HUMAN REPRODUCTION BIOLOGY 269

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HUMAN REPRODUCTIONBIOLOGY 269
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Recall Three Periods of Prenatal Development
Pre-embryonic Fertilization to 2
weeks Embryonic 2 weeks to
8 weeks Fetal 8 weeks
to 38 weeks (Birth)
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Typical Pregnancy
Mother Uterus reaches to ribcage
Weight gain 25 pounds
Full-term fetus 8.0 lb Placenta 1.4
lb Amniotic fluid 2.0 lb Enlarged uterus 2.0
lb Enlarged breasts 1.0 lb Increased blood
volume 4.0 lb Fluid retention 2.7 lb Maternal
storage fat 3.5 lb
24.6 lb (From Mitchell et al, Nutrition
in Health and Disease, 16th ed.)
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(Mother) Fetal nutrition Significant extra
load on her system
- Problems regulating nutrients
- Increased
risk of diabetes
Fetal wastes Significant extra load on her
kidneys - Increased
urination - Urine more
concentrated -
Increased risk of kidney failure
Milk production stimulated by prolactin from
pituitary - Breasts
enlarged and tender -
Expression of colostrum
Joint between two pubic bones softens
- Problems standing and walking
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Fetus Surrounded by amnion and chorion.
Amniotic fluid 1 liter/quart
All organs mature, but
Lungs
No food
Temperature
Vision
Blood
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Few weeks before birth - Fetus rotates
- Myometrium begins Stronger
contractions Cervix
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Triggering Events - Adrenal glands of
fetus stimulate placenta to produce chemicals
called prostaglandins.
- Prostaglandins cross placenta into
mothers blood stimulate her pituitary gland to
secrete oxytocin.
- Prostaglandins also cause placenta to stop
producing progesterone
Myometrium (muscle layer) of uterus begins
strong, coordinated, rhythmic contractions
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Three Stages of Labor
(thinning) and 8-24 hrs
(widening) of cervix
15-30 min
10-45 min
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Stage 1 Effacement and dilation of cervix
Contractions begin many minutes apart, relatively
weak Gradually increase in
strength and frequency
Cervix thins, shortens due to pressure of fetal
head
Cervical opening widens to about 10 cm -
Amnion/chorion usually ruptures toward end of
this stage
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Stage 2 Expulsion of fetus
Contractions of uterus strong, regular 1-2
minutes apart. Mother may push with diaphragm
and abdominal muscles.
Head enters vagina, Stretches vagina labia
Head turns so top of head faces front
Head widest part, so rest of body follows easily
Shoulders rotate as they pass through vagina, so
baby faces right or left
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Stage 3 Delivery of placenta
Once breathing, baby no longer dependent on
umbilical cord. Can be cut.
Placenta still attached to endometrium of uterus.
Ruptured amnion and chorion attached to
placenta. Umbilical cord extends out vagina.
Contractions of uterus continue, loosening
placenta
Placenta expelled through vagina
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Adjustments after Birth
Mother
Uterus continues to contract for days to expell
remaining functional layer of endometrium.
Uterus becomes smaller over weeks / months
Pubic joint (and other joints) tighten over over
weeks / months
Prolactin from pituitary gland continues to
stimulate production of milk in breasts
Oxytocin from pituitary gland stimulates
expression of milk from breasts
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Milk
First few days High in fat, protein, mineral,
antibodies
Later
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Adjustments after Birth
Infant
As body cools,.
As infant nurses,.
Starts breathing,
Blood starts flowing
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Lots of things can go wrong during or after
birth 1) Labor delivery begins too early
or too late 2) Amnion/chorion ruptures too
early or too late 3) Strong contractions can
not develop 4) Fetus not head-down in uterus
5) Placenta over cervix 6) Placenta separates
from uterus too early or too late 7) Fetus (or
just head) too large to fit through cervix and
vagina 8) Fetus (or just head) too large to
fit through pelvic bones 9) Umbilical cord
wrapped around fetus gets constricted 10)
Maternal hemorrhage
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