9. Placental function and dysfunction

Question 1

What two lays in the blastocyst for the placenta membranes?

Answer 1

Syncytiotrophoblast and cytotrophoblast.

Question 2

What happens on implantation of the blastocyst into the endometrium?

Answer 2

Communication between the trophoblast and endometrium. Endometrium swells, increasing glycogen stores, and the trophoblast secretes enzymes to dissolve away the wall of the endometrium. Paracrine are secreted which increase the number of capillaries, allowing more oxygen and nutrients into the area. Blastocyst becomes embedded within the endometrium.

Question 3

What happen to the yolk sac after the primitive gut tube has been pinched off?

Answer 3

Regresses

Question 4

What happens to the amniotic sac as the embryo grows?

Answer 4

Enlarges in the chorionic sac, until the amniotic membrane is touching the walls of the chorionic membrane. Villius chorion regress on one side, so the placenta is left in one place only.

Question 5

What needs to be lost to allow implantation of the blastocyst to occur?

Answer 5

The zona pellucida.

Question 6

What is a chorionic villus?

Answer 6

Finger-like projections, at the chorion frondosum, of the trophoblast with an inner connective tissue core containing foetal cells.

Question 7

What are primary, secondary and tertiary villi?

Answer 7

Primary (13-15 days) - early finger-like projections of trophoblast.
Secondary (16-21 days) - invasion of mesenchyme into the core.
Tertiary (21st day) - invasion of mesenchyme core by fetal vessels.

Question 8

What is the role of the chorionic villi?

Answer 8

Anchor the placenta and establish blood flow within the placenta.

Question 9

What is an ectopic pregnancy?

Answer 9

Implantation at a site other than the uterine body (most commonly the Fallopian tube). Can be peritoneal or ovarian.

Question 10

What can ectopic pregnancy very quickly become life-threatening?

Answer 10

In the presence of a conceptus, the endometrium becomes the decidua, and the deciding reaction provides the balancing force for the invasive force of the trophoblast. In an ectopic pregnancy there is no deciduous and so no control, so can perforate through the Fallopian tube.

Question 11

What is placenta praevia?

Answer 11

Implantation in the lower uterine segment.

Question 12

When can placenta praevia cause haemorrhage in pregnancy?

Answer 12

If it crosses the os of the cervix.

Question 13

What is placental insufficiency?

Answer 13

Failure of the placenta to deliver sufficient nutrients to the fetus during pregnancy, and is often a result of insufficient blood flow to the placenta and deferred implantation.

Question 14

What is pre-eclampsia?

Answer 14

Pre-eclampsia is a placental insufficiency and maternal syndrome.

Question 15

What can cause pre-eclampsia?

Answer 15

Deferred implantation, shallow invasion.

Question 16

How does the structure of the chorionic villus change from the first trimester to the third trimester?

Answer 16

First trimester villus - thicker placental barrier. Metabolic needs of foetus not that great, so barrier for transport doesn’t need to be optimised, layer of syncytiotrophoblast and cytotrophoblast acts as a stem cell layer for this.
Third trimester villus - barrier at optimal thinness, where there is only one layer of trophoblast separating the maternal blood from fatal capillary wall. Metabolic demands at peak, less cytotrophoblasts (still some in case there is damage so can regrow). Optimum thickness for transport.

Question 17

How many umbilical arteries and veins re there?

Answer 17

Two umbilical arteries take deoxygenated blood from the fetus to the placenta.
One umbilical vein takes oxygenated blood from he placenta to the fetus.

Question 18

What steroidal hormones are produced by the placenta?

Answer 18

Progesterone and oestrogen.

Question 19

What is the role of the placental steroid hormones?

Answer 19

Responsible for maintaining the pregnant state, placental production takes over the corpus luteum by the 11th week.

Question 20

What protein hormones are produced by the placenta?

Answer 20

Human chorionic gonadotrophin.
Human chorionic somatomammotrophin.
Human chorionic thyrotrophin.
Human chorionic corticotrophin.

Question 21

What is the role of human chorionic gonadotrophin?

Answer 21

Produced during the first 2 months of pregnancy to support the secretory function of the corpus luteum.

Question 22

What is human chorionic gonadrotrophin produced by, thus making it pregnancy specific and therefore used as the basis for pregnancy testing (excreted in maternal urine)?

Answer 22

Syncytiotrophoblast.

Question 23

Name two gestational trophoblastic diseases that also result in the production of human chorionic gonadotrophin

Answer 23

Molar pregnancy.

Choriocarcinoma.

Question 24

What placental hormone increases maternal appetite?

Answer 24

Progesterone.

Question 25

What placental hormone increases glucose availability to the fetus by creating a diabetogenic state in the mother?

Answer 25

hPL (human placental lactin)

Question 26

What molecules cross the placental membrane by simple diffusion?

Answer 26

Water, electrolytes, urea and uric acid, gases.

Question 27

What molecules cross the placental membrane by facilitated diffusion?

Answer 27

Glucose.

Question 28

Why is maintenance of adequate blood flow in the placenta essential?

Answer 28

Fatal O2 store are small, and gas exchange is flow-limited not diffusion-limited.

Question 29

What molecules cross the placental membrane by active transport?

Answer 29

Amino acids, iron, vitamins.

Question 30

What are specific transporters expressed by to allow active transport of some molecules across the placental membrane?

Answer 30

Syncytiotrophoblast.

Question 31

How is passive immunity transferred from mother to fetus?

Answer 31

Receptor-mediated process, maturing as pregnancy progresses in anticipation of independent life after. Is immunoglobulin class-specific and IgG only is transferred.

Question 32

Are IgG concentrations higher in fetal plasma or maternal circulation?

Answer 32

Feta plasma.

Question 33

Name 3 harmful substances that can cross the placenta and how they affect the fetus.

Answer 33

Thalidomide - limb defects.
Alcohol - FAS and ARND.
Therapeutic drugs eg anti-epileptic drugs, warfarin, ACE inhibitors.
Drugs of abuse - leading to dependancy in the fetus and newborn.
Maternal smoking - changes placenta (smaller and more calcifications) and baby therefore smaller.

Question 34

When is there greatest risk for teratogenesis in a foetus?

Answer 34

Pre-embryonic (weeks 0-2) - lethal.

Embryonic (weeks 3-8) - embryo most sensitive, and each organ system has a period of peak sensitivity.

Question 35

After the embryonic period the risk of structural defects is very low, except for which system?

Answer 35

CNS.

Question 36

Name 3 infections capable of transplacental infection that can have adverse pregnancy outcomes?

Answer 36

Listeriosis.
TB.
Syphilis.
Malaria.
Toxoplasmosis.
Chicken pox.

Question 37

Name 3 possible outcomes of transplacental infection

Answer 37

First trimester fetal death.
Second trimester fetal death.
Stillbirth.
Premature labour.
Intrauterine growth restriction.
Fatal hydrops.
Severe neonatal infection.
Increased severity of maternal disease.