16) Placenta

Question 1

What happens to placental membrane over the course of pregnancy?

Answer 1

Becomes progressively thinner

Question 2

What are the aims of implantation?

Answer 2

Establish basic unit of exchange - chorionic villi
Anchor placenta - cytotrophoblast shell
Establish maternal blood flow in placenta

Question 3

Describe the development of chorionic villi:

Answer 3

Primary - finger like projections of trophoblast
Secondary - invasion of mesenchyme into core
Tertiary - invasion of mesenchyme ore by fetal vessels

Question 4

Give examples of implantation defects:

Answer 4

Ectopic pregnancy

Placenta praevia

Question 5

What are pre-decidual/decidual cells?

Answer 5

Specialised cells of endometrium which control degree of implantation

Question 6

What vascular modifications are required for endometrial vessels?

Answer 6

Creation of low resistance, high flow vascular bed by trophoblast invasion of spiral arteries

Question 7

If there is inadequate modification of vessel walls, what can occur?

Answer 7

Pre-eclampsia

Question 8

What can occur if invasion is incomplete?

Answer 8

Placental insufficiency

Question 9

Describe the macrostructure of the placenta :

Answer 9

Covered in amniochorion

Organised into cotyledons

Question 10

Describe the blood supply in the chorionic villi:

Answer 10

Two umbilical arteries - deoxygenated blood from fetus to placenta
Umbilical vein - oxygenated blood from placenta to fetus

Question 11

What are anchoring villi?

Answer 11

Villi with cytotrophoblast cells that migrate to endometrial spiral arteries to develop uteroplacental circulation

Question 12

What is the difference between placental barrier in 1st and 3rd trimester?

Answer 12

1st trimester - thick with complete layer of cytotrophoblast
3rd trimester - thin with scattered cytotrophoblast layer

Question 13

What are the metabolic and endocrine functions of the placenta?

Answer 13

Synthesis of glycogen, cholesterol and fatty acids

Production of hormones

Question 14

What steroid hormones does the placenta produce?

Answer 14

Progesterone and oestrogen

Question 15

What protein hormones does the placenta produce?

Answer 15

hCG, hC somatomammotropin, hC thyrotropin, hC corticotropin

Question 16

What is the function of hCG?

Answer 16

Maintain secretory function of corpus luteum

Question 17

What can hCG be used for clinically?

Answer 17

Pregnancy testing - excreted in maternal urine

Question 18

What can cause a large hCG in pregnancy?

Answer 18

Twins

Trophoblast disease: molar pregnancy (overgrowth of placental tissue) or choriocarcinoma

Question 19

What is the function of human placental lactogen?

Answer 19

Increases glucose availability to fetus

Question 20

How can substances be transported across the placenta? Give examples:

Answer 20

Simple diffusion - water, gases
Facilitated diffusion - glucose
Active transport - AAs, iron
Receptor mediated endocytosis - IgG

Question 21

Why is it important for IgG to be transferred to the fetus?

Answer 21

Provides passive immunity as fetal immune system matures

Question 22

What is transferred from fetus to mother across the placenta?

Answer 22

Waste products e.g. CO2, urea

Hormones

Question 23

What is transferred from mother to fetus across the placenta?

Answer 23

Oxygen
Nutrients
Antibodies
Harmful substances

Question 24

Give some examples of teratogens:

Answer 24

Drugs - thalidomide, alcohol

Infectious agents - varicella zoster, rubella

Question 25

What is haemolytic disease of the newborn?

Answer 25

Where there is rhesus blood group incompatibility between mother and fetus so IgG transfer destroys fetal RBCs