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TOB (Semester 1) > Embryology > Flashcards

Embryology Flashcards

1
Q

What is the embryonic period?

A

This is weeks 3-8.

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2
Q

How many days are an oocyte and sperm viable for?

A

An oocyte is viable for one day whilst sperm is viable for three days

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3
Q

Where does fertilisation of the egg occur?

A

In the ampulla, a widening in the Fallopian tube.

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4
Q

What is the name of a fertilised oocyte?

A

Zygote

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5
Q

What is the ideal site of implantation?

A

The posterior uterine wall.

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6
Q

What is cleavage?

A

This is the first mitotic division in which results in two blastomeres. This occurs approximately 30 hours after fertilisation.

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7
Q

What is the name of the glycoprotein shell which forms around the zygote to recent further sperm entry?

A

Zona pellucida.

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8
Q

At what point is an in vitro fertilisation zygote stopped for implantation.

A

When it reaches the stage of the morula.

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9
Q

What can be said about the cells of the morula?

A

They are totipotent and all have the ability to become any cell type.

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10
Q

What is the name of the two cell types which are present by day 4?

A

Embryoblast and trophoblast. The trophoblast is the outer cell mass.

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11
Q

What is compaction?

A

This is segregation of the two cell masses. (Embryoblast and trophoblast)

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12
Q

What is the blastocyst cavity?

A

This is a fluid filled cavity. This fluid is secreted by cells of the trophoblast and also by fluid which enters through the zona pellucida.

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13
Q

What is the importance of hatching?

A

This occurs around day 5 and means that the size is no longer restricted. It also means that interaction with the uterine surface can occur which leads to Implantation.

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14
Q

At which stage are cells pluripotent and what does this mean?

A

After differentiation into initial two cell types: embryoblast and trophoblast. This means that whilst cell types are different they still have the capability to become one of many different cell types.

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15
Q

At the end of the first week, what is the main focus for the conceptus?

A

The main focus is made to establish and maintain the pregnancy so this includes focusing on the placenta as opposed to the embryo.

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16
Q

What is synchiotrophoblast?

A

This is a multi nucleated sheet which is good for diffusion.

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17
Q

What are the two layers of the bilaminar disk?

A

Epiblast and hypoblast.

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18
Q

Describe where the amniotic cavity is found.

A

This is where the embryo will grow and is found at the top of the bilaminar disk. It is surrounded by epiblast cells.

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19
Q

Where is the embryo implanted?

A

The embryo is implanted in the uterine stroma and so the epithelium is breached. This is an invasive procedure and can lead to bleeding meaning an error in dating can occur.

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20
Q

What does the process of implantation establish?

A

It establishes maternal blood flow in the placenta. This means the embryo is supported histotrophically and haemotrophically.

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21
Q

What is an ectopic pregnancy? What is the major risk of this?

A

This is where implantation occurs outside of the uterus in an inappropriate location. These sites do not have endometrium and so implantation can lead to life threatening haemorrhage.

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22
Q

What is the name for the condition where the placenta forms too low in the uterus?

A

This is called placenta previa.

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23
Q

What is the primative yolk sack?

A

This is surrounded by cells of hypoblast origin and is in contact with the cytotrophoblast layer.

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24
Q

What are lacunae in the synchiotrophoblast?

A

These are lakes which will become filled with maternal blood.

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25
Q

What is it that reseals the uterine epithelium after implantation?

A

Fibrin plug

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26
Q

What is the role of extra embryonic mesoderm?

A

This pushes the primative yolk sac membrane away from the cytotrophoblast.

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27
Q

What is a sinusoid?

A

These contain blood in the uterine wall. The synchiotrophoblast invades these and lacunae become continuous with sinusoids.

28
Q

When does uroplacental circulation begin?

A

Around day 12, when the lacunae and sinusoids have become continuous.

29
Q

What is the secondary yolk sac?

A

This is a small amount of the primative yolk sac which is pinched off. This is called the definitive yolk sac.

30
Q

What is the chorionic cavity? When does it form?

A

This is the result of merging of extra embryonic mesoderm. It forms at the end of the second week, on day 14.

31
Q

How is the embryo suspended in the cavity?

A

By a column of mesoderm called the connecting stalk. This will later become the umbilical cord

32
Q

What happens during the process of gastrulation?

A

This is the process in which the three germ layers are established, the origins of all tissues of the body.

33
Q

What is the primative streak?

A

This is a narrow groove with bulging edges. The primative node is found at the cranial end.

34
Q

What happens as the primative streak regresses?

A

As it regresses, the three germ layers are established.

35
Q

What is migration and invagination?

