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nutrition thru life > embryo/fetal development > Flashcards

embryo/fetal development Flashcards

1
Q

True/False: The leading cause of infant mortality in the US is birth defects - this is due to a higher prevalence of birth defects in the US mainly because of overexposure to chemicals.

A

False. The main reason birth defects has become the number one cause is because improved obstetrical care has reduced other causes/complications.
*however: the increase of medications/drug use/environmental toxins could also play a role.

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2
Q

How might the maternal physiological state cause teratogenesis? (5)

A
  • illness (infection, metabolic disorder, malabsorption)
  • deficiencies
  • drugs/chemical intake (drugs, alcohol, environmental toxins)
  • genetics (susceptibility to toxins, genetic makeup)
  • radiation exposure
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3
Q

An anomaly present at birth is a ____ anomaly.

A

Congenital

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4
Q

What is the leading cause of newborn/infant mortality in the US?

A

Birth Defects

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5
Q

Define “teratogenesis”

A

Production of birth defects/malformations - can be internal or external, or microscopic

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6
Q

List the causes of teratogenesis. (7)

A
  • Genetic
  • Chromosomal aberrations
  • Metabolic
  • Radiation
  • Infection
  • Drugs/Chemicals
  • Unknown???
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7
Q

The prevalence of birth defects per live births is about ___%

A

2-3%

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8
Q

True/False: The incidence of mortality due to birth defects increases for the 2 yr old age group in comparison to newborns. Why?

A

True; some defects may be symptomless at birth and may be discovered or manifest later.

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9
Q

Of the known causes of defects in humans, the largest percentage is due to ____ and _____.

A

Genetics and chromosomal aberrations

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10
Q

Defects in the ____ make up the largest proportion of causes of death due to birth defects in US infants.

A

Heart

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11
Q

True/False: the leading cause of developmental defects is due to drugs/chemicals.

A

False; 65-70% of defects have UNKNOWN causes.

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12
Q

True/False: less than 50% of fertilized eggs will result in a healthy infant

A

True

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13
Q

define “post-implantation loss”

A

A fertilized egg is shed due to the uterus lining being unprepared for pregnancy.

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14
Q

When is the fetus at its most vulnerable point?

A

Organogenic period 3-8 weeks

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15
Q

True/False: some birth defects may not manifest until adulthood.

A

True.

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16
Q

Most pregnancy failures are due to ______.

A

Post implantation losses (31%)

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17
Q

Why is the organogenic period so critical?

A

It is the period of maximum cell division and differentiation.

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18
Q

What does the organogenesis stage include?

A

Conception (zygote forming)
Implantation
Ovum dividing/differentiating

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19
Q

Why might folate supplementation be suggested for women who are trying to become pregnant?

A

The neural tube closes within 28 days, before the woman may even know she is pregnant. Folate is essential to ensure proper neural tube development, so she should ensure her levels are adequate.

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20
Q

True/False: the Neural Tube should close in the late first trimester.

A

False. The neural tube should close in the early first trimester, by 28 days.

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21
Q

True/False: Adequate folate is extremely important as soon as a woman knows she is pregnant.

A

False; adequate folate levels are especially important for any woman capable of becoming pregnant. But folate is also important for any other individual.

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22
Q

List the stages of development from fertilization to fetus:

A

zygote, morula, blastocyst, embryo, fetus

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23
Q

List the stages of cell growth during pregnancy.

A

Hyperplasia
Hyperplasia + Hypertrophy
Hypertrophy

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24
Q

How might the effects of deficiencies during the hyperplasia stage vs the hypertrophic stage differ?

A

Hyperplasia is max period of cell division; if impacted, causes a permanent reduction in cell number.
Hypertrophy is the period of cell size increase and differentiation; if affected, there is risk of biochemical or organ malfunction.

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25
Q

True/False: Hyperplasia describes an increase in cell size, while hypertrophy is an increase in cell number.

A

False. Hyperplasia is the increase in cell number (division) while hypertrophy is an increase in cell size.

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26
Q

True/False: exposure to toxicants during the zygote/blastocyst phase (<1 week) has extremely severe consequences.

