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Human Development > Microanatomy 3 > Flashcards

Microanatomy 3 Flashcards

1
Q

what is the placenta

A
  • this is a temporary structure which arises from both fetal and maternal cells
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2
Q

what is the function of the placenta

A
  • nutrient trasnrpot
  • waste removal
  • gases transport
  • site of synthesis for a variety of molecules including hCG and relaxin and steroid hormones particular oestrogen’s and progesterone
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3
Q

what week does the placenta assume the role of steroid hormone synthesis

A 
12 week (between the 2nd and third months of pregnancy) -
- takes over form the corpus luteum which degenerates and becomes the corpus albicans
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4
Q

what are the keys stages in placentation

A
  • implantation and invasion into uterine tissues
  • differentiation of the trophoblast
  • develop of the villous structure
  • remodelling of the spiral arteries
  • maturation
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5
Q

describe the development of the blastocyst

A
  • fertilising occurs in the ampulla of the uterine tube
  • 3-4 days after fertilisation the morula arrives in the uterine body where implantation occurs
  • by day 5 the blastocyst has formed and has hatched through the zone pelluida
  • at the blastocyst stage the blastomeres of the inner cell mass are also called the embryo blast as they give rise to the embryo proper
  • peripheral blastomeres constitute the trophoblast which gives rise to the fetal component of the placenta
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6
Q

when does implantation occur

A
  • when the endometrium mucosa is sufficiently prepared for implantation in the secretory phase of the central cycle - days 22-24
  • it can provide a suitable cellular and nutrient environment for the embryo, the trophoblast cells over the inner cell mass adhere to its surface
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7
Q

what is the stromal reaction

A
  • this is also called the decidual reaction
  • involves the thickening of the endometrium at the site of implantation
  • local endometrial glands enlarge
  • the area become more vascularised and oedematous
  • inflammatory cells also invade
  • secretions of the decidual cells and the endometrial glands are through to support the growth of implanting embryo
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8
Q

what is the stormal reaction also called

A

the decidual reaction

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9
Q

what do the stromal cells differentiate into

A
  • the stromal cells of the endometrium differentiated into metabolically active secretory cells called decidual cells
  • by the end of two weeks, storm cell changes and increased vascularisation spreads throughout the endometrium which is now known as the decidua
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10
Q

describe the differentiation of the trophoblast

A
  • happens around day 7
  • the trophoblast at the embryonic pole proliferates when it is contact with the endometrium
  • some of the cell loose there plasma membranes and form a syncytium called the syncytiotrophoblast
  • the cells lining the blastocyst are now called the cytotrophoblast
  • the synctitrophoblast starts to invade and erode the underlying endometrium
  • the rapidly proliferating cut-trophoblast cells will continue to add to the non dividing mass of the syncytiotrophoblast
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11
Q

what does the trophoblast divide into

A
  • syncytiotrophoblast

- cytotrophoblast

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12
Q

when does trophoblast differentiation happen

A

day 7

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13
Q

what does the embryoblsat differntatie into

A

epiblast

hypoblast

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14
Q

what does the epiblast and hypoblast form

A
  • bilayered embryonic disc

- and form two extraembyronic membranes that enclose the amnionic and yolk sac cavities

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15
Q

what draws the blastocyst into the endometrial mucosa

A
  • the syncytiotrophoblast continues to erode into the endometrium and its fingerlike projects draw the blastocyst in to the endometrial mucosa
  • by day 9 only a small fibrin clot marks the post the blastocyst implanted
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16
Q

by what day does the syntriotrophoblast cover the entire blastocyst

A
  • around day 11
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17
Q

what happens once the synctiotrophoblasts cover the entire blastocyst

A
  • one it covers the entire blastocyst it begins to develop vacuoles called trophoblastic lacunae
  • the maternal capillaries widen to form sinusoids and are eroded by the syncytiotrophoblast causing the trophoblastic lacunae to fill with blood
  • at the same time the extra embryonic mesoderm begins to form under the cytotrophoblast
18
Q

