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BB20149 > Extraembryonic membranes > Flashcards

Extraembryonic membranes Flashcards

1
Q

What are extra-embryonic membranes, aside from just membranes?

A

They are organs.

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2
Q

What are amniotes?

A

A clade of tetrapod vertebrates comprising the reptiles, birds and mammals.

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3
Q

What is one hypothesis in the evolution of the amniotic egg?

A

Replacement of the jelly layer with a shell which provided better support and movement of oxygen.

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4
Q

What is one potential purpose of an egg shell?

A

It can be broken down to provide calcium for growing skeletal structures.

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5
Q

What is an amniotic egg?

A

A series of fluid filled membranes that enabled the first land animals to lay their eggs on dryland.

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6
Q

How is the amniotic egg of reptiles different to the eggs of amphibians and fish?

A

It is internally fertilized through sexual contact and has a protective outer membrane to prevent it from drying out.

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7
Q

What is the allantois?

A

A sac that holds wastes until the embryo hatches, and also provides some oxygen. It gets bigger with age.

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8
Q

What is extraembryonic tissue?

A

Embryo derived tissue that will not be part of the living organism after birth/hatching.

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9
Q

What are the 4 extraembryonic membranes?

A

Amnion, allantois, chorion and yolk sac.

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10
Q

What is the yolk sac?

A

It encloses a reserve of nutrients and gets smaller with age.

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11
Q

What is the amnion?

A

It protects embryos in a fluid filled sac.

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12
Q

What is the chorion?

A

It allows gas exchange together with allantois membranes.

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13
Q

What are extra-embryonic membranes?

A

Membranous structures surrounding the embryo, they are present in some invertebrate animals, sharks, all higher vetrebrates and man. They are important for life activities of the embryo and ensure protection from injury.

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14
Q

When is the yolk sac first seen?

A

Within the gestational sac during pregnancy - 3 days gestation.

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15
Q

Where is the yolk sac located?

A

The ventral aspect of the embryo - it is lined by extra-embryonic endoderm outside of which is a layer of extra-embryonic mesenchyme that is derived from the mesoderm.

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16
Q

How is blood supplied to the wall of the yolk sac?

A

The primitive aorta. After circulating it is returned by the vitelline veins to the tubular heart of the embryo.

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17
Q

What happens at the end of the fourth week, in terms of the yolk sac?

A

It has the appearance of a small pear-shaped opening into the digestive tube by a long narrow tube - the vitelline duct.

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18
Q

What does the endoderm form?

A

The gastrointestinal tract, the yolk sac and allantois.

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19
Q

What are some of the other functions of the yolk sac?

A

It acts a preliminary circulatory system that delivers nutrients via a primitive aorta - the vetelline circulation.

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20
Q

What do the visceral endoderm cells of the yolk sac do?

A

They synthesise serum proteins.

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21
Q

What is the eventual fate of the yolk sac?

A

It is absorbed into the gut of the embryo.

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22
Q

What is the yolk sac lined by?

A

Extra-embryonic endoderm and mesoderm.

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23
Q

Where are primitive erthroid cells derived from?

A

Yolk sac blood islands - extraembrynoic hemotopoeisis.

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24
Q

What is the origin of the allantois?

A

Endoderm - it is an extension from the early hindgut, then cloaca into the connecting stalk of placental animals.

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25
Q

What is the allantois connected to?

A

The superior end of the developing bladder.

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26
Q

What does the allantois act as in birds and reptiles?

A

A reservoir for wastes.

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27
Q

What does the allantois act as in mammals?

A

It is associated with connecting stalk/placental cord fetal-maternal interface.

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28
Q

What happens to the allantois throughout development?

A

The size decreases and it becomes an elongated sac and part of the umbilical cord.

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29
Q

What do the blood vessels of the allantois become?

A

Blood vessels of the umbilical cord.

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30
Q

What is the urachus?

A

A fibrous remenant of the allantois that removes nitrogenous waste from the fetal bladder.

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31
Q

What eventually happens to the urachus?

A

The channel is usually sealed off and it obliterates at around the 12th week of gestation - all that is left is a small fibrous cord between the bladder and umbilicus called the median umbilical ligament.

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32
Q

When do disorders of the urachus occur?

A

When there are abnormalities with the sealing off of the channel during fetal development.

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33
Q

What is the amniotic cavity/amnion?

A

The closed sac between the embryo and the amnion - containing the amniotic fluid.

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34
Q

What is the amniotic cavity lined with?

A

Ectoderm and covered with extra-embryonic mesoderm.

35
Q

How is the amniotic cavity/sac formed?

A

During week 3-4, folding of the embryonic disc draws the amniotic membrane ventrally over the embryo leading to the enclosing of the embryo within the amniotic sac.

36
Q

How is the amniotic fluid circulated?

A

Fetal inhaling and swallowing.

37
Q

How is the amniotic fluid replaced?

A

Fetal exhalation and urination.

38
Q

What are low magnesium levels associated with the amniotic fluid?

A

Preeclampsia (high blood pressure and damage to other organs in mother) and diabetes.

39
Q

What is amniotic fluid?

A

A bioactive medium containing proteins, lipids and phospholipids, urea and eletrolytes.

40
Q

Where is amniotic fluid derived from?

A

It is actively secreted by cells lining the amniotic cavity.

41
Q

What is early gestation called?

A

Organogenesis.

42
Q

How does amniotic fluid volume increase in early gestation?

A

Water is gained from the mother’s plasma which is transported to the fetus through fetal membranes.

43
Q

What is the cause of bidirectional fluid diffusion between amniotic fluid and the fetus?

