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Block 1 > Embryology > Flashcards

Embryology Flashcards

1
Q

Define ‘oocyte’

A

Cell in ovary which undergoes meiotic division to form ovum

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2
Q

Define ‘zygote’

A

Fertilized ovum (diploid cell); oocyte + sperm

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3
Q

Define ‘blastocyst’

A

Hollow sphere of cells with a cell inner cell mass, just before implantation

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4
Q

Define ‘monozygotic’

A

Twins derived from a single ovum (identical twins)

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5
Q

Define ‘dizygotic’

A

Twins derived from two ovum (fraternal twins)

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6
Q

Define ‘cytotrophoblasts’

A

Interior cell layer of blastocyst

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7
Q

Define ‘syncytiotrophoblast’

A

Outer layer of cells of blastocyst; no plasma membrane but many nuclei; invasive into uterine wall

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8
Q

Define ‘embryo’

A

Implanted bundle of cells less than 8 weeks after conception

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9
Q

Define ‘fetus’

A

Implanted cells more than 8 weeks after conception

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10
Q

Describe the embryonic and fetal periods of development

A

Embryonic period (0-8 weeks): Establishment of organ systems

Fetal period (9 weeks to birth): Growth and maturation of organ system; stuff just gets bigger

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11
Q

Describe the first week of human development and pathogenesis and outcome ectopic pregnancies

A

First week:

  1. Day 0: oocyte released from ovary; fertilization occurs in uterine tube
  2. Day 2: Zygote completes first division (2 cells)
  3. Day 3: 4 cells and 8 cells; size stays constant
  4. Day 4: Morula (solid ball of cells)
  5. Day 5-6: Embryo “hatches” from zona pellucida; increases size of mass
  6. Day 7: Blastocyst forms and implants

Ectopic pregnancy locations:

  • Ectopic pregnancies are located outside uterine walls
  • Most common ectopic location is ampulla of uterine tube (dilated part that curves over ovary)
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12
Q

Explain how home pregnancy tests work

A

Pregnancy test detect elevated hCG (human chorionic gonadotropin) in maternal urine and blood.

  1. Trophoblast produces hCG
  2. hCG maintains corpus luteum
  3. corpus luteum produces progesterone
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13
Q

Describe process of in vitro fertilisation

A

Two methods:

  • oocyte is washed over by sperm
  • single sperm is injected into oocyte

Embryo is placed in uterus after 3 days

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14
Q

Describe process of genetic screening

A
  • Cells can be removed from early embryo (before 8 cell stage) since remaining cells are totipotent (no side effects from removal.
  • Cell can be screened from genetic diseases
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15
Q

Describe multiple gestations

A
  • Identical twins: single fertilized zygote divides into two

- Fraternal twins: two fertilized zygotes

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16
Q

Describe molar pregnancy

A
  • Occurs when sperm fertilizes an egg, but maternal nucleus is lost (empty egg with only paternal DNA)
  • Results in a placenta but NO embryo.
17
Q

Describe gastrulation phase

A
  • Two layered embryos is converted into three layers (Epiblast [outer layer] and hypoblast [inner layer])
  • Mesoderm cells fill between layers
18
Q

Describe the three primary germ layers

A

1) Ectoderm -> outer layer - epidermis and CNS
2) mesoderm -> middle layer - dermis, muscles, connective tissue, cardiovascular system, reproductive
3) endoderm -> inner layer - lines viscera, gastrointestinal tract

19
Q

Describe neurulation phase

A
  • Embryo has three layers
  • Neural plate forms (thickening of ectoderm)
  • Neural groove forms as walls of neural plate grow upward
  • Neural tube forms when neural groove closes in middle region
  • Anterior and posterior neuropore close later
20
Q

Describe organogenic period

A
  • Organs of body are developed from three layers

- occurs from week 4 to week 8

21
Q

Describe fetal period

A
  • 9 weeks to 38 weeks
  • fetus grows from 3cm long to 36 cm long
  • Start: villi around all uterine wall
  • Middle: villi restricted to maternal attachment site
  • End: uterine cavity obliterated
  • hCG decreases and progesterone and estrogen increase
22
Q

Describe fetus sampling

A
  • Chorionic villous sampling (8-10 weeks): small piece of placenta is removed and cultured
23
Q

Describe fetal anomaly scan

A
  • 18 weeks
  • look for congenital malformations
  • can determine sex
24
Q

Define primary prevention

A

address root of cause of birth defect (e.g. drug or behvaiour that causes defect)

25
Q

Define secondary prevention

A

aim to detect and treat birth defect early on

26
Q

Define anencephaly

A

Failure of head end of neural tube to close; baby born without skull covering brain

27
Q

Define spina bifida

A

Failure of lower end of neural tube to close; baby born with spinal cord exposed

28
Q

Describe role of folic acid in neural tube defect prevention

A
  • Folic acid reduced risk of neural tube defects by 50~70%
  • Found in dark green vegetables, liver, and beans
  • Added to all bread
  • Women aren’t aware they are pregnant when neural tube is developing. Need folic acid before awareness
29
Q

Describe time frame for major malformations

A
  • Organs are most sensitive to damage during the early stages of development (critical development time)
  • After critical development, damage will cause minor defects (e.g. abnormal size)
  • Most malformation damage happens during 3 to 8 weeks
30
Q

Describe the different types of defects

A
  • Genetic origin (25%): e.g. Down syndrome (trisomy 21); Holt-Oram syndrome
  • Potentially preventable cause (10%): e.g. maternal diabetes or infection; drugs or alcohol
  • Unknown cause (65%): note that large majority of birth defects have unknown causes
31
Q

Describe categorization of risk of drugs in pregnancy

A

A -> No evidence of harmful effects
B -> animal studies; no human studies; may or may not have effects
C -> May have effects
D -> suspected on causing damage
X -> high risk of damage; NO NEED TO TAKE THESE WHILE PREGNANT

32
Q

Describe birth defect agent: thalidomide

A
  • Severely malformed limbs
  • Not teratogenic in rats and mice, but was in humans
  • Very common drug and caused 10000 malformed children
33
Q

Describe birth defect agent: Isotretinoin (accutane)

A
  • High risk of severe congenial malformation
  • Vitamin A analogue
  • Treats acne so no reason to take during pregnancy
34
Q

Describe birth defect agent: anticonvulsants

A
  • Increase risk of birth defect by 2-4 fold
  • Increase risk of spina bifida by 5-10 fold
  • Convulsions can injury fetus too so it’s a trade-off
35
Q

Describe birth defect agent: alcohol

A
  • Increase risk of mental retardation, and major birth defects (usually heart defects)
  • Caused by excessive maternal alcohol in take
  • no safe limit of alcohol is proven: some say NO alcohol, some say low amount is acceptable
  • If blood alcohol level doesn’t reach excessive levels, it’s alright
36
Q

Describe detection of teratogenic drugs

A
  • All new drugs are tested in animals before release:
    1) must be two different species
    2) maximum tolerated dose is used, and fetus is examined before birth
  • All that is tested is that it does NOT cause increase in chance of defect
  • Information is collected from human after release:
    1) 100 human pregnancy with no defects = does NOT cause 4-fold increase in defects (95% significance)
    2) 600 human pregnancy with no defects = does NOT cause 2-fold increase in defects (95% significance)

Block 1 (9 decks)

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