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IASM > L19-21 Embryology > Flashcards

L19-21 Embryology Flashcards

1
Q

3 stages of prenatal development

A
  1. Germinal period: wk 1-2
  2. Embryonic period: wk 3-9
  3. Fetal period: wk 9 onwards
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2
Q

Clinical age vs postovulatory age

A

Clinical age: date of last menstrual period

Ovulatory date: 14 days less than clinical age

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3
Q

Three trimester

A

1st: Rudiments of major organ
2nd: Complete development of organ
3rd: Rapid fetal growth, fully functional organ at the end

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4
Q

Meiosis

A
  1. Pairing of homologous chromosome
  2. Chiasma exchange of genetic materials
  3. 1st meiotic division: separation of homologous chromosome
  4. 2nd meiotic division: separation of sister chromatids
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5
Q

Oogenesis

A

Primordial germ cells
—> arrive at ovary
—> Oogonia
—> Primary oocyte (46 double, arrest at prophase 1) —> meiosis 1
—> Secondary oocyte (23 double, arrest at metaphase) + first polar body (within mature vesticular follicle) —> meiosis 2
—> Mature oocyte (23 single)

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6
Q

Spermatogenesis

A 
Spermatogonium
—> Primary spermatocyte
—> Secondary spermatocyte
—> Spermatids —> spermiogenesis
—> Mature sperms (Spermatozoa)
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7
Q

Spermiogenesis

A
  1. Cytoplasm loss
  2. Tail development
  3. Acrosome formation
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8
Q

Overall 5 main stages for embryo development in first week (germinal period)

A
  1. Fertilisation
  2. Cleavage
  3. Compaction
  4. Blastogenesis
  5. Implantation
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9
Q

Site of fertilisation

A

Ampullary region of uterine tube

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10
Q

Fertilisation

A

Haploid Sperm (23 single) + Haploid Secondary oocyte (23 double)
—> Penetration trigger secondary oocyte to complete meiosis 2
—> Penetrate Corona radiata, Zona pellucida
—> Zona reaction (Prevent sperm binding) + Cortical reaction (impenetrable)
—> Restore diplody + sex determination
—> Cleavage of zygote (repeated cell division with little or no growth)

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11
Q

2 phases of implantation

A
  1. Attachment phase: increase in vascular permeability in stroma, change in ECM
  2. Invasion phase: cytotrophoblast fuse and erode endometrial tissue
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12
Q

Importance of cleavage

A
  1. Restore cytoplasm:nucleus ratio
  2. Activate transcription and protein synthesis
  3. Hexose monophosphate —> glycolysis pathway
  4. Recognition of pregnancy
  5. Cell fate determination
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13
Q

Development of the zygote

A 
Each cell called blastomere
2 cell —> 4 cell —> 8 cell —> compaction (formation of tight junction)
—> Morula (12 cell)
—> Blastocyst (4-5 day)
—> Implanting blastocyst (6 day)
—> Implanting embryo (7.5 day)
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14
Q

Development of blastocyst

A
  1. Trophoblast
    - Cytotrophoblast
    - Syncytiotrophoblast
  2. Embryoblast
    - Epiblast (dorsal)
    - Hypoblast (ventral)
  3. Blastocystic cavity
  4. Zona pellucida: shedding to allow blastocyst to grow in size
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15
Q

2nd and 3rd week of development of embryo

A

2nd week:

  • Embryoblast —> Epiblast + Hypoblast (Bilaminar germ disc)
  • Trophoblast —> Cytotrophoblast + Syncytiotrophoblast
  • Extraembryonic mesoderm: Visceral (Splanchnic) + Parietal (Somatic)
  • 3 cavities: Amniotic cavity + Yolk sac + Extraembryonic cavity
3rd week (gastrulation):
Ectoderm + Mesoderm + Endoderm (Trilaminar germ disc)
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16
Q

Determination of cranial-caudal axis

A

Caudal

  • Primitive streak
  • Primitive node (secrete nodal growth factor to determine left side)
  • Cloacal membrane

Cranial
- Oropharyngeal membrane

17
Q

Process of gastrulation

A
  1. Epiblast cell move towards the primitive streak and node
    —> Leave the epiblast
    —> Go towards hypoblast
    —> Create Mesoderm and Endoderm

Some epiblast cell migrate through the primitive node towards oropharyngeal membrane
—> form the Prechordal mesoderm and Notochord

