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Reproduction > 8.1 The Placenta > Flashcards

8.1 The Placenta Flashcards

1
Q

When does implantation occur?

A

Day 6 of the pregnancy

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2
Q

How does implantation occur?

A

trophoblast cells interact with the endometrial lining of the uterus once it has ‘hatched’ and lost the zona pellucida.

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3
Q

Where does implantation typically occur?

A

Superior body of the uterus

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4
Q

What is an ectopic pregnancy?

A

An implantation outside of the endometrium

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5
Q

What is placenta praevia?

A

Implantation of the blastocyst within the lower uterine segment (close to or covering the internal os)

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6
Q

What is placenta accreta?

A

Invasion of the placenta too deep, resulting in attachment to the myometrium

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7
Q

What is pre-eclampsia?

A

Disorder of pregnancy characterised by hypertension, proteinuria. Can be caused by incomplete invasion of the conceptus

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8
Q

How does the endometrium adapt in preparation for implantation?

A

Increased vasculature

Increased secretory glands

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9
Q

When does the placenta begin to develop?

A

In the second week of pregnancy

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10
Q

What is the placenta?

A

Specialisation of an area of fetal membranes surrounding the foetus

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11
Q

What structure does the placenta develop from?

A

The trophoblast

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12
Q

What are the layers of the trophoblast?

A

Outer syncytiotrophoblast

Inner cytotrophoblast

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13
Q

What is the function of the villi?

A

The initial unit of exchange between conceptus and maternal blood supply. Contain foetal blood vessels with an outer membrane of syncytiotrophoblast

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14
Q

What forms the barrier between foetal and maternal blood supplies?

A

A single layer of trophoblast surrounding the edge of villi. In the first trimester barrier is thick with a full layer of cytotrophoblast and syncytiotrophoblast. As pregnancy progresses the barrier becomes progressively less.

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15
Q

Why does the barrier between foetal and maternal blood supply thin throughout pregnancy?

A

Number of cytotrophoblast cells reduce to optimise transport between blood supplies

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16
Q

What is the decidua?

A

Decidua relates to the cells of the endometrium that become specialized in the presence of the conceptus.

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17
Q

What happens if there is no decidua in implantation site?

A

There is no inhibition over decidualisation and therefore no control over the extent of the invasion. Invasive force of the trophoblast is unopposed and can invade other structures such as blood vessels causing haemorrhage.
Occurs in tubal ectopic pregnancy

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18
Q

What happens if the decidual reaction is suboptimal?

A

Implantation may not be able to go deep enough causing:
Miscarriage or infertility
Placental insufficiency (pre-eclampsia)

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19
Q

What are maternal blood vessels called?

A

Endometrial arteries and veins

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20
Q

What is the function of the endometrial arteries and veins?

A

To bathe the villi in maternal blood for exchange of gases to occur

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21
Q

What are the fetal blood vessels in the villi called?

A

Umbilical arteries (paired) and umbilical vein (singular)

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22
Q

What is the endocrine function of the placenta?

A
  • produce human chorionic gonadotrophin (hCG)
  • produces steroid hormones oestrogen and progesterone
  • produces human chorionic somatomammotrophin, human chorionic thyrotrophin, human chorionic cortiotrophin.
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23
Q

What cells produce hCG?

A

Syncytiotrophoblast cells in the first 2 months of pregnancy

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24
Q

What hormone is analysed in urinary and serum pregnancy testing?

A

HCG

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25
Q

What is the purpose of the hormone hCG?

A

Sustains the corpus luteum in the first trimester. Similar to LH

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26
Q

Why does the placenta produce steroid hormones?

A

To take on the role of the corpus luteum after the first trimester to keep HPG axis in a ‘pregnant state’

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27
Q

What placental hormones have an impact on maternal metabolism?

A

Progesterone

Human placental lactogen (hPL)

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28
Q

What impact does placental progesterone have on the maternal metabolism?

A

increase in appetite to allow an increased fat deposition to help support the fetus and breastfeeding later on in the pregnancy. Releases energy from fat stores

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29
Q

What impact does the hormone human placental lactogen (hPL) have on maternal metabolism?

A

creates a diabetogenic state to cause insulin resistance in the mother, increasing the glucose availability to the fetus.

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30
Q

How does transport at the placenta occur?

A
  1. Simple diffusion across concentration gradient
  2. Facilitated diffusion
  3. Active transport
31
Q

What substances can diffuse across the placenta down a concentration gradient?

A

Gases
Electrolytes
Water
Urea and uric acid.

32
Q

What substances diffuse across the placenta via facilitated diffusion?

A

Glucose

33
Q

What substances diffuse across the placenta via active transport?

A

Amino acids
Iron
Vitamins

34
Q

How is the rate of gas exchange between the foetal and maternal blood systems limited?

A

Flow limited

35
Q

When might uteroplacental circulation be inadequate?

A

During labour as contractions can lead to compression of blood vessels

36
Q

How does the foetus build its immune system before birth?

A

Antibodies transported across the placenta into the foetal circulation. Only IgG immunoglobulins can cross the placenta

37
Q

What is a teratogen?

A

An agent or factor which causes malformation of an embryo and access the foetus via the placenta

38
Q

Give some examples of the 4 types of teratogens?

