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Physiology 2 > Reproduction: Implantation, placentation and hormone changes during pregnancy > Flashcards

Reproduction: Implantation, placentation and hormone changes during pregnancy Flashcards

1
Q

What 2 things do you need for implantation to occur?

A
  • A fully developed blastocyst - fully expanded and hatched out of zona pellucida
  • A receptive endometrium - thickened endometrial lining and has blastocyst receptivity markers
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2
Q

How is the fully developed blastocyst able to hatch out of the zona pellucida?

A
  • Enzymes dissolve the zona pellucida at abembryonic pole (opposite end from developing embryo)
  • Series of expansions and contractions allow blastocyst to bulge out of zona pellucida
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3
Q

What are the stages of implantation?

A
  1. Apposition
  2. Attachment
  3. Invasion
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4
Q

Describe the first events of implantation once the blastocyst gets close to endometrial wall

A
  1. Blastocyst attaches itslef to the surface of the endometrial wall (decidua basalis)
  2. Once attached to the decidua basalis the trophoblast cells begin to form a syncytiotrophoblast to help blastocyst invade decidua basalis
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5
Q

What is a syncytiotrophoblast?

A

A multi-nucleated single cell made up of massive amounts of trophoblast cells

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6
Q

What occurs a result of the formation of the syncytiotrophoblast?

A
  • Syncytiotrophoblast continues to invade decidua basalis until entire trophoblast is almost completely buried within the decidua basalis
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7
Q

What occurs once the blastocyst is completely buried within the decidua basalis?

A
  • Decidual reaction occurs - Cells within the decidua begin to enlarge and become coated with fluid rich in lipids and glycogen
  • Fluid is taken up by trophoblast cells of blastocyst which helps sustain these cells before blastocyst develops connection with placenta
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8
Q

What triggers the decidual reaction?

A

High progesterone levels due to secretions of progesterone from corpus luteum

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9
Q

What processes occur to the blastocyst after the decidual reaction?

A
  • Cells of the syncytiotrophoblast form tree-like structures called primary villi which surrond blastocyst
  • Primary villi begin to digest cells of the decidua basalis which form empty paces within the decidua called lacunae
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10
Q

What happens after the formation of the lacunae within the decidua basalis?

A
  • Maternal arteries and veins grow into the decidua basalis
  • These blood vessels then merge with the lacunae and so the lacunae become filled with blood
  • Blood-filled lacunae then merge into a single pool of blood known as the junctional zone
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11
Q

What organ does the functional zone form the basis of?

A

Functional zone froms basis of placenta

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12
Q

Explain what processes occur during the first stages of placental formation

A
  • Foetal mesoderm cells start to form blood vessels within the primary villi surronding the blastocyst
  • The primary villi also enlarge to form the chorionic frondosum
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13
Q

At the beginning stages of placental formation what layers seperate the maternal and foetal circulations?

A
  • Lining of the primary villi
  • Endothelial cell lining of the decidua basalis
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14
Q

What does the umbilical cord connect to once it’s formed within the developing embryo?

A

Once umbilical cord forms it the connects to the capillaries within the primary villi that are formed by the mesoderm

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15
Q

What happens to the placenta during 4th/5th months of pregnancy?

A
  • The decidual septa form and as a result they divide the placenta into regions called cotyledons
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16
Q

What advantages are there of each cotelydon having its own maternal blood supply?

A
  • It makes the maternal-foetal gas exchange much more efficient
  • This is because it increases surface area in which maternal-foetal gas exchnage can take place
17
Q

What are some of the functions of the placenta?

A
  • Metabolism e.g. synthesis of glycogen.
  • Barrier to infection
  • Removes foetal waste products
  • Site of endocrine secretion e.g. hCG, oestrogens, progesterone, HPL, cortisol.
18
Q

Why is the placenta able to carry out its functions effectively?

A
  • Has a huge maternal uterine blood supply that’s at low pressure - this allows it to filter substances more efficiently
  • Has a huge surface area in contact with maternal blood
19
Q

What are the main symptoms of pre-eclampsia?

A
  • Maternal hypertension
  • Proteinurea - excess proteins within the urine
20
Q

How does pre-eclampsia affect the placenta?

A
  • Results in placental insufficiency which is inadequate maternal blood flow to the placenta during pregnancy
21
Q

How can pre-eclampsia develop during pregnancy?

A
  • In normal pregnancies spiral arteries that supply placenta dilate to allow more blood flow
  • However, in pre-eclampsia these spiral arteries narrow due to them being fibrous
  • This limits the blood supply to the placenta
22
Q

How does the placenta respond to the lack of blood flow caused by pre-eclampsia and what does this result in?

A
  • Placenta secretes pro-inflammatory proteins which then enter the maternal circulation
  • Once in the maternal circulation the pro-inflammatory proteins cause the dysfunction of endothelial cells of the blood vessels of the mother
23
Q

How does the dysfunction of the endothelial cells of the maternal blood vessels cause hypertension and proteinurea?

A
  • Endothelial cell dysfunction causes Vasoconstriction of arteries
  • This vasoconstriction results in hypertension
  • Vasoconstriction affects arteries that supply kidneys and by extension the capillaries of the glomerulas
  • This results in impaired glomerular filtration which leads to proteinurea
24
Q

What is placental abruption?

A

Separation of all or part of the placenta from the endometrium

25
Q

What are the symptoms of placental abruption?

A
  • Vaginal bleeding
  • Pain in the back and abdomen
26
Q

What are some of the risk factors of placental abruption?

A
  • Blunt force trauma
  • Smoking/recreational drugs
  • Hypertension due to pre-eclampsia
27
Q

Explain how placental abruption can occur?

A
  • Degeneration of maternal arteries supplying blood to the placenta.
  • Degenerated vessels rupture causing haemorrhage and separation of the placenta.
28
Q

What maternal complications can arise due to placental abruption?

A
  • Hypovolemic shock - Isn’t enough blood for heart to pump around entire body
  • Sheehan syndrome - degeneration of the pituitary gland
  • Renal failure
29
Q

How does placental abruption lead to sheehan syndrome?

A
  • Due to hypovolemic shock there’s isn’t enough blood and oxygen being supplied to pituitary so it degenerates
30
Q

What foetal complications can arise from placental abruption?

A
  • Intrauterine hypoxia and asphyxia
  • Premature birth
31
Q

What is placenta previa?

A

Occurs wehn the placenta implants in the lower uterus and either partially or fully covers interal os of cervix

32
Q

Once the blastocyst implants within the endometrium what hormone does it secrete?

A

Trophoblast cells of blastocyst secrete hCG

33
Q

What is the effect of the secretion of hCG from the trophoblast cells?

A
  • hCG binds to LH receptors on corpus luteum causing corpus luteum to secrete oestrogen and mainly progesterone
34
Q

At what week of pregnancy does the placenta begin to take over secretion of oestrogen and progesterone from the corpus luteum?

A

Week 7

35
Q

Apart from oestrogen and progesterone what other hormone is produced by the placenta?

A

hPL (Human placental lactogen)

36
Q

During pregnancy why do you see a massive rise in hCG levels early on and then a rapid fall later on in pregnancy?

A
  • Rapid rise due to the fact that hCG needed to keep corpus luteum alive and in early stages of pregnancy corpus luteum is what secretes oestrogen and progesterone
  • Later on in pregnancy placenta takes over oestrogen and progesterone secretion from corpus luteum so corpus luteum no longer needed
  • This results in massive decline in hCG levels

Physiology 2 (29 decks)

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