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Flashcards in Placentation Deck (102):
1

What does the inner cell mass differentiate into?

1. Epiblast
2. Hypoblast

2

What is the epiblast?

Contacts the trophoblast

Gives rise to the three primary germ layers during gastrulation

Extends to form the amnion over the dorsal surfaces of the germ disc

3

What is the hypoblast?

Faces the blastocoel

Forms the primary yolk sac

Gives rise to extra-embryonic mesoderm

4

Where does extra-embryonic mesoderm come from?

Hypoblast

5

What does extra-embryonic mesoderm give rise to?

1. Chorion
2. Cell layer that covers outside of yolk sac and amnion

6

What is the extra-embryonic coelom?

The space between the chorion and the amnion

7

How does the secondary yolk sac arise?

The primary yolk sac pinches off

8

What is the connecting stalk?

Connects the conceptus to the chorion

Future umbilical cord

9

What happens to the extra-embryonic coelom?

Obliterated at 12 weeks

Amnion pushed against inner surface of chorion

10

Where is the first site of haematopoiesis?

Yolk sac

11

What is exchanged between the mother and the yolk sac?

1. Amino acids
2. Other nutrients

12

How does maternal-fetal exchange take place with the yolk sac?

Nutrients transported across chorion into fluid in the coelom, which bathes the yolk sac

13

What are the properties of the outer surface of the yolk sac?

1. Absorptive epithelium
2. GLUT1 and other transporters
3. Synthesises many proteins like alpha-fetoprotein

14

What are the eight functions of the placenta?

1. Gas transfer
2. Excretion
3. Immune
4. Metabolic functions
5. Synthetic functions
6. Catabolic and resorptive functions
7. Secretory functions
8. Haematopoiesis

15

Where is the chorionic plate of the placenta?

Faces the fetus

16

Where is the basal plate of the placenta?

Apposed to decidua basalis

Where maternal blood enters

17

What is haemochorial placentation?

Maternal blood comes in direct contact with fetal chorion

Fetal villous trees arise from the chorionic plate and are bathed directly in maternal blood circulating in the intervillous space

18

Where are fetal capillaries located in the placenta?

Inside the villi

19

What does the trophoblast differentiate into?

1. Syncytiotrophoblast
2. Cytotrophoblast

20

How is the syncytiotrophoblast formed?

Non-proliferative

Generated by continual fusion of cytotrophoblast cells

21

What is the structure of the syncytiotrophoblast?

Erodes into decidua

Breaks into endometrial glands and decidual capillaries

Spaces appear and coalesce to form lacunae

22

What fills the lacunae of the syncytiotrophoblast?

1. Maternal blood
2. Glandular secretions

23

How are the earliest placental villi formed?

Cytotrophoblast cells and extraembryonic mesoderm penetrate into the trabeculae between the lacunae of the syncytiotrophoblast

Vascular network develops in the mesoderm and connects back to the fetus through the connecting stalk

24

How is the placental villus tree formed?

Repeated branching of the early villus

25

What is the intervillous space?

The lacunae once the villus tree forms

26

What is the stem villus?

Extends from chorionic plate

27

What is the anchoring villus?

Attached to basal plate

28

What are the side branches of the villi?

Intermediate villi from which terminal villi arise

29

When are terminal villi formed?

Second half of gestation

30

Where do placental villi form?

Initially, all over chorionic sac

Then, regress over superficial pole to leave discoid placenta

31

What does the rest of the chorionic sac form?

Placental membranes

Rupture at birth

32

When is maternal arterial circulation established?

10-12 weeks

33

What is histiotrophic nutrition?

Uptake of oviductal/uterine secretions by trophoblast or yolk sac

34

What is haemotrophic nutrition?

Nutrient, waste and gas exchange between maternal and fetal circulations

35

What is the principal source of nutrients in early pregnancy?

Carbohydrate and lipid-rich secretions from endometrial glands

36

What are endometrial glands stimulated by?

1. Progesterone from corpus luteum
2. Signals from trophoblast

37

What protects the embryo from teratogenesis in embryogenesis?

Low oxygen environment

Protects from teratogenesis due to reactive oxygen species

Low oxygen favours fetal and placental stem cells

38

What is the embryonic period?

When most major organ systems are differentiating

First trimester

39

What is the fetal period?

Major growth period

Second and third trimesters

40

When is the switch from histiotrophic to haemotrophic nutrition?

First --> second trimester

Embryonic --> fetal period

41

At which stage of development is the fetus most sensitive to congenital malformations?

Embryonic phase

3 - 8 weeks

42

What is the surface area of the fetal villous tree?

12 - 14 m^2

43

What forms the uterine blood supply?

Arterial arcade formed by uterine and ovarian arteries in lateral walls of uterus, gives rise to arcuate arteries that encircle the uterus

44

What are the spiral arteries?

Arise from arcuate arteries

Supply blood to endometrium

Highly coiled, allowing for extension as uterus expands

45

Which arteries supply the placenta?

Spiral arteries

Muscular walls

46

What is involved in the conversion of spiral arteries during pregnancy?

1. Endometrium invaded by extravillous trophoblast
2. Loss of smooth muscle and endothelial lining in spiral arteries
3. Vessel dilatation and loss of vasoreactivity
4. Slows rate of inflow and reduces pressure

47

What condition is associated with failure of conversion of the spiral arteries?

Pre-eclampsia

48

What replaces the smooth muscle in converted spiral arteries?

Fibrinoid tissue

49

How are villi arranged in the placenta?

Lobules

50

How does the syncytiotrophoblast layer escape immune recognition?

Does not express MHC I or II antigens

51

What are the cells of the maternal immune system?

