The Reproductive System
practice good nutrition, eating high-quality food, not just
more food. The mother should also avoid any harm-ful
substances that could pass through the placenta into the
fetal blood such as alcohol, drugs, and nicotine.
Childbirth is called parturition (par-tyoo-RISH-un).
The fetus is expelled from the uterus through a process
called labor. The hormone oxytocin causes contraction of
the smooth muscles of the uterus. At this time, the pla-centa
releases prostaglandins. The combination of these
hormones produces more powerful and more frequent
contractions of the uterus, forcing the fetus out of the
uterus. The stages of labor include the dilation stage, the
expulsion stage, and the placental stage (Figure 19 - 13).
During the dilation stage, the cervix of the uterus is
fully dilated by the head of the fetus. The amnion rup-tures
releasing the amniotic fluid. This is commonly
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referred to as the water breaking. The dilation stage is the
longest stage of labor, lasting up to 12 hours. During the
expulsion stage, the child moves through the cervix and
vagina to the outside world. This stage usually lasts about
50 minutes in the first birth to about 20 minutes in future
births. Usually, the head of the child emerges first, and the
nose and mouth are cleared of mucus so the child can
breathe. The umbilical cord is cut and clamped after the
rest of the body of the child emerges. A breech birth is one
in which the buttocks emerge first and delivery is more
difficult. During the placental stage, the placenta detaches
from the uterus within 15 minutes after birth. This placenta
and its attached fetal membranes are called the afterbirth.
The removal of all placental material will prevent
prolonged bleeding after delivery.Placenta Urinary Pubic (^)
bladder^ bone^
(^)
(^)
(^)
Urethra^
(^) Vagina (^)
(A)
(^) Cervix (^)
(^) Rectum (^)
(^) ®
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Partially dilated cervix
(B)
(^) ®
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(C)
(^) ®
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Placenta Uterus
(D)
Umbilical cord
(^) ®
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Figure 19- 13 The stages of labor. (A) Position of the fetus prior to labor. (B) First stage of labor, cervical
dilation. (C) Second stage of labor, fetal delivery. (D) Third stage of labor, placental delivery.