Please feel free to chat amongst yourselves until we begin at the top of the hour. 1

Seminar Agenda Review of Course Information The Organogenetic Period Discussion Questions Questions & Answers 2

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. 3

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 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? 7

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? 8

Embryonic Development Teratogens: agents such as viruses or drugs that produce or increase the incidence of congenital anomalies. 9

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. 10

Beginning of the Fourth Week 11 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.

12 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.

Embryo appearance at 56 days 13

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? 14

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. 15

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)? 16

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. 17

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? 18

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. 19

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? 20

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. 21

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? 22

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. 23

Questions? 24