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ESA 1 Revision > Embryology > Flashcards

Embryology Flashcards

1
Q

Where abouts is the oocyte fertilised?

A

Ampulla

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2
Q

What is a fertilised oocyte called?

A

Zygote

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3
Q

When is the pre embryonic period from and til?

A

Fertilisation to the end of week 2 of pregnancy

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4
Q

When is the embryonic period from and til?

A

Start of week 3 to the end of week 8

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5
Q

How long is pregnancy?

A

38 weeks, plus 2 weeks since the last menstrual period

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6
Q

What does cleavage of the zygote form?

A

Morulla

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7
Q

What does compaction of the morulla form?

A

Blastocyst

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8
Q

What is implantation and when does it occur?

A

The process by which the pre embryo gains access to the maternal tissue and associated blood supply (day 6)

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9
Q

Where is the ideal site of implantation?

A

The posterior uterine wall

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10
Q
A
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11
Q

Define: zygote

A

The cell produce when an ovum is fertilised by a spermatozoan, contains all the genetic information for a new individual

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12
Q

Define: cleavage

A

Successive divisions of the zygote to form a morulla. The first division into two masses produces blastomeres, 30 hours after fertilisation

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13
Q

Define: zona pellucida

A

The glycoprotein membrane surrounding the plasma membrane of an oocyte to prevent polyspermy, present before implantation

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14
Q

Define: morula

A

The result of cleavage, a ball of totipotent identical cells

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15
Q

Define: Ovary

A

Female reproductive organ that produces oocytes and steroid hormones in a regular cycle, in response to anterior pituitary hormones (FSH/LH)

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16
Q

Define: fallopian tube

A

tube which eggs travel along from the ovaries to the uterus. Eggs are fertilised in the ampulla

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17
Q

Define: uterus

A

Female reproductive organ where the blastocyst embres and growth of the embryo occurs.

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18
Q

Define: blastocyst

A

forms after compaction, as the inner and outer cell masses form, and the blastocyst cavity develops

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19
Q

Define: trophoblast

A

the outer cell mass of the blastocyst, which will later form support structures for the embryo

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20
Q

Define: embryoblast

A

The innter cell mass, will later become the bilaminar disk

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21
Q

Define: implantation

A

The attachment of the blastocyst to the wall of the uterus at day 6/7

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22
Q

Define:Cytotrophoblast

A

an inner layer of mononucleated cells in the trophiblast, placental membrane around the yolk sac

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23
Q

Define: syncytiotrophoblast

A

An outer mononucleated zone of the trophoblast,cells that invate maternal sinusoids (irregular blood vessels) resulting in uteroplacental circulation

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24
Q

When does cleavage occur?

A

30 hours after fertilisation

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25
Q

what does the first cleavage result in?

A

2 blastomeres

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26
Q

What day does the morula form in?

A

Day 3

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27
Q

What happens on day 4?

A

Compaction

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28
Q

Compaction makes the cells pluripotent, what does this mean?

A

The cells have the capacity to become one of many cell types, they are somewhat differentiated

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29
Q

What happens on day 5?

A

Hatching

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30
Q

What is hatching?

A

The blastocyst hatches from the zona pellucida, it is no longer constrained and is free to enlarge and implant on the uterine surface

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31
Q

When does implantation begin?

A

Day 6 to 7

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32
Q

What type of epithelium is the endometrial surface?

A

Simple columnar epithelium

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33
Q

How many cells at the implantation stage? How many will make the embryo and how many will make the foetal membrane?

A

107 cells. 8 will make the embryo, 99 will make the foetal membrane

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34
Q

How to remember week 2

A

The week of 2s

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35
Q

What has priority out of the embryo and placenta at the earlier stages?

A

The placenta

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36
Q

What forms from the embryoblast?

A

Epiblast (inner) and hypoblast (outer)

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37
Q

What forms from the trophoblast?

