Human Development - Weeks 9 - 40
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Introduction
At week nine, the embryo is called a fetus. Tthe transition is gradual, as by the end of the eighth week organogenesis is mostly complete. As such, the fetal period is characterized by rapid body growth, requiring glucose and amino acids. The fetal pancreas secretes insulin.
Intrauterine growth retardation (IUGR) can result from many factors, including cigarettes, alcohol, poor maternal nutrition, multiple pregnancy, social drugs, impaired uterine blood flow, and genetic factors.
- 9-12
- 13-16
- 17-20
- 21-25
- 26-29
- 30-34
- 35-40
9 to 12 Weeks
Primary ossification centres appear in the skeleton
External genetalia develop and become distinguishable at the end of the twelfth week.
Blood cell formation decreases in the liver and increases in the spleen.
Urine formation begins between the 9th and 12th weeks.
13 to 16 Weeks
Growth is very rapid.
Ossification of skeleton progresses
17 to 20 Weeks
Fetal movements, known as quickening, are first felt by mother
Ovaries and testes begin to descend
21 to 25 Weeks
Substantial weight gain occurs
Lungs begin to secrete surfactant
Fetus becomes viable
26 to 29 Weeks
Lungs are capable of breathing air
CNS can direct rhythmic breathing movements and body temperature
Eyelids open
Erythropoiesis moves from the spleen to the bone marrow
35-40 Weeks
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