Lecture 13 - Placenta

Question 1

Implantation

Answer 1

Trophoblasts interact with the endometrial lining of the uterus

Blastocyst is embedded within the endometrium, increasing its blood supply and secretory glands develop.

Question 2

What day does implantation occur

Answer 2

Day 6

Question 3

Week 2

Answer 3

Trophoblast differentiates into the syncytiotrophoblast and cytotrophoblast

The embryoblast becomes the hypoblast and epiblast

Conceptus implants

Amniotic cavity and yolk cavity is formed from the epiblast and hypoblast

Suspended by the connecting stalk in the chorionic cavity

Question 4

Embryonic spaces

Answer 4

Yolk sac disappears
Amniotic sac enlarges and fuses with the chorionic membrane to form the amniotic membrane
Chorionic sac is occupied by the expanding amniotic sac

Question 5

What does implantation achieve?

Answer 5

Placental membrane:
Primary villi - early projections of trophoblast (single layer)
Secondary villi - invasion of mesenchyme into core
Tertiary villi - invasion of foetal vessels into mesenchyme core

Placenta is anchored to maintain the pregnancy

Maternal blood flow writhing the placenta surround villi allowing exchange to occur

Question 6

Placental membrane

Answer 6

Initially the barrier is thick with syncytiotrophoblast and trophoblasts but as the pregnancy progresses, the barrier becomes thinner as it lose the cytotrophoblast and only 1 layer of syncytiotrophoblasts remain

Short diffusion pathway for optimal exchange
2 circulations never mix - better control

Question 7

Chorionic fondosum

Answer 7

Outer layer of the placenta with chorionic villi

Question 8

Incomplete invasion

Answer 8

Pre-eclampsia

Placental insufficiency

Question 9

Decidual reaction

Answer 9

Transformation of the endometrium in the presence of a conceptus to maintain the pregnancy

• inhibits invasion - balance

Question 10

Chorionic villus

Answer 10

Finger like projection of the chorionic membrane that allows exchange with the maternal circulation

Question 11

Cotyledons

Answer 11

When placenta is removed the cotyledons should be completely intact

If lost and remains inside the woman, can cause post partake haemorrhage

Question 12

3 cellular layers for oxygen to cross

Answer 12

Capillary endothelium of foetus
Cytotrophoblast
Syncytiotrophoblast

Question 13

Umbilical vein

Answer 13

Carries oxygenated blood from the placenta to foetus

Question 14

umbilical arteries

Answer 14

2

Carry deoxygenated blood from foetus to the placenta and maternal circulation

Question 15

Endometrial veins and arteries

Answer 15

Veins - doexygenated blood from maternal circulation

Arteries - (spiral) oxygenated blood from maternal circulation

Question 16

Hormones produced by the placenta

Answer 16

Protein hormones:

• HCG
• human chorionic somatomammotrophin
• human chorionic thyrotrophin
• human chorionic corticotrophin

Steroid hormones: after 1st trimester

• oestrogen
• progesterone

Question 17

Beta HCG

Answer 17

Produced during first 2 months of pregnancy then decreases
Analogous to LH - supports the corpus luteum to secrete oestrogen and progesterone
Produced by the syncytiotrophoblast - pregnancy test

Question 18

Trophoblast disease

Answer 18

Hyatidiform mole - uterus enlarges more rapidly due to abnormal placental growth

Choriocarcinoma

Question 19

Steroid hormones

Answer 19

Oestrogen and progesterone maintain pregnancy state

Placental production begins in the 11 th week

Question 20

Progesterone

Answer 20

Increase appetite

Increased fat deposition which aid breast feeding

Question 21

Human placental lactogen

Answer 21

Also called human chorionic somatomammotrophin
-increases glucose availability to foetus

• maternal insulin resistance so less glucose is absorbed into maternal cells - diabetogenic state

Question 22

Simple diffusion

Answer 22

Water
Electrolytes
Urea
Gases

• exchange limited by circulation flow
• small foetal O2 stores - requires adequate flow

Question 23

Facilitated diffusion

Answer 23

Glucose

Question 24

Active transport

Answer 24

Amino acids
Iron
Vitamins

Transporters expressed on the syncytiotrophoblast

Question 25

Foetal distress

Answer 25

Inadequate uteroplacental circulation

E.g during labour contractions, the blood vessels are compressed causing a decreased circulation and foetal distress

Question 26

Immunity

Answer 26

Foetal immune system is immature
At time of birth only has IgG
IgG concentrations in the foetus exceed maternal concentration
IgG is transported from the maternal circulation to the foetal circulation by receptor mediated exocytosis and endocytosis

Question 27

Teratogens

Answer 27

Teratogens can access the foetus via the placenta

Pre- embryonic stage - lethal
Embryonic - highly sensitive to structural defects and deformation
Foetal - less sensitive except for CNS

Question 28

Rhesus incompatibility

Answer 28

Maternal antigens cross into the foetal circulation and attack the foetal blood cells - haemolytic

Question 29

Harmful substances

Answer 29

Thalidomide - limb defects

Alcohol

• FAS
• alcohol related neurological delay (ARND)

Therapeutic drugs

• anti-epileptic drugs
• warfarin
• ACE inhibitors

Drugs of abuse
- dependency in foetus

Smoking
- thinner and lighter placenta