Info
|
Stage |
Time Period |
Major Events |
|
Period of cleavage |
First week |
Cells undergo mitosis, blastocyst forms; inner cell mass appears; blastocyst implants in uterine wall Size: 1/4 inch (0.63 centimeters), weight: 1/120 ounce (0.21 grams) |
|
Embryonic stage |
Second through eighth week |
Inner cell mass becomes embryonic disk; primary germ layers form, embryo proper becomes cylindrical; main internal organs and external body structures appear; placenta and umbilical cord form, embryo proper is suspended in amniotic fluid Size: 1 inch (2.5 centimeters), weight: 1/30 ounce (0.8 grams) |
|
Fetal stage |
Ninth through twelfth week |
Ossification centers appear in bones, sex organs differentiate, nerves and muscles coordinate so that the fetus can move its limbs Size: 4 inches (10 centimeters), weight: 1 ounce (28 grams) |
Essentials of Human Physiology
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.
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