A&P Exam 4 (Ch 29 pt 2)

Parturition

process by which a baby is born, blood levels of estrogen and progesterone decrease dramatically due to the removal of the placenta, precise trigger of parturition is unknown

Gestation Period

length of pregnancy calculated by physicians, 280 days (40 weeks) from last menstrual period to date of delivery of infant

Changes Near End of Pregnancy

uterus becomes more excitable and usually exhibits occasional contraction

cervix gradually dilates

strong uterine contractions help expel the fetus from the uterus through the vagina

Labor

period during which uterine contractions occur to eventually expel the fetus and placenta

3 Stages of Labor

dilation

expulsion

placental

Dilation Stage

first stage of labor, begins with onset of regular uterine contractions, extends until the cervix is dilated, amniotic sac ruptures, usually lasts 8-24 hours, head of fetus is positioned inferior to force cervix and vagina to open during contractions

Expulsion Stage

second stage of labor, lasts from the time of maximum cervical dilation until the fetus exit the vagina, lasts from a minute to an hour or more

Contractions During Expulsion Stage of Labor

contractions of the abdominal muscles assist the uterine contractions

contractions generate enough pressure to compress blood vessels in the placenta so blood flow to fetus stops, blood flow is restored during relaxation

Placental Stage

third stage of labor, occurs after birth, placenta is expelled from the uterus, uterine contractions cause the placenta to tear away from the uterine wall, some bleeding from uterine wall occurs, contraction compresses blood vessels to placenta to limit bleeding

4-5 Weeks After Parturition

uterus becomes smaller, cells of uterine lining become smaller and many degenerate, vaginal discharge is composed of small amounts of blood and degenerating endometrium for 1 week or more

Maternal Hormones Before Parturition

progesterone concentration in maternal blood is at its highest level and inhibits uterine smooth muscle cells

Hormones Near End of Pregnancy

estrogen levels rapidly increase in maternal blood and have excitatory influence overcomes progesterone’s inhibition

Fetal Hormones Before Parturition

adrenal glands of fetus are greatly enlarged, acth secretion (anterior pituitary) increases due to stress of confined space and limited oxygen supply

ACTH Effect on Fetus

causes fetal adrenal cortex to produce glucocorticoids, alters hormone secretion from the placenta

Glucocorticoids Effect on Fetus

decrease the rate of progesterone secretion and increase rate of estrogen synthesis, stimulates prostaglandin synthesis to stimulate uterine contractions

Hormones During Parturition

stretching of uterine cervix stimulates the release of oxytocin from maternal posterior pituitary

Oxytocin

stimulates uterine contraction, moves fetus farther into cervix causing stretching (positive feedback), after delivery cervix is not stretching and oxytocin secretion decreases

Hormones of Parturition Diagram

Stages of Labor Diagram