18
Q

Neural plate induction and neural tube formation

A

Notochord + prechordal mesoderm induces ectoderm to form neural plate / neuroectoderm (cranial to caudal sequence)

Neural tube: neural crest —> neural groove —> neural fold —> neural tube

Formation of somite (zip upwards and downwards) —> anterior neuropore (close at day 25)+ posterior neuropore (close at day 28) —> gastrulation complete

19
Q

Fate of neural crest cells

A

Originate from lateral edges of neural plate —> remain of neural crest cells —> All ganglion, adrenal medulla, mesenchyme

20
Q

Ectodermal derivatives

A
  1. Surface ectoderm: skin, nails, hair, sweat gland, lens of eye
  2. Neural crest: all ganglion, adrenal medulla, mesenchyme
  3. Neural tube: CNS
  4. Amnion: protective bag
21
Q

Mesodermal derivatives

A
  1. Notochord: Nucleus pulposus of intervertebral disc
  2. Paraxial mesoderm / somite:
    - Dermatome: Dermis
    - Myotome: Muscle
    - Sclerotome: Vertebrae, Ribs, Bone
  3. Intermediate mesoderm: Urogenital (Gonads, Kidneys, Uterus etc.)
  4. Lateral plate mesoderm:
    - Somatic: Dermis, Connective tissue of body wall
    - Splanchnic: Pleura, Peritoneum, Pericardium, Heart
22
Q

How endoderm become gut

A
  1. Cephalocaudal fold
  2. Lateral body fold
  3. Formation of intraembryonic cavity by Lateral mesoderm
    - pericardial, pleural, peritoneal cavity
23
Q

Endodermal derivatives

A
  1. Gut tube endoderm: GI tract, Trachea, Bronchial Tree
  2. Cloaca: Rectum, Anal canal, Bladder
  3. Oropharyngeal pouches (foregut): Auditory tube, Thymus, Parathyroid gland
  4. Yolk sac: pressed into umbilical cord then disappear
  5. Allantois: Urachus, umbilical cord part disappear
24
Q

Placental barrier

A 
Fetal blood —>
1. Fetal endothelium
2. Fetal connective tissue
3. Cytotrophoblast
4. Syncytiotrophoblast
—> Maternal blood
25
Q

Types of twins

A
  1. Identical / Monovular / Monozygotic
    - dichorial, diamniotic
    - monochorial, diamniotic
    - monochorial, monoamniotic
  2. Fraternal / Biovular / Dizygotic
26
Q

Formation of monozygotic twins

A
  1. Splitting at 2 cell stage: separate placenta, amniotic and chorionic cavity
  2. Splitting of Embryoblast: common placenta and chorionic cavity, separate amniotic cavity
  3. Splitting at later stage of inner cell mass: common placenta, amniotic and chorionic cavity
27
Q

Reasons for conjoined twins

A
  1. Duplication of primitive streak at rostral end, rostral half, caudal end.
  2. Incomplete duplication of germ layers: rostrally (craniopagus), centrally (thoracopagus), caudally (pyropagus)
28
Q

Formation of triploidy

A
  1. Dispermic fertilisation
    —> 3 haploid pronuclei
    —> 23 chromosome triplets
  2. Nondisjunction
    —> Fail to separate homologous chromosome in meiosis 1
    —> monosomy (Turner’s syndrome) / trisomy (Down’s syndrome)
29
Q

Indication for prenatal diagnosis

A
  1. Maternal age > 35
  2. Previous child with de novo chromosomal abnormality
  3. Family history of genetic defect
  4. X linked disorders e.g. Thalassaemia
  5. Chromosomal structural abnormality
30
Q

Teratogens

A
  1. Cigarette smoke
  2. Alcohol
  3. Drugs e.g. anticonvulsant, progesterone, testosterone
  4. Environmental:
    - Mercury
    - Infectious agent e.g. Rubella
    - Radiation
    - Mechanical
31
Q

Prenatal diagnosis

A
  1. Ultrasound (fetal size, biparietal diameter of skull, genitalia)
  2. Maternal serum screening
  3. Amniocentesis (16-18 weeks, karyotyping of fetal cells, Alpha-fetal protein assay)
  4. Chorionic villus sampling (9-12 weeks, chromosomal abnormalities, inborn errors of metabolism, X-linked disorders)

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