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Semester 3 - reproduction > 13. The placenta; anatomy, physiology and functio > Flashcards

13. The placenta; anatomy, physiology and functio Flashcards

1
Q

When does the placenta develop?

A

second week of development

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2
Q

What is the focus of early development?

A

ensuring development of the “fetal membranes”

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3
Q

What do the fetal membranes include?

A

– i.e. the sacs supporting the embryo/fetus

– and the placenta

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4
Q

What is the outer cell mass called and what layers emerge from this?

A

Trophoblast, produces:

- cytotrophoblast and syncytiotrophoblast

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5
Q

What layers emerge from the inner cell mass?

A

• inner cell mass becomes the bilaminar disk
– epiblast
– hypoblast

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6
Q

What will the outer cell mass become?

A

fetal membranes

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7
Q

What day does implantation begin?

A

Day 6

- trophoblast cells interact with the endometrium once the embryo has hatched from zona pellucida

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8
Q

What happens to the yolk sac, amniotic sac and chorionic sac??

A
  • yolk sac disappears
  • amniotic sac enlarges and surrounds entire fetus
  • As the amniotic sac enlarges, the chorionic sac is displaced, and the amniotic membrane fuses with the chorionic membrane to produce a single amniotic cavity
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9
Q

What is the amniochorionic membrane?

A

Composite membrane formed from the amniotic membrane and chorionic membrane
- ruptures during onset of parturition

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10
Q

What does implantation achieve?

A
  • establishes the basic unit of exchange
  • anchor the placenta
  • establish maternal blood flow within the placenta
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11
Q

What are the different developmental stages of the chorionic villi?

A
  • primary villi: early finger-like projections of trophoblast
  • secondary villi: invasion of mesenchyme into core
  • tertiary villi: invasion of mesenchyme core by fetal vessels
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12
Q

What is the basic unit of exchange?

A

Chorionic villus

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13
Q

what happens during implantation?

A

the uterine epithelium is breached and the conceptus implants within the stroma

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14
Q

What is a chorionic villus?

A 
functional unit of the placenta
• Finger-like projections
- made from Trophoblast
- Inner connective tissue core
• Fetal vessels
Maternal blood vessels then surround these villi, allowing exchange to occur
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15
Q

What happens to placental membrane as fetus develops and why?

A

Becomes progressively thinner as the needs of the fetus increase

In the first trimester, this barrier between fetal and maternal blood is relatively thick with a full layer of cytotrophoblast and syncytiotrophoblast. As the pregnancy progresses, this barrier becomes progressively less by reducing the number of
cytotrophoblast cells to be more optimised for transport.

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16
Q

What separates maternal blood from foetal blood by the third trimester?

A

The barrier between maternal and fetal blood flow is a single layer of trophoblast and metal capillary endothelial for optimal transport, but the two circulations never mix.

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17
Q

what is the placenta a specialisation of?

A

The placenta is a specialisation of the chorionic membrane

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18
Q

What are 2 conditions that involve implantation at the wrong site?

A

Ectopic pregnancy and placenta praeviae

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19
Q

what are the two conditions due to incomplete invasion?

A

– placental insufficiency

– pre-eclampsia

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20
Q

What is an ectopic pregnancy?

A
  • implantation at site other than uterine
    body (most commonly Fallopian tube)
  • can be peritoneal or ovarian
  • can very quickly become life threatening emergency
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21
Q

What is placenta praevia?

A
  • implantation in the lower uterine segment
  • can cause haemorrhage in pregnancy
  • can require C-section delivery
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22
Q

What is the endometrium transformed to in presence of the conceptus?

A

Decidua - modulate the degree of invasion of the conceptus once it has implanted

23
Q

What is the decidual reaction?

A

Provides the balancing force for the invasive force of the trophoblast - syncytiotrophoblast release enzymes that burrow through surface but the decimal layer is resistant to some of these enzymes

24
Q

What happens if implantation occurs where there is no decidua?

A

no decidua therefore no control e.g ectopic pregnancy

  • conceptus can invade through the wall where it has implanted
  • can invade into the pelvic cavity and into blood vessels causing massive haemorrhage
25
Q

What happens if the decidual reaction is sub-optimal(not deep enough)?

A

Range of complications where the pregnancy is either not maintained (which can lead to miscarriage or infertility), or a spectrum of placental insufficiency including pre-eclampsia

26
Q

in preeclampsia, what is the depth of invasion of trophoblast

A

not deep enough

27
Q

in which condition does trophoblast invade too deeply?