how does the formation of chorionic villi take place

A
  • the extra embryonic mesoderm induces the overlying cut-trophoblast to proliferate and form projects that extend into the trophoblastic lacunae
  • the trophoblast layers with the underlying extra embryonic mesoderm forms the chorion
  • these projects of the trophoblast are therefore called the primary chorionic stem vili
19
Q

why do we form chorionic vili

A
  • embryo is rapidly growing in week 2 therefore there is need for a more efficient nutritional and gas exchange
  • hypoxia stimulates placental villus invasion into the endometrium
20
Q

where and when does the chorionic cavity develop

A
  • by 16 days

- develops in the middle of the extra embryonic mesoderm

21
Q

what forms the three primary germ layers of the embryo

A
  • gastrulation
22
Q

what suspends the embryo in the chorionic cavity

A
  • the embryo is now suspended in the chorionic cavity by a connecting stalk of extra embryonic mesoderm
23
Q

what covers primary chorionic stem vili into secondary chorionic stem vili

A
  • the extra embryonic mesoderm penetrates the core of the primary chorionic stem vili transforming them into secondary chorionic stem vili
24
Q

how does the cytotrophoblast shell form

A
  • the columns of cytotrophoblast invading into the synctiotrophoblast extend out to the periphery forming the interface between the trophoblast and the endometrium
  • this is the cytotrophoblast shell
25
Q

what does the secondary chorionic villus differentiate into

A
  • by day 21 the extra embryonic mesenchymal core of the secondary chorionic villus differentiates into connective tissue and blood vessels
  • this vili is called tertiary stem vili
26
Q

what do the tertiary stem vili develop into

A
  • these connect with vessels forming the embryo proper linked to the primitive heart
27
Q

when does the primitive heart start beating

A

day 22

28
Q

what are the four tissues materials must pass

A
  • the endothelium of the villus capillaries
  • the loose connective tissue in the core
  • a layer of cytotrophoblast
  • a layer of syncytiotrophoblast
29
Q

how does remodelling of spiral arteries happen

A
  • the extravillus trophophoblasts invade the spiral arteries and replace the smooth muscle and endothelium there with trophoblasts
  • this creates high flow low resistance vessels which supply the lacunae with maternal blood
30
Q

what do trophoblasts do in spiral arteries

A
  • this creates high flow low resistance vessels which supply the lacunae with maternal blood
31
Q

where the embryo is implanted what is the maternal endometrium called

A

the decidua basalis

32
Q

on the opposite pole to the embryo what is the endometrium called

A

decidua capsularis

33
Q

what happens to the placenta at 4 and 1/2 weeks

A
  • the chorionic vili extend completely around the growing embryo into both decidua
34
Q

what happens with further maturation to the decidua capsularis

A
  • it looses its chorionic vili and vascular role of rate fetus
35
Q

what does the decidua basalis do in further maturation

A
  • with its chorionic vili it form the mature disc shaped placenta
36
Q

when is the placenta fully developed

A

from the fourth month onwards

37
Q

what happens to the placenta after it is fully developed

A
  • it will only increase in diameter as uterine growth proceeds
  • the cytotrophoblast layer within the villi becomes smaller
  • the barrier between the maternal blood in the lacunae and capillaries can be reduced to a layer of synctiotrophoblasts and the endothelium of the foetal capillary is separated only by a shared basement membrane
38
Q

describe the umbilical arteries

A
  • have a smaller diameter and thicker muscular wall than the veins
39
Q

what are the umbilical arteries and veins supported by

A
  • they are supported by a mucoid connective tissue called Wharton’s jelly
40
Q

describe the structure of Wharton’s jelly

A

it is mainly made of ground substance with fibroblasts - like precursors “mesenchymal cells”

Human Development (28 decks)

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