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ESA 4 - Reproductive System > Structure and Function of Placenta > Flashcards

Structure and Function of Placenta Flashcards

1
Q

What takes precedence in early embryonic development?

A

The establishment of the placenta

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2
Q

Why does the establishment of the placenta take precedence in early embryonic development?

A

Ensures support for pregnancy

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3
Q

What happens in week 2 of embryonic development?

A

Differentiation

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4
Q

What is formed from differentation in week 2 of embryonic development?

A

Two distinct cellular layers, the outer cell mass and the inner cell mass

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5
Q

What is the outer cell mass formed from?

A
  • Syncytiotrophoblast
  • Cytotrophoblast
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6
Q

What does the inner cell mass become?

A

The bilaminar disc

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7
Q

What does the bilaminar disc consist of?

A
  • Epiblast
  • Hypoblast
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8
Q

What happens on day 6 of embryonic development?

A

The synctiotrophoblast breaches the uterine epithelium, and the conceptus becomes embedded

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9
Q

What is the breaching of the uterine epithelium by the syncytiotrophoblast under the control of?

A

The ovary

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10
Q

What has happened in embryonic development by the end of the second week?

A
  • The conceptus has implanted, and is now embedded in endometrium
  • Two cavities have been formed
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11
Q

When does the implantation process continue into?

A

Continues into the 1st trimester

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12
Q

What are the two cavities formed by the end of the second week of embryonic development?

A
  • Amniotic cavity
  • Yolk sac
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13
Q

What is the yolk sac suspended within?

A

A supporting sac, the chorionic cavity

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14
Q

How is the yolk sac suspended in the supporting sac?

A

By a connecting stalk

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15
Q

What happens to the embryonic spaces as the embryo develops?

A

They change;

  • Yolk sac disappears
  • Amniotic sac enlarges a lot
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16
Q

What is the remnant of the yolk sac?

A

Vestigial structure in the umbilical cord

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17
Q

Why does the amniotic sac enlarge a lot?

A

Needs to meet the needs of the growing embryo and fetus

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18
Q

What is the chorionic sac occupied by?

A

The expanding amniotic sac

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19
Q

What happens to the amniotic and chorionic membrane?

A

It gets pushed together, and fuses

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20
Q

What is the clinical relavence of the membrane formed from the fusion of the amniotic and chorionic membrane?

A

It is the membrane that ruptures when the ‘waters break’

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21
Q

What is true of implantation?

A

It is interstitial

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22
Q

What happens in implantation?

A

The uterine epithleium is breached, and the conceptus implants within the stroma

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23
Q

What is the result of the breaching of the uterine epithelium in implantation?

A

There is a very close relationship between the fetal and maternal tissue

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24
Q

What can breaching cause in implantation?

A

Bleeding

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25
Q

What is the relavence of bleeding caused by breaching in implantation?

A

It can lead to dating confusion, as it can be confused with a light menstrual period

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26
Q

What happens to the placental membrane as the needs of the fetus increase?

A

It gets thinner

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27
Q

What is shown by the thinning of the placental membrane as the needs of the fetus increase?

A

The placenta itself has a develomental programme required to keep up with the needs of the fetus

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28
Q

What is meant by the human placenta being haemomonochorial?

A

One layer of trophoblast ultimately seperates maternal blood from fetal capillary wall

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29
Q

What are the aims of implantation?

A
  • Establish basic unit of exchange
  • Anchor placenta within endometrium
  • Establish maternal blood flow within the placenta
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30
Q

What is the basic unit of exchange in the placenta?

A

Villi

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31
Q

What are the stages in villi development?

A
  1. Primary
  2. Secondary
    Tertiary
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32
Q

When are primary villi formed?

A

Day 13

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33
Q

What are primary villi?

A

Early finger-like projections of trophoblast

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34
Q

What do primary villi consist of?

A

Cytotrophoblast surrounded by syncytiotrophoblast

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35
Q

When are secondary villi formed?

A

Days 15-16

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36
Q

What happens in the development of secondary villi?

A

Invasion and population of mesenchyme into core

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37
Q

When are tertiary villi formed?

A

Day 23

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38
Q

What happens in tertiary villi formation?

A

Invasion of mesenchyme core by fetal vessels

39
Q

What is true of tertiary villi?

A

Structure now capable of conducting exchange

40
Q

How is the placenta anchored within the endometrium?

A

With the establishment of the outermost cytotrophoblast shell

41
Q

How is the endometrium prepared for implantation?

A
  • Pre-decidual cells begin to develop
  • Elaboration of the spiral artery blood supply
42
Q

What are pre-decidual cells?

A

Specialised endometrial cells that control implantation

43
Q

What is the purpose of the deciudal reaction?

A

Provides balancing force for invasive force of trophoblast

44
Q

Why is it required that there is a balancing force for the invasive force of the trophoblast?

A

Prevents going through myometrium, into the vascular structures of the pelvis. Implantation is a very tissue destructive process, so needs to be mediated

45
Q

What is created by the elaboration of the spiral arterial blood supply?

A

Creation of a low resistance vascular bed

46
Q

Why is the creation of a low resistance vascular bed critical?

A

Because it maintains the high flow required to meet the fetal demand, particularly in late destation

47
Q

What happens in elaboration of the spiral arterial blood supply in normal implantation?

A

The trophoblast starts to invade the spiral arteries and the maternal endothelium is displaced, so fetal tissue lines the spiral arteries

48
Q

What does fetal tissue lining the spiral arteries allow?

