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IMMS > Embryology > Flashcards

Embryology Flashcards

1
Q

Fate of ectoderm

A

• CNS- central nervous system
• PNS- peripheral nervous system
• epidermis of skin, hair and nails
• Mammary, sweet and sebaceous glands
• Pituitary gland
• Enamel of teeth

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2
Q

Fate of mesoderm

A

• the musculoskeletal system
• Skin- deep layers
• Abdominal and chest walls and lining
• Bowel wall (not epithelium)
• Urogential system

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3
Q

Fate of endoderm

A

• epithelial lining of gastrointestinal tract, respiratory tract and bladder
• Parenchyma of thyroid gland, parathyroids, liver and pancreas

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4
Q

3 germ layers

A

Ectoderm
Mesoderm
Endoderm

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5
Q

Embryology: day 1

A

Fertilisation

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6
Q

Embryology: day 2

A

Formation of the zygote- cell formed by fusion of egg and sperm

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7
Q

Embryology: day 3

A

Cell division - formation of the morula

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8
Q

Embryology: day 5

A

Late blastocyst - cavity formed within the morula

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9
Q

Embryology: day 6-12

A

Implantation into uterine endometrium

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10
Q

Embryology: day 8-9

A

Formation of bilaminar disc (will become the embryo)

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11
Q

Embryology: week 3

A

Gastrulation- bilaminar disc becomes trilaminar disc: 3 germ layers form)

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12
Q

Embryology: week 4

A

Neurulation (neural tube forms) and embryonic folding (flat disc into a cylindrical form)

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13
Q

Fertilisation

A

Fusion of gametes = genetically unique individual
•Millions sperm enter the female reproductive tract
•Can survive for several days
•Travel through the uterus by muscular contractions

Relatively few sperm reach the uterine tube
•Sperm ‘conditioned’ in the tube (capacitation) before they are capable of fertilisation
•Capacitated sperm penetrate the corona radiata and bind to the zona pellucida
•After binding, the acrosome reaction occurs - sperm can penetrate the ZP
•The ZP changes so no more sperm can enter the oocyte - prevents polyspermy

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14
Q

2 required process for fertilisation

A

Capacitation
Acrosomal reaction

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15
Q

Capacitation

A

epithelial interactions between sperm, uterine wall
Glycoprotein coat and seminal plasma proteins covering acrosomal region removed → easier enzyme release → acrosomal reaction

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16
Q

Acrosomal reaction

A

after binding to zona pellucida
Release of enzymes (eg acrosin, hyaluronidase) needed to penetrate zona pellucida

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17
Q

How long are oocytes viable after ovulation

A

12-24 hours

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18
Q

How long are sperm viable after ejaculation

A

Up to 6 days

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19
Q

1st phase of fertilisation

A

Penetration of corona radiata: capacitated spermatozoa allowed to pass through corona radiata

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20
Q

2nd phase of fertilisation

A

Penetration of zona pellucida and sperm binding
• zona pellucida- glycoprotein layer surrounding oocyte
• approx. 500 spermatozoa arrive at this layer
• sperm binding initiates release of acrosin (hydrolysis enzyme) → sperm cell penetrates zona pellucida → sperm makes contact with oocyte → cortical reaction (release of lysosomal enzymes from cortical granules of oocyte) → cortical granules initiate zona reaction, prevent further sperm penetration (polyspermy) by forming protective hyaline layer, inactive receptor sites on zona pellucida
• also activates oocyte to prepare for 2nd meiotic division

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21
Q

3rd phase of fertilisation

A

Fusion of oocyte and sperm cell- forms zygote
• Interactions between integrins and ligands → adhesion of sperm, oocyte (fusion of sperm, egg plasma membranes)
• secondary oocyte completes meiosis II → forms female pronucleus, second polar body
• head, tail of spermatozoa enters oocyte → travels to female pronucleus (containing 23 chromosomes) using tail, energy generated by mitochondria
• tail, mitochondria detach → sperm nucleus becomes male pronucleus
• male, female pronuclei merge into single nucleus → cell becomes diploid
• prepared for mitotic division

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22
Q

Molar pregnancy

A

• compete mole- sperm fertilises an egg that doesn’t contain any genetic material. Abnormal trophoblast (forms placenta) develops but not an embryo
• Partial mole- normal egg fertilised by 2 sperm. An embryo starts to develop but is not viable
Complications of molar pregnancy:
• retained molar tissue can lead to form a cancer (choriocarcinoma)- treatment is very successful

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23
Q

Scientific relevance of molar pregnancy

A

fact that trophoblast can develop in the absence of maternal DNA suggests paternal DNA is important for trophoblast development

