Placenta

Question 1

When does the placenta first develop?

Answer 1

Begins in second week of development - first organ to develop

In early development focus on fetal membranes sacs supporting the embryo and placenta)

Can’t be a healthy Pregnancy without a healthy placenta

Question 2

What do the outer and inner cell masses become in week 2?

Answer 2

OCM -> syncytiotrophoblast (outer most) and cytotrophoblast

ICM -> bilaminar disc (epiblast and hypoblast)

Question 3

When does implantation begin?

Answer 3

Day 8-9 as a blastocyst

(Day 5 morula becomes blastocyst)

(Day 6-7 loses zona pellucida)

Question 4

Describe the structure of the embryo by the end of the 2nd week? what happens to each of these structures?

Answer 4

The concepts has impmayed

The embryo and it’s two cavities (amniotic cavity and yolk sac) are suspended by the connecting stalk within a supporting sac (chorionic cavity)

…

Yolk sac disappears ( remnant = umbilical vesicle)

Amniotic sac enlarges (becomes surrounded by placenta/ villus chorionic and attached to it by umbilical cord)

Chorionic sac occupied by expanding amniotic sac

See slide 7

Question 5

What does implantation achieve?

Answer 5

Establishes basic unit of exchange

Primary villi (projections of trophoblast ) 
Secondary villi (invasion of mesenchyme into core) 
Tertiary villi (invasion of mesenchyme core by fetal vessels) 

Anchors the placenta

Establishes maternal blood flow within placenta

Question 6

Where does the concepts impact in the uterus and what happens to the placental membrane over time?

Answer 6

Uterine epithelium is breached and concepts implants within stroma

Placental membrane becomes progressively thinner as needs of foetus increase -> one layer of trophoblast separates maternal blood flow from fetal capillary wall by third trimester

but the two circulations never mix

Question 7

What makes up the chorionic villus?

Answer 7

Placenta is a specialisation of chorionic membrane

Villi, trophoblast, inner CT core (day 15/16), fetal vessels (day 23)

Very good for exchange

Question 8

Explain how invasion in implantation is controlled

Answer 8

In the presence of a concepts endometrium -> decidua

The decidual reaction provides balancing force for invasive force of trophoblast (ectopic pregnancy no decidua so no control)

If decidual reaction is sub-optimal -> range of problems e.g. pre-eclampsia, placental praevia, miscarriage

Need far enough but not too far e.g. into myometrium

Question 9

What is a chorionic villus? Describe the structure of a chorionic villus, how does it change from first to third trimester?

Answer 9

Chorionic villus are projections that sprout from the chorion (part of the placenta) to provide max contact area with maternal blood

Surrounded by amnion
Contain arteries and fetal veins and branch to form anteriocapillary venous networks at ends. CT core, Hofbauer, cytotrophoblast and synctiotrophoblast cells

Third trimester: barrier at optimal thinness , syncytial knot, fibrinoid

Question 10

What is the amniochorionic membrane made of that you can see on gross morphology?

Answer 10

Cotyledons

Question 11

How many of each and what does each carry: umbilical artery and umbilical vein?

Answer 11

Two umbilical arteries carry deoxygenated blood and waste from foetus to placenta

One umbilical vein carries oxygenated blood from placenta to foetus

Question 12

What hormones does the placenta produce by the end of trimester 1?

Answer 12

Protein: human chorionic gonadotropin (placental FSH/ LH),

HC somatomammotrophin (prolactin)- increases glucose available to foetus,

HC thyrotrophin (prolactin),

HC corticotrophin (ACTH)

Steroid:
progesterone (increases appetite) & oestrogen (both maintain the pregnant state) takes over from corpus Luteum 11th week

Question 13

What is hCG? What produces it? When else can cause its production as well as pregnancy?

Answer 13

Human Chorionic Gonadotrophin - produced during first 2 months of pregnancy, acts as LH to support the secretory function of the corpus luteum -> progesterone

Produced by syncytiotrophoblast excreted in maternal urine used pregnancy testing or marker for trophoblast disease e.g. molar pregnancy (hydatidiform mole), choriocarcinoma

Question 14

What uses facilitated diffusion in the placenta?

Answer 14

Glucose transport

Question 15

What molecules use specific active transporters expressed by the syncytiotrophoblast?

Answer 15

Amino acids

Iron

Vitamins

Question 16

How does transfer of passive immunity occur? Why could this cause a Problem?

Answer 16

Fetal and newborn immune system immature

Receptor mediated process, maturing as pregnancy progress

Immunoglobulin-class specific

IgG are the only maternal antibodies that CNS pass to foetus

Against conc grad (foetus higher concentration)

• if mum and foetus Rheusus incompatible -> haemolytic disease of newborn (rhesus screening)

Question 17

What harmful substances (teratogens) could pass to the foetus form maternal blood and what problems could they cause?

Answer 17

Thalidomide -> limb defects

Alcohol - FAS, ARND

Therapeutic drugs (anti-epileptic, warfarin, ACE inhibitors)

Drugs of abuse - dependence (withdrawal period)

Maternal smoking - shape and size of placenta changed, thinner/ increased calcification -> growth restriction and insufficiency

Question 18

How can the severity of problems caused by teratogenesis change during the embryonic Period?

Answer 18

Timing is key

Pre-embryonic: lethal effects 0-2 weeks

Embryonic: v sensitive to structural changes (narrow windows for some systems) 3-8 weeks

Fetal: decreased sensitivity, Post- embryonic risk structural defects v low bar CNS (particularly from alcohol) 9-38 weeks

Question 19

Name some defects that may occur for each system and timings where vulnerable

Answer 19

CNS - neural tube defects, mental retardation (3 weeks ->38+)

Heart - TA, ASD, VSD (3-9)

Upper limb - amelia/ meromelia (4-9)

Lower limb - Amelia/ meromelia (4-9)

Upper lip - cleft lip ((5-9)

Ears - low set malformed and deafness (4-32)

Eyes- microphthalmia, cataracts, glaucoma (4-38)

Teeth - enamel hypoplasia, staining (6-38)

External genitalia - masculinization of female genitalia ( 7-38)

Lower sensitivity near end but CNS only low sensitivity at 32 weeks