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Placentation Flashcards

1
Q

What does the inner cell mass differentiate into?

A
  1. Epiblast

2. Hypoblast

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2
Q

What is the epiblast?

A

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

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3
Q

What is the hypoblast?

A

Faces the blastocoel

Forms the primary yolk sac

Gives rise to extra-embryonic mesoderm

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4
Q

Where does extra-embryonic mesoderm come from?

A

Hypoblast

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5
Q

What does extra-embryonic mesoderm give rise to?

A
  1. Chorion

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

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6
Q

What is the extra-embryonic coelom?

A

The space between the chorion and the amnion

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7
Q

How does the secondary yolk sac arise?

A

The primary yolk sac pinches off

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8
Q

What is the connecting stalk?

A

Connects the conceptus to the chorion

Future umbilical cord

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9
Q

What happens to the extra-embryonic coelom?

A

Obliterated at 12 weeks

Amnion pushed against inner surface of chorion

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10
Q

Where is the first site of haematopoiesis?

A

Yolk sac

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11
Q

What is exchanged between the mother and the yolk sac?

A
  1. Amino acids

2. Other nutrients

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12
Q

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

A

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

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13
Q

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

A
  1. Absorptive epithelium
  2. GLUT1 and other transporters
  3. Synthesises many proteins like alpha-fetoprotein
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14
Q

What are the eight functions of the placenta?

A
  1. Gas transfer
  2. Excretion
  3. Immune
  4. Metabolic functions
  5. Synthetic functions
  6. Catabolic and resorptive functions
  7. Secretory functions
  8. Haematopoiesis
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15
Q

Where is the chorionic plate of the placenta?

A

Faces the fetus

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16
Q

Where is the basal plate of the placenta?

A

Apposed to decidua basalis

Where maternal blood enters

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17
Q

What is haemochorial placentation?

A

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

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18
Q

Where are fetal capillaries located in the placenta?

A

Inside the villi

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19
Q

What does the trophoblast differentiate into?

A
  1. Syncytiotrophoblast

2. Cytotrophoblast

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20
Q

How is the syncytiotrophoblast formed?

A

Non-proliferative

Generated by continual fusion of cytotrophoblast cells

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21
Q

What is the structure of the syncytiotrophoblast?

A

Erodes into decidua

Breaks into endometrial glands and decidual capillaries

Spaces appear and coalesce to form lacunae

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22
Q

What fills the lacunae of the syncytiotrophoblast?

A
  1. Maternal blood

2. Glandular secretions

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23
Q

How are the earliest placental villi formed?

A

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

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24
Q

How is the placental villus tree formed?

A

Repeated branching of the early villus

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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

Human Reproduction (17 decks)

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