Implantation and placental function

Question 1

Where in the vaginal system does fertilisation and implantation take place?

Answer 1

Fertilisation- fallopian tube

Implantation- endometrium in the uterus

Question 2

How does the embryo communicate its presence to the mother?

Answer 2

1.It establishes physical and nutritional contact, for nutrients to grow (placentation)

2. It signals its presence to the mother. This is required to prevent luteal regression
   (maternal recognition of pregnancy)

Question 3

List the key stages for implantation and placental development

Answer 3

1. First Differentiation step (inner cell mass is foetus, outer is placenta)
2. Apposition- positioning of the blastocyst within the uterine cavity
3. Adhesion- Trophoblast cells fix to maternal tissues and eachother (adhesion molecules, laminin and fibronectin
4. Trophoblast, through proteolytic processes, penetrates into the maternal decidua and endometrial spiral arteries.

Question 4

What happens on day 6-7 of trophoblast differentiation?

Answer 4

Trophectoderm differentiates into cytotrophoblast and syncytiotrophoblast

Question 5

What is the difference between a cytotrophoblast and a syncytiotrophoblast?

Answer 5

Cytotrophoblast -
Have single nucleus
divide rapidly in vivo

syncytiotrophoblast-
multinucleated cell
do not divide in vivo
derived from fused cytotrophoblasts

Question 6

What happens when the trophoblast reaches the spiral arteries?

Answer 6

Spiral arteries are converted from narrow to wide vessels
This allows a much greater flow of maternal blood around the villi

Oxygen tension gradient is [resent and increases towards maternal side

Question 7

What is the barrier between maternal and fetal circulation?

Answer 7

Villous trophoblast is the barrier between maternal and fetal circulation

Question 8

Name 3 molecules thought to play a part in successful implantation?

Answer 8

Human leukocyte antigen-G -(HLA-G) - inhibits antigen-specific lymphocyte response & decreases NK cell function

• Transforming growth factor β (TGFβ) - regulates invasion and proliferation
• Vascular endothelial growth factor (VEGF) - involved in angiogenesis

Question 9

What happens when fertilisation and implantation do occur?

Answer 9

Corpus luteum does not degenerate because of hCG.

2. Progesterone levels do not fall because progesterone secretion is maintained by the corpus luteum (oestrogen levels do not fall either)
3. Progesterone maintains the endometrium and becomes what is called the decidua.

Question 10

Describe the fetal and maternal side of the infection?

Answer 10

Fetal- smooth & covered in amnion
Umbilical cord inserted in the centre, with vessels radiating from it

Maternal- dull, greyish and divided into 15-20 cotyledons
Each cotyledon is formed of branches of one main villus stem covered by the decidua basalis

Question 11

What is the function of the umbilical vein and artery?

Answer 11

Vein- Used to deliver oxygen, nutrients and hormones to the baby

Arteries- Used to remove deliver waste and carbon dioxide from the baby

Question 12

What is the function of the placenta?

Answer 12

Site for exchange of gases (02 and C02) via simple diffusion and other molecules between maternal and fetal blood

Synthesis of hormones, proteins and enzymes

Nutrient exchange- 
Glucose- facilitated diffusion via glucose transporter protein
Amino acids- active transporter proteins
Fatty acids- simple diffusion
Large proteins and cells- pinocytosis 

Waste exchange
Urea- simple diffusion

Question 13

What effects the rate of O2 and CO2 diffusion in the placenta?

Answer 13

maternal/fetal gases gradient
maternal and fetal blood flow
placental permeability
placental surface area

Question 14

What will the placenta allow to enter the babies circulation?

Answer 14

IgG antibodies
hormones
antibiotics
sedatives
some viruses, e.g. rubella
some organisms, e.g. treponema pallida (syphilis)

Question 15

What will the placenta allow to enter the mothers circulation?

Answer 15

Granulocytes
Nucleated red blood cells
Lymphocytes 
Trophoblast cells
Gametocytes

Question 16

Name the 2 hormones produced by the placenta and state there function

Answer 16

1. Human chorionic gonadotropin (hCG):
   Synthesisbegins before implantation
   Maintains corpus luteum –> progesterone and oestrogen secretion

2. Human placental lactogen (hPL):
Increases free fatty acids by its lipolytic action
Inhibits gluconeogenesis
Promotes fetal growth
Promotes mammary duct proliferation

Relaxin:
Produced by decidual cells
Softens the cervix and pelvic ligaments in preparation for childbirth.

Question 17

Why is the foetus not rejected by the mother?

Answer 17

Normally ‘foreign‘ cells express particular human leukocyte antigens recognised by ‘host’ immune system so cells rejected

Trophoblast cells express HLA G. This is not recognised by ‘host’ immune system so cells not rejected

Infiltrating leucocytes secrete IL-2 which regulates the immune system

Decidual cells swell and tighten around developing fetus, forming a barrier brtween mother and implanting embryo

Question 18

Later on during pregnancy what produces oestrogen and progesterone to maintain the pregnancy?

Answer 18

The placenta