A

The system to be low resistance

49
Q

Describe the fetal membranes in week 5

A

Chorion has villi all round

50
Q

Describe the fetal membranes in week 12

A

Chorion loses villi away from decidua basalis, and final disc shape achieved

51
Q

Describe the fetal membranes in week 22

A

Amniochorionic membrane fuses to decidua parietalis, becoming composite membranes

52
Q

To what extent to monozygotic twins share a membrane?

A

Varies, can be;

  • Entirely independant
  • Two amnions, but shared chorion
  • Amnion and chorion are both shared
53
Q

What degree of membrane sharing is most risky for monozygotic twins?

A

Amnion and chorion both shared

54
Q

Give an example of an condition that may occur when the amnion and chorion are both shared

A

Twin to twin transfusion syndrome

55
Q

What is the maternal aspect of the placenta divided into?

A

Cotyledons

56
Q

Describe the 1st trimester placenta

A
  • Placenta established
  • Placental barrier still relatively thick
  • Complete cytotrophoblast layer beneath syncytiotrophoblast
57
Q

What is the importance of the cytotrophoblast layer of the 1st trimester placenta?

A

Acts as a stem cell layer, as the syncytiotrophoblast layer is lost, and so needs to be replaced

58
Q

Describe a term placenta

A
  • Surface area for exchange dramatically increased
  • Placental barrier now thin
59
Q

What is the placental barrier made up of in a term placenta?

A

Just syncytiotrophoblast and fetal capillary endothelium

60
Q

How does the placental barrier thin to reach the stage its at in a term placenta?

A

The cytotrophoblast layer is lost, and the distance between the capillary endothelium and syncytiotrophoblast gradually reduces due to morphological developmental programme of the villi, where undifferentiated mesoderm reduces

61
Q

What is the importance of the thinning of the placental barrier?

A

Short distance for nutrients to get into fetal circulation

62
Q

What makes up the fetal circulation?

A

Two umbilical arteries, and one umbilical vein

63
Q

What do the umbilical arteries carry?

A

Deoxygenated blood, from the fetus to the placenta

64
Q

What does the umbilical vein carry?

A

Oxygenated blood, from placenta to fetus

65
Q

What are the functions of the placenta?

A
  • Placental synthesis
  • Endocrine function
  • Transport
66
Q

What does the placenta synthesise?

A
  • Glycogen
  • Cholesterol
  • Fatty acids
67
Q

Why does the fetus require cholesterol?

A

Precursor for the key steroid hormones to support pregnancy, oestrogen and progesterone

68
Q

What are the categories of hormones produced by the placenta?

A
  • Protein
  • Steroid
69
Q

What protein hormones are produced by the placenta?

A
  • Human chorionic gonadotrophin (hCG)
  • Human chorionic somatomammotrophin
  • Human chorionic thyrotrophin
  • Human chorionic corticotrophin
70
Q

When is hCG produced?

A

During the first two months of pregnancy

71
Q

What is the function of hCG?

A

Supports the secretory function of the corpus luteum, maintaining it until the placenta takes over the production of progesterone and oestrogen

72
Q

What is the clinical importance of hCG?

A

Excreted in maternal urine, therefore used as a basis for pregnancy testing

73
Q

What may cause an increase in hCG?

A
  • Twin pregnancy
  • Trophoblast disease
74
Q

What does human chorionic somatomammotrophin and hPL do?

A

Increases glucose availability to fetus

75
Q

What are steroid hormones responsible for in pregnancy?

A

Maintaining the pregnant state by shutting down the hCG axis

76
Q

When does placental production of steroid hormones take over from the corpus luteum?

A

By the 11th week

77
Q

What is the effect of progesterone in pregnancy?

A

Increased appetite

78
Q

Why is an increase in appetite needed in pregnancy?

A

To lay down fat stores early in pregnancy for use later

79
Q

What forms of transport are used in the placenta?

A
  • Simple diffusion
    Facilitated diffusion
  • Active transport
80
Q

What is simple diffusion?

A

Molecules moving down a concentration gradient

81
Q

What molecules move by simple diffusion across the placenta?

A
  • Water
  • Electrolytes
  • Urea and uric acid
  • Gases
82
Q

What limits gas diffusion in placenta?

A

Flow limited, not gas limited

83
Q

What is the result of gas diffusion across the placenta being flow limited?

A

It is dependant on good flow through the utero-placental circulation

84
Q

Why is maintenance of adequate flow to the placenta essential?

A

Fetal O2 stores are small, and so fetus can’t tolerate interference with exchange for very long

85
Q

What is transported by facilitated diffusion in the placenta?

A

Glucose

86
Q

How is active transport achieved in the placenta?

A

Specific transports are expressed by the synctiotrophoblast

87
Q

What is transported by active transport in the placenta?

A
  • Amino acids
  • Iron
  • Viramins
88
Q

What are amino acids, iron, and vitamins required for by the fetus?

A

Development and growth of new structures

89
Q

Why is passive immunity required in the fetus?

A

Fetal immune system is immature

90
Q

Why is passive immunity effective?

A

Because the newborn is likely to encounter the same type of infections as the mother, and so it can borrow her immune system to afford the baby a degree of protection until its own system can mount an immune response

91
Q

How does passive immunity pass to a fetus?

A

Receptor mediated process, maturing as pregnancy progresses

92
Q

Is passive immunity to the fetus immunoglobulin class specific?

A

Yes, IgG only

93
Q

How do IgG levels in fetal circualation compare to those in the mothers?

A

They are higher

94
Q

What is the purpose of IgG in breastmilk?

A

Tops it up

ESA 4 - Reproductive System (31 decks)

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