Describe the key changes that take place in the growing embryo up to eight weeks. Outline how hormones regulate birth. Outline how hormones regulate lactation. Compare and contrast the role that each hormone plays in birth with the role played in lactation.
During the first eight weeks of development, embryos develop the central nervous system, major organs, eyes, mouth, nose, ears, arms, legs, fingers, and toes. The heart also begins beating during this time. Estrogen, progesterone, placental growth factor, human placental lactogen, and relaxin are instrumental hormones during pregnancy. Prolactin and oxytocin are instrumental hormones during lactation.
Embryonic and Fetal Development
2 weeks: Approximately 2 weeks past a woman's menstrual period, an egg is released into the fallopian tube. After the egg and sperm meet in the fallopian tube, the fertilized egg takes 3-4 days to travel down the fallopian tube into the uterus to implant. There the blastocyst rapidly divides and develops.
3 weeks: As the blastocyst continues to implant into the lining of the uterus, the amount of amniotic fluid increases to protect and nourish the blastocyst.
4 weeks: At this time, the embryo is the size of a poppy seed. It consists of two layers, the hypoblast and epiblast, that will develop into organs over the next few weeks. The egg's yolk will also develop into red blood cells and blood vessels.
5 weeks: The baby is now the size of a poppy seed. There are now 3 layers that will become the baby's central nervous system (including the brain and spinal cord), lungs, heart, and major organs.
6 weeks: The baby is the size of a bean and has a heartbeat. The...
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