A

placenta accreta

28
Q

What is the gross morphology of the placenta from the maternal aspect?

A
  • cobblestone like appearance
  • lots of cotyledons
  • amniochorion
29
Q

What is the gross morphology of the placenta from the fetal aspect?

A
  • Shiny due to the amniotic membrane (transparent) covering

- Can see the umbilical vessel and chorionic vessels protruding from beneath the amnion

30
Q

What are cotyledons?

A

Any of the major convex sub-divisions of the mature placenta. Each cotyledon contains a major branch of the umbilical blood vessels, which branch further into numerous villi that make up the surface of the cotyledon. - contain chorionic villi

31
Q

Why must the placenta be assessed post-partum?

A

Ensure complete placenta is delivered

- retained cotyledons within the uterus can lead to post-partum haemorrhage

32
Q

what are the maternal blood vessels?

A

The maternal blood vessels are called the endometrial arteries and veins, which essentially bathe the outside of the villi in maternal blood for exchange to occur.

33
Q

what are the metal blood vessels?

A

The fetal blood vessels bring waste products to the villi through the umbilical arteries (paired), and takes oxygen and nutrients to the fetus via the umbilical vein (singular).

34
Q

in the first trimester, what is the placental membrane made of?

A

syncytiotrophoblast
cytotrophoblast
endothelium of metal capillary

35
Q

in the third trimester, what os the placental membrane made of?

A

syncytiotrophoblast

endothelium of metal capillary

36
Q

how many umbilical arteries and veins are there and what do they carry?

A 
• Two umbilical arteries
– Deoxygenated blood from fetus to
placenta
• One umbilical vein
– Oxygenated blood from placenta to fetus
37
Q

what are the two types of hormones produced by the placenta?

A

Protein

Steroid

38
Q

Which steroids does the placenta produce?

A

progesterone and oestrogen

39
Q

Which proteins does the placenta produce?

A

Human chorionic gonadotrophin (hCG)
Human chorionic somatomammotrophin/hPL
Human chorionic thyrotrophin
Human chorionic corticotrophin

40
Q

what does the placenta takeover from?

A

corpus luteum

41
Q

What produces hCG, when and what is its function?

A

Produce by the syncytiotrophoblast during the first 2 months pf pregnancy
- supports the secretory function of corpus luteum to keep progesterone and oestrogen high until placenta takes over

42
Q

What does a pregnancy test test for?

A

hCG in urine

- hCG can also be tested for in the blood

43
Q

In which week does the placenta take over from the corpus luteum?

A

By the 11th week

44
Q

how does progesterone influence maternal metabolism?

A

increases appetite to allow an increased fat deposition to help support the fetus and breastfeeding later on in the pregnancy.

45
Q

how does human placental lactogen (hPL) influence maternal metabolism?

A

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

46
Q

Which molecules are transported across the placenta by simple diffusion?

A
  • water
  • electrolytes
  • urea & uric acid
  • gases
47
Q

Which molecules are transported across the placenta by facilitated diffusion?

A

applies to glucose transport

48
Q

Other than for pregnancy when might hCG be tested for?

A

Trophoblast disease:

  • molar pregnancy (hydatidiform mole)
  • choriocarcinoma
49
Q

What limits gas exchange between fetal and maternal blood?

A

rate of exchange in gas exchange is flow limited, not diffusion limited. Therefore adequate uteroplacental circulation is required, and if compromised e.g. during labour, contraction can lead to compression of the blood vessels and ‘fetal distress’.

50
Q

Which molecules are transported across the placenta by active transport?

A

specific “transporters” expressed by the syncytiotrophoblast

  • amino acids
  • iron
  • vitamins
51
Q

Describe transfer of immunity.

A

The immune system of the fetus is very immature. However, antibodies can be transported across the placenta into the fetal circulation so that at the time of birth the fetus has some defence against infection.
• IgGonly
•IgG concentrations in fetal plasma exceedt hose in maternal circulation

52
Q

When do teratogens have greatest effect?

A

Early pregnancy, particularly in the embryonic stage (3-8 weeks) as this is a key time for development of the body systems
- in fetal period most systems already developed, just need to grow

53
Q

What is haemolytic disease of the newborn (HDN)?

A

Mother has antibodies against rhesus positive blood, these can cross the placenta (IgG) and attach fetal blood (if its rhesus positive) destroying fetal blood cells

Semester 3 - reproduction (19 decks)

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