A

False. Cells are still in hyperplasia, and are pleuripotent (large restorative capacity).
The blastocyst is not yet implanted, so there is less exposure to toxins.
So: there is low susceptibility/incidence of abnormalities (either causes lethality or no effect)

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27
Q

Cavity formed in the center of the developing zygote:

A

Blastocele

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28
Q

In what period of growth during pregnancy does the cell number increase at a maximum rate, but not the cell size?

A

Hyperplasia

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29
Q

What are the 3 germ layers formed during gastrulation?

A

Ectoderm
Mesoderm
Endoderm

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30
Q

The developing embryo is more at risk of teratogenic effects at 8 days or 16 days after fertilization?

A

16 days; during gastrulation period (cell differentiation)

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31
Q

Before the placenta forms, how does the early blastocyst derive its nutrients? What is this stage called?

A

Phagocytosis; histiotrophic nutritional phase

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32
Q

What systems form from the mesoderm?

A

cardiovascular, muscles, excretory

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33
Q

What step does gastrulation begin with?

A

Invagination in the future cranial area, forms HENSON’S NODE -> form primitive streak

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34
Q

Why is the organogenic period so susceptible to teratogenic effects?

A

It is the period of cell proliferation/migration/interactions, tissue remodelling. Key organs/structures are being established.

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35
Q

What are the cell types in a blastocyst, and what are their purposes?

A

embryoblast: pleuripotent cells on the inside, forms the embryo
trophoblast: will secrete proteolytic enzymes to erode lining of uterus for implantation, and will form the endometrium to start forming placenta

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36
Q

Which of the germ layers goes on to form the nervous system? What is this process known as?

A

Ectoderm (forms brain, CNS)

neurulation

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37
Q

What systems form from the endoderm?

A

respiratory, digestive, glandular

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38
Q

Why is it essential for the closing of the neural tube by day 27?

A

If it does not close, the precursor cells are exposed to amniotic fluid and will be damaged, leading to serious defects in the CNS.

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39
Q

What happens during neurulation?

A
  1. The ectoderm differentiates into the NEURAL PLATE
  2. The edges rise, to form the NEURAL GROOVE
  3. The NEURAL CREST CELLS fold in and fuse, and segregate to form the NEURAL TUBE (precursor of CNS), and also the future face/skull
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40
Q

What differentiates a fetus from an embryo?

A

Placenta is developed

All essential internal/external structures are developed

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41
Q

True/False: the stage at which the fetus is exposed to teratogens will affect what organs systems are impacted

A

True; different organs systems develop at varying times. Each has their own critical period of growth.

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42
Q

Exposure to toxins after the 8th week will cause abnormalities in ____ and _____ rather than morphological defects. Why?

A 
growth
function
Organs are mostly finished differentiating (except genitalia), but still require growth and maturation.
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43
Q

What is the teratogen most associated with fetal abnormalities? What does it cause?

A

Alcohol

Fetal Alcohol Syndrome

44
Q

What are the classes of teratogens?

A 
Medications
Drugs
Environmental toxins
High temperature
Infectious disease
Chronic disease
Nutrient excess/deficiency
45
Q

The characteristic defects associated with a particular agent are classified as a _____.

A

syndrome

46
Q

True/False: hot tubs can potentially be teratogenic

A

True. prolonged raising of the body core temp can have teratogenic effects.

47
Q

Pesticides and alcohol fall under the ____ and ____ classes of teratogens

A

environmental toxins

drugs

48
Q

True/False: The placenta acts as a barrier and will protect the fetus from most medications.

A

False. Most medications are able to cross the placenta.

49
Q

True/False: Extra vitamin A supplementation is recommended for pregnant women, to ensure proper development of the eyes and brain in the fetus.

A

False. Excess vitamin A will cause defects in the CNS!

50
Q

What are the causes of nutrient excesses/deficiencies?

A

Diet or drug induced

51
Q

What is the cause of cretinism? What are its symptoms?

A

Iodine deficiency

Potbelly, facial abnormalities, mental/physical retardation

52
Q

What nutrient is essential for the closing of the neural tube?

