V) Fertilization, Pregnancy and Birth  Birth

V) Fertilization, Pregnancy and Birth V) Birth

  approximately 226 days after implantation uterine contractions begin signaling the beginning of parturition (labour).

  the cervix thins and begins to dilate.   the amnion is forced into the birth canal

  it often bursts and the fluid lubricates the canal (breaking of the water).

  as the cervix dilates uterine contractions move the baby through the birth canal.

  after the birth the placenta is delivered.

V) Fertilization, Pregnancy and Birth V) Birth   as the cervix dilates uterine contractions move the baby through the birth

canal.   after the birth the placenta is delivered.

  hormones play a vital role in the birthing process   Relaxin,

  produced by the placenta prior to labour   causes the ligaments within the pelvis to loosen and the cervix to

soften.   provides a more flexible passageway for the baby during

delivery.   the decrease in progesterone is important to the onset of delivery.

V) Fertilization, Pregnancy and Birth V) Birth

  causes the ligaments within the pelvis to loosen and the cervix to soften.

  provides a more flexible passageway for the baby during delivery.

  the decrease in progesterone is important to the onset of delivery.

  Oxytocin   a hormone from the pituitary gland   causes strong uterine contractions   appears in the mother’s blood prior to labour.

  labour can be induced by administering prostaglandins or pitocin which is a synthetic form of oxytocin.

V) Fertilization, Pregnancy and Birth V) Birth

V) Fertilization, Pregnancy and Birth V) Birth

Estrogen Oxytocin

from ovaries

Induces oxytocin receptors on uterus

from fetus and mother’s posterior pituitary

Stimulates uterus to contract

Stimulates placenta to make

Prostaglandins

Stimulate more contractions

of uterus

Posi

tive

feed

back

+

+

Placenta Umbilical cord

Uterus Cervix

Dilation of the cervix 1

V) Fertilization, Pregnancy and Birth V) Birth

Expulsion: delivery of the infant 2

V) Fertilization, Pregnancy and Birth V) Birth

Delivery of the placenta

Uterus

Placenta (detaching)

Umbilical cord

3

V) Fertilization, Pregnancy and Birth V) Birth

V) Fertilization, Pregnancy and Birth

VI) Lactation

V) Fertilization, Pregnancy and Birth VI) Lactation

  elevated estrogen and progesterone levels during pregnancy prepare the breasts for milk.   each breast contains about 20 lobes of glandular tissue each

with a duct that carries fluid toward the nipple.   prolactin stimulates the glands to produce fluid.   prolactin is a hormone that is produced by the pituitary gland.

  estrogen stimulates the release of prolactin during pregnancy   the action of prolactin is inhibited by progesterone.

V) Fertilization, Pregnancy and Birth VI) Lactation

  estrogen stimulates the release of prolactin during pregnancy   the action of prolactin is inhibited by progesterone.

  a decrease in progesterone and estrogen after birth results in   a decrease in prolactin production   an increase in prolactin activity

  prolactin initially causes the production of colostrum   colostrum closely resembles breast milk.   contains milk sugar and milk proteins but lacks the milk fats.

  a few days after birth, prolactin stimulates the production of milk.

V) Fertilization, Pregnancy and Birth VI) Lactation

  colostrum closely resembles breast milk.   contains milk sugar and milk proteins but lacks the milk fats.

  a few days after birth, prolactin stimulates the production of milk.

  colostrum and mother’s milk supply the baby with nutrients and antibodies.

  prolactin may increase milk production but the milk still does not flow easily.   Milk produced in the lobes of the glandular tissue must be forced

into the ducts that lead to the nipple.   newborn suckling stimulates nerve endings in the areola of the

breast.   sensory nerves carry information to the pituitary gland.

V) Fertilization, Pregnancy and Birth VI) Lactation

  newborn suckling stimulates nerve endings in the areola of the breast.   sensory nerves carry information to the pituitary gland.

  oxytocin is released.   oxytocin is carried by the blood to the breasts and

uterus.   in the breast oxytocin causes weak contractions of

smooth muscle, forcing milk into the ducts.   in the uterus oxytocin causes weak contractions of

smooth muscle allowing the uterus to return to pre-pregnancy size and shape.

