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Fertilization to Birth (First Trimester (The blastocyst forms in the…
Fertilization to Birth
First Trimester
Second Trimester
Third Trimester
Between the seventh and eighth months, the fetus doubles in mass and continues developing the organs. If born during before 8 months, the baby is considered premature and may not have fully developed lungs.
The lungs are the last thing to fully develop in the fetus, mostly because they are not completely necessary while in the womb. However, the fetus starts "breathing" movements before the lungs fully develop.
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The fetus begins storing its own minerals and vitamins, like calcium and phosphorus.
Many factors combine to trigger labor and childbirth. One of those factors are hormones released by the mother's pituitary gland. These hormones trigger the uterus to begin labor and rhythmically contract to push the baby out.
The cervix expands to allow the baby's head to pass through, and the amniotic sac breaks. At this point, the uterus turns the baby around and pushes it out through the vagina, usually headfirst.
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The blastocyst forms in the fallopian tubes, and implants itself in the uterine lining. Once implanted, gastrulation occurs. Cells divide to form three cell layers.
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The mesoderm will form the internal structures, such as the muscles, bones, blood cells, and reproductive organs.
The endoderm will form the organ linings of the digestive, respiratory, and excretory systems).
Neurulation begins in the second month. The ectoderm begins to form a neural tube that will turn into the brain and spinal cord. Specialized membranes form to protect and nourish the embryo, such as the amniotic sac. Other membranes form the placenta to nourish the embryo and dispose of its wastes.
After 8 weeks, the embryo is a fetus. After 3 months, most major organs are formed but not ready to function on their own. The fetus can move and has reflexes.