A

Folate

53
Q

What nutrient excesses are of particular concern?

A

Vit A, Vit D, Iodine, Fluorides

54
Q

A deficiency in vitamin ___ causes eye abnormalities and microcephaly

A

A

55
Q

What are the effects of excess vit A on the fetus?

A

CNS abnormalities

56
Q

Besides, folate, a period of deficiency in ____ can also lead to neural tube defects.

A

Zinc

57
Q

What is microcephaly? What deficiencies might cause microcephaly?

A

Microcephaly = small head

Severe protein deficiency, or vit A deficiency

58
Q

What nutrient deficiencies are of particular concern?

A

Protein
Vit A, Vit D, Vit E, Vit K, Folate
Iodine, K, Cu, Zn

59
Q

What are the effects of excess vit D on the fetus?

A

Facial abnormalities

Mental retardation

60
Q

What are the effects of excess iodine on the fetus?

A

Congenital goitre

Mental and physical retardation

61
Q

What is coumadin syndrome caused by?

A

Vitamin K deficiency

consumption of anticoagulants during pregnancy

62
Q

True/False: Excess vitamin A intake from food has a higher risk of causing birth defects than excess intake from supplements.

A

False. Excess intake from supplements has higher incidence rate.

63
Q

What is the effect of excess Fluorides on the fetus?

A

Spina Bifida Occulta

64
Q

Fetal rickets is characterized by: ____, _____, and _____. Why?

A

tooth enamel hypoplasia, decreased bone density, growth failure.
This is caused by vitamin D deficiency, which would impair absorption of Calcium

65
Q

What could cause a Cu deficiency in the mother? What outcomes in the infant could this cause?

A

severe deficiency in diet, metabolic disorder (Menkes kinky hair), or Cu chelating drugs
Abnormalities in blood vessels, bones, brain

66
Q

Would a mild-moderate protein deficiency result in microcephaly in the infant? Why or why not?

A

No, microcephaly is caused by severe protein deficiency. In less severe cases, the fetus can draw from maternal stores.

67
Q

The use of what drug in particular is known to decrease vit E stores?

A

Smoking (nicotine)

68
Q

The deficiency of vitamin D can cause _____.

A

Fetal rickets

69
Q

When is the fetal brain most sensitive to the effects of alcohol?

A

3rd trimester, and the weeks following birth

70
Q

True/False: the body can mobilize Zinc to the infant, so in the case of deficiency in the diet, the fetus will draw on maternal stores.

A

False; zinc is not well mobilized. Short periods of deficiency can cause NTD.

71
Q

The deficiency of vitamin ____ causes nonspecific birth defects/abnormalities.

A

E

72
Q

A deficiency in potassium can cause _____.

A

kidney abnormalities

73
Q

The Alcohol Related Birth Defects include:

A

Microcephaly
Heart/lung malformations
Minor physical abnormalities

74
Q

What are the differences between “small for gestational age” vs “premature?”

A

Small for gest. age: less than expected size/weight for development time (retarded growth)
Premature: appropriate age-for-size but born early

75
Q

True/False: regardless of dose, any alcohol will have the same damaging effects on the developing fetus.

A

False: dose-response effect. Greater consumption = greater risk of abnormalities/damage

76
Q

What are some key characteristics of FAS?

A

Facial abnormalities (long face, short upper lip, underdeveloped jaw)
motor and mental retardation
low fat stores
growth retardation (small head, low weight/height percentile)

77
Q

What metabolic factors make a dose of alcohol more harmful to the fetus than the mother?

A
  1. Freely crosses the placenta
  2. Developing CNS and brain much more susceptible than adult tissue
  3. detoxification mechanisms not fully developed in fetus
  4. Fetus is smaller body weight, recieves much higher dose per weight
78
Q

What are the toxic effects of alcohol? (list 6)

A
  1. displaces other nutrients
  2. interferes with metabolism/absorption of nutrients/minerals (Folate, Zn, K)
  3. metabolism produces more toxic byproducts
  4. Inflammation (free radicals, causes damage)
  5. Placental toxicity (damage placenta)
  6. cell death
79
Q

How might the metabolism of alcohol make it more dangerous?