A

Syncytiotrophoblast and cytotrophoblast

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38
Q

What does the epiblast form?

A

THe amniotic cavity

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39
Q

What does the hypoblast become?

A

The bilaminar disk

40
Q

What type of epithelium is the hypoblast?

A

Cuboidal

41
Q

What type of epithelium is the epiblast?

A

columnar

42
Q

What are two conditions concerned with implantation at inappropriate sites?

A

Ectopic pregnancy and placenta praevia

43
Q

What is ectopic pregnancy?

A

Implantation at sites other than the uterine body. Can quickly become a life threatening emergency. Can be peritoneal or ovarian

44
Q

What is placenta praevia?

A

Implantation is lower uterine segment, placenta grows across cervical opening, can haermorrage. Needs C section delivery.

45
Q

Describe the endometrial stroma

A

Highly vascular, lots of serous fluid, glands secrete glycogen/mucus

46
Q

What happens on day 9?

A

Implantation complete. fibrin plug, development of syncytiotrophoblast, primitive yolk sac formation

47
Q

What two types of support foes implantation provide?

A

Histiotrophic (tissue, diffusion), haemotrophic (blood support, circulation_

48
Q

Where does the primitive yolk sac develop?

A

Abembryonic pole. from the blastocyst cavity

49
Q

What happens on day 11?

A

The primitive yolk sca membrane is pushed away from the cytotrophoblast layer by an acellular extraembryonic reticulum, later converted to extraembryonic mesoderm.

50
Q

What happens on day 12?

A

Uteroplacental circulation begins

51
Q

Describe the invasion of maternal sinusoids

A

Maternal sinusoid invaded by syncytiotrophoblast, lacunae become continuous with it. Maternal blood enters the lacunar system.

52
Q

What is a sinusoid?

A

Maternal capillaries which are congested and dilated.

53
Q

When and how does the secondary yolk sac form?

A

Day 13, by pinching off from the primary yolk sac.

54
Q

What happens on day 14?

A

Spaces in extraembryonic mesoderm merge to form the chorionic cavity.

55
Q

What does the connecting stalk do?

What is it made of?

What will it become?

A

Suspends the embryo and its cavities in the chorionic cavity.

A column of mesoderm

The umbilical chord.

56
Q

Why do the gut, heart and lungs become eveloped by serosal membranes?

A

They develop next to a bag like cavity in which they invaginate

57
Q

Define: Bilaminar disk

A

The epiblast and the hypoblast. Derived from the embryoblast. Will later become the trilaminar disk with the formation of the primitive streak

58
Q

Define: Germ layer

A

A layer from which other developed tissues originated from

3 primary tissues of the trilaminar disk: ectoderm, mesoderm and endoderm.

Arise through gastrulation and give rise to all tissues of the body

59
Q

Define: ectoderm

A

The outer most layer of cells in the trilaminar disk.

Gives rise to the epidermis and nerve tissue - all with contact to the outside world

60
Q

Define: endoderm

A

Inner most germ layer of the trilaminar disk

Gives rise to the gut lining

61
Q

Define: dorsal surface

A

Outermost layer during early development

Dorsal means towards the back

62
Q

Define: ventral surface

A

The innermost surface during early development

Ventral means towards the front - belly, abdomen

63
Q

Define: mesoderm

A

Middle germ layer of the trilaminar disk

Giving rise to muscle bone and more

64
Q

Define: primitive streak

A

A narrow groove that develops on the dorsal surface of the epiblast

Important role in orientation of the embryo, determining the front and back

Begins as a thickened region of the epiblast at the caudal end of the bilaminar disk

Is the site from which gastrulation proceeds

65
Q

Define gastrulation

A

The process establishing the 3 germ layers and hence the origin of all the tissues of the body

66
Q

Define: trilaminar disk

A

The three germ layers prodcued by gastrulation

Ectoderm

Mesoderm

Endoderm

67
Q

What are the most important ectodermal derivatives?

