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4) Nutrition Through Life > 2) Embryology and Teratology (Part I) > Flashcards

2) Embryology and Teratology (Part I) Flashcards

1
Q

What is teratogenesis?

A

The production of congenital birth defects in an embryo or fetus

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2
Q

What are malfunctions?

A

Non-reversible morphological defects present at birth

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3
Q

What are the three types of malfunctions?

A
  • External malfunctions (e.g. cleft palate)
  • Internal malfunctions (e.g. malfunction in an organ)
  • Microscopically visible malfunction
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4
Q

What are congenital anomalies?

A

Present at birth

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5
Q

How many types of congenital anomalies are there? What can they range from?

A
  • 200 types

- Range from physical abnormalities to fatality

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6
Q

Birth defects are present in what percentage of live births?

A

2-3%

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7
Q

What are deaths to birth defects primarily due to?

A

Structural and functional defects in vital organs

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8
Q

Structural and functional defects in which vital organs are particularly susceptible to cause death?

A
  • CNS
  • Respiratory system
  • Heart
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9
Q

What is the leading cause of infant death in North America?

A

Birth defects

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10
Q

What are the three reasons that explain why birth defects are the leading cause of infant death in North America?

A

1) Improvements in obstetrical care
2) Increased medications and social drug use
3) Contribution of environmental contaminants to teratogenesis

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11
Q

How does the incidence of birth defects vary at two years old? Why?

A
  • At two years old, the incidence increases from 4 to 6%

- Due to the discovery of internal organ defects, which may have been symptomless at birth

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12
Q

Birth defects account for more than ___ of all deaths in infants below a year old, and ___ of all deaths in children above 15 years old.

A
  • 1/3

- 1/4

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13
Q

Around 20 to 25% of the causes of birth defects are due to what? How are they identified?

A
  • Genetic causes and chromosomal aberrations

- Identified by a constellation of characteristics of defects that are present together

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14
Q

Which factors play a role in the development of birth defects, apart from genetic and chromosomal aberrations?

A
  • Metabolic (maternal illnesses)
  • Radiation
  • Infection (maternal illnesses)
  • Exposure to drugs or chemicals
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15
Q

What is the susceptibility of teratogenesis heavily influenced by?

A

The genetics of the mother and infant, as well as environmental factors

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16
Q

What percentage of human pregnancies result in a healthy, normal infant?

A

Less than 50%

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17
Q

What do anomalies occurring during the early stages of embryogenesis lead to?

A

An early miscarriage

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18
Q

What three outcomes may the formation of a zygote lead to?

A

1) Healthy pregnancy that comes to term
2) Pregnancy that comes to term with the formation of anomalies
3) Pregnancy that does not come to term

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19
Q

What is the largest contributor to an unsuccessful pregnancy?

A

Post-implantation losses

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20
Q

What are post-implantation losses?

A

If the uterus is not ready to receive the zygote, then the fertilized egg is shed along with uterine tissue during the following menstrual cycle

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21
Q

What occurs during the conception period of reproduction?

A

1) Conception is the formation of a zygote from the union of the ovum and sperm
2) Implantation of the zygote into the uterine wall

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22
Q

What occurs during organogenesis?

A

The division and differentiation of the ovum to form tissues and organs

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23
Q

When does organogenesis occur?

A

Weeks 3 to 8 during pregnancy

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24
Q

What is the teratogenic period?

A

The most susceptible period to birth defects

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25
Q

When is the teratogenic period?

A

17 to 57 days post-fertilization

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26
Q

When does the neural tube close?

A

Within 28 days of gestation, when most women do not know they are pregnant yet

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27
Q

What is necessary for women to be CAPABLE of becoming pregnant, and avoiding a neural tube defect?

A

Adequate nutrition, specifically folate, PRIOR to conception

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28
Q

For all women, there is a __-day period following ovulation.

