Structure and Function of Placenta Flashcards Preview

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

Flashcards in Structure and Function of Placenta Deck (94):
1

What takes precedence in early embryonic development? 

The establishment of the placenta

2

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

Ensures support for pregnancy

3

What happens in week 2 of embryonic development?

Differentiation 

4

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

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

5

What is the outer cell mass formed from? 

  • Syncytiotrophoblast 
  • Cytotrophoblast 

 

6

What does the inner cell mass become? 

The bilaminar disc

7

What does the bilaminar disc consist of? 

  • Epiblast 
  • Hypoblast 

 

8

What happens on day 6 of embryonic development? 

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

9

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

The ovary

10

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

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

11

When does the implantation process continue into? 

Continues into the 1st trimester

12

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

  • Amniotic cavity
  • Yolk sac

 

13

What is the yolk sac suspended within? 

A supporting sac, the chorionic cavity 

14

How is the yolk sac suspended in the supporting sac? 

By a connecting stalk 

15

What happens to the embryonic spaces as the embryo develops? 

They change; 

  • Yolk sac disappears
  • Amniotic sac enlarges a lot 

 

16

What is the remnant of the yolk sac? 

Vestigial structure in the umbilical cord

17

Why does the amniotic sac enlarge a lot? 

Needs to meet the needs of the growing embryo and fetus 

18

What is the chorionic sac occupied by? 

The expanding amniotic sac

19

What happens to the amniotic and chorionic membrane? 

It gets pushed together, and fuses

20

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

It is the membrane that ruptures when the 'waters break'

21

What is true of implantation? 

It is interstitial 

22

What happens in implantation? 

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

23

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

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

24

What can breaching cause in implantation? 

Bleeding

25

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

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

26

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

It gets thinner 

27

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

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

28

What is meant by the human placenta being haemomonochorial? 

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

29

What are the aims of implantation? 

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

 

30

What is the basic unit of exchange in the placenta? 

Villi

31

What are the stages in villi development? 

  1. Primary
  2. Secondary
    Tertiary

 

32

When are primary villi formed? 

Day 13

33

What are primary villi? 

Early finger-like projections of trophoblast 

34

What do primary villi consist of? 

Cytotrophoblast surrounded by syncytiotrophoblast 

35

When are secondary villi formed? 

Days 15-16

36

What happens in the development of secondary villi? 

Invasion and population of mesenchyme into core

37

When are tertiary villi formed? 

Day 23

38

What happens in tertiary villi formation? 

Invasion of mesenchyme core by fetal vessels

39

What is true of tertiary villi? 

Structure now capable of conducting exchange

40

How is the placenta anchored within the endometrium?

With the establishment of the outermost cytotrophoblast shell

41

How is the endometrium prepared for implantation? 

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

 

42

What are pre-decidual cells? 

Specialised endometrial cells that control implantation 

43

What is the purpose of the deciudal reaction? 

Provides balancing force for invasive force of trophoblast 

44

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

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

45

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

Creation of a low resistance vascular bed

46

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

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

47

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

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

48

What does fetal tissue lining the spiral arteries allow? 

The system to be low resistance

49

Describe the fetal membranes in week 5

Chorion has villi all round

50

Describe the fetal membranes in week 12

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

51

Describe the fetal membranes in week 22

Amniochorionic membrane fuses to decidua parietalis, becoming composite membranes

52

To what extent to monozygotic twins share a membrane? 

Varies, can be;

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

 

53

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

Amnion and chorion both shared

54

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

Twin to twin transfusion syndrome

55

What is the maternal aspect of the placenta divided into? 

Cotyledons

56

Describe the 1st trimester placenta

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

 

57

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

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

58

Describe a term placenta 

 

  • Surface area for exchange dramatically increased
  • Placental barrier now thin

 

59

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

Just syncytiotrophoblast and fetal capillary endothelium 

60

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

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

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

Short distance for nutrients to get into fetal circulation 

62

What makes up the fetal circulation? 

Two umbilical arteries, and one umbilical vein

63

What do the umbilical arteries carry? 

Deoxygenated blood, from the fetus to the placenta

64

What does the umbilical vein carry? 

Oxygenated blood, from placenta to fetus

65

What are the functions of the placenta?

  • Placental synthesis
  • Endocrine function
  • Transport

 

66

What does the placenta synthesise? 

  • Glycogen
  • Cholesterol
  • Fatty acids

 

67

Why does the fetus require cholesterol? 

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

68

What are the categories of hormones produced by the placenta? 

  • Protein
  • Steroid

 

69

What protein hormones are produced by the placenta? 

  • Human chorionic gonadotrophin (hCG)
  • Human chorionic somatomammotrophin
  • Human chorionic thyrotrophin
  • Human chorionic corticotrophin

70

When is hCG produced? 

During the first two months of pregnancy 

71

What is the function of hCG? 

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

72

What is the clinical importance of hCG? 

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

73

What may cause an increase in hCG? 

  • Twin pregnancy
  • Trophoblast disease

74

What does human chorionic somatomammotrophin and hPL do? 

Increases glucose availability to fetus

75

What are steroid hormones responsible for in pregnancy? 

Maintaining the pregnant state by shutting down the hCG axis

76

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

By the 11th week

77

What is the effect of progesterone in pregnancy? 

Increased appetite 

78

Why is an increase in appetite needed in pregnancy? 

To lay down fat stores early in pregnancy for use later 

79

What forms of transport are used in the placenta? 

  • Simple diffusion
    Facilitated diffusion
  • Active transport

 

80

What is simple diffusion? 

Molecules moving down a concentration gradient 

81

What molecules move by simple diffusion across the placenta? 

  • Water
  • Electrolytes
  • Urea and uric acid
  • Gases

 

 

82

What limits gas diffusion in placenta? 

Flow limited, not gas limited

83

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

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

84

Why is maintenance of adequate flow to the placenta essential? 

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

85

What is transported by facilitated diffusion in the placenta?

Glucose 

86

How is active transport achieved in the placenta? 

Specific transports are expressed by the synctiotrophoblast 

87

What is transported by active transport in the placenta? 

  • Amino acids
  • Iron
  • Viramins

 

88

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

Development and growth of new structures

89

Why is passive immunity required in the fetus? 

Fetal immune system is immature 

90

Why is passive immunity effective? 

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

How does passive immunity pass to a fetus? 

Receptor mediated process, maturing as pregnancy progresses

92

Is passive immunity to the fetus immunoglobulin class specific? 

Yes, IgG only 

93

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

They are higher

94

What is the purpose of IgG in breastmilk? 

Tops it up