A

Organs and structure that maintain contact with the outside world

Skin

Skin derivates (hair, nails, lens and cornea of eye, lining of mouth and anus)

Brain and spinal cord

Peripheral nerves

Retina and iris of eye

68
Q

What are the most important mesodermal derivatives?

A

Supporting tissues (greatest variety)

Smooth, skeletal and cardiac muscle

Connective tissue

Bone

Cartilage

Blood and blood vessels

Urinary system

69
Q

What are the most important endodermal derivatives?

A

Internal structures

Lining of the GI tract

Glands associated with digestion (pancreas, liver, parenchyma)

Other gut derivatives such as the lungs

70
Q

What has happened by the end of week 2?

A

Oocyte has been fertilised

Zygotes have undergone cleavage and compaction to produce a blastocyst

Implantation and has started to differentiate

Bilaminar disk hsas formed inside the ICM

Extraembryonic spaces started to organise (amniotic sac, yolk sac)

Suspended connecting stalk

Supporting sac: chorionic cavity

71
Q

Generally, what happens in weeks 3 to 8?

A

Period of greatest change

All major structures and systems are formed

Most perilous time for the developing child

Woman may not realise she is pregnant

72
Q

Generally, what happens in the third week after fertilisation?

A

The week of 3s

3 cavities: amniotic cavity, yolk sac, chorionic cavity

3 germ layers: ectoderm, mesoderm, endoderm. Rudimentary lineages

Gastrulation: establishes 3 germ layers and sets axes observed in an adult

73
Q

What axes are set in gastrulation?

A

Anterior/posterior (head and toe of embryo/front and back of adult)

Dorsal/ventral (front and back of embryo)

Right/left

74
Q

How does the primitive streak form?

A

Primitive streak starts to vaguely form on the surface of the epiblast on days 13 to 14 DORSAL SURFACE

Day 15 to 16: becomes clearly visible a nararow groove with bulges outside

Primitve node is located at the cranial end of the streak, molecular signals from here

Primitive pit is at the centre of the node

Development proceeds in a cranial/rostral to caudal direction

As gastrulation proeeds and the three germ layers are established, the primitive streak regresses

75
Q

Describe how mesoderm migrates through the primitive streak and 3 layers are formed

A

Cells on the epiblast migrate to the primitive streak

They invaginate into the epiblast and displace the hypoblast, with endoderm

creating a 3rd layer, the mesoderm

Cells remaining in the epiblast form the ectoderm

ALL BODY CELLS FROM THE EPIBLAST

Now is the trilaminar disk

As more cells migreate through the streak they spread laterally and cephalad (towards head)

Mesoderm spreads between the ectoderm and endoderm like sandwich filing, leaving two gaps/hole for future mouth and anus

76
Q

How is the fate of the invaginating epiblast decided?

ie which layer in trilaminar disk

A

Depends on WHERE in they streak or node they invaginate

77
Q

How is the notochord formed?

What does it do?

A

Defines the phylum chordata and is the basis for the axial skeleton

Drives formation ofthe nervous system: neuralation

Prenotochordal cells migrate through the cranial part of the primitive pit

Form a solid rod of cells running through the midline with an important signalling role - defines the midline

Axial skeleton forms around it

It regresses afterwards

78
Q

What does the notochord become in adults?

A

Nucleus pulposus

Of the intervertebral disk

79
Q

How do the primitive streak and node define the axes?

A

Set in the early embryo

Streak appears at one end of the bilaminar disk, defines the front and back: anterior/rostral and posterior/caudal

Molecular signals from the primitive node ensure corret dorsal ventral and left right development

Cilitated cells beat signalling molecules left, side specific cascade intiated. Right: liver and lung with 3 lobes. Left: stomach and spleen, lung with 2 lobes

80
Q

What causes mirror dispostion of organs?