A

14

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29
Q

What is the period of maximal cell division and differentiation? What is it also referred to as?

A
  • The organogenic period

- The critical period of growth

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30
Q

What should occur by the end of the organogenic period?

A

The development of the major fetal structures should be completed

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31
Q

What are the two types of growth during pregnancy?

A
  • Hyperplasia

- Hypertrophy

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32
Q

What is hyperplasia?

A

Increase in cell number

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33
Q

What is hypertrophy?

A

Increase in cell size

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34
Q

When does hyperplasia occur? What is it characterized by?

A
  • Day 17 to 8 weeks following fertilization

- Maximum vulnerability to teratogenic effects

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35
Q

What does interference with hyperplasia (e.g. toxicity or nutrition deficiencies) result in?

A

In a permanent reduction in cell NUMBER, which cannot be compensated for later, even with proper nutrition

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36
Q

What occurs after the hyperplasia period?

A
  • Hypertrophy and hyperplasia

- Then, hypertrophy alone

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37
Q

When does hypertrophy occur? What is it characterized by?

A
  • 8 weeks following fertilization

- Risk for development of organ or biochemical malfunctions

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38
Q

What is ovulation?

A

Ovum is expelled by the ovary into the Fallopian tubes

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39
Q

How may poor nutrition and toxic exposure affect fertilization?

A

Can decrease gamete viability (sperm or ovum), which may lead to decreased fertility or poor cell division

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40
Q

What does the zygote produce as it begins to cleave? How?

A
  • Increase in the number of cells (but no increase in volume)
  • The zygote produces the morula
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41
Q

What does the morula produce as a cavity forms in its center? What is the cavity called?

A
  • The cavity is called the blastocele

- The morula produces the blastocyst

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42
Q

What types of cells does the blastocyst contain? Where are they located?

A
  • Embryoblasts (inside)

- Trophoblasts (outside)

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43
Q

What is the primary function of trophoblast cells?

A

They secrete proteolytic enzymes, which erode epithelial uterine lining, allowing for the creation of an implantation site for the blastocyst

44
Q

When does the histiotrophic phase occur?

A

20 to 25 days after fertilization

45
Q

What occurs during the histiotrophic phase?

A
  • Fluid and nutrients are derived from the erosion of the uterine lining
  • They are absorbed by trophoblast cells through phagocytosis to provide nutrients for the blastocyst
46
Q

Why is the histiotrophic phase necessary?

A

Because there is no placenta or fetal circulation to provide the fetus with nutrients

47
Q

The trophoblast forms a cord of cells that extend into the ____________ and attach to start forming the _________.

A

endometrium

placenta

48
Q

When does the formation of a zygote occur?

A

In the first week after ovulation

49
Q

What is the pre-implantation period characterized by?

A
  • An increase in cell number

- NO increase in cell size

50
Q

What are the possible effects of exposure to toxins during the pre-implantation period? Why?

A
  • No effect, slight decrease in growth, or lethality
  • As the fate of the cells has not yet been determined (pluripotent nature), providing them with great restorative capacity
  • Also, there is a decreased exposure to toxins due to poorer accessibility of the conceptus (not yet attached to uterine wall)
51
Q

What is the susceptibility of teratogens during the pre-implantation period?

A

Low susceptibility to teratogens, and few developmental abnormalities

52
Q

Which cells within the blastocyst form an embryo?

A
  • The embryoblasts form an embryo

- Trophoblast cells do NOT become an embryo

53
Q

What occurs at day 14, following implantation?

A

The inner cell mass starts to differentiate into different types of cells, starting with the formation of the Henson’s node (invagination)

54
Q

Where does the formation of Henson’s node occur? How does it move?

A

In the future cranial area of the ectoderm, which moves caudally (front to back) to form the primitive streak

55
Q

When does gastrulation occur?

A

2 to 3 weeks

56
Q

What is gastrulation characterized by? What is gastrulation?