1. Macrophages
2. Lymphocytes
3. Uterine natural killer cells

52

What causes placental stress?

Abnormal interaction between trophoblast and maternal immune cells leads to deficient conversion of spiral arteries so uterine malperfusion

53

What causes intrauterine growth restriction?

1. Poor placental development
2. Poor placental function

54

What does effective placental exchange require?

1. Stable low-pressure, high-volume maternal blood supply
2. Large surface area
3. Transporter mechanisms for large or hydrophilic molecules
4. High transplacental gradient

55

How does the villous become specialised locally?

1. Thick regions for hormone synthesis
2. Thin vasculosyncytial regions for diffusional exchange

56

How much oxygen does the placenta use?

30% of total O2 used by feto-placental unit

57

What causes the double Bohr shift in the placenta?

1. Loss of CO2 from fetal blood increases pH and O2 binding
2. Gain of CO2 by maternal blood reduces pH and O2 binding

58

What is the pO2 in the uterine artery?

90mmHg

59

What is the pO2 in the uterine vein?

45mmHg

60

What is the pO2 in the umbilical vein?

30mmHg

61

What is the pO2 in the umbilical artery?

20mmHg

62

How do materials pass across the placenta?

1. Passive diffusion
2. Facilitated diffusion
3. Active transport
4. Endocytosis

63

What is transported across the placenta by passive diffusion?

1. Gases
2. Free fatty acids
3. Urea

64

What is transported across the placenta by facilitated diffusion?

1. Glucose
2. Free fatty acids

65

What is transported across the placenta by active transport?

Amino acids

66

Which proteins facilitate glucose transport?

GLUT proteins

67

Where is GLUT1 expressed?

Apical membrane of syncytiotrophoblast

Microvilli

68

Why are amino acids transported by active transport?

Fetal:maternal plasma ration is greater than 1 so going against gradient

69

What are the three main amino acid carrier systems?

1. Systems A and AC
2. System XAG
3. System L

70

What do systems A and AC carry?

Neutral amino acids

Alanine, glycine

Na+-dependent

71

What does system XAG carry?

Acidic amino acids

Glutamic acid, aspartic acid

Na+-dependent

72

What does system L carry?

Neutral amino acids

Leucine, phenylalanine

Na+-independent

73

What is carried by receptor-mediated endocytosis in the placenta?

IgG antibodies

74

When are IgG antibodies transported?

Third trimester of pregnancy

75

How is IgG transported?

Binds to receptors on microvillus membrane

Concentrated in coated pits at base of microvillus

76

How is maternal metabolism modulated?

Placental hormones

77

What happens to maternal metabolism in early pregnancy?

1. Appetite stimulated
2. Deposition of nutrient resources

78

What happens to maternal metabolism in later pregnancy?

1. Resources mobilised for transfer to fetus
2. Mobilised for use in lactation

79

Where does hCG act?

LH receptors in corpus luteum

80

Where is hCG synthesised?

Syncytiotrophoblast

81

What is the role of hCG?

Maintain corpus luteum so that it continues producing progesterone until the placenta takes over

82

What is the structure of hCG?

Glycoprotein with two non-covalently linked subunits

Alpha subunit identical to LH, FSH and TSH

Beta subunit unique but very similar to LH

83

What is hPL?

Human placental lactogen

1. Appetite stimulant
2. Stimulates lipolysis and raises maternal FFAs
3. Induces growth and differentiation of mammary glandular tissues

84

Where is hPL synthesised?

Syncytiotrophoblast

85

How do hPL levels change throughout pregnancy?

Synthesis begins at 10 weeks

Continues to rise until birth

86

What is the function of placental growth hormone?

1. Stimulates lipolysis
2. Stimulates gluconeogenesis
3. Regulates maternal IGF1 levels and insulin sensitivity
4. Elevates maternal glucose levels - glucose intolerance
5. Suppresses maternal growth hormone secretion

87

Where is placental growth hormone synthesised?

Syncytiotrophoblast

88

What is the role of leptin?

1. Appetite stimulant
2. Stimulates expression of placental transporter proteins

89

How does maternal sensitivity to leptin change in pregnancy?

Peripheral leptin resistance allows mother to lay down adipose reserves

90

Where is leptin synthesised?

Syncytium

91

Which hormones regulate leptin?

1. Oestrogen
2. hCG

92

When do leptin levels peak?

End of 2nd/start of 3rd trimester

93

What is PAPP-A?

Pregnancy associated protein A

Protease that cleaves IGF proteins to increase their bioavailability

94

How do PAPP-A levels change throughout pregnancy?

Rise continuously

95

What is the role of progesterone in pregnancy?

1. Maintains uterine quiescence
2. Stimulates endometrial glands
3. Appetite stimulant
4. Immunomodulatory

96

Where is progesterone synthesised in pregnancy?

Syncytiotrophoblast of placenta

97

What is progesterone synthesised from?

Cholesterol taken up from apical surface of placenta

98

What occurs to steroid hormones in the fetus?

1. Conjugates steroid hormones in liver or adrenal gland to inactivate them and protect the fetus from masculinisation

2. Placenta de-sulphates them and converts them to oestrogens and secretes them into maternal circulation

99

What do oestriol levels indicate?

Fetal well-being

Indication of fetal liver function

100

What allows the fetal HPA axis to mature in isolation?

11ß-hydroxysteroid dehydrogenase metabolises maternal cortisol to inactive cortisone

101

What is maternal microchimerism?

Male cells found in female thyroid tissue after pregnancy

May be responsible for autoimmune diseases

May be repair

102

What kind of fetal DNA is found in the maternal circulation?

Fetal cell-free DNA and RNA

10% of circulating DNA

Short fragments