Lesson 6: Birth and Lactation

Question 1

Birth

Answer 1

During pregnancy, the
progesterone and estrogen
produced by the placenta
maintain the endometrium
(uterine lining), suppress the
menstrual cycle and promote the
growth of breast tissue.

After about nine months the
levels of progesterone and
estrogen produced by the
placenta begin to fall and this signals the onset of the uterine contractions known as labour.
At the same time the endometrium begins
secretes a group of hormones known as
prostaglandins that initiate the uterine
contractions, while stretch receptors in the
cervix stimulate the hypothalamus to signal
the pituitary gland to secrete oxytocin.

Oxytocin is a hormone that continues to
stimulate the muscles of the uterus to
contract. Oxytocin is controlled by positive
feedback, a small uterine contraction triggers
the release of more oxytocin, strengthening
the next contraction.

Question 2

Three Stages of Birth

Answer 2

1. Dilation Stage

lasts about 2-20 hours.

uterine contractions and
oxytocin cause the cervix to
dilate

amnion breaks and fluid is
released2. Expulsion Stage

lasts about 0.5-2 hours

contractions become so forceful that the
baby is pushed through the cervix into
birth canal

the head of the baby rotates making it
easier to pass through the birth canal

3. Placental Stage

the placenta and umbilical cord are
expelled from the uterus

usually happens between 10-15 minutes
after the baby is born

Question 3

Lactation

Answer 3

After birth the blood levels of the hormone, prolactin, from the anterior
pituitary, increase.

Prolactin stimulates the milk production by the mammary glands.

As the baby suckles, prolactin secretion is maintained and oxytocin is released
from the posterior pituitary.

Oxytocin causes milk to be released from milk ducts.