A
  • Cell migration through the primitive streak

- Process that gives rise to the three germ layers (ectoderm, mesoderm, endoderm)

57
Q

What are examples of the ectoderm?

A
  • Brain
  • CNS
  • Skin
58
Q

What are examples of the mesoderm?

A
  • Voluntary muscles
  • Cardiovascular system
  • Excretory system
59
Q

What are examples of the endoderm?

A
  • Digestive system
  • Respiratory system
  • Glandular organs
60
Q

Which period is very susceptible to teratogens?

A

Gastrulation

61
Q

Describe the process of neurulation.

A
  • The ectoderm differentiates into the neural plate, forming the neural groove
  • The edges of the neural groove connect, forming the neural tube
62
Q

What occurs to neural crest cells during neurulation? What are neural crest cells?

A

Neural crest cells (precursor cells to the embryo’s CNS) segregate during neurulation

63
Q

What are characteristics of the embryo at 27 to 29 days post-ovulation?

A
  • The shape of the embryo is established, and the heart starts beating
  • Major organ development begins
  • The embryo is smaller than an inch, or an ounce
64
Q

What occurs if the neural tube does not close?

A
  • Degeneration of nerves

- The precursor cells that are supposed to become CNS cells are exposed to amnionic fluid, which may cause degeneration

65
Q

What factors may cause a NTD at 27 to 29 days?

A
  • Factors that interfere with cell division (creation of the neural groove)
  • Factors that interfere with cell fusion (joining of the edges to form the neural tube)
66
Q

The growth during the organogenesis period is solely ___________.

A

hyperplasia (increase in cell number, but not size)

67
Q

What occurs during organogenesis?

A
  • Cell proliferation
  • Cell migration
  • Cell-cell interactions
  • Tissue remodeling
68
Q

Is organogenesis susceptible to teratogens?

A
  • VERY susceptible to teratogenesis

- There are periods of maximum susceptibility for each forming structure

69
Q

What occurs at the 8th week of gestation?

A
  • The conceptus is now considered a fetus

- All the essential internal and external structures are present

70
Q

When does the placenta account for most nutrient needs of the fetus?

A

At the 8th week of gestation

71
Q

What is the fetal growth period characterized? Which organs are characterized by differentiation?

A
  • Tissue differentiation, growth, and physical maturation of the fetus occur
  • Differentiation of the external genitalia
72
Q

Is the fetal growth period susceptible to teratogens?

A
  • Functional and growth abnormalities occur rather than morphological abnormalities (apart from the genitalia)
  • CNS and reproductive anomalies, as well as behavioural and motor deficits
73
Q

Which organs are primarily susceptible during the embryonic period?

A
  • Central nervous system
  • Heart
  • Limbs
  • Ears
  • Eyes
74
Q

The period of greatest susceptibility to teratogenesis is characterized by ___________ defects, while latter defects are ________ or __________.

A

morphological

physiological, functional

75
Q

The spectrum of defects depends on the _______ of the teratogenic influence.

A

timing

76
Q

What are the three classes of teratogens?

A
  • Medications
  • Social drugs (alcohol, cocaine, smoking)
  • Environmental agents (solvents, pesticides, PCBs)
77
Q

How may the type of teratogenic exposure be identified?

A

By the occurrence of symptoms associated with the agents used

78
Q

What substance is responsible for the most fetal abnormalities?

A

Alcohol

79
Q

Differentiate a premature infant and a small for gestational age infant.

A
  • Premature infant may be the proper size for the number of weeks it has been in gestation
  • Small for gestational age infant are small for the number of weeks that it has been in gestation
80
Q

What type of drug is Dilantin? What defects does it result in?

A
  • Anti-epilectic drug

- Fetal hydantoin syndrome

81
Q

What type of drug is Thalidomide? What defects does it result in?

