1. The nucleus contains 46 chromosomes made of DNA and genes that provide instructions for building body parts. Cells divide through mitosis or meiosis. 2. Fertilization of an egg and sperm forms a zygote that develops through stages like a morula, blastula, and blastocyst over 1-3 weeks to become an embryo. 3. The blastocyst develops three cell layers - ectoderm, mesoderm, and endoderm - that form the nervous system/skin, muscles/bones, and digestive/respiratory organs, respectively.

1. EMBRYOLOGY BASICS
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2. BASIC CONCEPTS
All* the cells in our body have a nucleus.
The nucleus is a sac containing 46 X-shaped objects called cromosomes.
If you look at each cromosome veeery closely, you will see that each cromosome is made of
little bricks called genes. Each gene is made of DNA, a special type of acid produced in
the nucleus.
The difference in size of cromosomes means that they contain more or less genes.
Each gene contains the instructions on how to produce and assemble body parts.
In order to grow, all* the cells in our body must divide in 2 through a process called mitosis.
Mitosis division results in 2 identical cells containing 46 cromosomes each.
*The exception are the gonads (ovaries and testicles) where cells do not divide in 2 identical
cells, but in 2 halves each, containing 23 cromosomes. This division process is called
meiosis.
Ovaries contain cells called “oocytes” or eggs. One oocyte contains 23 cromosomes.
Testicles contain ‘spematozoids”. One spermatozoid contains 23 cromosomes.
When the oocyte and the sperm fuse (fertilization) a new cell (zygote) containing 46
cromosomes is formed. This cell divides through mitosis to form the newborn. Division
continues throughout lifespan [One exception: mature nerve cells do not divide] 2

3. EMBRYOLOGY 1 – FERTILIZATION
ZYGOTE – MORULA – BLASTULA – BLASTOCYST (1-layer=1wk, 2-layers=2wk, 3-layers=3wk) – EMBRYO - FETUS
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4. EMBRYOLOGY 3 – 3 LAYER BLASTOCYST
From now on it’s an embryo
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5. EMBRYOLOGY 2 - IMPLANTATION
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6. EMBRYOLOGY 3 – 3 LAYERS OF EMBRYO
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7. EMBRYOLOGY 4 - ORGAN FORMATION
ECTODERM: Nervous system and skin
MESODERM: Muscles, bones, ligaments, tendons, heart, blood vessels, kidneys, and gonads.
ENDODERM: Respiratory and digestive organs (i.e.: lungs, intestines, liver, gallbladder, pancreas, spleen)
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8. TERATOGEN
Greek for “monster forming”
Anything that can harm the baby during pregnancy
Remember: Most sensitive period of pregnancy is 1st trimester
(exception: Herpes virus [3rd trimester & delivery])
Teratogens:
• Common substances: Alcohol & tobacco
• Toxic substances: Lead, mercury, arsenic, insecticides.
• Microbes: ToRCHeS (Toxoplasm, Rubella, Chickenpox,
Cytomegalovirus, Herpes, Syphillis).
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9. EXERCISES
The nucleus in like a containing (number) (shape) objects called
If you look at each veeery closely, you will see that each of them is made of
little bricks called . Each is made of , a special type of acid
produced in the nucleus.
The difference in size of cromosomes means that they contain more or less
Each contains the instructions on how to produce&assemble body parts.
In order to grow, the cells in our body must divide in 2 through:
All cells: division results in 2 cells containing cromosomes each.
Gonad cells: division results in 2 half-cells containing cromosomes each.
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10. Mention the stages of development from fertilization:
O + S =Z M B B E F
How many layers does the blastocyst develop per week?
What are the names of the layers of a 3-layer blastocyst?
Which organs develop from each layer?
What is a teratogen?
Name 2 common teratogens, 2 toxic teratogens and 5 microbial teratogens.
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