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24
Q

Cleavage

A

series of fast mitotic divisions of zygote → increase number of cells, decrease size
• 36 hours after fertilisation → first cleavage division → 2 cells (blastomeres)
• after 3rd cleavage, blastomeres (8) form compact ball of cells connected by tight junctions (compaction)
• 3 days after fertilisation, cells ot compacted embryo divide again → mulberry-shaped 16-cell morula (composed of 2 zones: inner cell mass and outer cell mass)
• 4-5 days after fertilisation, embryo consists of approx. 100 cells
• fluid accumulates within internal cavity (blastocoel) → blastocyst

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25
Q

Morula

A

composed of 2 zones: inner cell mass and outer cell mass

Still surrounded by zona pellucida (glycoprotein coat)

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26
Q

2 zones of blastocyst

A

Trophoblast
Embryoblast

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27
Q

Trophoblast

A

single layer of large flattered cells, stemming from morula’s outer cell mass; gives rise to placenta

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28
Q

Embryoblast

A

20-30 pluripotent cells located on one side, stemming from inner cell mass: gives rise to embryo

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29
Q

Inner cell mass

A

lies at embryonic pole of blastocyst- develops into embryo and may split into identical twins

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30
Q

Outer cell mass

A

develops into the placenta

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31
Q

Blastomeres

A

Cells in morula

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32
Q

IVF

A

In IVF, a blastomere can be removed for genetic testing prior to transfer into the uterus

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33
Q

Blastocyst hatching

A

Day 6:
• blastocyst hatches from the zona pellucida before uterine implantation

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34
Q

Implantation

A
  1. Capture of blastocyst on endometrium- Endometrium must be ready- window of implantation
  2. Blastocyst attaches more firmly to endometrium and trophoblast invade endometrium
  3. complex signalling between endometrium and trophoblast

Blastocyst must implant deeply enough but not too deep- endometrium closes by a fibrin plug

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35
Q

Trophoblast differentiation

A

Trophoblast:
• proliferates, forms 2 layers
1. Cytotrophoblast (cellular trophoblast): inner layer of moronucleated cells
Produces primary chorionic villi, protrudes into syncytiotrophoblast
2. Syncytiotrophoblast: outer multinucleated mass of cells (without distinct cell boundaries)
Invades decidua basalis with finger-like processes; makes enzymes that erode uterine cells; blastocyst burrows into decidua basalis surrounded by pool of blood leaked from degraded blood vessels

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36
Q

Cytotrophoblast

A

at the embryonic pole proliferates

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37
Q

Syncytiotrophoblast

A

invades the endometrium

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38
Q

Maternal vessels and lacunae

A

Trophoblast contacts maternal vessels which form blood filled spaces called lacunae - these will bathe the forming placental villi and allow gas exchange

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39
Q

Embryoblast

A

differentiates into 2 layers, forms flat bilaminar disc
1. Hypoblast - small cuboidal cells adjacent to blastocyst → yolk sac
2. Epiblast - columnar cells. Cavity forms inside (amniotic cavity). Lined with amnioblasts

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40
Q

hCG

A

Human chronic gonadotropin (hCG) maintains viability of corpus luteum → secretes oestrogen and progesterone until week 8

41
Q

Amniotic cavity

A

Develops between trophoblast and epiblast

42
Q

What forms the primitive yolk sac

A

Blastocyst cavity

43
Q

Abnormal zygotes

A

Abnormal zygotes and blastocysts are common eg problems with cell division, molar pregnancy
• Estimate: 50% of conceptuses are lost (spontaneous abortion) early

44
Q

Implantation problems

A

• implantation may fail - may be due to an abnormal embryo or uterine anomalies
• Implantation may be ectopic – outside the body of the uterus eg uterine tube, cervix, ovary
• Can result in later placental problems

45
Q

Invasive placentation

A

Trophoblast must invade – but not too far.
• Placenta accreta - attachment(s) to the myometrium
• Placenta increta – invasion of the myometrium
• Placenta percreta – invasion of the uterine wall +/- adjacent organs
• Placenta does not come away easily after birth- may result in catastrophic haemorrhage

46
Q

Pre-eclampsia

A

Pre-eclampsia:
• Cytotrophoblast does not fully invade the maternal arteries
• Maternal arteries do not ‘transform’ into wide, low resistance vessels.
• Remain narrow and high-resistance
• Restrict fetal growth
• Systemic problems in the mother:
-High blood pressure
-Protein in the urine
-Can lead to seizures (eclampsia)