A
  • Immunomodulatory drug

- Limb and ear abnormalities

82
Q

What type of drugs are antineoplastic drugs? What defects do they result in?

A
  • Chemotherapy drug

- Congenital abnormalities

83
Q

What type of drug is Diethylstilbestrol? What defects does it result in?

A
  • Endocrine disruptor

- Uterine and cervical defects

84
Q

What type of drug is Dextromethorphan? What defects does it result in?

A
  • Cough-suppressant

- CNS abnormalities

85
Q

Why should women who are pregnant (or planning to become pregnant) verify with their physician prior to consuming any sort of drugs (prescribed or not)?

A

Because almost all medications cross the placental wall

86
Q

What are the four factors contributing to the risk of developing a defect, following exposure to drugs?

A

1) Type of medication
2) Time of exposure
3) Individual variation
4) Length of time of exposure

87
Q

What four factors or health states may result in teratogenesis?

A

1) High temperature or fever
2) Infectious diseases
3) Chronic diseases
4) Nutrient deficiency or excess through dietary and drug intake

88
Q

What are the effects of excess iodide?

A
  • Congenital goitre

- Mental and physical retardation

89
Q

What are the effects of excess fluoride?

A

Spina bifida occulta

90
Q

What are the effects of excess vitamin D?

A
  • Facial abnormalities

- Mental retardation

91
Q

What are the effects of excess vitamin A?

A

CNS abnormalities

92
Q

What are the effects of an intake of 10 000 IU of vitamin A?

A

Increased risk of NTDs by 4.8

93
Q

What is the risk of NTD development due to vitamin A intake associated with?

A
  • The timing of intake

- The highest risk occurs during the first six weeks of pregnancy

94
Q

What are the effects of protein deficiency?

A

Microcephaly, characterized by a small head and brain

95
Q

What are the effects of vitamin A deficiency?

A
  • Eye abnormalities and microcephaly

- The teratogenic effects of vitamin A excess and deficiency are similar

96
Q

What are the effects of vitamin D deficiency?

A
  • Fetal rickets
  • Hypoplasia of tooth enamal
  • Growth failure due to decreased calcium availability to the fetus
97
Q

What are the effects of vitamin E deficiency? What lifestyle factor increases the risk of vitamin E deficiency?

A
  • Congenital abnormalities
  • Smoking (pro-oxidant) decreases body vitamin E stores, which creates non-specific birth defects and spontaneous abortions
98
Q

What are the effects of vitamin K deficiency? What factor may increase the likelihood of vitamin K deficiency?

A
  • Coumadin syndrome

- If anticoagulants are consumed

99
Q

What are the effects of folate deficiency? What factors may increase the likelihood of folate deficiency?

A
  • NTDs

- Poor diet, maternal drug intake, or a genetic susceptibility to abnormalities in folate metabolism

100
Q

What are the effects of iodine deficiency? What are its characteristics?

A

Cretinism, which is a syndrome of mental and physical retardation, characterized by a potbelly, large tongue, and the facial characteristics of Down syndrome

101
Q

What is the world leading cause of mental retardation?

A

Cretinism

102
Q

What are the effects of copper deficiency? What may cause an increased risk in copper deficiency?

A
  • Connective brain tissue defects
  • Brain and bone abnormalities
  • Copper-chelating drugs increase the risk of copper deficiency
103
Q

What is Menkes kinky hair syndrome? What are the effects?

A
  • Genetic inborn errors of copper metabolism

- Causes major developmental abnormalities in brain, bones, and blood vessels

104
Q

According to animal studies, what do short periods of zinc deficiency cause? Why?

A
  • NTDs

- As mothers cannot mobilize zinc in time to meet embryonic needs

105
Q

What is acrodermatitis enterpathica? What is it associated with?

A
  • Result of the inability to absorb zinc
  • Characterized by rashes, hair loss, diarrhea, and poor growth
  • Associated with an increased risk of birth defects and pregnancy complications

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