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Pregnancy and Parturition > Placenta > Flashcards

Placenta Flashcards

1
Q

What is the 3 structures that form the structure of the placenta and blood supply of each?

A

Umbilical cord
- 2 arteries (deoxygenated), 1 vein (oxygenated)
- vein is larger than arteries

Chorionic villi (tree like structure)
- fetal capillaries enclosed on trophoblast

Intervillous space
- filled with maternal blood supplied by spiral arteries from endometrium

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2
Q

Placental development:
What occurs at the pre-implantation stage?

A
  1. fertilisation and cleavage from blastocyst (until day 4-5 post fertalisation)
    - forms an outer layer trophoblast
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3
Q

Placental development:
What occurs at the implantation stage?

A
  1. trophoblast proliferation, differentiation and invasion (day 8 post fertilisation)

-Trophoblast is made up of cytotrophoblast cells which differentiate into syncytiotrophoblast
- when the blastocyst implants into uterine wall the synctiotophoblast invades endometrium by secreting proteolytic enzymes

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4
Q

Placental development:
What occurs at the post-implantation stage?

A
  1. Lacunae formation (cavity)
  • these are initially filled with tissue fluids and uterine secretions until the maternal capillaries get eroded and they fill with maternal blood
  • these eventually merge to form intervillous spaces
  1. Villi formation
  • cytotrohpblast projections invade syncytiotrophoblast and embryonic mesoderm follows
  • fetal capillaries are formed in villi
  • trophoblast forms above villi to close off intervillous space
  • branching continues until week 20 then villi mature
  1. Spiral artery remodelling
  • trophoblast cells invade maternal spiral arteries to break down endothelium and smooth muscle cells
  • results in large, low resistance vessels which provides continuous blood supply into intervillous space
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5
Q

When is the placenta fully formed?

A

18-20 weeks

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6
Q

How much of the ueterus endometrium is covered by the placenta

A

40%

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7
Q

There are morphological variations in placental structure in mammals. What are the different gross shapes and distribution of chorionic villi types?

A
  1. diffuse (pig, horses, kangaroos)
    - chorionic villi found all around
  2. multicotyledonary (cows, sheep, deer)
    - chorionic villi spotted across placenta
  3. zonary (dogs, cats, bears)
    - chorionic villi located in one zone of placenta
  4. discoid (human type, rabbits, mice)
    - chorionic villi in one spherical area of placenta
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8
Q

There are morphological variations in placental structure in mammals. What are the different tissue indigitations found?

A
  1. folded
  2. lamellar
  3. trabecular
  4. villous (human)
  5. labyrinthine
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9
Q

There are morphological variations in placental structure in mammals. What are the different types of tissue layers among placentas?

A
  1. epitheliochorial
  2. endotheliochorial
  3. hemochorial (humans)
    - humans are known as haemo-mono-chorial
    (blood does not mix between mother and fetus)
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10
Q

The placenta has many functions. One of its functions is to mediate the transportation of oxygen, nutrients and waste. What are the different ways transportation occurs through the placenta?

A
  1. diffusion
  2. transporter mediated
  3. endocytosis/exocytosis
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11
Q

Materials that can pass through the placenta to the fetus do not always stay the same. What else can happen to them?

A
  1. partial consumption by the placenta
  2. metabolised from one product to another by the placenta
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12
Q

Another function of the placenta is to protect the fetus. However it is not the perfect barrier. What can pass through the placenta that could cause damage to the fetus?

A
  • alcohol
  • steroids or arrhythmia medication
  • certain infections: rubella, COVID
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13
Q

The placenta also has endocrine functions. How does the placenta know to release hormones?

A

through signalling from mother and fetus

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14
Q

What hormones from the fetus affect hormone synthesis of the placenta?

A

glucocorticoids
leptin
insulin

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15
Q

What hormones from the mother which affect hormone synthesis of the placenta?

A

glucocorticoids
mineralocorticoids
leptin/ adiponectin
insulin
angiotensin 2

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16
Q

The placenta has the ability to release hormones based on the hormone released by mother or fetus. What are the common hormones released by the placenta?

A

chorionic gonadotrophin
prolactins
placental growth hormone
prostaglandins
sex steroids
leptin

17
Q

What are the common outcomes when placentation goes wrong?

A

pre-eclampsia
placenta accreta
placenta previa
placental abruption still birth

18
Q

What goes wrong with the placenta fro pre-eclampsia to occur?

A

spiral arteries in the endometrium do not reshape properly due to inadequate invasion of trophoblast cells

19
Q

What happens when placenta accreta occurs?

A

placenta does not attach to the stratum basalis of endometrium. It continue to invade and attached to myometrium

20
Q

What happens when placenta previa occurs?

A

This is then the placenta inplants at the bottom of the uterus rather than the side results in the cervix being covered or partially covered. Natural birth cannot occur.

21
Q

What happens when placental abruption occurs?

A

This is when the placenta detaches from endometrium. This can starve the fetus of nutrients and oxygen. Depending on how far along in pregnancy this occurs a c-section will be required

22
Q

How does the abnormal placentation result in still birth?

A

still birth = loss of fetus after 20 weeks of gestation

all previous placental probelsm are common contributors and also long hyper-twisted umbilical cords
- restricts blood to fetus

23
Q

Recent studies have began looking at the relationship between imprinted genes and placentation. What is the theory as to why imprinting genes are involved?

A

balance of parental resources and is important for growth of fetus.

Note: imprinting is an epigenetic phenomenon which describes the parent of origin of gene expression

Pregnancy and Parturition (10 decks)

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