A

This is a process where the epiblast cells multiply and migrate at the edge of the primative streak. They push through the epiblast to form the third embryonic layer. Hypoblast cells are displaced at this point.

36
Q

What are the three germ layers?

A

Ectoderm, mesoderm, endoderm.

37
Q

What are the two exceptions for mesoderm lying between the ectoderm and endoderm.

A

There are two points where there is no mesoderm. These pointers will become the future mouth and anus.

38
Q

What is the name of the structure which drives nervous system formation?

A

Notochord.

39
Q

What is the notochord?

A

This is made up from cells which invaginate at the most cranial end of the primative streak. It is the basis for the axial skeleton.

40
Q

What is the primative pit?

A

This is found at the centre of the primative node

41
Q

What process does the notochord drive?

A

Neurulation. After this process it regresses. The reminant found in adults is the nucleus purposes of the intervertebral disc.

42
Q

What is another word for the dorsal axis?

A

It is in the direction towards the back. The opposite to this is the ventral, towards the front.

43
Q

What ensures that correct development in terms of symmetrical limbs and asymmetrical viscera?

A

Molecular signals from the node.

44
Q

What is situs Inversus?

A

This is where a complete mirror image occurs of the viscera. This usually results from immobile cilia at the node.

45
Q

What causes differentiation of visceral position?

A

Cilia at the node result in leftward flowing of signalling molecules meaning a side specific cascade is established.

46
Q

What structures are derived from mesoderm?

A

Connective tissue such as bone, muscle, cartilage and also the vascular system.

47
Q

What germ layer gives rise to the skin and the nervous system?

A

Ectoderm.

48
Q

What does endoderm differentiate to?

A

Lining of the GI and respiratory systems.

49
Q

What is the difference between mono and dizygotic twins?

A

Monozygotic twins are both derived from a single oocyte and this leads to two identical siblings. Dizygotic twins are actually just siblings.

50
Q

State two different scenarios in which monozygotic twins arises.

A

If the embryo splits after first cleavage then this leads to twins each with their own placenta. Alternatively if this splitting occurs late then twins which share the same placenta and amniotic cavity can occur. In this case, conjoined twins can arise.

51
Q

What is teratogenesis?

A

This is disruption to normal embryonic development. Teratogenic agents are chemicals/infectious agents known to cause developmental defects.

52
Q

What is meant by the pre embryonic period?

A

This is the first two weeks after conception.

53
Q

What is neurulation?

A

This is a process driven by the notochord which directs conversion of ectoderm to Neuroectoderm.

54
Q

Describe how the neural tube is created.

A

The edges of the neural plate curve out of the plane of disk towards each other creating the neural tube.

55
Q

Name the four differentiated types of mesoderm, and what they lead to.

A

Paraxial mesoderm, intermediate mesoderm - urogenital system, somatic mesoderm - skeletal muscle, splanchic mesoderm - organs (gut)

56
Q

What is the intraembryonic coelom?

A

This is the gap at the edge of the disc which is between the somatic and splanchic mesoderm.

57
Q

What are somites?

A

This is organisation of the paraxial mesoderm into segments.

58
Q

On what day do the first pair of somites form?

A

Day 20

59
Q

How many somites form?

A

Up towards week 5, 42/44 pairs of somites are present and then some of these disappear to give 31 pairs.

60
Q

What is formed by organised degeneration of somites, and what does this give rise to?

A

Organised degeneration of somites leads to formation of schlerotome which is the section which will give rise to hard tissue.

61
Q

Describe the further organisation of the dorsal portion of somites.

A

After breakdown, combined dermamyotome forms. Dermatome is the skin section and myotonic is the muscle section. The myotome migrates and proliferates. Dermatome disperses.

62
Q

What does segmentation of mesoderm give rise to?

A

Somites. This is responsible for producing the repeating structures such as ribs, vertebrae, and spinal cord segments.

63
Q

Explain the link between somites an development of nerves.

A

Somites guide innervation. Epimere this is done by the dorsal branch and in the hypomere this is done by the ventral branch.

64
Q

Clinically, how do we describe dermatome and myotome?

A

Dermatome is a section of skin supplied by one nerve, and myotome is a group of muscles supplied by one nerve.

65
Q

Name two purposes of embryonic folding.

A

It moves the heart into the correct position and also means that the whole embryo becomes suspended in the amniotic sac.

66
Q

What happens to the connecting stalk in embryonic folding?

A

It is pulled centrally so that it is at the position of the tummy of the embryo.

67
Q

Why is the incorporation of space into the embryo during folding important?

A

It allows space for the embryo’s body systems to develop.

TOB (Semester 1) (14 decks)

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