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Flashcards in 8.1 Deck (35):
1

When does the blastocyst implant into the endometrium?

Day 6

Fully imbedded by day 10

2

What occurs in implantation?

Interaction between invasive trophoblast cells and epithelium of the uterus.

3

What are 3 aims of implantation?

Establish basic unit of exchange
Anchor the placenta
- Establishment of outermost cytotrophoblast shell.
Establish maternal blood flow within the placenta.

4

What does haemonochorial mean?

Placenta is haemonochorial
One layer of trophoblast ultimately separates maternal blood from the fetal capillary wall.

5

How does the placenta membrane change over time?

Placenta membrane becomes progressively thinner as needs of fetus increases.

6

What are the primary, secondary and tertiary villi?

• Primary villi
o Early, finger-like projections of trophoblast
• Secondary villi
o Invasion of mesenchyme into core
• Tertiary villi
o Invasion of mesenchyme core by fetal vessels

7

What are the two components of the trophoblast?

Syncytiotrophoblast
Cytotrophoblast

8

How is the endometrium prepared for implantation?

Decidualisation
Pre decimal cells
The decimal reaction provides balancing force for the invasive force of the trophoblast.
Stimualted by progesterone.
Without this, conditions characterised by excessive invasion - haemorrhage, ectopic pregnancy can occur.

Remodelling of the spiral arteries
Creation of low resistance vascular bed
Maintains the high flow required to meet fetal demand, particularly in late gestation.

9

Describe decidualisation

Pre decidual cells
The decimal reaction provides balancing force for the invasive force of the trophoblast.
Stimualted by progesterone.
Without this, conditions characterised by excessive invasion - haemorrhage, ectopic pregnancy can occur.

10

Describe remodelling of the spiral arteries.

Creation of low resistance vascular bed
Maintains the high flow required to meet fetal demand, particularly in late gestation.

11

Describe ectopic pregnacny.

o Implantation at site other than uterine body
o Most commonly fallopian tube
o Can be peritoneal or ovarian
o Can very quickly become a life-threatening emergency

12

Describe placenta praevia.

o Implantation in the lower uterine segment
o Can cause haemorrhage in pregnancy
o Requires C-Section delivery

13

What is pre-eclampsia?

Hypertension and high protein in urine.

14

What are the 2 components of the placenta and what forms them?

1. A fetal portion
o Formed by the chorion frondsum
o Bordered by the chorionic plate

2. A maternal portion
o Formed by the decidua basalis
o The decidual plate is most intimately incorporated into the placenta

15

What is found between the decidua and chorionic plate?

Intervillous spaces, filled with maternal blood.

16

What are cotyledons?

Dedcidua form a number of decimal septa which project into intervillous spas but do not reach the chorionic plate.
These divide the placenta into cotyledon compartments.

17

Describe the first trimester placenta.

• Placenta established
• Placental ‘barrier’ to diffusion still relatively thick
• Complete cytotrophoblast layer beneath syncytiotrophoblast

18

Describe the term placenta.

• Surface area for exchange dramatically increased
• Placental ‘barrier’ is now thin
• Cytotrophoblast layer beneath syncytiotrophoblast lost

19

Descibe the umbilical cord vessels.

Two Umbilical Arteries
• Deoxygenated blood from fetus → Placenta

One Umbilical Vein
• Oxygenated blood from Placenta → Fetus

20

How do cotyledons receive blood?

Cotyledons receive their blood through 80 – 100 spiral arteries that pierce the decidual plate. Pressure in these arteries forces oxygenated blood deep into the intervillous spaces and bathes the numerous small villi of the villous tree in oxygenated blood.

As the pressure decreases, blood flows back form the chorionic plate towards the decidua, where it enters the endometrial veins.

21

What are the factors influencing the passive diffusion of substances across the placenta?

• Concentration Gradient
o The steeper the gradient, the more diffusion
• Barrier to diffusion
o Placental membrane gradually thins throughout pregnancy as the demand of the fetus increases
• Diffusion distance
o Haemomonochorial

22

What substances pass through the placenta by simple diffusion?

• Water
• Electrolytes
• Urea and uric acid
• Gases
o Flow limited, not diffusion-limited
o Fetal O2 stores are small – maintenance of adequate flow is essential

23

What substances pass through the placenta by facilitated diffusion?

Glucose

24

What substances pass through the placenta by active transport?

Specific transporters are expressed by the syncytiotrophoblast:
• Amino acids
• Iron
• Vitamins

25

Why the placenta not a true barrier?

Teratogens can access the fetus via the placenta, giving physiological consequences. Teratogens are particularly damaging during critical stages of development.

26

Give some drugs that are teratogens

• Thalidomide
• Alcohol
• Therapeutic drugs
• Drugs of abuse
• Maternal smoking

27

Give some pathogens that can cross the placenta.

• Varicella zoster
• Cytomegalovirus
• Treponema Pallidum
• Toxoplasma gondii
• Rubella

28

What are the two kinds of hormones produced by the placenta?

Protein
Steroid

29

Give protein hormones produced by the placenta.

Human Chorionic Gonadotrophin
Human chorionic somatomotrophin
Human chorionic thyrotrophin
Human chrorionic corticotrophin

30

What aret steroid hormones from the placenta?
What else is synthesised in the placenta?

Progesterone
Oestrogen

Glycogen
Cholesterol
Fatty acids

31

What are the functions of hCG, hCS?

hCG
o Produced during the first two months of pregnancy
o Supports the secretory function of the corpus luteum
o Produced by syncytiotrophoblast, therefore is pregnancy specific


hCS
o Influences maternal metabolism, increasing the availability of glucose to the fetus

32

What is the effect of placental progesterone?

o Placenta takes over production from the corpus luteum (Week 11)
o Influences maternal metabolism by increasing appetite

33

Describe passie immunity.

• Immunological competence begins to develop late in the first trimester, by which time the fetus makes all of the components of complement.
• Fetal immunoglobulins consist almost entirely of Maternal Immunoglobulin (IgG), which begins to be transported from mother to fetus at approximately 14 weeks.
• The IgG is transported via Receptor Mediated Pinocytosis.
• Eventually the concentration of IgG in fetal plasma exceeds that of maternal plasma.

34

Describe haemolytic disease in newborns

• Rhesus blood group incompatibility of mother and fetus
• Mother previously sensitised to rhesus antigen (e.g. previous pregnancy)
• IgG against rhesus crosses the placenta and attacked foetal RBCs
• Now uncommon because of prophylactic treatment

35

Why is haemolytic disease now uncommon?

Rhesus –‘ve mothers pregnant with Rhesus +’ve fetus given Rhesus specific IgG throughout pregnancy, to prevent sensitisation in the event of exposure to the antigen (The given IgG will bind to antigen before the mother’s immune system can mount a response)