which allows the uterus to remain in a relaxed state (so no contractions)
- What effect does increasing oestrogen have on OXTR expression?increases it
3 main functions of oxytocin
- Increases connectivity of myocytes in myometrium
- destabilise membrane potentials to lower threshold for contraction
- Enhances liberation of intracellular Ca2+ ion stores
What are the 3 primary prostaglandins (PGs) synthesized during labour?
- PGE2, what is its main role?
- cervix re-modelling, how?Promotes leukocyte infiltration into the cervix, IL-8 release and collagen bundle re-modelling
- PGF2 alpha, what is it’s main role?myometrial contractionsby destabilising membrane potentials and promotes connectivity of myocytes (with Oxytocin)
- PGI2, what is its main role?
Promotes myometrial smooth muscle relaxation and relaxation of lower uterine segment
- How does an increase in oestrogen levels drive prostaglandin action (2 ways)?
- Increasing oestrogen activates phospholipase A2 enzyme, which generates more arachidonic acid for PG synthesis
- increases oxytocin receptor expression which promotes PG release