A

Usually immobile cilia

SITUS INVERSUS

Organs wrong way round

No associated morbidity

81
Q

Describe how twinning can arise

A

Monozygotic: 1 fertilised oocyte, 2 identical infants

Splitting:

After first cleavage, 2 embryos and 2 placentas

Inner cell mass duplicates: 1 placenta

2 inner cell masses touching, duplication of primitive streak, same placenta and same amniotic sac, sometimes conjoined twins

82
Q

What is teratogenesis?

Explain what happens when it occurs at particular time intervals

A

Process by which normal embryonic development is disrupted

If in first 2 weeks, abortionwe

eks 3 to 8, most sensitive

Each organ has a sensitive window for abnormalities

Early: major congenital defects

Later: minor functional defects

Agents such as thalidominde, rubella, alcohol and some therapeutic drugs can cause it.

83
Q

What has occured by the end of week 3 in the embryonic period?

A

Embryo has gastrulated and the bilaminar disk has become a trilaminar disk

Axes have been set

Three germ layer, ectoderm, mesoderm and endoderm

84
Q

What is the notochord?
What does the notochord signal?

A

Solid rod of cells running down midline

Directs the conversion of ectoderm to neuroectoderm

Signals overlying ectoderm to thicken, key hole shaped neural plate

Edges elevate out of the plane of the disc and curl towards each other, creating a neural tube

Neural tube drops below ectoderm proper

85
Q

How are somites formed?

A

Segments of paraxial mesoderm

1st pair appears at day 20

3 pairs per day in a craniocaudal sequence until there are 42-44 pairs by the end of week 5

31 pairs left in total, 31 pairs of spinal nerves

86
Q

What do somites give rise to?

A

Repeating structures

Vertebrae

Ribs

Intercostal muscles

This guides innervation

87
Q

Explain the differentiation of somites into dermatome, myotome and sclerotome

A

Somites appear as regular blocks of mesoderm cells aorund a small cavity

Followed by organised degeneration, leadign to the formation of the scleortome, ventral wall breaks down

Dorsal portion forms dermomyotome

Myotome proliferates and migrates

Dermotome disperses just below ectoderm

88
Q

What do the following structures become?

Dermatome

Myotome

Sclerotome

A

Skin dermis

Muscle

Hard tissues like bone

89
Q

Explain how dermatome and myotome are used as terms to describe adult innervation of skin and muscles

A

Each myotome and dermatome retains innervation from its segment of origin

Dermatome is a stip of skin supplied by a single spinal nerve

The myotome is a muscle or group of muscles supplied by a single spinal nerve

Can be examined clinically

The neural tube produces the nerves that innovate the dermomyotome

90
Q

What is an epimere?

What is a hypomere?

A

Innervated by a dorsal branch of spinal nerve
, epimere

Innervate by ventral branch of spinal nerve, hypomere

91
Q

What is formed from the mesoderm?

A

Notochord

Paraxial: axial skeleton (vertebral column and ribs), dermis, muscles of axial body wall, some limb muscles

Somatic (lateral plate): connective tissue of the limbs, contributes to the axial body wall

Splanchnic (lateral plate): smooth musculature, connective tissue and vasculature of gut

Immediate mesoderm: urogenital system, kidneys, ureters, gonads

92
Q

Describe cephalocaudal folding

A

Seen by saggital section

Heart lies at the cranial end, moves to future chest

Yolk sac is drawn up and extends out of the embryo to form a connection between the yolk sac and gut

93
Q

Describe lateral folding

A

Driven by somite growth

Seen in transverse section

Pulls amniotic membrane around disc so it is suspended

Forms gut tube from yolk sac

Surrounded by intra embryonic coelem, lateral branches of mesoderm connect

94
Q

What does folding achieve?

A

3D structure

Creates ventral body wall

Pulls amnion around disc so embryo is suspended

Pulls connecting stalk ventrally

Creation of new cavity within the embryo, the coelom

95
Q
A
96
Q

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A

ESA 1 Revision (8 decks)

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