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biology 3201 15.3 late development.notebook
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Biology 3201 Unit 2
Reproduction: 15.3 Later Development
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• zygote – a young reproductive cell in humans formed from sperm and egg • embryo – a human offspring in the early stages of development where it undergoes cleavage up until it forms bone cells • fetus – an unborn vertebrate at a stage where all the structural features of the adult are recognizable and the first bone cells form, especially an unborn human after 8 weeks of development • human gestation 38 weeks (from conception)
biology 3201 15.3 late development.notebook
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1 to 2 inches long
heart has divided into right and left chambers.
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3 inches long
organs and muscles beginning to function
biology 3201 15.3 late development.notebook
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baby is covered with a layer of thick, downy hair called lanugo (La nu go).
heartbeat can be heard clearly.
baby's first kicking.
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lungs are filled with amniotic fluid
breathing motions begin.
can hear sounds.
biology 3201 15.3 late development.notebook
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turned head down in preparation for birth
4 5 pounds
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6 8 pounds
1822 inches
biology 3201 15.3 late development.notebook
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Stages of Childbirth
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1. Dilating Stage
• the uterus contracts mildly at first then strongly and regularly (early and active labour).
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• cervix dilates with each contraction, and the baby’s head rotates to fit through the mothers pelvis.• leads to a transition phase of intense contractions and full dilation of the cervix
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2. Expulsion stage• the mother pushes, or bears down, in response to pressure against her pelvic muscles. • baby’s head becomes visible
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• babys shoulders, which emerge one at a time with the next contractions. The rest of the body then slides out relatively easily
• the umbilical cord is sealed and cut.
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3. Placental stage
• within ten minutes of the baby’s birth.
• uterus continues to contract, expelling the severed umbilical cord and placenta.
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Monitoring Fetal Development
• There are various methods to monitor how well the fetus is developing inside the female: • 1) ultrasound – a procedure where sound waves are used to take a picture of the developing fetus • 2) amniocentesis – medical procedure in which a sample of cells from the amniotic fluid is tested for abnormalities in a fetus • 3) fetoscopy – medical procedure that involves direct observation of the fetus with an endoscope • 4) CVS (chrorionic villi sampling) – sampling of cells from the chorion to test for genetic conditions in a fetus.