47
Q

Gastrulation

A

establishes 3 germ layers
• begins with formation of primitive groove (narrow depression into centre ef epiblast layer). Starts at caudal end and grows towards cranial end → cranial -caudal axis. Groove forms in dorsal side of embryo (dorsal-ventral axis). Two sides of groove- left and right side of body (bilateral symmetry)
• Primitive node forms at cephalic end of primitive groove. Contains primitive pit and surrounded by slightly elevated area of ectoderm
• Epiblast cells migrate towards primitive groove →move to bottom and slide under (invagination)
• After invagination, cells differentiate into 3 new layers of embryonic disc (trilaminar disc)
• Cells of trilaminar disc are multipotent
• Some epiblast cells displace ventral hypoblast layer and form endoderm
• Invaginated epiblast cells between newly formed endoderm and epiblast → mesoderm layer
• Rest of epiblast forms ectoderm layer
• Body axes are also established- head and ‘tail’ ends, front an back, left and right

48
Q

Primitive streak

A

Appears as a groove at the caudal (tail end) of the epiblast
•Epiblast cells migrate towards the primitive streak
•Invaginate through it
•Settle between the epiblast and hypoblast to form a third layer, the mesoderm

49
Q

Gastrulation- clinical relevance

A

Gastrulation is a critical time - embryo is vulnerable
• Insufficient mesoderm in the cranial or caudal regions can significantly affect the development of the head and lower limbs, respectively.
• Laterality defects may occur - conditions of ‘abnormal sidedness’
-Situs inversus - thoracic and abdominal viscera are ‘flipped’
-Dextrocardia - the heart is ‘flipped’

50
Q

Which hormone guides tissue differentiation

A

Sonic hedgehog protein (SHH)

51
Q

Neuralation

A

• mesoderm cells around notochord differentiate into 3 specialised types of cells: paraxial mesoderm, intermediate mesoderm and lateral plate mesoderm
• Notochord starts neurulation →stimulates cells of ectoderm to form neural plate
• Neural plate fold and forms neural groove with edges called neural folds
• Neural plate continues to grow and neural folds come together. Pinch off from surface of ectoderm to form neural tube between ectoderm and mesoderm
• Neural crest cells at top of folds form many tissues eg PNS
• Trophoblast continues to develop vasculogenesis
• Cranial end → brain
• Caudal end →spinal cord
1. Primary villi made up of cytotrophoblastic core covered by syncytial layer
2. Secondary villi form when extraembryonic somatic mesoderm cells penetrate primary villi →grow toward decidua
3. Tertiary villi form when mesodermal cells differentiate into small blood vessels → form villus capillary system → foetal contribution to placenta

52
Q

Neural tube defects

A

• The neural tube fuses along its length
• Failure of closure = neural tube defects
• Failure of closure caudally (tail end) = spina bifida
• Can be seen on fetal ultrasound in pregnancy
• Can be prevented by mother taking folic acid supplement in first 12 weeks of pregnancy
• Protrusion of meninges

53
Q

Neural plate

A

Thickening of the ectoderm

54
Q

What induces neural plate formation

A

Notochord

55
Q

What do neural crest cells form

A

Many tissues including the PNS

56
Q

How does the mesoderm form

A

Epiblast cells migrate through the primitive streak and form a third layer during Gastrulation

57
Q

When are body axes established

A

Gastrulation

58
Q

Hypoblast

A

Ventral
Lines yolk sac

59
Q

Epiblast

A

Dorsal
Becomes germ layers
Lines amniotic sac
Extraembryonic mesoderm

60
Q

Blastocyst

A

Fluid accumulates within internal cavity (blastocoel) of morula

61
Q

What prevents polyspermy

A

sperm binding initiates release of acrosin (hydrolysis enzyme) → sperm cell penetrates zona pellucida → sperm makes contact with oocyte → cortical reaction (release of lysosomal enzymes from cortical granules of oocyte) → cortical granules initiate zona reaction, prevent further sperm penetration (polyspermy) by forming protective hyaline layer, inactive receptor sites on zona pellucida

62
Q

Embryo

A

developing human during the embryonic stage (to end of the 8th week)

63
Q

Fetus

A

from 9th week of development to birth

64
Q

Folding

A

week 4, the embryo starts folding
•Transforms from a flat disc into a ‘cylinder’
•Folding is in two planes:
•Lateral – like making a tube out of a piece of paper. The two edges curve anteriorly and fuse to close the cylinder and form the lateral and anterior abdominal walls.
•Craniocaudal – the embryo’s body takes on a curved shape, from head to bum (tail).

65
Q

Lateral folding

A

like making a tube out of a piece of paper. The two edges curve anteriorly and fuse to close the cylinder and form the lateral and anterior abdominal walls.