VII) Twins

  there are two basic types of twins:   monozygotic or identical   dizygotic or fraternal

VII) Twins   two thirds of all twins are dizygotic.

  occurs when two sperm fertilize two distinct eggs (in trizygotic triplets, three eggs are fertilized by three sperm)

  dizygotic can be one of three combinations:   two males

  represents about 25% of all dizygotic twin sets   two females

  represents about 25% of all dizygotic twin sets   one male and one female

  represents 50% of all dizygotic twin sets

VII) Twins   two males

  represents about 25% of all dizygotic twin sets   two females

  represents about 25% of all dizygotic twin sets   one male and one female

  represents 50% of all dizygotic twin sets

  the fertilization of two eggs by two sperm results in two separate embryos each with its own:   chorion (outer membrane of the amniotic sac)   amnion (inner membrane of the amniotic sac)   placenta

  in some instances, if the embryos implant very nearby each other along the uterine wall, the placentas can become fused.

VII) Twins   chorion (outer membrane of the amniotic sac)   amnion (inner membrane of the amniotic sac)   placenta

  in some instances, if the embryos implant very nearby each other along the

uterine wall, the placentas can become fused.

VII) Twins

  in monozygotic twins one sperm fertilizes one egg.   shortly after fertilization, instead of the blastocyst

remaining as one cell group, it splits in two.   when the split happens it will determine how the

twins will implant in the uterine lining.   the earlier the split, the more independent the

embryos will be.

VII) Twins   the earlier the split, the more independent the embryos will be.

  some scenarios include:

  a very early split leading to the embryos having separate chorions, amnions and placentas. (This happens in approximately one-third of identical twins.)

  twins having separate amnions and separate placentas but share one chorion.

  twins having separate amnions but share one chorion and one fused placenta.

  twins share one chorion, one amnion and one placenta (rarest combination).

VII) Twins   twins having separate amnions and separate placentas but share one chorion.   twins having separate amnions but share one chorion and one fused placenta.   twins share one chorion, one amnion and one placenta (rarest combination).

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VII) Twins   twins having separate amnions and separate placentas but share one chorion.   twins having separate amnions but share one chorion and one fused placenta.   twins share one chorion, one amnion and one placenta (rarest combination).

VII) Twins

  the placenta provides the developing baby with the nourishment and oxygen it requires.   it is advantageous for the monozygotic twins to have

separate placentas (even if they are fused).   monozygotic twins who share a placenta will not

develop equally because one twin will receive more nourishment via the placenta than the other twin does.   this is known as fetal growth restriction.

VII) Twins

VII) Twins   monozygotic twins who share a placenta will not develop equally because one twin

will receive more nourishment via the placenta than the other twin does.   this is known as fetal growth restriction.

  monozygotic twins come from the same fertilized egg   they share identical genetic material.

  they can only be same-sex   if splitting occurs very late and is incomplete, conjoined

twins result.

VII) Twins   conjoined twins are monozygotic twins who are joined at some region of their bodies.

  they are classified by the area where the attachment is located:   Terata Catadidyma refers to twins joined in the lower portion of their body, or they

may appear to be two bodies on top and one body on the bottom.   Pygopagus - back-to-back, joined at the rump   Ischiopagus - joined sacrum to sacrum   Dicephalus - one body with two separate heads

  Diprosopus - single body and head, but bearing two faces

VII) Twins   Terata Anadidyma refers to twins with one single upper body with a double

lower half or twins who are connected by a single body part.   Cephalopagus - connected at the head   Syncephalus - connected in the facial region   Cephalothoracopagus - connected in the facial region and at the thorax   Dipygus - one upper body with two lower bodies (including the abdomen,

pelvis and legs)

VII) Twins   Terata Anacatadidyma refers to

twins who are joined somewhere along the midsection of the body.

  Thoracopagus - joined at the chest; may share a single heart or have some cardiac connection; some organs in the abdominal region may be malformed

  Omphalopagus - joined at the chest

  Rachipagus - back-to-back, joined along the spine above the sacrum