Fetal Physiology

Question 1

Placenta

Answer 1

vital connecting organ between maternal uterus and foetus

Question 2

pre-implantation

Answer 2

development of placenta begins during implantation of blastocyst

Question 3

blastocyst embryonic cell types

Answer 3

outer trophoblast cells (form placenta)

inner cell mast (form foetus and foetal membranes)

Question 4

Site of normal implantation

Answer 4

anterior or posterior wall of the body of the uterus

Question 5

Most common ectopic implantation site

Answer 5

ampulla of fallopian tubes

Question 6

Implantation: 6th day

Answer 6

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.

Question 7

Implantation: 8th day

Answer 7

trophoblast cells differentiate into outer multinucleate synctiotrophoblast and inner mono nucleated cut-trophoblast

Question 8

Outer multinucleate synctiotrophoblast

Answer 8

erodes maternal tissue by sending out projections

Responsible for producing hormones such as HCG

Question 9

Inner mono nucleated cut-trophoblast

Answer 9

Actively proliferating

Question 10

Post-implantation

Answer 10

Takes place 9th day Lacunae spaces form within synctiotrophoblast. Erodes maternal tissues allowing maternal blood from uterine special arteries to enter lacunar network

Question 11

what is established by week 2

Answer 11

early uteroplacental circulation

Question 12

3rd week post-implantation

Answer 12

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

Question 13

Purpose of branching villi post-impkantation

Answer 13

provide surface area for the exchange of metabolites between mother and foetus

Question 14

establishment of circulation

Answer 14

Maternal spinal arteries undergo remodelling to produce low resistance, high blood flow condition in order to meet demands of the foetus

Question 15

What cells invade maternal spinal arteries

Answer 15

Cytotrophoblast cells

Question 16

Pre-eclampsia

Answer 16

trophoblastic disorder related to failed or incomplete differentiation of cytotrophoblastic cells during epithelial to endothelial transformation

Question 17

Placenta barrier

Answer 17

Not a true barrier as it allows many substances to pass between maternal and foetal circulation.

Question 18

Separation of maternal and foetal blood

Answer 18

maternal blood in intervillous specs is separated from the foetal blood by chorionic derivatives.
Human placenta: haemochorial type.

Question 19

Placenta barrier in first trimester

Answer 19

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

Question 20

placenta barrier in Second and third trimester

Answer 20

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

Question 21

Compartments of placenta

Answer 21

Cotyledons

Placenta divided by septa

Cotyledons receive blood supply through 80-100 spiral arteries that pierce decidual plate.

Question 22

Full term placenta

Answer 22

Discoid in shape
Diameter: 15-25cm
Approx: 3cm thickness
Weight: 500-600g

Question 23

Maternal side of full term placenta

Answer 23

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

Question 24

Placenta changes: End of pregnancy

Answer 24

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)

Question 25

placental abruption

Answer 25

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.

Question 26

Placental abruption risk factors

Answer 26

``` previous placental abruption Pre-eclampsyia Abnormal lie of foetus Polyhydramnios Smoking multiple pregnancy underlying thrombophilia abdo traum ```

Question 27

Presentation and exam of placental abruption

Answer 27

Painful vaginal bleeding Uterus may be woody (tense) and painful on palpation

Question 28

Foetal heart structure

Answer 28

``` Umbilical Vein Umbilical Arteries Ductus venous Ductus Arteriosus Foramen Ovale ```

Question 29

umbilical vein

Answer 29

delivers oxygenated blood from the placenta to the foetus, providing oxygen and nutrients

Question 30

umbilical arteries

Answer 30

transport deoxygenated blood away from the fetal tissue and back towards placenta for re-oxygenation

Question 31

ductus venous

Answer 31

allows blood for placenta to bypass liver (highly demanding but relatively inactive

Question 32

ductus arteriosus

Answer 32

fusion of primitive pulmonary artery to the aorta, allowing blood to pass straight from right ventricle into aorta and bypass inactive lungs

Question 33

foramen ovale

Answer 33

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

Question 34

partial pressure of O2 in foetal circulation

Answer 34

4kPa (comparison to adult-13kPa_

Question 35

How does foetus maintain adequate oxygen delivery to tissue

Answer 35

Shunt Reltive polycythaemia Properties of Fetal haemoglobin

Question 36

Fetal haemoglobin

Answer 36

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.

Question 37

Adaptation of fetal heart to neonatal heart

Answer 37

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

Question 38

Structural remnants of fetal circulatory structures

Answer 38

Fossa Ovalis- Foramen Ovale Ligamentum Arteriosum - Ductus arteriosus Ligamentum Venosum - Ductus venous

Question 39

patent ductus arteriosus

Answer 39

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

Question 40

Recognition of Patent Ductus Arteriosus

Answer 40

Continuous, machinery murmur over upper left sternal border. Generally asymptomatic