Fetal Physiology Flashcards
Placenta
vital connecting organ between maternal uterus and foetus
pre-implantation
development of placenta begins during implantation of blastocyst
blastocyst embryonic cell types
outer trophoblast cells (form placenta)
inner cell mast (form foetus and foetal membranes)
Site of normal implantation
anterior or posterior wall of the body of the uterus
Most common ectopic implantation site
ampulla of fallopian tubes
Implantation: 6th day
zone pellucid disintegrates and blastocyst hatches allowing implantation to take place.
Trophoblast cells interact with endometrial decidual epithelia to enable invasion into maternal uterine cells.
Implantation: 8th day
trophoblast cells differentiate into outer multinucleate synctiotrophoblast and inner mono nucleated cut-trophoblast
Outer multinucleate synctiotrophoblast
erodes maternal tissue by sending out projections
Responsible for producing hormones such as HCG
Inner mono nucleated cut-trophoblast
Actively proliferating
Post-implantation
Takes place 9th day Lacunae spaces form within synctiotrophoblast. Erodes maternal tissues allowing maternal blood from uterine special arteries to enter lacunar network
what is established by week 2
early uteroplacental circulation
3rd week post-implantation
Extra-embryonic mesoderm grows into villi, forming a core of loose connective tissue
By end of week embryonic vessels begin to form in embryonic mesoderm of secondary chorionic villi
Anchoring and branching villi form
Purpose of branching villi post-impkantation
provide surface area for the exchange of metabolites between mother and foetus
establishment of circulation
Maternal spinal arteries undergo remodelling to produce low resistance, high blood flow condition in order to meet demands of the foetus
What cells invade maternal spinal arteries
Cytotrophoblast cells
Pre-eclampsia
trophoblastic disorder related to failed or incomplete differentiation of cytotrophoblastic cells during epithelial to endothelial transformation
Placenta barrier
Not a true barrier as it allows many substances to pass between maternal and foetal circulation.
Separation of maternal and foetal blood
maternal blood in intervillous specs is separated from the foetal blood by chorionic derivatives.
Human placenta: haemochorial type.
Placenta barrier in first trimester
0-13 weeks
Surface of chorionic villi formed by synctiotrophoblst. Cells rest on a layer of cytotrophoblstic cells that cover a vascular endothelium
Barrier relatively thick
placenta barrier in Second and third trimester
Chorion frondosum formed was more villi develop on embryonic pole.
On foetal surface, placenta is covered by chorionic plate.
On maternal side, it is bordered by decide basalis
Decidual plate most intimately incorporated into placenta
Compartments of placenta
Cotyledons
Placenta divided by septa
Cotyledons receive blood supply through 80-100 spiral arteries that pierce decidual plate.
Full term placenta
Discoid in shape
Diameter: 15-25cm
Approx: 3cm thickness
Weight: 500-600g
Maternal side of full term placenta
15-20 bulging areas (cotyledons) covered by a thin layer of decider basalis.
Fully grown placenta contains intervillous lakes
Hold approx 150 ml of maternal blood
Placenta changes: End of pregnancy
Aim: reduce exchange between maternal and foetal circulations
Increase in fibrous tissue in core of villus
Thickening of foetal capillary basement membranes
Obliterative changes in small capillaries of villi
Deposition of fibrinoid on surface of villi in junctional zone and in chorionic plate. (leads to infarction of intervillous lake -> turns whitish)
placental abruption
part, or all of, the placenta separates prematurely from uterine wall.
Occurs following aa rupture of maternal vessels within basal layer of endometrium.
Blood accumulates and causes placenta to split from basal layer.
Detached portion us unable to function and can lead to rapid foetal compromise.
Placental abruption risk factors
previous placental abruption Pre-eclampsyia Abnormal lie of foetus Polyhydramnios Smoking multiple pregnancy underlying thrombophilia abdo traum
Presentation and exam of placental abruption
Painful vaginal bleeding
Uterus may be woody (tense) and painful on palpation
Foetal heart structure
Umbilical Vein Umbilical Arteries Ductus venous Ductus Arteriosus Foramen Ovale
umbilical vein
delivers oxygenated blood from the placenta to the foetus, providing oxygen and nutrients
umbilical arteries
transport deoxygenated blood away from the fetal tissue and back towards placenta for re-oxygenation
ductus venous
allows blood for placenta to bypass liver (highly demanding but relatively inactive
ductus arteriosus
fusion of primitive pulmonary artery to the aorta, allowing blood to pass straight from right ventricle into aorta and bypass inactive lungs
foramen ovale
creates a shunt between right atrium and left atrium so oxygenated blood from placenta can move to left atrium. allows oxygenated blood to pass through left ventricle and into ascending aorta, oxygenating the brain
partial pressure of O2 in foetal circulation
4kPa (comparison to adult-13kPa_
How does foetus maintain adequate oxygen delivery to tissue
Shunt
Reltive polycythaemia
Properties of Fetal haemoglobin
Fetal haemoglobin
2 alpha subunits and 2 gamma subunits
Change in structure of protein mean foetal haemoglobin can bind more readily to oxygen from maternal circulation.
Allows for adequate oxygenation of tissues.
Adaptation of fetal heart to neonatal heart
First breath causes a rise in partial pressure of O2.
Increase in O2 pressure causes pulmonary vasodilation
Leads to drop in right heart pressure.
Simultaneously placental circulation ceases, causing left heart pressure to rise.
Combined factors -> formane ovale shuts
Pulmonary and systemic circulations become separate.
Final step: closure of ductus arterioles, occurring 2-3 days after birth
Structural remnants of fetal circulatory structures
Fossa Ovalis- Foramen Ovale
Ligamentum Arteriosum - Ductus arteriosus
Ligamentum Venosum - Ductus venous
patent ductus arteriosus
If ductus arteriosus remains open beyond
- 3 months of life (pre-term)
- 1 year (full term)
- -> Persistent patent ductus arteriosus
Prostaglandin E2 is responsible for keeping PDAs open
Recognition of Patent Ductus Arteriosus
Continuous, machinery murmur over upper left sternal border.
Generally asymptomatic
