Embryology - Early Development Flashcards

1
Q

What is the timeline of an embryo?

A

Developing organism during the first 8/40 weeks.

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2
Q

What is the timeline of a fetus?

A

After 8 weeks.

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3
Q

What happens during the embryonic period?

A

Most organs have differentiated.

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4
Q

What happens during the fetal period?

A

Time for the organs to undergo maturation.

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5
Q

When do congenital defects occur?

A

Typically in the embryo stage.

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6
Q

What is the first stages in the embryonic period?

A

Zygote (fertilised egg) undergoes cleavage to produce a morula.

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7
Q

What is the second stage i the embryonic period?

A

The morula travels along the uterine tube towards the uterus and it further divides and a fluid filled cavity appears. The morula becomes a blastocyst.

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8
Q

What is the third stage in the embryonic period?

A

6 days after fertilisation the blastocyst is implanted into the uterine mucosa.

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9
Q

What is the outer layer of cells in the blastocyst called?

A

Trophoblast.

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10
Q

What is the trophoblast destined to become?

A

Placental.

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11
Q

What are the remainder of cells in the blastocyst called?

A

Inner cell mass.

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12
Q

What does the inner cell mass attach to?

A

The inner layer of the trophoblast.

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13
Q

What does the inner cell mass divide into?

A
  1. Amnion.
  2. Yolk sac.
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14
Q

What separates the amnion and yolk sac?

A

Embryonic plate - mass of cells.

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15
Q

What will the embryonic plate differentiate into?

A

Tissues and organs of the embryo.

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16
Q

What is the amniotic aspect of the embryonic plate?

A

Ectoderm.

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17
Q

What is the yolk sac aspect of the embryonic plate?

A

Endoderm.

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18
Q

What is between the endoderm and ectoderm?

A

Primary mesoderm.

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19
Q

What is the secondary mesoderm derived from?

A

Cells of the ectoderm.

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20
Q

What grows in from the ectoderm towards the endoderm?

A

Notochord - axial rod of cells.

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21
Q

What is the dorsal surface of the embryonic plate?

A

Ectoderm and amniotic.

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22
Q

What develops on the dorsal surface of the embryonic plate?

A

Neural groove develops.

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23
Q

What happens with the neural groove?

A

The edges unite to form the neural tube. The tube becomes depressed below the surface.

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24
Q

Where does the brain and spinal cord develop from?

A

Neural tube.

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25
Q

Where is the neural crest formed from?

A

Cells from the edges of the groove that become isolated between the tube and the overlying ectoderm.

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26
Q

What will the neural crest develop into?

A
  1. Posterior root ganglia of spinal nerves.
  2. Corresponding ganglia of cranial nerves.
  3. Autonomic ganglia.
  4. Satellite cells of ganglia.
  5. Schwann cells of peripheral nerves.
  6. Chromaffin cells of suprarenal medulla.
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27
Q

How does the mesoderm lie?

A

In three longitudinal strips - alongside the notochord and neural tube.

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28
Q

What is the paraxial mesoderm?

A

The longitudinal strip nearest the midline.

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29
Q

What does the paraxial mesoderm become segmented into/

A

Masses of cells - mesodermal somites.

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30
Q

What do the mesodermal somites produce?

A
  1. Sclerotome - medially.
  2. Myotome - laterally.
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31
Q

What does the sclerotome surround and produce?

A

Surrounds the neural tube and notochord. Produces the vertebrae and dura mater.

32
Q

What does the myotome produce?

A

Muscles of the body wall.

33
Q

What is the intermediate strop of mesoderm?

A

Intermediate cell mass.

34
Q

Where does the intermediate cell mass project?

A

Ventrally between the other two strips.

35
Q

What does the lateral side in the craniocaudal sequence of the intermediate strip of mesoderm develop into?

A
  1. Pronephros.
  2. Mesonephros.
  3. Metanephros.
  4. Associated ducts.
    (Progenitors of the urinary and genitla systems).
36
Q

What does the medial side in the craniocaudal sequence of the intermediate strip of mesoderm develop into?

A
  1. Gonad.
  2. Cortex of the suprarenal gland.
37
Q

What is the most lateral strip of mesoderm?

A

Lateral plate - unsegmented.

