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Seminar Agenda
 Review of Course Information
 The Organogenetic Period
 Discussion Questions
 Questions & Answers
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Review of Course Information:
Projects
 Project 2 is due at the end of Units 7 and 9.
 Some guidelines:
 Use Microsoft Word
 Be sure to complete all parts of the assignment
 Use clear and concise language and proofread
your work.
 Your work should be free of spelling and
grammatical errors.
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Unit 7-9 Project: Embryology
 Topic Proposal: Select a topic from one of
the following stages of human development:
 Gametogenesis
 Fertilization and preimplantation period
 Post-implantation and first three weeks of
development
 Organogenesis
 Fetal period
 Placentation
Unit 7-9 Project: Embryology
 For the topic that you have selected, you should:
 Describe the normal processes in human development
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during that period.
Identify common diseases that occur during this period
that can have adverse outcomes on human development
Explain various environmental factors that affect human
development during this period.
Discuss briefly how these factors/diseases can be
avoided/treated
References: The document should also include the
references that you used (at least 3 other than your
book).
Unit 7-9 Project: Embryology
NOTE:
 Topic Choice, Outline and List of References are
due at the end of Unit 7: 25 points
 Complete Paper (Part 2; Embryology) due at the
end of Unit 9: 50 points
Questions?
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Embryonic Development
 All major external and internal structures are
established during the fourth to eighth weeks.
 The tissues and organs are differentiating rapidly
during this time.
 The embryos are particularly sensitive to teratogens
during this period of development.
 What is a teratogens?
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Embryonic Development
 Teratogens: agents such as viruses or
drugs that produce or increase the
incidence of congenital anomalies.
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Embryonic Development:
Three Phases
 Phase 1 – Growth: cell division and the
elaboration of cell products.
 Phase 2 – Morphogenesis: development
of shape, size or features of a particular
organ or part of the whole of the body.
 Phase 3 – Differentiation: maturation of
physiological processes.
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Beginning of the Fourth Week
 The flat trilaminar embryonic disc is folded into a C-
shaped cylindrical embryo.
 Three germ layers differentiate into various tissues and
organs, so at the end of the embryonic period, the
beginnings of all the main organ systems have been
established.
 The external appearance of the embryo is greatly
affected by the formation of the brain, heart, liver,
somites, limbs, ears, nose and eyes.
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Germ layers:
Ectoderm – central nervous
system; peripheral nervous
system; sensory epithelia of the
eye, ear and nose; hair and nails;
mammary glands; pituitary
glands; neural crest etc.
Mesoderm – connective tissue;
cartilage; bone; striated and
smooth muscle; heart, blood and
lymphatic vessels; kidneys;
ovaries; testes etc.
Endoderm – epithelial lining of
the gastrointestinal and
respiratory tracts; thyroid; liver;
etc.
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Embryo
appearance
at 56 days
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Discussion Question 1
 Why are the third to eighth weeks of
embryogenesis so important for normal
development and the most sensitive for
induction of structural defects?
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Discussion Question 1
 Cell populations responsible for organ formation are being
established. In the fourth week, differentiation of the central
nervous system is initiated and over the next five weeks the
primordia for all the major organ systems is established.
 At these times, cells are rapidly proliferating, and critical cell-
cell signals are occurring.
 Particularly sensitive to disruption by outside factors, such as
environmental hazards, pharmaceutical agents and drugs of
abuse. This exposure can result in birth defects and
congenital malformations.
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Discussion Question 2
 A 28-year-old woman who has been a heavy cigarette
smoker since her teens was informed that she was in
the second month of pregnancy.
 What would the doctor likely tell the patient about her
smoking habit and the use of other drugs (e.g.,
alcohol)?
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Discussion Question 2
 Her embryo at a critical stage of development.
 Heavy cigarette smoking is likely to cause intrauterine
growth restriction (IUGR) and underweight babies.
Also that the incidence of prematurity increases with
the number of cigarettes smoked.
 Recommend her not to drink – alcohol is a teratogen
and results in fetal alcohol syndrome.
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Discussion Question 3
 A patient was concerned about what she had read in
the newspaper about recent effects of drugs on
laboratory animals.
 Can one predict the possible harmful effects of drugs
on the human embryo from studies performed in
experimental animals?
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Discussion Question 3
 One cannot predict how a drug will affect the human
embryo because human and animal embryos may
differ in their response to a drug.
 For example thalidomide is extremely teratogenic to
human embryos and has little effect on some
experimental animals like rats and mice.
 Thalidomide is a sedative.
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Discussion Question 4
 A woman who had just become pregnant told her
doctor that she had accidentally taken a sleeping pill
given to her by a friend. She wondered whether it
could harm the development of her baby’s limbs.
 Would a drug known to cause severe limb defects
likely to cause these abnormalities if it was
administered during the eighth week?
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Discussion Question 4
No – to cause severe limb defects a known
teratogenic drug would have to act during the
critical period of limb development (24-36 days
after fertilization). Teratogens interfere with
differentiation of tissues and organs, often
disrupting or arresting their development.
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Discussion Question 5
 A pregnant woman asked her physician whether there
are any drugs considered safe during early pregnancy.
 Can you name some commonly prescribed drugs that
are safe to use?
 What commonly used drugs should be avoided during
pregnancy?
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Discussion Question 5
 Penicillin has been widely used during pregnancy for
more than 30 years without any suggestion of
teratogenicity. Small doses of aspiring and other
salicylates are ingested by most pregnant woman and
the teratogenic risk is very low.
 Chronic consumption of large doses of aspirin during
early pregnancy may be harmful. Alcohol and other
social drugs, such as cocaine, should be avoided.
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Questions?
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