A

Physical agents - ionising agents, hyperthermia
Metabolic conditions - diabetes, phenylketonuria
Infection - rubella, cytomegalovirus, varicella herpes simplex
Drugs and chemicals - organic mercury compounds, alcohol, smoking

39
Q

When do teratogens have their greatest effect? Explain why

A

Pre-embryonic = lethality effects
Embryonic stage of pregnancy ( 3 - 8 weeks) sensitivity is high as this is the key time development of body systems.
Risks of structural defects reduces as baby develops, except CNS

40
Q

What is Rhesus disease also known as?

A

Erythroblastosis fetalis

41
Q

What is Rhesus disease?

A

When there is a blood group incompatibility between foetus and mother. Maternal antibodies (IgG) cross into foetal circulation and attack foetal RBC causing sever haemolytic disease

42
Q

Why might infections have more serious complications in pregnancy?

A

As mother is in an immune compromised state.

43
Q

What happens in the second week of pregnancy?

A

Week of 2s

  • outer cell mass differentiates into syncytiotrophoblast and cytotrophoblast
  • inner cell mass becomes the bilaminar disk, consisting of epiblast and hypoblast
  • 2 cavities - amniotic sac and yolk sac
44
Q

Why does the outer cell mass develop before the inner cells mass develops?

A

Early placenta needs to be established to support the development of the embryo

45
Q

By day 9 of pregnancy, what has happened to the embryo?

A

Has implanted and entirely moved into endometrial layer

46
Q

How is the conceptus suspended in the chorionic cavity?

A

Suspended from the placenta via the connecting stalk

47
Q

What is the fate of the yolk sac?

A

Initially within the hypoblast/endoderm
Part of the yolk sac pitched off to provide primitive gut.
Reduces in size to become the umbilical vesicle remnant

48
Q

What happens to the amniotic sac?

A

Initially a cavity in the embryoblast.
Enlarges to surround the embryo.
Eventually fills the chorionic sac and displaces the chorionic cavity

49
Q

What happens to the chorionic sac?

A

Initially is a large cavity that the conceptus is suspended in.
In displaced by the rapidly growing amniotic cavity

50
Q

How is the aminochorionic membrane formed?

A

Amniotic membrane and chorionic membrane fuse after amniotic sac grows to occupy the chorionic cavity

51
Q

What is the clinical significance of the aminochorionic membrane?

A

Breaks at the onset of labour to release amniotic fluid

52
Q

What is the structure of primary villi?

A

Early finger like projections of trophoblast

53
Q

What is the structure of secondary villi?

A

Invasion of mesenchyme into close

54
Q

What is the structure of tertiary villi?

A

Invasion of mesenchyme core by fetal vessels

55
Q

What does implantation achieve?

A

Establishes basic unit of exchange
Anchor the placenta
Establish maternal blood flow

56
Q

In what structure does the conceptus implant into?

A

In the stroma of the uterus

57
Q

Why does the requirement for metabolites and blood transport increase as the foetus develops?

A

Due to the large size of the foetal brain, energy requirements of bran development is very large.

58
Q

What is a chorionic villus?

A

A finger-like projection of the placenta (specialisation of chorionic membrane). Increases SA to volume ratio for maternal foetal exchange.
A.k.a chorion frondosum

59
Q

What adaptations does the chorionic villus have to improve foetal maternal exchange?

A

High SA to volume ratio
Very thin - one cell of syncytiotrophoblast between maternal and foetal blood vessels
Good vascular supply

60
Q

What are the implantation defects that can occur?

A 
Implantation in the wrong place (ectopic pregnancy, placenta praevia)
Incomplete invasion (placental insufficiency, pre-eclampsia)
61
Q

Where can ectopic pregnancy occur?

A

Fallopian tube
Peritoneum
Ovary

62
Q

Why must a foetus implanted in the lower uterine segment be delivered via c-section?

A

Placenta praevia can can cause haemorrhage as placenta blocks cervix.

63
Q

What is the function of the umbilical cord?

A

Connects the fetal aspect of the placenta to the foetus

64
Q

Describe the structure of the maternal aspect of the placenta

A

Cotyledons have a bumpy cobblestone appearance and are the functional units that contain the chorionic villi.
Surrounded by the aminochorion

65
Q

What happens to cotyledons during labour?

A

Should come out along with child and placenta

66
Q

Describe the structure of the fetal circulation

A

2 umbilical arteries from the descending aorta, carrying deoxygenated blood.
1 umbilical vein carrying oxygenated blood from placenta to foetus.

67
Q

Why is hCG measured?

A

To determine pregnancy

As a marker of trophoblastic diseases (molar pregnancy, choriocarcinoma) that would upregulated production of hCG.

68
Q

What is human chorionic somatomammotrophin?

A

Human placental somatomammotrophin. Increases glucose availability to foetus.

69
Q

How doe transfer of passive immunity occur?

A

Receptor-mediated exocytosis/ endocytosis

70
Q

What waste products are moved from the foetus circulation to the maternal?

A 
CO2
Water
Urea and uric acid
Bilirubin
RBC antigens 
Hormones
71
Q

What can thalidomide harm the foetus?

A

Limb defects.

72
Q

What harm can alcohol do the foetus?

A

Foetal alcohol syndrome

Alcohol related neurological delay

73
Q

What drugs are teratogens?

A 
Anti-epileptic drugs
Warfarin
ACE inhibitors 
Drugs of abuse 
Smoking

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