38
Q

Why does the embryo being to curl up early on?

A

Because of rapid growth of the dorsal (ectodermal) surface.

39
Q

Describe the concave and convex of the embryo?

A
  1. Convex towards amnion.
  2. Concave towards yolk sac.
40
Q

What does the lateral plate curl around to enclose?

A

Yolk sac.

41
Q

What happens to the mesoderm in the lateral plate as it curls around the yolk sca?

A

Splits into two layers by a space that appears within it.

42
Q

What does this space between the mesoderm layers in the lateral plate become?

A

Beginning of the intraembryonic coelom/body cavity.

43
Q

What is the inner layer of the mesoderm?

A

Splanchnopleure.

44
Q

What innervates the spanchnopleure?

A

Autonomic nervous system.

45
Q

How does the splanchnopleure enclose the yolk sac?

A

In a hour glass constriction.

46
Q

What does the yolk sac part inside the embryo become?

A

The alimentary canal - gut tract.

47
Q

What does the yolk sac outside in the umbilical cord become?

A

Vitellointestinal duct.

48
Q

What is the outer layer of the lateral plate of mesoderm?

A

Somatopleure.

49
Q

What innervates the somatopleure?

A

Somatic (spinal) nervous system.

50
Q

What migrates into the somatopleure?

A

Paraxial myotomes.

51
Q

How do paraxial myotomes migrate?

A

Into segments.

52
Q

What do the paraxial myotomes segment into?

A

Flexor and extensor muscle layers of the body wall.

53
Q

What does the coelomic cavity give rise to?

A

Originally one continuous layer of pleura and peritoneum, which separate later.

54
Q

What is the lining of the coelomic cavity?

A

Mesodermal.

55
Q

What innervates the parietal layer of the membranes (pleura/peritoneum)?

A

Somatic.

56
Q

What innervates the visceral layer of the membranes?

A

Autonomic.

57
Q

Where do the limb buds develop from?

A

Lateral plate mesoderm. Their muscles develop in situ.

58
Q

Is the somatopleure segmented?

A

No it is unsegmented.

59
Q

How do the motor fibres that grow into the somatopleure arrange themselves?

A

The fibres that come form spinal cord plexuses arrange their distribution in a segmented way.

60
Q

What does the septum transversum consist of?

A

Mesoderm that lays on the cranial aspect of the coelomic cavity.

61
Q

What does the cranial part of the septum transversum contain?

A

Pericardial cavity.

62
Q

What do the walls of the septum transversum develop into?

A
  1. Pericardial membranes.
  2. Part of the diaphragm.
63
Q

What invades the cranial part of the septum transversum?

A

Muscles from cervical myotomes - mainly 4th.

64
Q

What do the cervical myotomes produce?

A

The muscle of the diaphragm.

65
Q

What invades the caudal part of the septum transversum?

A

Developing liver, surrounds as the ventral mesogastrium.

66
Q

What happens when the septum transversum finally descends?

A

Takes the heart with it and goes to the final position of the diaphragm.

67
Q

What does the body stalk later become?

A

Umbilical cord.

68
Q

Where does the greatest amount of folding occur?

A

Head end of the embryo.

69
Q

What happens by the end of the first fortnight?

A

The forebrain capsule is folded down over the pericardium and a mouth pit (stomp drum) is a dimple between the two.

70
Q

What happens to the gut cavity within the body of the embryo?

A

Travels up cranially and dorsal to the pericardium, goes as far as the buccopharyngeal membrane. This encloses the bottom of the mouth pit.

71
Q

What happens to the buccopharyngeal membrane?

A

By the 3rd week it breaks down and disappears.

72
Q

What is the mouth pit lined with on the cranial side of the mouth pit?

A

Ectoderm - all the mandiubular and maxillary teeth and probably submandibular and sublingual glands, possibly anterior 2/3 of the tongue.

73
Q

Where does rathke’s pouch arise from?

A

The ectoderm in the mouth pit.

74
Q

What does rathke’s pouch form?

A

Anterior lobe of the pituitary gland.

75
Q

What is caudal to the buccopharyngeal membrane?

A

Pharynx.

76
Q

What lines the pharynx?

A

Endoderm.

77
Q

What does it lie dorsal to?

A

Pericardium.