How does the body deal with this?

A

Alcohol is initially broken down to ACETALDEHYDE, which is more toxic.
aldehyde dehydrogenase is needed to convert this to acetic acid.

80
Q

What enzyme breaks down alcohol?

A

Alcohol dehydrogenase

81
Q

What are the most severe forms of NTDs? Define them.

A

Anencephaly - no skull

Exencephaly - brain protrudes from skull

82
Q

True/False: genetics play a role in NTDs

A

True.
about 12% cases have identifiable cause, and mothers with previous instances of NTDs are more at risk for another NTD pregnancy

83
Q

In addition to deficiencies, NTDs can also be cause by?

A

Genetics (chromosomal aberrations, genetic mutations)
Raised core temperature during early pregnancy
Maternal obesity
Maternal type II diabetes
Abnormalities in folate metabolism

84
Q

What study was key in proving the essential role of folate in preventing NTDs?

A

the MRC vitamin study

85
Q

If the spine does not close properly and the cord protrudes, this is known as ____ ____.
What can this cause?

A

Spina Bifida

Can cause paralysis, impaired motor control, impaired bladder/bowel control, fatality

86
Q

What did the MRC study show?

A

Folate supplementation is effective in preventing NTDs, while only a multivitamin supplement did not have such benefits

87
Q

What converts SAM to SAH? How?

A

Methyltransferase

translocates a methyl group from SAM to a substrate

88
Q

What vitamin is needed for conversion of homocysteine to cysteine?

A

B6

89
Q

Vitamin B12 and Folate are needed for the _____ pathway.

A

Homocysteine/methionine

90
Q

What is the homocysteine cycle used to produce?

A

Cysteine

91
Q

What converts homocysteine to methionine?

A

Methionine synthase catalyzes the transfer to create methionine.

92
Q

What is the role of 5-methyl-TH4-folate in the homocysteine cycle?

A

Contributes the methyl group to homocysteine.

93
Q

What is required to regenerate methionine synthase?

A

B12 (cobalamin)

94
Q

If there are high levels of homocysteine, then ___ levels (precursor) will increase. Why?

A

SAH

due to equilibrium dynamics; reaction forward will not proceed

95
Q

DNA expression can be regulated through _____.

A

methylation

96
Q

What enzyme regenerates the methyl donor for the conversion of homocysteine to methionine?

A

5-Methylene TH4-Folate reductase

97
Q

What are the teratogenic effects of high homocysteine? (2)

A
  • buildup of SAH -> decreased methylation

- oxidative stress

98
Q

True/False: high homocysteine levels and SAH buildup will lead to DNA hypermethylation.

A

False. It will inhibit methylation (hypomethylation).

99
Q

True/False: homocysteine levels are usually expected to rise slightly during pregnancy due to increased synthesis rates in the body.

A

False. Homocysteine levels should decrease 30-60% due to hemodilution.

100
Q

oxidative stress caused by high homocysteine will lower enzyme activity of ____ ____, and limit availability of vitamin ___.

A

methionine synthase, B12

101
Q

True/False: Folate supplementation can lower homocysteine levels

A

True

102
Q

High homocysteine can lead to a potentially fatal condition known as:

A

pre-eclampsia (dangerously high BP)

103
Q

Families with history of NTDs may have a shortage in the _____ enzyme.

A

Methyl TH4-folate reductase

104
Q

Why is folate supplementation considered more important than B12 or B6 supplementation, when all are vital for the homocysteine cycle?

A

folate is low in food and poorly absorbed. Deficiencies in B12 and B6 are rare.

105
Q

True/False: high homocysteine can cause miscarriages, spontaneous abortions, and newborn obesity.

A

False; higher homocysteine correlated with lower birth weight.

106
Q

Is the monoglutamate or polyglutamate form of folate better absorbed? What are the sources of each?

A

Monoglutamate

mono is from supplements, poly is from food.

107
Q

Why might natural sources (food) not be sufficient? (3)

A

Variability in sources
Absorption is less, also variable
Losses from cooking

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