A

8-10 week gestation - the skin is not keratinized so the fluid can flow.

44
Q

When does ketatinization of the fetal skin occur?

A

20 weeks.

45
Q

When is the AF volume at its maximum, and what is this volume?

A

800ml at 28 weeks gestation.

46
Q

How much amniotic fluid is consumed by the foetus?

A

250mL/kg/d.

47
Q

What is amniotic fluid important for and what percentage of nutrients does it make up?

A

Only 15% of nutrients but is important for development and maturation of the gut.

48
Q

What are some of the compontents of amniotic fluid?

A

Amino acids, protein, minerals, hormones, growth factors, cells.

49
Q

What are some of the growth factors in the amniotic fluid?

A

GF-1, insulin-like growth factor, epidermal growth factor, transforming growth factor, hepatocyte growth factor, erthropoietin, granulocyte colony stimulating factorm, interleukin.

50
Q

What are amniotic fluid stem cells?

A

They show some features of pluripotency and are able to differentiate in cells derived from all three germ layers “in vitro”.

51
Q

What is the chorionic cavity lined with?

A

Extraembryonic mesoderm. It is covered in trophoblast cells forming villi.

52
Q

Where does the chorionic cavity form in mammals?

A

It forms outside the yolk sac and surrounds the amniotic sac.

53
Q

What is the difference in location between the amnion and the chorion?

A

The amnion is the sac that covers the embryo and the chorion surrounds the amnion on the outside.

54
Q

What organisms is the amnion present in?

A

Reptiles, birds and mammals but not amphibians and fish.

55
Q

What does the chorion contribute to the growth of?

A

The placenta.

56
Q

How is the formation of the amnion and chorion different?

A

The amnion is formed by ectoderm and extraembryonic mesoderm, whereas the chorion is formed by trophoblast and mesoderm.

57
Q

What is the purpose of the chorionic villi?

A

It acts as a barrier between maternal blood and fetal blood.

58
Q

What are within the chorionic villi?

A

Capillaries through which fetal blood circulates.

59
Q

What occurs in the chorionic villi?

A

Exchanges between maternal and fetal circulations through the tissues forming the walls of the villi.

60
Q

Where are chorionic villi formed from?

A

Offshoots from the surface of the trophoblast.

61
Q

Where are chorionic villi first formed?

A

All over the trophoblast and then grow into the surrounding decidua.

62
Q

How is blood circulated through the placenta?

A

Both arteries and the vein open into the roof of the cotyledon and the pressure of the blood in the artery is sufficient to drive blood to the fetal end of the intervillious space.

63
Q

What are the functions of the placenta?

A

Multiple functions - acts as the lungs, kidney, liver, gestrointestinal, endocrine and immune systems for the fetus. It produces hormones to help maintain pregnancy and support fetal development. It protects the fetus from the mother’s immune system.

64
Q

What are amniotic bands?

A

Bands of amnion peel away from the sack and wrap around part of the babies body.

65
Q

What is hydramnios?

A

A condition where too much fluid accumulates during pregnancy.

66
Q

What is oligohydramnios?

A

Less fluid than expected for age.

67
Q

When does implantation begin?

A

6 days after fetilisation.

68
Q

What happens in implantation?

A

The blastocyst attaches to the endometrial epithelium, which is usually adjacent to the embryonic pole.

69
Q

What is interstitial implantation?

A

The blastocyst goes deeper and deeper into the uterine mucosa until the whole of it comes to lie with in the thickness of the endometrium.

70
Q

What happens by the end of the 7th day in implantation?

A

The blastocyst gets implated into the superficial compact layer of endometrium and derives its nourishmnet from the eroded endometrium.

71
Q

What are the final stages in implantation?

A

The blastocyst gradually embeds deeper in the endometrium and by the 10th day it is completely buried within the functional layer of the endometrium.

72
Q

What do implantation sites determine?

A

The site of formation of the placenta.

73
Q

Where does implantation normally occur?

A

The upper part of the body of uterus, more often on the posterior wall.

74
Q

What is the uterine endometrium called after implantation of the embryo?

A

The decidua.

75
Q

What happens to the endometrium after implantation?

A

Features are intensified - stomal cells are enlarged and become vacuolated and store glycogen and lipids.

76
Q

What is the change in stromal cells called during implantation?

A

Decidual reaction.

77
Q

What are the two layers the trophoblast differentiates into?

A

Cytotrophoblast/Langhan’s layer - the inner cellular layer, and the outer mass of syncytiotrophoblaast (which is multinucleated protoplasm with no cell boundaries).

78
Q

What are the features of the syncytiotrophoblast?

A

There are finger-like processes that extend through the endometrium and invade the endometrial connective tissue.

79
Q

What happens to the syncytiotrophoblast in implantation?

A

Small cavities (the lacunae) appear and get filled with maternal blood which estavlishes primitive uteroplacental circulation.

80
Q

What does the syncytiotrophoblast grow into?

A

The endometrium - it is eroded. Some of the blood vessels are opened and blood from them fills the lacunar space.

81
Q

What happens after the syncytiotrophoblast has grown into the endometrium?

A

Blood vessels of the villus establish connections with the circulatory system of the embryo, and fetal blood now circulates through the villi while the maternal blood circulates through the intervillous space.

82
Q

What lines the walls of the body cavity?

A

The parietal layers of the membranes.

83
Q

What covers the organs?

A

The visceral layer of the membrane - the viscera.

84
Q

What is between the parietal and visceral layers?

A

A very thin, fluid-filled serous space/cavity.

BB20149 (16 decks)

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