8. The Placenta

Question 1

When does the placenta begin to develop?

Answer 1

Second week of development

Question 2

What is the fate of the embryonic spaces from early embryonic development?

Answer 2

Yolk sac disappears
Amniotic sac enlarges
Chorionic sac is occupied by expanding amniotic sac

Question 3

What does implantation achieve?

Answer 3

Establishes basic unit of exchange - primary villi, secondary villi, tertiary villi
Anchor the placenta
Establish maternal blood flow within the placenta

Question 4

What are the role of the different villi?

Answer 4

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

Question 5

Why is implantation interstitial?

Answer 5

Uterine epithelium is breached and the conceptus implants within the stroma

Question 6

What is the chorion frondosum?

Answer 6

Finger-like projections between trophoblast and inner connective tissue
Chorionic villus

Question 7

What are the types of implantation defects?

Answer 7

Implantation in wrong place - ectopic pregnancy, placenta praevia
Incomplete invasion - placental insufficiency, pre-eclampsia

Question 8

What does the endometrium become known as in the presence of a conceptus?

Answer 8

Decidua

Question 9

What happens to the decidua in ectopic pregnancy?

Answer 9

Decidua reaction provides the balancing force for the invasive force of the trophoblast, however as there is no decidua, there is no control

Question 10

What happens if the decidual reaction is sub-optimal?

Answer 10

Can lead to a range of adverse pregnancy outcomes

Question 11

What happens the the structure of chorionic villus in third trimester?

Answer 11

Barrier at optimal thinness
Syncytiotrophoblast has thinned and cytotrophoblast almost disappeared
To provide fast transport of nutrients

Question 12

Describe the umbilical cord vessels

Answer 12

2 umbilical arteries - deoxygenated blood from fetus to placenta
1 umbilical vein - oxygenated blood from placenta to fetus

Question 13

What hormones are produced by the placenta?

Answer 13

Protein - hCG, human chorionic somatomammotrophin, human chorionic thyrotrophin, human chorionic corticotrophin
Steroid - progesterone, oestrogen

Question 14

What is the role of hCG in pregnancy?

Answer 14

Produced during first 2 months of pregnancy
Supports secretory function of corpus luteum
Produced by syncytiotrophoblast
Produced in trophoblast disease e.g. molar pregnancy, choriocarcinoma

Question 15

What is the role of placental steroid hormones?

Answer 15

Responsible for maintaining the pregnant state

Placental production takes over from corpus luteum by 11th week

Question 16

What is the specific role of hCS?

Answer 16

Increases glucose availability to fetus

Question 17

What are the transport functions of the placenta?

Answer 17

Simple diffusion - water, electrolytes, urea and uric acid, gases
Facilitated diffusion - applies to glucose transport
Active transport - amino acids, iron, vitamins
Passive immunity (endo/exocytosis)

Question 18

Describe what happens in transfer of passive immunity

Answer 18

Receptor-mediated process
Immunoglobulin class-specific
IgG only
IgG concentrations in fetal plasma exceed those in maternal circulation

Question 19

What are some harmful substances that cross the placenta?

Answer 19

Thalidomide
Alcohol 
Therapeutic drugs - anti-epileptic drugs, warfarin, ACE inhibitors
Drugs of abuse
Maternal smoking