Lateral folds grow anteriorly
•Fuse in the anterior midline
•Fusion ‘pinches off’ most of the yolk sac
•Primitive body cavity formed
•Portion of the yolk sac incorporated into the body cavity - the primitive gut

66
Q

Craniocaudal folding

A

the embryo’s body takes on a curved shape, from head to bum (tail).

67
Q

Week 4 mesoderm

A

• paraxial, intermediate and lateral plate mesoderm
• lateral plate mesoderm starts as a solid block but later splits

68
Q

Fate of paraxial mesoderm

A

either side of the midline
• develops into the axial skeleton (vertebrae, ribs, sternum), skeletal muscles and associated dermis of the skin

69
Q

Fate of intermediate mesoderm

A

between the paraxial and lateral plate mesoderm
• kidneys
• Gonads (ovaries and testes)

70
Q

Fate of lateral plate mesoderm

A

split into 2 layers that associate with ectoderm and endoderm
• outer/somatic/parietal layer- parietal pleural and parietal peritoneum
• Inner/ splanchnic/visceral layer- visceral pleura and visceral peritoneum

71
Q

Cephalocaudal folding

A

Curving structure head to tail of embryo

72
Q

Organogenesis

A

organ systems development in the first 8 weeks

73
Q

Brain development

A

neural tube develops in week 4 and closes along its length
• Rapid expansion of the cranial end of the neural tube → brain
• The caudal end remains tubular → spinal cord
• Failure of closure leads to neural tube defects due to exposure to amniotic fluid
• Folic acid supplements in the first 12 weeks of pregnancy reduce the incidence of NTDs

74
Q

When does brain development begin

A

Week 4

75
Q

What reduces the incidence of neural tube defects

A

Folic acid supplements

76
Q

Cardiovascular development

A

heart develops as a tube in week 3
• Heart tube starts to bend in week 4- cardiac looping
• Parts of tube dilate
• Septae formed in weeks 4-5: grown and divide the right and left atria and the right and left ventricles
• Mitral and tricupsid valves form in weeks 4-5
• Heart is not symmetrical- left and right patterning is important

77
Q

When does heart start to develop

A

Week 3

78
Q

When does cardiac looping occur

A

Week 4

79
Q

When does septae form in heart

A

Weeks 4-5

80
Q

When do mitral and tricuspid valves form

A

Weeks 4-5

81
Q

Heart anomalies

A

most common type of congenital anomaly
• Septal defects
• Outflow tract defects (aorta and pulmonary trunk)
• Valve anomalies
• Laterality defects

82
Q

Gut development

A

• primitive gut tube develops in week 4
• Segments of the gut then differentiate
• Different genes involved
• A concentration gradient of retinoic acid is vital for normal differentiation
• Parts of the gut elongate, coil and rotate into their final positions
• Positions of the small and large intestine are established in week 10
• Abdominal viscera are not symmetrical- may be affected by laterality abnormalities eg situs inversus (mirror image flip of thoracic and abdominal organs)

83
Q

When does primitive gut tube develop

A

Week 4 as lateral body folds grow and fuse anteriorly

84
Q

When are portions of the small and large intestine established

A

Week 10

85
Q

Potential MSK developmental anomalies

A

• Amelia - a limb does not develop
• Meromelia - a limb is shortened
• Syndactyly (webbing) - apoptosis fails or is incomplete between the digits
• Polydactyly (extra digits)

86
Q

Musculoskeletal development

A

• limb buds appear in week 4- the development of the lower limb lags behind the upper limb by
a few days
• Week 6- hand and foot plates appear (expands at one end) and cartilage condenses in limbs
• Digital rays then develop- apoptosis between rays separates the digits from each other
• Limbs rotate in week 7- lower limbs rotate medially and upper limbs rotate laterally
• Fingers and toes formed by week 8
• Proximo-distal, dorso-ventral and antero-posterior patterning are important

87
Q

When do limb buds develop

A

Week 4

88
Q

When do hand and foot plates appear and cartilage condense

A

Week 6

89
Q

When do limbs rotate

A

Week 7

90
Q

How do lower limbs rotate

A

Medially

91
Q

How do upper limbs rotate

A

Laterally

92
Q

When are fingers and toes formed by

A

Week 8

93
Q

How do digital rays develop

A

apoptosis between rays separates the digits from each other

94
Q

When does implantation occur

A

6-7 days post fertilisation

95
Q

Epiblasts in a 3 week embryo will become

A

Ectoderm

96
Q

The paraxial mesodermal cells form

A

Somites

97
Q

The midgut is in continuity with the

A

Yolk sac

98
Q

Circulation is formed from

A

Lateral plate mesodermal cells

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